Jean-François Gajewski
email: gajewski@univ-savoie.fr

Li Li
email: l.li@montpellier-bs.com

Can Internet-Based Disclosure Reduce Information Asymmetry? 1 CAN INTERNET-BASED DISCLOSURE REDUCE INFORMATION ASYMMETRY?

Keywords: JEL classification: G14, G15, G32 Internet-based disclosure, Information asymmetry, Spread, PIN

The Internet is widely used by listed companies to manage investor relations.

Since

January 2007, the French Financial Authority has required companies listed on Euronext-Paris to disclose all mandatory financial information via the Internet in order to enhance information transparency. This paper examines the impact of Internet-based disclosure on the French stock market by analyzing the relationship between information asymmetry and Internet disclosure practices. Extending previous studies on Web-based disclosure, a checklist of 40 items is developed to evaluate the level of Internet-based voluntary disclosure. Measuring information asymmetry by the spread and the probability of informed trading, we show that greater Web-based disclosure lowers information asymmetry in the French financial market.

Introduction

The Internet has triggered a revolution in the area of financial transparency for both listed companies and investors in financial markets. Compared with traditional media, such as the paper-based annual report, the Internet allows firms to aggregate and disseminate different types of information (video, sound, flash, text, etc.) on their websites. Internet disclosure offers firms the opportunity to enhance communication quality, improve reputation, attract potential investors, and reduce information distribution costs [START_REF] Ettredge | Dissemination of information for investors at corporate web sites[END_REF]. As a consequence, firms that improve their communication to investors may reduce their cost of capital. The investors may also benefit from Web disclosure, because Internet-based technologies facilitate the information gathering process. Via the Internet, investors can very quickly obtain different types of financial information, which is presented in various formats (Word, Excel or Pdf, etc.) and is directly usable. Web disclosure may also help investors to bridge the information gap between themselves and managers. Moreover, as Web information is widely disseminated, it may be able to reduce the information asymmetry between informed and uninformed investors. As [START_REF] Hodge | Does search-facilitating technology improve the transparency of financial reporting[END_REF] point out, Internet technology helps investors to access, analyze and understand information, which, in turn, leads to better interpretation. those of [START_REF] Leuz | The economic consequences of increased disclosure[END_REF], [START_REF] Hail | The impact of voluntary corporate disclosures on the ex-ante cost of capital for swiss firms[END_REF], [START_REF] Petersen | Voluntary disclosure and information asymmetry in Denmark[END_REF], have focused on European companies, and none have studied French listed companies. As [START_REF] Jaggi | Impact of culture, market forces, and legal system on financial disclosures[END_REF] show, the legislative system and culture influence financial practices. Compared with Anglo-American firms, the capital concentration of French firms is relatively high and generally characterized by state, family or cross shareholding. Investor protection is also weaker in France than in the U.S. In light of these differences, it is valuable to examine whether the results obtained through empirical studies using other samples are valid in the case of France. While quarterly earnings announcements are legally required in the US, French firms generally publish semi-annual earnings 2 . [START_REF] Gajewski | A comparison of the effects of earnings disclosures on information asymmetry: evidence from France and the US[END_REF] study the effect of earnings disclosures on information asymmetry in France and the US and prove that the lower frequency of earnings announcements in France induces a steeper decrease of information asymmetry at the time of release of semi-annual earnings.

Lastly, empirical studies on information asymmetry generally use the spread-based measure as a proxy for information asymmetry. This metric lacks precision in the sense that spreads do not only represent adverse selection costs.

The paper here estimates the probability of informed trading in order to capture more precisely the extent of information asymmetry on the stock market [START_REF] Easley | Liquidity, information, and infrequently traded stocks[END_REF][START_REF] Duarte | Why is pin priced?[END_REF].

The remainder of the article is structured as follows: Section 2 describes the French institutional context of accounting disclosure. Section 3 gives a literature review and develops our hypotheses. Section 4 sets out the methodology chosen for the empirical study, the data selection procedure and the regression models. Section 5 interprets the empirical results and section 6 concludes.

The regulation of information disclosure in France

As part of the European continental system, the French accounting disclosure regulation is less equity-outsider oriented than the Anglo-American system [START_REF] Nobes | Towards a general model of the reasons for international differences in financial reporting[END_REF]. For instance, French regulations do not require firms to publish their results for the first and third quarter, while all four quarterly earnings announcements are legally required in the US. French firms must publish only their sales quarterly and their earnings semi-annually.

In France, Internet financial disclosure has been voluntary and unregulated for many years. In order to guarantee a high level of investor protection and efficient markets, the European transparency directive 3 (2004/109/CE) has established the detailed requirements for disclosure of periodic and on-going information concerning issuers whose securities are already admitted to trading on a regulated market. France has adopted this directive and modified the AMF's General Regulations 4 (Book II: Issuers and financial disclosure). Since January 2007, all listed companies on Euronext-Paris must ensure that the regulated information is disseminated effectively and in full. Furthermore, the regulated information should be posted "on its website as soon as it has been disseminated" and be kept as stored data for at least five years. These new regulations are designed to improve the integrity of the information dissemination system, reduce the opacity of financial statements, and protect investors from accounting fraud. Appendix I provides a summary of regulated financial information for the firms listed on the French capital market.

Literature review and hypotheses

Literature review on Internet-based disclosure

Studies on Web-based disclosure started in the mid-1990s when the Internet began to have a powerful impact on culture and the business environment. The research from this early stage is generally descriptive, with most studies providing an overall observation of the extent of Internet-based disclosure internationally [START_REF] Petravick | Financial reporting on the world wide web[END_REF][START_REF] Gray | Corporate reporting on the internet: Opportunities and challenges[END_REF][START_REF] Trites | Democratizing disclosure[END_REF][START_REF] Gowthorpe | External reporting of accounting and financial information via the internet in Spain[END_REF][START_REF] Deller | A survey on the use of the internet for investor relations in the USA, the UK and Germany[END_REF][START_REF] Ettredge | The presentation of financial information at corporate web sites[END_REF]. By extending the earlier descriptive studies on Internet-based disclosure, more recent studies have sought to explain the determinants of Internet-based disclosure [START_REF] Ashbaugh | Corporate reporting on the internet[END_REF][START_REF] Craven | Financial reporting on the internet by leading UK companies[END_REF][START_REF] Brennan | Corporate reporting on the internet by irish companies[END_REF][START_REF] Debreceny | The determinants of internet financial reporting[END_REF][START_REF] Marston | Corporate reporting on the internet by German companies[END_REF][START_REF] Trabelsi | Incremental voluntary disclosure on corporate websites, determinants and consequences[END_REF]. Since the release of information via Internet has been a voluntary choice for listed companies for several years, these studies have introduced agency theory, signal theory and cost-benefits analyses, which are generally used in voluntary disclosure studies.

It is assumed that these theories can explain voluntary disclosure via both the traditional media, such as annual reports, and the new channels, such as the Internet [START_REF] Marston | Corporate reporting on the internet by German companies[END_REF][START_REF] Trabelsi | Incremental voluntary disclosure on corporate websites, determinants and consequences[END_REF].

One common finding in prior studies is the positive relationship between firm size and Web reporting. The empirical results from different countries show that firm size is the most important determinant of the Internet used to disseminate information. As [START_REF] Buzby | Company size, listed versus unlisted stocks, and the extent of financial disclosure[END_REF] points out, the cost of information disclosure is relatively low for larger firms. Furthermore, large companies are more exposed to public scrutiny. As a result, they are motivated to enhance information transparency to satisfy the needs of information users.

It is generally accepted that corporate governance factors can influence a company's communication strategy, particularly regarding voluntary disclosure [START_REF] Gul | Board leadership, outside directors' expertise and voluntary corporate disclosures[END_REF][START_REF] Ajinkya | The association between outside directors, institutional investors and the properties of management earnings forecasts[END_REF][START_REF] Velury | Institutional ownership and the quality of earnings[END_REF]. [START_REF] Kelton | The impact of corporate governance on internet financial reporting[END_REF] extend these studies by focusing on the relationship between governance mechanisms and voluntary Web disclosure. They show that better Internet-based disclosure is positively linked to weaker shareholder rights, lower capital concentration, a higher percentage of independent directors and financial experts on the board, and a greater frequency of audit committee meetings. The findings of [START_REF] Kelton | The impact of corporate governance on internet financial reporting[END_REF] emphasize the importance of corporate governance in Web practices.

On the contrary, [START_REF] Alali | The use of the internet for corporate reporting in the mercosur (southern common market): The Argentina case[END_REF] find that highly concentrated firms in Argentina disclose more information on their websites than firms with less concentration.

Later, empirical research began to investigate the effects of Internet-based disclosure on the financial market. For example, [START_REF] Cormier | Attributes of Social and Human Capital Disclosure and Information Asymmetry between Managers and Investors[END_REF] find a negative impact of the web based social and human capital disclosure on stock volatility and Tobin's Q. [START_REF] Yoon | Does xbrl adoption reduce information asymmetry[END_REF] show that the technique of XBRL improves financial transparency and reduces information asymmetry in the capital market. [START_REF] Blankespoor | The role of Dissemination in Market Liquidity: Evidence from Firms' Use of Twitter[END_REF] find that dissemination via Twitter is negatively associated with information asymmetry. Efendi, Park and Smith (2013) show that XBRL filings can improve informational efficiency because XBRL filings make the financial data easier to use and analyze for all the information users. [START_REF] Chang | Does disclosure quality via investor relations affect information asymmetry[END_REF] examine the relationship between information asymmetry and Internet-based disclosure in Australia. They find that the bid-ask spread is negatively related to disclosure quality, but this relationship becomes weaker in the presence of other factors. Based on the preceding research, higher Internet-based voluntary disclosure should reduce the degree of information asymmetry.

Development of hypotheses

Situations concerning information asymmetry are more likely to occur when some informed investors possess information that others, the uninformed, do not have. These situations are detrimental to firms when the informed investors trade using this informational advantage, such as through insider trading.

These trades lead to an adverse selection problem, because the uninformed will flee the market if they detect such information asymmetry. In order to keep the uninformed in the market and trade with them, the informed would have to revise their bids. This creates an adverse selection problem that could be resolved through increased disclosure, such as Web-based disclosure, by the firms.

Theoretical research shows that the release of public information may, both directly and indirectly, help to reduce information asymmetry. On the one hand, the publication of accounting information should lower the informational advantage of pre-informed agents, and therefore the extent of information asymmetry. Using this argument, [START_REF] Verrecchia | The use of mathematical models in financial accounting[END_REF] treats public disclosure as a substitute for private information and shows that private information loses its usefulness when information is published. On the other hand, public information indirectly affects information asymmetry by reducing the incentive for investors to acquire costly private information. The theoretical models of [START_REF] Kim | Market reaction to anticipated announcements[END_REF], [START_REF] Demski | Market response to financial reports[END_REF], [START_REF] Mcnichols | Public disclosure, private information collection, and short-term trading[END_REF] show that some agents are highly motivated to acquire private information before publication of the financial results, and are able to benefit from this advantage before it is neutralized by the corresponding report. But, if firms increase their public disclosure, the incentive for investors to search for costly private information will be reduced [START_REF] Fama | Information on capital markets[END_REF][START_REF] Hakansson | Interim disclosure and public forecasts: An economic analysis and a framework for choice[END_REF][START_REF] Diamond | Optimal release of information by firms[END_REF]. [START_REF] Brown | How disclosure quality affects the level of information asymmetry[END_REF] empirically show that the incentive to collect private information declines with disclosure quality.

The release of public information may also change the trading behavior of uninformed investors on the capital market, according to the investor recognition hypothesis [START_REF] Merton | A simple model of capital market equilibrium with incomplete information[END_REF]. Internet-based disclosure can in fact enhance a firm's visibility and mitigate incomplete information. As investors prefer to invest in companies with which they are familiar, more investors will be attracted to trade in the stock [START_REF] Fishman | Disclosure decisions by firms and the competition for price efficiency[END_REF]. As a result, information coverage (analysts, press coverage) will increase, thus leading to a reduction in information asymmetry, ceteris paribus. However, the larger the investor base, the higher the probability of informed trading. [START_REF] Kyle | Continuous auctions and insider trading[END_REF] theoretically demonstrates that the informed could have an incentive to increase their trades when there are more uninformed investors in the market.

Their strategies become even less visible with more uninformed investors in the market. Although information asymmetry in the market depends on the balance between the informed and the uninformed, [START_REF] Brown | How disclosure quality affects the level of information asymmetry[END_REF] empirically prove that the balance between the informed and the uninformed changes in favor of uninformed trading with disclosure quality. This is probably due to limited capital constraints and risk aversion. To sum up, Internet-based voluntary disclosure may reduce situations of information asymmetry, because the informed have less incentive to acquire private information.

Empirically, [START_REF] Heflin | Disclosure policy and market liquidity: Impact of depth quotes and order sizes[END_REF] demonstrate that increased disclosure (measured by analysts' evaluations) is associated with lower spreads. [START_REF] Petersen | Voluntary disclosure and information asymmetry in Denmark[END_REF] also prove that quoted companies can reduce the spread by publishing more information voluntarily. [START_REF] Brown | How disclosure quality affects the level of information asymmetry[END_REF] find a negative relationship between the quality of annual report disclosure and information asymmetry. This negative association becomes stronger when the initial level of information asymmetry between the firm and investors is higher. Public information disclosure not only concerns content, but also presentation. The adoption of online disclosure enhances a firm's capacity to present information and make its homepage a user-friendly information center.

For example, search engines facilitate finding information, especially for novice investors with little experience. Financial data in Excel format facilitate the processing of data. Hyperlinks make it easier for investors to compare firm stock with market indexes. Furthermore, the Internet makes real-time disclosures accessible to all investors, and this is particularly important for foreign investors, who experience greater difficulties with information collection via traditional media. The organization of the website may improve disclosure quality and, as this can reduce information asymmetry, the presentation is a means of lowering this asymmetry.

Prior empirical studies have shown the positive impact of some Web technologies on information asymmetry. For example, the XBRL technique can improve financial transparency and reduce information asymmetry in the capital market [START_REF] Yoon | Does xbrl adoption reduce information asymmetry[END_REF]. Later, Efendi, Park and Smith (2013) prove that XBRL filings can improve informational efficiency. Based on the preceding arguments and research, greater use of network technology should reduce the level of information asymmetry. This leads to the core hypothesis:

Hypothesis: There is a negative relationship between information asymmetry and the degree of Internet-based voluntary disclosure.

Research design

The empirical investigation consists of observing the relationship between Internet-based disclosure and information asymmetry. After presenting the research sample (4.1), the measurements of the main variables are set out (4.2).

Lastly, the regression models are discussed (4.3).

Sample description and data collection methods

The initial sample contains publicly traded French companies belonging to the SBF 250 index. We excluded twenty-nine companies in the financial sector due to their disclosure practices, which are heavily influenced by regulatory requirements [START_REF] Botosan | Disclosure level and the cost of equity capital[END_REF]) and subject to different disclosure requirements.

Forty-one companies were also rejected for lack of sufficient information. The final sample therefore consists of 180 companies covering nine sectors: Oil and Gas, Basic Materials, Industrials, Consumer Goods, Health Care, Consumer Services, Telecommunications, Utilities and Technology. Table 1 presents the elements of the research sample.

TABLE 1 ABOUT HERE

Data on ownership structure were extracted from Thomson ONE Banker.

Information on corporate governance was collected from websites and annual

Can Internet-Based Disclosure Reduce Information Asymmetry? 16

reports. Other financial and accounting data were obtained from Datastream and Worldscope. All data relate to the 2007 financial year.

Measurement of variables

Information asymmetry measurement

In order to study the relationship between information asymmetry and firm reporting on the Internet, we first need to assess the extent of information asymmetry in the stock market. Prior research has developed various methods of assessing the level of information asymmetry. Of these, the bid-ask spread (difference between the best selling price and the best buying price for a given security) appears to be the most frequently-used proxy to measure information asymmetry in previous studies on accounting information [START_REF] Welker | Disclosure policy, information asymmetry, and liquidity in equity markets[END_REF][START_REF] Leuz | The economic consequences of increased disclosure[END_REF][START_REF] Petersen | Voluntary disclosure and information asymmetry in Denmark[END_REF].

Being consistent with prior works [START_REF] Petersen | Voluntary disclosure and information asymmetry in Denmark[END_REF][START_REF] Yoon | Does xbrl adoption reduce information asymmetry[END_REF], this study also uses the spread as a proxy of information asymmetry and calculates the relative spread (R_Spread) by the following formula:

𝑅𝑅_𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑑𝑑 = (𝐴𝐴𝐴𝐴𝐴𝐴 𝑆𝑆𝑆𝑆𝑝𝑝𝑝𝑝𝑆𝑆 -𝐵𝐵𝑝𝑝𝑑𝑑 𝑆𝑆𝑆𝑆𝑝𝑝𝑝𝑝𝑆𝑆) (𝐵𝐵𝑝𝑝𝑑𝑑 𝑃𝑃𝑆𝑆𝑝𝑝𝑝𝑝𝑆𝑆 + 𝐴𝐴𝐴𝐴𝐴𝐴 𝑃𝑃𝑆𝑆𝑝𝑝𝑝𝑝𝑆𝑆)/2 . ( 1
)
As stocks in the sample are continuously traded, we compute also timeweighted average bid-ask spreads (W_Spread) and average effective spreads (E_Spread) from time-stamped data. Assuming that there are N quotation updates in the interval [t0;tN], the time-weighted average bid-ask spread is then computed using the following formula:

𝑊𝑊_𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑑𝑑 = 1 (𝑡𝑡 𝑁𝑁 -𝑡𝑡 0 ) � 𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑑𝑑 𝑖𝑖 × (𝑡𝑡 𝑖𝑖 -𝑡𝑡 𝑖𝑖-1 ) 𝑁𝑁 𝑖𝑖=1
.

(2)

The effective spread is computed by comparing the mid-price to the trading price:

𝐸𝐸_𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑑𝑑 = 2 × � 𝑇𝑇𝑆𝑆𝑆𝑆𝑑𝑑𝑝𝑝𝑇𝑇𝑇𝑇 𝑆𝑆𝑆𝑆𝑝𝑝𝑝𝑝𝑆𝑆 -(𝐵𝐵𝑝𝑝𝑑𝑑 𝑃𝑃𝑆𝑆𝑝𝑝𝑝𝑝𝑆𝑆 + 𝐴𝐴𝐴𝐴𝐴𝐴 𝑃𝑃𝑆𝑆𝑝𝑝𝑝𝑝𝑆𝑆)/2 (𝐵𝐵𝑝𝑝𝑑𝑑 𝑃𝑃𝑆𝑆𝑝𝑝𝑝𝑝𝑆𝑆 + 𝐴𝐴𝐴𝐴𝐴𝐴 𝑃𝑃𝑆𝑆𝑝𝑝𝑝𝑝𝑆𝑆)/2 �. (3)
However, the bid-ask spread measures transaction costs that also include other components. In an order-driven market, there could also be a component linked to inventory costs and another linked to asymmetric information costs.

To some extent, spreads do not measure adverse selection costs exactly.

In order to have more robust results, we rely on the model developed by [START_REF] Easley | One day in the life of a very common stock[END_REF] to measure information asymmetry. Their model allows the probability of informed trading to be estimated from the observation of the order flow. We computed the PIN measure defined by [START_REF] Easley | Liquidity, information, and infrequently traded stocks[END_REF], which is based on trade direction.

The probability of observing B buys and S sells on a given day can be expressed as follows:

( )( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) ! ! 1 ! ! ! ! 1 , ,
ε µ ε δ α ε µ ε αδ ε ε α ε µ δ α µ ε µ ε ε + × - + + × + × - = + - + - - , ( 4
)
where α is the probability of an information event that is bad news with probability δ , and good news with probability 1-δ. The arrival rate of informed trades is µ. ε is the rate of uninformed buy and sell trade arrivals. Over an observation period of T days, the likelihood of observing ( )

T t t t S B 1 ,
= buys and sells corresponds to the product of the daily likelihoods:

( ) ( ) ( )( ) ( ) ∏ = = =       T t t t T t t t S B L S B L 1 1 , , , , , , , , ε µ δ α ε µ δ α . ( 5
)
In order to estimate the parameters, we maximize the likelihood defined in equation ( 5), and the PIN is calculated as:

ε αµ αµ 2 + = PIN . ( 6
)
The PIN measure may also include potential effects of liquidity unrelated to information asymmetry. In order to control these effects, we have also computed the adjusted measure of PIN developed by [START_REF] Duarte | Why is pin priced?[END_REF].

AdjPIN is calculated as:

( ) ( ) ε θ α αθ ∆ αµ αµ 2 1 ' 2 + - + × + = AdjPIN . ( 7
)
where θ measures the probability of an event that is conditional on the absence of private information. θ' is the probability of an event that is conditional on the arrival of private information. ∆ measures the additional arrival rate of buys and sells.

Development of the index of Internet disclosure

Two methods are generally used to assess the level of information disclosure. The direct method uses estimates published by professional institutions that regularly assess the supply of information by quoted Can Internet-Based Disclosure Reduce Information Asymmetry? 20 companies. For example, the Association for Investment and Management Research (AIMR) publishes an annual ranking of financial transparency in a report giving assessments by analysts on the disclosure practices of firms that has been used as a proxy of disclosure policy in many prior studies. [START_REF] Lang | Cross-sectional determinants of analyst ratings of corporate disclosures[END_REF], 1996;[START_REF] Welker | Disclosure policy, information asymmetry, and liquidity in equity markets[END_REF][START_REF] Sengupta | Corporate disclosure quality and the cost of debt[END_REF] Marston & Polei 2004) that have analyzed online disclosure practices. As [START_REF] Wallace | The relationship between the comprehensiveness of corporate annual reports and firm characteristics in Spain[END_REF] indicate in their research, there is no general theory on how to build an index and its content changes from one research to another according to the focus of the study.

We first summarize all the items used in these prior studies on firm reporting via the Internet. In order to limit our study to the field of voluntary disclosure, all the mandatory items (according to the AMF regulations) are excluded from the index. Second, we choose the items according to the focus of the study. The main objective of this study is to test whether the technological features of Internet disclosure can reduce information asymmetry.

As a result, all items of this nature in the previous works are given priority consideration. Internet disclosure is generally considered as "timely" and "user-friendly." In addition, we want to emphasize the "compatibility" of the website. The Internet is a multi-medium that assembles paper-based reports, video and voice documentations, etc. For this reason, some items 6 , which are considered to be informational in prior research, can also be treated as an advantage of the Internet disclosure presentation in our study. We also introduce some new items, which have not been used in prior studies but are closely related to the technological features and advantages of Internet disclosure 7 .

Can Internet-Based Disclosure Reduce Information Asymmetry? 22

We assign one point to each item presented on the firm's own website and which is available to the general public. The maximum possible score that a listed firm can obtain is 40 points. For each company, the total score is presented as the percentage of the actual score in relation to the maximum possible score. Therefore, the level of Internet-based disclosure (Score) of each company varies between 0 and 1, with 1 being the highest score and 0 the lowest.

We want to point out that only the items presented on a HTML webpage can be considered in the data collection. The information contained in the annual or semester reports (PDF or Word format) was not scored in order to avoid repetition. We have focussed on the investor section which regroups all the important information for investors. However, we also consider the complete firm website because several technological feature items (such as "help site" "site plan", "internal search engine") of our index are designed for the whole website. All the firms' websites in our sample were analyzed during the month of May and June in 2007. The entire index is presented in the Appendix II.

Analysis method

The main purpose of this study is to analyze how Internet disclosure is related to information asymmetry. When studying this relationship, the reverse causality between these two factors should be considered. As prior research points out, disclosure can reduce the level of information asymmetry, and firms that experience high information asymmetry may be more persuaded to release information so as to limit the adverse selection problem, ceteris paribus [START_REF] Dye | Disclosure of nonproprietary information[END_REF][START_REF] Lang | Cross-sectional determinants of analyst ratings of corporate disclosures[END_REF][START_REF] Welker | Disclosure policy, information asymmetry, and liquidity in equity markets[END_REF][START_REF] Heflin | Disclosure policy and market liquidity: Impact of depth quotes and order sizes[END_REF]. To address the potential endogeneity problem, we run a Hausman test in order to choose between the OLS and the 2SLS methods.

A dummy variable governance system is introduced as an instrumental variable in our tests. In fact, French legislation allows domestic publicly-listed companies to choose between a one-tier system 8 , mandatory in the Anglo-American system, and a two-tier system, which is mandatory in countries such as Germany or Slovenia for example. This opportunity is unique in Europe.

Because the two-tier system clearly separates the functions of management and control, it is supposed to provide a more effective management style. Therefore, the two-tier system should be associated with higher disclosure quality [START_REF] Charreaux | Le gouvernement des entreprises[END_REF]. Furthermore, no prior literature suggests that the government system may have a direct impact on information asymmetry.

In addition to Internet-based disclosure, a series of variables was also

 Trading volume (Turnover)

From a theoretical point of view, there are several arguments supporting the fact that trading volume should reduce information asymmetry and also the bid-ask spread. [START_REF] Copeland | Information effects on the bid-ask spread[END_REF] study information effects on the spread and show that the bid-ask spread and also information asymmetry is a negative function of measures of trading activity. In their model, the probability of informed trading is higher for thinly traded stocks, because these stocks are on average more closely held. As a consequence of holding the size as constant, low trading volume means less frequent trading. Thus, trading volume is negatively associated with information asymmetry and bid-ask spreads. This explanation holds if the size of transaction remains constant.

Moreover, if we focus on information asymmetry, trading volume captures the degree of trading activity and stock market liquidity. It indicates the willingness of market participants to sell and buy shares. [START_REF] Leuz | The economic consequences of increased disclosure[END_REF] suggest that trading activity reflects the attractiveness of a stock. Stocks with higher liquidity are relatively more attractive to investors, and this could improve the degree of public information (analysts, press coverage) and reduce

Can Internet-Based Disclosure Reduce Information Asymmetry? 25 information asymmetry to this extent. Finally, [START_REF] Ho | Optimal dealer pricing under transactions and return uncertainty[END_REF] predict that trading volume should reduce spreads due to economies of scale. Among the different measures of volume, the rotation rate with the best properties would seem to be the metric. Consequently, we define trading volume as:

Turnover = log Daily trading volume NOSH×NOSHFF . ( 8
)
where trading volume is the total number of traded shares on a given day.

NOSH is the total number of ordinary shares, NOSHFF is the free-float percentage of total shares available to ordinary investors 9 . All variables were extracted from Datastream.

 Stock return volatility (Volatility)

Stock return volatility should enlarge the bid-ask spread due to risk-bearing [START_REF] Roll | A simple implicit measure of the effective bid-ask spread in an efficient market[END_REF][START_REF] Glosten | Components of the bid-ask spread and the statistical properties of transaction prices[END_REF]). In the capital market, stock return volatility generally indicates the degree of uncertainty or risk. In this case, the risk of not holding an optimal position increases. As a consequence, higher volatility leads to greater spreads. [START_REF] Copeland | Information effects on the bid-ask spread[END_REF] insist on the role of specific risk in their model. As specific risk increases, information asymmetry should also increase. Stock return volatility is measured by the standard deviation of daily stock returns.

 Stock Price (LnPrice)

Price level allows for the effect of discreteness to be controlled. Stocks with low price levels tend to be new, smaller in size and above all riskier. This additional risk leads to an enlargement of the bid-ask spread. [START_REF] Stoll | Friction[END_REF] has proved that the relative spread is negatively related to the price level in logarithm. The stock price is therefore measured in logarithm.

 Ownership concentration (Bloc)

Agency theory suggests that individual investors are in an unfavorable informational position relative to managers and majority shareholders.

Therefore, when ownership structure is more dispersed, the risk of information asymmetry is more likely to be effective. These situations increase agency problems and imply higher monitoring costs. The study of [START_REF] Glosten | Bid, ask and transactions prices in a specialist market with heteregeneously informed traders[END_REF] point out that large shareholders attempt to trade on their insider information and extract private benefits and firm control. Such an agency problem results in a larger spread and lower stock liquidity. Moreover, [START_REF] Attig | Effects of large shareholding on information asymmetry and stock liquidity[END_REF] provide empirical evidence on the positive relationship between ownership concentration and information asymmetry. Therefore, it is supposed that the ownership concentration is positively linked to the level of information asymmetry. Ownership concentration is measured by the proportion of capital held by blockholders (investors owning 5% or more of a firm's stock).

The next equation summarizes the regression model:

𝑰𝑰𝑰𝑰𝑰𝑰𝑰𝑰𝑰𝑰𝑰𝑰𝑰𝑰𝑰𝑰𝑰𝑰𝑰𝑰𝑰𝑰 𝑰𝑰𝒂𝒂𝒂𝒂𝑰𝑰𝑰𝑰𝒂𝒂𝑰𝑰𝑰𝑰𝒂𝒂 = 𝛼𝛼 + 𝛽𝛽 1 𝐼𝐼𝑇𝑇𝑡𝑡𝑆𝑆𝑆𝑆𝑇𝑇𝑆𝑆𝑡𝑡_𝑏𝑏𝑆𝑆𝐴𝐴𝑆𝑆𝑑𝑑 𝑑𝑑𝑝𝑝𝐴𝐴𝑝𝑝𝑑𝑑𝑑𝑑𝐴𝐴𝑑𝑑𝑆𝑆𝑆𝑆 + 𝛽𝛽 2 𝑇𝑇𝑑𝑑𝑆𝑆𝑇𝑇𝑑𝑑𝑇𝑇𝑆𝑆𝑆𝑆 + 𝛽𝛽 3 𝑉𝑉𝑑𝑑𝑑𝑑𝑆𝑆𝑡𝑡𝑝𝑝𝑑𝑑𝑝𝑝𝑡𝑡𝑉𝑉 + 𝛽𝛽 4 𝑃𝑃𝑆𝑆𝑝𝑝𝑝𝑝𝑆𝑆 + 𝛽𝛽 5 𝐵𝐵𝑑𝑑𝑑𝑑𝑝𝑝 +ε.
(9)

Empirical results

Descriptive statistics

The statistics are set out in Table 2. The results of the overall Internet-based voluntary disclosure (Score) indicate that the highest score achieved by any company is 0.85, while the lowest is 0.125. The mean value is 0.422. These results suggest that, across the 180 listed companies in the sample, there is widespread variation in the global level of voluntary disclosure via the Internet.

As far as information asymmetry is concerned, relative spreads vary from 0.04% to a maximum of 4.23%. The means are 0.68 % and 0.70% respectively for three and six months. By comparison, Yoon, Zo and Ciganek (2011) find a mean of 0.7% for the South-Korean market over the period 2007-2008. The mean of the PIN estimates over three and six months are respectively equal to 0.1818 and 0.1794, which is consistent with the estimation given by [START_REF] Easley | Is information risk a determinant of asset returns[END_REF]. [START_REF] Duarte | Why is pin priced?[END_REF] calculate a median for adjusted PIN equal to 0.17, a result confirmed by our estimates of 0.14 and 0.15 respectively for three and six months.

On average, 51.9% of the outstanding shares are held by blockholders. With an American sample, [START_REF] Kelton | The impact of corporate governance on internet financial reporting[END_REF] highlight that the average percentage of capital held by block shareholders is about 20%. Marston and Polei's study (2004) shows that the average free-float coefficients of German listed companies is 42.75%. Compared with their counterparts, French companies have a much higher concentration of capital. is negatively related to all these measures of information asymmetry. A higher level of information disclosure through the Internet may lead to a lower level of information asymmetry.

TABLE 2 ABOUT HERE

Correlation analysis

Can Internet-Based Disclosure Reduce Information Asymmetry? 29

Moreover, variables Spread, PIN and AdjPIN are also negatively related to the turnover ratio, and to the standard-deviation of stock returns. These results are consistent with previous empirical findings in the field of market microstructure (e.g. [START_REF] Huang | Dealer versus auction markets: A paired comparison of execution costs on the NASDAQ and the NYSE[END_REF][START_REF] Stoll | Friction[END_REF][START_REF] Venkataraman | Automated versus floor trading: An analysis of execution costs on the paris and new york exchanges[END_REF].

The ownership concentration (Bloc) is negatively related to the Web disclosure but positively linked to all the 10 information asymmetry measures.

We also find that variable governance is negatively related to the internetbased disclosure. The result suggests that the firms under the one-tier government system release more information via the Internet. It seems that French firms use the two-tier system as a substitute for information transparency. Furthermore, no significant relationship between governance and the information asymmetry measures is observed. We may therefore use governance as an instrumental variable in the regression tests.

TABLE 3 ABOUT HERE

Regression estimation results

As discussed in the previous section, a reverse causality relationship may exist between information asymmetry and disclosure, and lead to an inconsistent OLS estimator. The Hausman test is therefore introduced to check for this potential endogenous problem. Using Governance as the instrumental variable, the Hausman test results (Table 4) indicate that the dependent variables are not affected by the endogeneous effect. The OLS regression model is therefore used in the next analysis.

TABLE 4 ABOUT HERE

As the link between Internet-based disclosure and information asymmetry is analyzed for two different periods (three and six months), the empirical results are presented through two different tables (Tables 5 and6). Both tables contain five models according to the measure of information asymmetry (Relative Spread, time-weighted quoted spreads, effective spreads, PIN and AdjPIN).

Models 1 to 3 are developed using the variations of spread in relation to the Web disclosure, the turnover ratio, the stock return volatility, the ownership concentration and the price level. Models 4 and 5 are developed to refine the analysis by using PIN and Adjusted PIN as dependent variables.

TABLES 5 AND 6 ABOUT HERE

We can observe that the coefficients of Score in the first three models are significantly negative at the 1% level. AdjPIN. This confirms our findings in models 1 to 3. The effect of Internetbased disclosure on the spread is only due to information asymmetry.

Therefore, models 4 and 5 provide strong support for the impact of Web-based disclosure on the reduction of information asymmetry. This result is proved whatever the period, either three or six months. Therefore, we validate our hypothesis.

Furthermore, we find that the Turnover coefficient is significantly negative in all the models. This is consistent with the theory that higher levels of trading volume will improve stock liquidity, therefore leading to a reduction of information asymmetry. We ran the VIF test to control the multicollinearity and the results show that no variance inflation factor values are greater than 1.8.

We used the Breusch-Pagan test to control for the potential risk of heteroscedasticity; the results indicate that some models do not satisfy the constant variance assumption. We therefore ran the regression with robust standard errors to control for the heteroscedasticity problem; the results (which are not reported here) indicate that the negative relationship between Internetbased disclosure and information asymmetry are not affected by heteroscedasticity. Our empirical results are therefore robust.

Overall, these results are consistent with the specificities of the French institutional environment. France belongs to the category of code-law countries (by opposition to the category of common-law countries). Code-law countries such as France are characterized by high ownership concentration, a model of corporate governance that is less oriented towards the shareholders and with less information content of accounting information that is reinforced by less frequent disclosure. As a consequence, Web-based disclosure in code-law countries may play a greater role in reducing information asymmetry between managers and shareholders. Furthermore, our findings highlight the importance of the network technology in the reduction of information asymmetry.

Conclusion

Firm disclosure is one of the fundamental elements affecting the efficiency of the capital market [START_REF] Healy | Information asymmetry, corporate disclosure, and the capital markets: A review of the empirical disclosure literature[END_REF][START_REF] Shaw | Corporate disclosure quality, earnings smoothing, and earnings' timeliness[END_REF]. It is important for managers, investors and regulators to understand the interaction between information disclosure practices and information asymmetry.

This paper focuses on online disclosure practices resulting from the rapid growth in the use of the Internet for financial reporting [START_REF] Marston | Corporate reporting on the internet by German companies[END_REF][START_REF] Bollen | Measuring and explaining the quality of internet investor relations activities: A multinational empirical analysis[END_REF]. The main objective is to analyze how the use of the Internet for disclosure affects information asymmetry in the capital market.

As an extension of previous research, an index consisting of 40 items is developed in order to assess the information released via the Internet in France.

Based on a sample of 180 French listed companies belonging to the SBF 250 index, we observe a strong negative relationship between Internet disclosure and the level of information asymmetry. These findings are consistent with research carried out in other countries, and the characteristics of the French institutional environment. The empirical findings suggest that it is important for French quoted companies to increase information transparency in order to reduce information asymmetry and improve investor relations.

The relationship between financial disclosure and information asymmetry is as "regulated information":

• The annual financial report;

• The half-yearly financial report;

• The quarterly financial disclosure;

• The report on internal control procedures and reports from independent auditors on the aforementioned reports;

• The news release concerning fees paid to independent auditors;

• Monthly statement on the total number of voting rights and the number of shares making up the share capital;

• The description of share buy-back programs;

• Privileged information;

• The news release setting out the procedures for providing a prospectus;

• The notice describing the means by which information will be made available to shareholders prior to a shareholders' meeting; 4 AMF ("Autorité des Marchés Français") stands for French Financial Authority.

5 Securities Exchange Committee 6 The item "annual reports of former years" is considered as information content in the study of [START_REF] Marston | Corporate reporting on the internet by German companies[END_REF]; we treat it as an advantage of Internet presentation in items 21 and 22.

7 For example, item 35: Investor club or forum, item 36: Site available in a choice of third language.

8 Under the one-tier system, a company is operated by one corporate body that undertakes both the management and monitoring functions. Under the two-tier system, a company is governed by two separate bodies: the board of directors takes the function of management while the supervisory board assures the function of control and supervision. One-tier firms are coded 0, while two-tier firms are coded 1.

Note:

R_Spread is the average quoted spread; W_Spread is the time-weighted average quoted spread; E_Spread is the average effective spread; PIN is the probability of informed trading defined by [START_REF] Easley | Liquidity, information, and infrequently traded stocks[END_REF]; AdjPIN is the adjusted PIN developed by [START_REF] Duarte | Why is pin priced?[END_REF].

Can Internet-Based Disclosure Reduce Information Asymmetry? 58

  ;[START_REF] Bamber | Discretionary management earnings forecast disclosures: Antecedents and outcomes associated with forecast venue and forecast specificity choices[END_REF][START_REF] Healy | Stock performance and intermediation changes surrounding sustained increases in disclosure[END_REF][START_REF] Botosan | A re-examination of disclosure level and the expected cost of equity capital[END_REF][START_REF] Brown | How disclosure quality affects the level of information asymmetry[END_REF].The indirect method uses an assessment index created by researchers. Since the work of[START_REF] Pirchegger | Financial information on the internet: A survey of the homepages of austrian companies[END_REF], the measurement of Internetbased disclosure has become increasingly sophisticated. This can be seen not only in the increase in the number of items on the checklist, but also by the introduction of new criteria in the division of items.[START_REF] Ettredge | Dissemination of information for investors at corporate web sites[END_REF] use a checklist of items that distinguishes the SEC 5 required disclosure from voluntary disclosure items and they attempt to analyze the respective determinants separately.Since no direct measurement of our sample of French listed companies is available, we choose to follow the indirect method. In order to evaluate Internet-based disclosure, an index of 40 items is created on the basis of five prior studies[START_REF] Deller | A survey on the use of the internet for investor relations in the USA, the UK and Germany[END_REF][START_REF] Debreceny | Financial reporting web sites: What users want in terms of form and content[END_REF][START_REF] Pirchegger | Financial information on the internet: A survey of the homepages of austrian companies[END_REF][START_REF] Ettredge | Dissemination of information for investors at corporate web sites[END_REF]

  incorporated in the regression model to analyze the determinants of information asymmetry. These include turnover, stock return volatility, share price and ownership concentration. The selection of the control variables is based on the prior literature[START_REF] Chang | Does disclosure quality via investor relations affect information asymmetry[END_REF][START_REF] Lang | Cross-sectional determinants of analyst ratings of corporate disclosures[END_REF][START_REF] Leuz | The economic consequences of increased disclosure[END_REF] Petersen & Plenborg 2006, etc.).

a

  classic subject and has been studied in prior research by examining traditional paper-based media such as annual reports. One might ask whether it is necessary to retest this relationship by analyzing the information spread via the Internet. Indeed, the Internet could be treated as an information media, along with other traditional paper-based media. However, certain special features of Internet-based disclosure highlights the necessity to retest the impact of this media. Internet technologies can gather a huge amount of information and this far exceeds traditional paper-based media. Another consequence is that rumors circulate fast online. Is Internet-based disclosure a useful communication tool to reduce the information gap, or is it a costly tool which causes more misunderstandings? Answers to these questions require Can Internet-Based Disclosure Reduce Information Asymmetry? 34 more testing. The empirical results of this study prove the positive effect of Web-based disclosure on the reduction of information asymmetry. Although there are some potential drawbacks, Internet-based disclosure can still effectively reduce the problem of information asymmetry. More importantly, our results show that Internet technologies have greatly enriched information presentation methods. And these user-friendly Web technologies, such as financial reports in Excel format, are useful to reduce the information gap. These findings emphasize the need for the normalization of Web disclosure in both content and presentation perceptions. This research is not without limitations. The negative effects of financial reporting, such as losing an advantage in a competitive market, are not considered in our research. Furthermore, the research only examines certain factors that may influence information asymmetry. Other new factors, such as the role of financial analysts, should be introduced into future research. Lastly, as firms are generally motivated to lower their cost of capital, it would be interesting to determine whether the impact of Web disclosure on information asymmetry helps the firm to benefit from a lower cost of capital over the release of January 22, 2007, summarized the following documents, which are listed in article 221-1 of the AMF's General Regulations,

  of quarterly accounts by French firms on 1st and 3rd quarters is not mandatory. Only turnover publication is required. 3 Directive 2004/109/CE of the European Parliament and the Council of 15 December, 2004, on the harmonization of transparency requirements in relation to information about issuers whose securities are admitted to trading on a regulated market.

Table 3 -

 3

Panel A shows the correlation of a three month period while Panel B presents a six month period. Both show the Pearson correlations between information asymmetry and the explanatory variables. At first, the five measures of information asymmetry (Relative Spread, time-weighted quoted spreads, effective spreads, PIN and AdjPIN) are significantly and positively related one to another. The level of Internet-based voluntary disclosure (Score)

  The results indicate that enhanced disclosure via the Internet reduces the level of spread which is in accordance with past research[START_REF] Petersen | Voluntary disclosure and information asymmetry in Denmark[END_REF]. Compared with Spread, PIN and AdjPIN are more precise measures of information asymmetry because they exclude other effects, such as fixed costs, inventory effects or liquidity effects.According to previous research in market microstructure, PIN and AdjPIN can better capture information asymmetry. Results in models 4 and 5 show that Web-based disclosure is negatively and significantly related to PIN and

Table 1 -Sample by sector

 1

	Sector	Number Percentage
	Oil and Gas	6	3.33%
	Basic Materials	4	2.22%
	Industrials	41	22.78%
	Consumer Goods	38	21.11%
	Health Care	14	7.78%
	Consumer Services	34	18.89%
	Telecommunications	2	1.11%
	Utilities	6	3.33%
	Technology	35	19.44%
	Total	180	100.00%

Table 2 -Descriptive statistics

 2

	Window	Variable	Mean	Std. Dev.	Min	Max
		Score	0.4219	0.1262	0.1250	0.8500
		LnPrice	3.6830	0.9044	0.0807	6.4629
		Bloc	0.5192	0.2394	0.0000	1.0000
		Governance	0.2889	0.4545	0.0000	1.0000
		R_Spread	0.0068	0.0066	0.0005	0.0406
		E_Spread	0.0047	0.0046	0.0004	0.0245
		W_Spread	0.0089	0.0063	0.0022	0.0472
	3 months	PIN	0.1818	0.1121	0.0000	0.7071
		AdjPIN	0.1578	0.0996	0.0000	0.7071
		Turnover	-12.8326	1.0501	-15.4618	-10.6601
		Volatility	0.6970	2.8034	0.0102	31.4317
		R_Spread	0.0070	0.0069	0.0004	0.0423
		E_Spread	0.0049	0.0048	0.0004	0.0266
		W_Spread	0.0091	0.0063	0.0023	0.0462
	6 months	PIN	0.1794	0.0979	0.0002	0.5461
		AdjPIN	0.1636	0.0805	0.0000	0.5461
		Turnover	-12.8634	1.0423	-15.4525	-10.7184
		Volatility	0.5281	2.0663	0.0116	21.3918
	is measured by the standard deviation of daily stock returns; LnPrice is the stock price
	measured in logarithm; Bloc represents the proportion of capital held by blockholders
	(those owning 5% or more of a firm's stock); Governance is a binary variable defined to

Note:

The number of observations is equal to 180; Score is the level of Internet-based disclosure; R_Spread is the average quoted spread; W_Spread is the time-weighted average quoted spreads; E_Spread is the average effective spread; PIN is the probability of informed trading defined by

[START_REF] Easley | Liquidity, information, and infrequently traded stocks[END_REF]

; AdjPIN is the adjusted PIN developed by

[START_REF] Duarte | Why is pin priced?[END_REF]

; Turnover is the rotation rate of stocks; Volatility

Table 3 -Pearson correlation coefficients Panel A -three month study period (July to September 2007)

 3

		Score	R_Spread E_Spread	W_Spread	PIN	AdjPIN	Turnover	Volatility	LnPrice	Bloc
	R_Spread	-0.581
		***
	E_Spread	-0.5812	0.9821
		***	***
	W_Spread	-0.5537	0.9497	0.9252
		***	***	***
	PIN	-0.4382	0.4726	0.4542	0.4718
		***	***	***	***
	AdjPIN	-0.4279	0.4067	0.4033	0.3864	0.6161
		***	***	***	***	***
	Turnover	0.5573	-0.7529	-0.753	-0.6738	-0.468	-0.5485
		***	***	***	***	***	***
	Volatility	0.1208	-0.1202	-0.122	-0.1289	-0.1303	-0.1547	0.1248
					*	*	**	*
	LnPrice	0.0593	0.029	-0.0186	0.0039	-0.025	0.0125	-0.1017	0.0566
	Bloc	-0.3768	0.4044	0.3871	0.4337	0.3071	0.451	-0.4717	-0.1819	0.1307
		***	***	***	***	***	***	***	**	*
	Governance	-0.1476	0.0873	0.0719	0.1009	-0.0138	0.063	-0.1273	-0.0765	0.0804	-0.0858
		**						*

six month study period (July to December 2007) Note: The

  E_Spread is the average effective spread; PIN is the probability of informed trading defined by Easley et al. AdjPIN is the adjusted PIN developed by[START_REF] Duarte | Why is pin priced?[END_REF]; Turnover is the rotation rate of stocks; Volatility is Can Internet-Based Disclosure Reduce Information Asymmetry? 56 measured by the standard deviation of daily stock returns; LnPrice is the stock price measured in logarithm; Bloc represents the proportion of capital held by blockholders (those owning 5% or more of a firm's stock); Governance is a binary variable defined to measure the governance system: one-tier firms are coded 0, while two-tier firms are coded 1.

	Can Internet-Based Disclosure Reduce Information Asymmetry?
					57
	R_Spread E_Spread W_Spread PIN AdjPIN Turnover Volatility LnPrice Bloc (1996); Score -0.5845 *** -0.5822 *** -0.5638 *** -0.4552 *** -0.4726 *** 0.5632 *** 0.1207 0.0593 -0.3768 *** Governance -0.1476	R_Spread 0.9838 *** 0.9549 *** 0.5663 *** 0.5316 *** -0.7706 *** -0.1279 * 0.0079 0.4189 *** 0.0807	E_Spread 0.9336 *** 0.5377 *** 0.5123 *** -0.7739 *** -0.1317 * -0.0472 0.3934 *** 0.0706	W_Spread 0.534 *** 0.5074 *** -0.7016 *** -0.1361 * -0.0195 0.4374 *** 0.0931	PIN 0.7064 *** -0.57 *** -0.1737 -0.1294 AdjPIN Turnover Volatility LnPrice -0.6147 *** 0.1293 ** * * 0.0074 0.0376 -0.0814 0.058 0.3644 0.4155 -0.491 -0.1794 0.1307 *** *** *** ** * 0.0543 0.0067 -0.1115 -0.0799 0.0804	Bloc -0.0858

number of observations is equal to 180; * indicates Significance at the 10% level, ** at the 5% level, *** at the 1% level Score is the level of Internet-based disclosure; R_Spread is the average quoted spread; W_Spread is the time-weighted average quoted spread; **

Table 4 -Hausman's Specification Test Results

 4

	Period	Dependent Variable	F	Prob>F
		R_Spread	0.21	0.6494
		E_Spread	0.59	0.4437
	3 months	W_Spread	0.09	0.763
		PIN	1.6	0.2072
		AdjPIN	0.1	0.7546
		R_Spread	0.17	0.6823
		E_Spread	0.41	0.5228
	6 months	W_Spread	0.05	0.8186
		PIN	0.05	0.8259
		AdjPIN	1.07	0.3031

Table 5 -Regression results for the 3 month study period Note:

 5 The number of observations is equal to 180; * indicates Significance at the 10% level, ** at the 5% level, *** at the 1% level Score is the level of Internet-based disclosure; R_Spread is the average quoted spread; W_Spread is the time-weighted average quoted spread; E_Spread is the average effective spread; PIN is the probability of informed trading defined by[START_REF] Easley | Liquidity, information, and infrequently traded stocks[END_REF]; AdjPIN is the adjusted PIN developed by[START_REF] Duarte | Why is pin priced?[END_REF]; Turnover is the rotation rate of stocks; Volatility is measured by the standard deviation of daily stock returns; LnPrice is the stock price measured in logarithm; Bloc represents the proportion of capital held by blockholders (those owning 5% or more of a firm's stock).

	Dependent Variable

Table 6 -Regression results for the 6 month study period Note:

 6 The number of observations is equal to 180; * indicates Significance at the 10% level, ** at the 5% level, *** at the 1% level Score is the level of Internet-based disclosure; R_Spread is the average quoted spread; W_Spread is the time-weighted average quoted spread; E_Spread is the average effective spread; PIN is the probability of informed trading defined by[START_REF] Easley | Liquidity, information, and infrequently traded stocks[END_REF]; AdjPIN is the adjusted PIN developed by[START_REF] Duarte | Why is pin priced?[END_REF]; Turnover is the rotation rate of stocks; Volatility is measured by the standard deviation of daily stock returns; LnPrice is the stock price measured in logarithm; Bloc represents the proportion of capital held by blockholders (those owning 5% or more of a firm's stock)

	Dependent Variable

[START_REF] Pirchegger | Financial information on the internet: A survey of the homepages of austrian companies[END_REF][START_REF] Ettredge | Dissemination of information for investors at corporate web sites[END_REF]

As we discard days with no trading activity, the logarithm of volume is always defined.

measure the governance system: one-tier firms are coded 0, while two-tier firms are coded 1.

• Information about modifications in the rights attached to different categories of shares and the issuances of new shares.

Notes:

Overlap with prior research: [START_REF] Marston | Corporate reporting on the internet by German companies[END_REF]


Abdallah Saffidine

Nicolas Jouandeau

Cédric Buron

Tristan Cazenave

Abdallah Sadine

Material Symmetry to Partition Endgame Tables

à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

Retrograde analysis is a tool to build omniscient endgame databases. It has been used in chess to build endgame databases of up to six pieces [START_REF] Thompson | Retrograde analysis of certain endgames[END_REF][START_REF] Thompson | 6-piece endgames[END_REF][START_REF] Nalimov | Space-ecient indexing of chess endgame tables[END_REF]. It has also been used in a similar way to build endgame databases for checkers [START_REF] Schaeer | Building the checkers 10-piece endgame databases[END_REF] that have helped solving the game [START_REF] Schaeer | Checkers is solved[END_REF]. It has also been successfully used for strongly solving the game of awari with a parallel implementation that evaluated all the possible positions of the game [START_REF] John W Romein | Solving awari with parallel retrograde analysis[END_REF]. Other games it has helped solving are fanorona [START_REF] Maarten | Best play in fanorona leads to draw[END_REF] and nine men's morris [START_REF] Gasser | Solving nine men's morris[END_REF]. Retrograde analysis has also been applied to chinese chess [START_REF] Haw-Ren Fang | Construction of chinese chess endgame databases by retrograde analysis[END_REF], kriegspiel [START_REF] Ciancarini | Solving kriegspiel endings with brute force: the case of KR vs[END_REF], and go [START_REF] Cazenave | Generation of patterns with external conditions for the game of Go[END_REF].

An important limitation on the use of endgame tables is the size needed to store all the computed results. Consequently, elaborate compression techniques have been proposed and they have been instrumental in achieving some of the aforementioned results [START_REF] Schaeer | Building the checkers 10-piece endgame databases[END_REF]. An orthogonal approach to alleviate the memory bottleneck is to use symmetries to avoid storing results that can be deduced from already stored results by a symmetry argument. There are two kinds of such symmetry arguments. Geometrical symmetry is the simplest case [START_REF] Joseph | Pattern databases[END_REF]: for instance if a chess position p does not feature any pawn and castling rights have been lost then any combination of the following operations yields a position equivalent to p. Flipping pieces along a vertical axis between the 4th and the 5th columns, ipping pieces along a horizontal axis between the 4th and the 5th rows, or rotating the board. Material symmetry is typical from card games, in particular when suits play an equivalent role. In most trick-taking games, for instance, if a position p only contains Hearts, any position obtained by replacing all cards with cards of same rank from an other suit is equivalent.

State-of-the-art engines for card games such as skat or bridge already use material symmetry detection in their transposition and endgame tables. However, recognising the most general form of material symmetry is not as straightforward in some other games, notably chinese dark chess. In this paper, we propose a principled framework to detect material symmetry and show how it can be applied to three games: chinese dark chess, dominoes, and skat. At the core of our method lies the sub-graph isomorphism problem which has been extensively studied in computer science [START_REF] Jerey | An algorithm for subgraph isomorphism[END_REF][START_REF] Kuramochi | Frequent subgraph discovery[END_REF].

Chinese dark chess is a popular game in Asia [START_REF] Chen | Chinese dark chess[END_REF]. One of the key feature of endgame databases in chinese dark chess is that some combinations of pieces are equivalent. It means that in some endgames, a piece can be replaced by another piece without changing the result of the endgame. Therefore an endgame computed with the rst piece can be used as is for the endgame positions containing the other piece in place of the rst piece. This property reduces the number of endgame databases that have to be computed. Using the relative ordering of pieces instead of the exact values is similar to partition search in bridge that store the relative ordering of cards in the transposition table instead of the exact values [START_REF] Matthew | Partition search[END_REF]. Dominoes is also a popular game and in the endgame some of the values of pieces can be replaced by other values without changing the outcome of the game. We use this property to compute a reduced number of endgame tables for the perfect information version of the game.

Skat is a popular game in Germany. Here again in the endgame, some cards can be replaced with other cards. We present in this paper the memory reduction that can be expected from using this property to compute complete information endgame tables. Perfect information endgame tables are important in skat since the Monte Carlo approach in Skat consists in solving many perfect information versions of the current hand [START_REF] Kupferschmid | A skat player based on Monte-Carlo simulation[END_REF][START_REF] Buro | Improving state evaluation, inference, and search in trick-based card games[END_REF][START_REF] Richard | Search, Inference and Opponent Modelling in an Expert-Caliber Skat Player[END_REF]. Using endgame tables enables to speedup the solver.

The second section describes chinese dark chess, dominoes, and skat.

We then show in Section 3 how material interaction graphs can be constructed for these domains. Section 4 recalls the principles of endgame table construction.

The fth section gives experimental results, and the last section concludes. k K , 7 7 all opponent piece except pawns Guard (G) g G , 6 6 all inferior opponent pieces Bishop (B) b B , 5 5 all inferior opponent pieces Knight (N) n N , 4 4 all inferior opponent pieces Rook (R) r R , 3 3 all inferior opponent pieces Cannon (C) c C , 2 2 all opponent pieces jump capture Pawn (P) p P , 1 1

opponent king and pawns

At the beginning, pieces are randomly placed on the board, facing down. Typical positions thus allow 3 types of moves, ipping an unknown piece, moving a piece to an adjacent free square, capturing an opponent piece.

If a player runs out of legal moves, possibly because all their pieces have been captured, the game ends and that player loses the game. The game ends with a draw if no capture is made for 40 plies. b5(k) d8(P); d7(R) d4(p); c7(G) c6(c); c4(C) c4-c6; c5(p) c3(B); b6(r) c3-c4; b6-c6 b7-b6; c2(C) c4-d4; b3(g) d4-c4; b3-c3 c4-d4;

It is now rst player's turn to play. First player is white. First player possible moves are: b5-b6; c3-b3; c3-c2; c3-d3; c5-c4. Second player possible moves are : c2-c5; c6-c5; c6-b6; c6-c7; d4-c4; d7-c7. [START_REF] Buro | Improving state evaluation, inference, and search in trick-based card games[END_REF] Sometimes, the outcome of the game depends only on player's turn, even if a player has stronger piece, as shown in Fig. 2. If it is black to play, then white wins (for example: b2-b1 c3-c2; b1-a1 c2-b2; a1-a2 b2-a2; white wins). If it is white to play, then it is a draw game (for example : c3-c2 b2-b3; c2-b2 b3-c3; b2-b3 c3-c2; b3-c3 c2-b2... until draw).

The game of Dominoes

The game of dominoes is an ancient game, played with rectangular tiles called dominoes. We do not know precisely when or where the game appeared, but it is widely played all around the world.

The tiles of the game are rectangular and are divided into two sides. Each side represents a number of points between 0 (empty) and 6, as shown in Fig. 3a.

They are called dominoes or simply tiles.

In this article, the tiles will be represented by the two numbers that are written on it. For instance the domino in Fig. 3a is represented by [START_REF] Buro | Improving state evaluation, inference, and search in trick-based card games[END_REF][START_REF] Joseph | Pattern databases[END_REF]. The tile (i, j) is the same as the tile (j, i) and only appears once in the set. Thus, there are 28 tiles: (0, 0), (0, 1), . . . , (0, 6), (1, 1), (1, 2), . . . , [START_REF] Haw-Ren Fang | Construction of chinese chess endgame databases by retrograde analysis[END_REF][START_REF] Haw-Ren Fang | Construction of chinese chess endgame databases by retrograde analysis[END_REF].

The board of the game of dominoes consists of a chain of dominoes already laid down. At the beginning of the game, the rst player puts his strongest domino (the one which has the most points) on the table and starts the chain.

Then, the players take turn laying down one tile they possess according to the following matching constraint. To play a tile, it must have at least one side with the same number of points of one of the tiles at the end of the chain on the table (Fig. 3). If a player cannot play a tile, they draw a tile from the stock or pass when there are no stock tiles remaining.

If a player has laid down all their tiles, or if the stock is empty and no player can play, the game ends and the player with fewer points in hand wins.

While there are multi-player variants of the game of dominoes, we focus in our experiments on the two-player case. Additionally, since we focus on the endgames, we assume that the stock is empty and, as a consequence, that the game is perfect information. Our method to detect material symmetry extends easily to other settings.

• • • • • • (a) (1, 5) domino. • • • • • • • • • • • • • • •
(b) Chain of three tiles after a player has played (3, 2).

Fig. 3: A tile and a chain of matching tiles in dominoes.

Skat

Skat is a card game for three players. Skat is played with 32 cards using 8 ranks (710, Jack, Queen, King, and Ace) and 4 suits (Club ♣, Spade ♠, Heart ♥, and Diamond ♦). Each card is associated to a suit and a rank, for instance we have the Jack of Heart (♥J) or the Ten of Spade (♠T). A game of skat is divided into a bidding and a playing phase. Before bidding, each player receives 10 cards and the two remaining ones are placed on the center, and called the Skat.

Bidding The bidding system is quite complex and can lead to three dierent types of game: suit game, grand game, or null game. 1 In each type, the player who made the highest bid gets the skat and plays against the two other ones.

In the suit game, a suit is chosen as trump. The order of cards is so: ♣J, ♠J, ♥J, ♦J, then the trump suit: A, T, K, Q, 9, 8, 7, then each of the remaining suits, in the same order.

In the grand game, there is no trump suit, but the Jacks are still considered as trumps. The order for the other cards are the same as in the suit game.

In the null game, there is no trump. The order of the cards is not the same as in the other games: A, K, Q, J, T, 9, 8, 7.

Playing endgames where all cards are Spades, and both are equivalent to that where all cards are Clubs and to that with Diamonds. Indeed, we can exhibit a mapping from one class C to an equivalent class C 0 that will associate to each position p ∈ C a position p 0 ∈ C 0 such that the score and optimal strategy in p can easily be deduced from the score and optimal strategy in p 0 .

As a result, it is only necessary to build one endgame database for each equivalence class of endgames, rather than one for each class of endgames. A 1 For more details, we refer to the rules from the International Skat Players Association: http://www.ispaworld.org/downloads/ISkO-rules-2007-Canada.pdf.

rst approach to avoid building unnecessary endgame databases is to proceed to some form of normalization. However, the normalization process to be adopted is not always trivial. We propose here a principled method to nd representatives of the equivalence classes. The basic idea is to represent interactions between pieces in a graph. The interaction can be specic to a game. For example in chinese dark chess the interaction is a capture whereas it is a connection in dominoes. Fig. 4 gives the graph for the pieces of chinese dark chess. There is an arrow from one piece to another if the rst piece can capture the second one. Fig. 6 gives the graph for dominoes and Fig. 5 gives the graph for skat assuming a suit game with Clubs as trump. rst endgame and to compare it with the sub-graph of the second endgame.

♣7 ♣8 ♣9 ♣Q ♣K ♣T ♣A ♣J ♠7 ♠8 ♠9 ♠Q ♠K ♠T ♠A ♠J ♥7 ♥8 ♥9 ♥Q ♥K ♥T ♥A ♥J ♦7 ♦8 ♦9 ♦Q ♦K ♦T ♦A ♦J
The comparison consists in nding if the two sub-graphs are isomorphic. Subgraph isomorphism is a hard problem, but for the games that we address a naive algorithm is fast enough to compare sub-graphs of interest [START_REF] Jerey | An algorithm for subgraph isomorphism[END_REF].

Endgame Tables

Retrograde analysis is completed in two steps. The rst step consists in enumerating all winning positions for one player. The second step consists in repeatedly nding the new winning positions two moves away from existing ones. When no new position is found the algorithm stops and the endgame table has been computed. For each combination of pieces a dierent endgame table is computed.

There are multiple ways to generate the new winning positions two moves away from already computed winning positions. A naive approach consists in running through all possible positions and checking if they are two moves away from already computed ones. A more elaborate approach consists in doing unmoves from already computed winning positions to nd a restricted set of candidate new winning positions.

because our generic implementation using sub-graph isomorphism is slower than existing domain specic implementations, so these results are not included.

The hash code of a position has to be computed in two steps. First, obtain the correspondence between the pieces and their representatives, then combine the representative pieces with their locations into a hash code. In our implementation, the sub-graph isomorphism part is not optimized. However it is possible to pre-compute all sub-graph isomorphims between tables and to have a fast correspondence between a table and its representative.

Equivalence classes

Assume that the endgame table is split in multiple tables depending on the number of game elements (pieces/tiles/cards). Assume also that the resulting tables are split further according to the sets of elements that constitute the positions.

Such a decomposition is natural and makes distributing the workload easier as there is no dependency between dierent sets of elements if they have the same number of elements [START_REF] Goldenberg | Trellisdag: A system for structured dag scheduling[END_REF]. Thus, each set of game elements has a corresponding endgame table which can be stored in its own le.

We begin by comparing the number of possible les without using the reduction and the number of remaining les with our method. Material symmetry allows us to reduce signicantly the number of needed les. For instance, for chinese dark chess with 4 elements, there are 1737 sets of elements that are consistent with the rules of the game. However many such sets are equivalent, and if we detect material symmetry, we can reduce the number of needed sets down to 186, which represent a reduction factor of 9.34. Table 2 shows the number of sets, the number of sets needed when material symmetry is used, and the resulting reduction factor for a given number of game elements in chinese dark chess and dominoes. The reduction factors presented in Table 2 do not necessarily match with the memory actually needed to store the endgame tables. Indeed, dierent sets of pieces might lead to tables of dierent size and equivalence classes might have dierent number of elements. For instance, in chinese dark chess the Kkm le corresponds to 29,760 positions, while the kPP le corresponds only to 14,880 positions because the two pawns are indistinguishable. In this section, we assume that we store the result for every position in the corresponding le using a perfect hashing function, or index.

We did not use any advanced compression mechanism [START_REF] Schaeer | Building the checkers 10-piece endgame databases[END_REF]. For instance, chinese dark chess has 2 geometrical symmetries and we used 2 bits to encode whether a position was won, lost, or draw. Therefore, for each le we need half as many bits as the number of positions.

Table 3 shows the size needed for endgame tables with various number of elements using a perfect hashing representation. In this table, we added the dierent possible positions of each le for a given number of elements with and without the reduction, and then calculated the real reduction factor. Notice that the reduction factor in Table 3 are close to those in Table 2 but are not always the same. We have presented a general method based on sub-graph isomorphism that allows detection material symmetries. We have shown that it could be applied to skat, dominoes, and chinese dark chess. Detecting material symmetry makes it easier to build larger endgame databases. While nding a representative for positions that are equivalent under material symmetry (that is, dening a normal form) for skat and dominoes is relatively easy, the chinese dark chess case is more intricate as the relationship between the dierent pieces is more elaborate.

Our approach solves this problem in chinese dark chess and allows a reduction factor between 5 and 10 in the size needed for storing the endgame tables.

Note that although we do not report any time measurement, a signicant reduction factor can also be expected for the time needed to compute the endgame tables. In our framework, we propose to store a le mapping sets of pieces to their representative. This le is much smaller than the corresponding endgame tables.

Thus, the only runtime cost induced by our method is an additional indirection when looking up a position in the database.

A generalisation of transposition tables has been proposed by Furtak and Buro in order to regroup cases that have similar structures but dierent payos [START_REF] Furtak | Using payo-similarity to speed up search[END_REF]. Determining to which extent the proposed method for detecting material symmetry can be extended to account for payo similarity seems to be a promising line for future work.

Fig. 1

 1 Fig. 1 shows the resulting board situation after the following 10 turns (Parentheses indicate revealed piece for ipping moves. Moving and capturing moves indicate two coordinates. Unknown pieces are represented with white circles.):

Fig. 1 :

 1 Fig. 1: Sample chinese dark chess position after 10 turns of play.

Fig. 2 :

 2 Fig. 2: Sample chinese dark chess endgame position where the outcome depends on who's next turn to play.

  The playing part of the game is a succession of tricks. Each trick, the player who won the previous trick plays rst, and decides which suit is played in the trick. The other players have to play this suit. If a player cannot play the suit the rst player played, he must play a trump. If he has neither the rst suit played nor trump, he can play any other suit.If there is a trump in the trick, the highest trump wins the trick. If there is not, the highest card of the suit the rst player played wins. The player who won the trick put the cards of the trick behind him and begins the next one.Counting the points When all the cards have been played, each team count their points. The team which got most of the points wins the round. The points are distributed as follows. A: 11 points, T: 10 points, K: 4 points, Q: 3 points, J: 2 points, 9,8, and 7: 0 points 3 Detecting material symmetry Multiple games feature classes of endgames that are globally equivalent one to another. For instance, in a trick-taking card game such as bridge, the class of 8 cards endgames where all cards are Hearts is equivalent to the class of 8 cards

Fig. 4 :

 4 Fig.4: Capture relationship in chinese dark chess. The allowed captures for black were not represented so as to avoid cluttering the graph.

Fig. 5 :Fig. 6 :

 56 Fig. 5: Trick winning relationship for cards in skat assuming Clubs (♣) are trumps. To avoid cluttering, not all edges are drawn. The full graph is obtained by taking the transitive closure of the graph represented.

Table 1 :

 1 Pieces representation and capture rules in chinese dark chess.

	2 Domains addressed
	2.1	Chinese dark chess
	Chinese dark chess is a stochastic perfect information game that involves
	two players on 4 × 8 rectangular board. Each player starts with one king, two
	guards, two bishop, two knights, two rooks, two cannons and ve pawns that are
	the same pieces as in chinese chess. The pieces can be denoted with Chinese
	characters or numbers as shown in Table 1. Pieces can move vertically and
	horizontally from one square to an adjacent free square. Captures are done on
	vertical and horizontal adjacent squares except for cannons that capture pieces by jumping over another piece. Such jump is done over a piece (called the jumping piece) and on a piece (called the target piece). Free spaces can stand between its
	initial position and the jumping piece and between the jumping piece and the
	target position. A piece can capture another piece according to the possibilities
	mentioned in Table 1. Considering numbers representation, pieces can capture
	lower or equal numbers (except the king that cannot capture any pawn, and
	except the cannon that can capture any piece).
		Table 1 summarizes alternative pieces' names, each side's icons and possible
	captures. Column titled Capture rule lists the pieces that a piece can capture.
		Names	Representation	Capture rule	Note
		King (K)

Table 2 :

 2 Total number of tables and number of representatives.

	Game	Elements Total Representatives Reduction factor
		2	49	8	6.13
	chinese dark chess	3 4 5 6	378 1737 5946 16,524	46 186 672 2240	8.22 9.34 8.92 7.38
		7	39,022	6694	5.83
		8	80,551	17,662	4.56
		3	4032	20	201.6
	dominoes	4 5	30,303 180,180	61 185	496.8 973.9
		6	868,140	563	1542.0

Table 3 :

 3 Size of the endgame database with a perfect hashing representation. the position with reversed colors is in the table. Finally, a position is a draw if it and the reverse position are not in table. Again, we can split the endgame table according to the set of pieces that constitute it and use one le for each possible set.We have computed endgames tables with only won positions. Table4gives the total number of won positions that would need to be stored for a given number of game elements. It also displays the number of positions that need to be stored if we use material symmetry and only store one representative le for each equivalence class. The last column indicate the savings in terms of number of stored positions when material symmetry is taken into account.

		Game	Elements	Total	Representatives	Reduction
				Positions Memory Positions Memory	factor
			2	4.961×10 4 2.97 KB 7.936×10 3	496 B	6.13
		chinese dark chess	3 4 5 6 7	9.999×10 6 610.3 KB 1.131×10 6 69.02 KB 1.140×10 9 67.92 MB 1.142×10 8 6.81 MB 9.036×10 10 5.26 GB 1.013×10 10 603.8 MB 5.440×10 12 316.7 GB 8.002×10 11 46.58 GB 2.601×10 14 14.78 TB 5.247×10 13 2.98 TB	8.84 9.92 8.92 6.80 4.96
			8	1.014×10 16 576.1 TB 2.756×10 15 156.7 TB	3.68
			3	21,168 2.58 KB	92 11.50 B	230.09
		dominoes	4 5	550,368 67.18 KB 8,026,200 979.76 KB	996 124.50 B 7,854 981.75 B 1021.93 552.58
			6	82,556,550 9.84 MB	53,790 6.57 KB 1541.99
	5.3	Won positions
	The following alternative representation for endgame tables can be used, we will
	show that reduction factors are similar under this representation as well. For a
	given set of pieces, store the list of won positions. We can detect that a position
	is lost if

Table 4 :

 4 Size of the endgame database when only storing won positions.

	Game	Elements	Total Representatives Reduction factor
	chinese dark chess	2 3 4	6448 1,650,763 156,204,805	744 171,516 15,418,377	8.67 9.62 10.13
	dominoes	3 4	22,785 409,234	104 747	219.09 547.84
		5	5,706,631	5,741	994.01
	6 Conclusion

ExperimentsIn this section we give experimental results for chinese dark chess and dominoes. We also experimented with skat but only for small numbers of cards


Nargess Nourbakhsh
email: nargess.nourbakhsh@nicta.com.au

Yang Wang
email: yang.wang@nicta.com.au

Fang Chen
email: fang.chen@nicta.com.au

GSR and Blink Features for Cognitive Load Classification

Keywords: Cognitive load, galvanic skin response, eye blink, machine learning

A system capable of monitoring its user's mental workload can evaluate the suitability of its interface and interactions for user's current cognitive status and properly change them when necessary. Galvanic skin response (GSR) and eye blinks are cognitive load measures which can be captured conveniently and at low cost. The present study has assessed multiple features of these two signals in classification of cognitive workload level. The experiment included arithmetic tasks with four difficulty levels and two types of machine learning algorithms have been applied for classification. Obtained results show that the studied features of blink and GSR can reasonably discriminate workload levels and combining features of the two modalities improves the accuracy of cognitive load classification. We have achieved around 75% for binary classification and more than 50% for four-class classification.

Introduction

Being continuously aware of user's mental status is an important step in making intelligent systems interacting with people. Such systems can properly change their interface and interactions to match the imposing workload with the current working memory of their user. In this way, the optimum performance will be obtained and many human errors will be avoided. Therefore, it is necessary to measure mental load accurately and in real-time.

Cognitive load is commonly used to refer to the load that performing a particular task imposes on the person's cognitive system [START_REF] Paas | Instructional Control of Cognitive Load in the Training of Complex Cognitive Tasks[END_REF]. Different methods have been applied for quantifying cognitive workload; however, not all of them are useful for developing adaptable systems. Subjective (self-reporting) [START_REF] Paas | Training Strategies for Attaining Transfer of Problem-Solving Skill in Statistics: A Cognitive-Load Approach[END_REF] and performance-based measurement [START_REF] Chandler | Cognitive Load While Learning to Use a Computer Program[END_REF] techniques have been widely used and, regarding implementation, are usually the most convenient methods. However, asking subjects to rate the experienced mental workload means several interruptions and distractions from performing the principal tasks. Moreover, both methods are post-task processing and can be done when the task is finished, thus are not useful for real-time cognitive load assessment. In contrast, human behaviors and physiological responses can continuously and nonintrusively demonstrate user's cognitive states while performing the intended task.

Several physiological signals have been used for cognitive load measurement: signals from heart [START_REF] Paas | Variability of Worked Examples and Transfer of Geometrical Problem-Solving Skills: A Cognitive-Load Approach[END_REF], eye [START_REF] Xu | Pupillary Response Based Cognitive Workload Measurement under Luminance Changes[END_REF], brain [START_REF] Berka | EEG Correlates of Task Engagement and Mental Workload in Vigilance, Learning, and Memory Tasks[END_REF][START_REF] Knoll | Measuring cognitive workload with low-cost electroencephalograph[END_REF] and skin [START_REF] Nourbakhsh | Using Galvanic Skin Response for Cognitive Load Measurement in Arithmetic and Reading Tasks[END_REF]. Galvanic skin response (GSR), which is electrical conductance of skin, is a low-cost, easily-captured, robust physiological signal. Previous studies have used skin conductance in detecting emotions [START_REF] Nakasone | Emotion Recognition from Electromyography and Skin Conductance[END_REF] or differentiating between stress and cognitive load conditions [START_REF] Niculescu | Stress and Cognitive Load in Multimodal Conversational Interactions[END_REF], and a few ones have found relations between GSR features and mental workload [START_REF] Nourbakhsh | Using Galvanic Skin Response for Cognitive Load Measurement in Arithmetic and Reading Tasks[END_REF][START_REF] Shi | Galvanic Skin Response (GSR) as an Index of Cognitive Load[END_REF]. Some others have tried but did not obtain satisfactory results for detecting cognitive load from GSR [START_REF] Haapalainen | Psycho-Physiological Measures for Assessing Cognitive Load[END_REF][START_REF] Ikehara | Assessing Cognitive Load with Physiological Sensors[END_REF].

Speech [START_REF] Huttunen | Effect of Cognitive Load on Speech Prosody in Aviation: Evidence from Military Simulator Flights[END_REF], pen input [START_REF] Ruiz | Using Pen Input Features as Indices of Cognitive Load[END_REF] and eye movements [START_REF] Chen | Eye Activity as a Measure of Human Effort in HCI[END_REF] are instances of behavioral signals used in cognitive load measurement. Eye activity can reveal valuable information about mental workload. In contrast with some eye based features (such as pupil dilation) which can only be gathered through an expensive eye tracker, eye blink can be obtained with an acceptable accuracy through a conventional camera. Therefore it is a low-cost and easily-obtained signal which can be used for cognitive load measurement. Some previous works have studied blink variations in regard to modality (visual versus acoustic) [START_REF] Lipp | Attentional Blink Reflex Modulation in a Continuous Performance Task is Modality Specific[END_REF] or location (central versus peripheral) [START_REF] Fogarty | Eye movements and blinks: Their Relationship to Higher Cognitive Processes[END_REF] of presenting stimuli. Another research has measured the blink rate in resting, reading and talking conditions [START_REF] Bentivoglio | Analysis of Blink Rate Patterns in Normal Subjects[END_REF]. A few studies have examined blink features in two cognitive load levels and found them related with mental load level [START_REF] Chen | Eye Activity as a Measure of Human Effort in HCI[END_REF][START_REF] Holland | Blinking and Mental Load[END_REF].

There are various application domains for cognitive load measurement, from braincomputer interactions to air traffic control. However, in some domains such as driving and education it is essential to be able to measure this load at a low cost, with short preparation time and minor restriction of users' movements. Considering that GSR and eye blink are suitable measures in such situations, in this paper we have explored features of these two signals captured during arithmetic experiments consisting of four cognitive load levels. We have assessed how useful every single feature is for classifying mental workload level and how combining features from the two signals affects the accuracy of cognitive load classification.

Support vector machines (SVM) and Naïve Bayesian classifiers are two popular machine learning algorithms in human-computer interaction studies [START_REF] Lotte | A Review of Classification Algorithms for EEG-Based Brain-Computer Interfaces[END_REF]. Some previous works have used SVM for recognizing drowsiness [START_REF] Yeo | Can SVM Be Used for Automatic EEG Detection of Drowsiness During Car Driving?[END_REF] or different emotions [START_REF] Horlings | Emotion Recognition Using Brain Activity[END_REF][START_REF] Sakr | Multi Level SVM for Subject Independent Agitation Detection[END_REF][START_REF] Setz | Discriminating Stress From Cognitive Load Using a Wearable EDA Device[END_REF] from physiological features. Naïve Bayesian classifiers have been used for detecting human emotions from facial expressions [START_REF] Sebe | Emotion Recognition Using a Cauchy Naive Bayes Classifier[END_REF] or physiological signals [START_REF] Chanel | Emotion assessment: Arousal evaluation using EEG's and peripheral physiological signals[END_REF][START_REF] Horlings | Emotion Recognition Using Brain Activity[END_REF]. In this study, we have used these two types of classifiers for cognitive load classification of GSR and blink features.

Experiment

The data was collected from thirteen healthy 24 to 35-year-old volunteers who signed consent forms before the experiment and were awarded with movie vouchers for their participation. The experiment included 8 arithmetic tasks with 4 difficulty levels.

Each subject performed two trials of each task level and the whole eight trials were performed in a randomized order. In each task four numbers were shown one by one, each for three seconds. Subjects were supposed to add-up these four numbers and select (by clicking the mouse using their right hand) the correct answer from three numbers which were next presented on the screen. First to fourth difficulty levels respectively included binary numbers (0 and 1), one-digit numbers, two-digit numbers and three-digit numbers. Before appearing the first number of each task, a slide containing one, two or three 'x' symbols (according to the number of digits in the task) was presented for three seconds. There was no time limit for answering and the background was always black. There was a 6-second rest time between consecutive tasks. After finishing the experiment, subjects rated task difficulty levels in a questionnaire (ranging from 1 to 9).

To collect galvanic skin response, the GSR device from ProComp Infiniti of Thought Technology Ltd was used and the sensors were attached to the subject's left hand finger (all subjects were right-handed). The sampling frequency was 10Hz. Eye activity data was recorded with a remote eye tracker (faceLAB 4.5 of Seeing Machines Ltd) which operated at a sampling rate of 50Hz and continuously recorded eye data. A 21" LCD monitor and a usual computer mouse were used for presenting the tasks and obtaining user inputs.

Cognitive Load Measurement

Figure 1 shows the average subjective ratings of the task difficulty levels. One-way analysis of variance (ANOVA) on the self-reporting scores showed a highly significant difference between task levels (F 3,48 =108.63, p<0.05).

Figure 1. Subjective rating of task difficulty levels

We also examined the response time for each task. By response time we mean the time between disappearing the last (fourth) number of the task and selecting the answer. Average response time of all subjects for each task difficulty level are shown in Figure 2. It can be seen that response time has a direct relation with the task difficulty level: harder tasks take longer response time. Results of ANOVA test on response time of different task levels are significant (F 3,48 =62.59, p<0.05). These observations about subjective rating and response time show that the designed tasks have effectively manipulated the cognitive load. Two GSR and two blink features were calculated for each task:  accumulative GSR (summation of GSR values over task time)  GSR power spectrum (frequency power)  blink number (number of blinks in the task)  blink rate (number of blinks in the task divided by task time)

The time between appearing the first number and inputting the answer was considered as the task time in which every feature was computed. We observed that GSR and blink values are highly subjective, that is they differ from person to person. In order to omit the subjective differences, we calibrated each feature of task j of participant i by dividing it by the average of all similar features of all tasks of that subject:

calibrated_feature(i,j)= ∑ ( 1
)
where m is the number of tasks (m=8). Furthermore, we averaged each feature between tasks with same difficulty levels for each subject. Figures 3 and4 show the average values of the studied (calibrated) features in the four task levels. One-way ANOVA test was applied to statistically evaluate cognitive load level discrimination of each feature. Table 1 represents the results of statistical analysis (ANOVA test) of the studied features for four task difficulty levels. As can be seen, the results are significant for all four features.

Table 1. ANOVA results of features for four task difficulty levels

Feature Results

Accummulative GSR F

Cognitive Load Classification

In this study, support vector machines (SVM) and Naïve Bayes classifiers were applied for cognitive load classification. For every feature, we have examined two-and four-class classification while the former means considering levels one and two as low load and levels three and four as high load. The cross validation method was leave-one-subject-out. In other words, in each round the classifier was trained by the data of the all subjects except one and data of the remaining subject was used for testing. The classification accuracies of all rounds were averaged. Tables 2 to 5 show the cognitive load classification accuracies of the single features for two and four classes. Results of all features are reasonable, GSR features outperform blink features in two-class classification and results of blink number are better than those of blink rate. It is also worth mentioning that in most cases the two types of classifiers have very near or even similar (Table 4) performances on the single features. The largest difference is in classifying by use of accumulative GSR (Table 2) where classification accuracies of Naïve Bayes learners are about 5% higher than those of SVM in both 2-class and 4-class classifications. In the next step, we examined cognitive load classification using combinations of GSR and blink features. The combination of blink number and GSR frequency power resulted in the highest classification accuracies which can be seen in Table 6. Comparison with tables 3 and 4 reveals that combining blink number and GSR frequency power improves the classification accuracy in both two-and four-class classifications up to about 10% in the former and 16% in the latter. It can be observed that for combination of the two modalities (Table 6), similar to single feature cognitive load classifications, the classification accuracies of SVM and Naïve Bayes classifiers are close. We have applied classification algorithms on blink and GSR features and combinations of them. Accumulative GSR, power spectrum of GSR, blink number and blink rate were significantly distinctive and had reasonable accuracies in both two-and four-class classification of cognitive load using support vector machines and naïve Bayes classifiers. Combining GSR and blink features improved the classification accuracy. As our next step towards fully automated and more precise cognitive load detection, we will apply automatic feature selection (e.g. [START_REF] Wang | Indexing Cognitive Workload Based on Pupillary Response under Luminance and Emotional Changes[END_REF]) of physiological cognitive measures.

Figure 2 .

 2 Figure 2. Response time for each task difficulty level (milliseconds)

Figure 3 .Figure 4 .

 34 Figure 3. Average GSR features of all subjects for the four task levels: accumulative GSR (left), GSR frequency power (right).

Table 2 .

 2 Classification accuracies of accummulative GSR

	Classification Algorithm 2-Class Classification	4-Class Classification
	SVM	66.4%	34.6%
	Naïve Bayes	71.2%	40.4%

Table 3 .

 3 Classification accuracies of GSR frequency power

	Classification Algorithm 2-Class Classification	4-Class Classification
	SVM	66.4%	37.5%
	Naïve Bayes	65.4%	35.6%

Table 4 .

 4 Classification accuracies of blink number

	Classification Algorithm 2-Class Classification	4-Class Classification
	SVM	62.5%	40.0%
	Naïve Bayes	62.5%	40.0%

Table 5 .

 5 Classification accuracies of blink rate

	Classification Algorithm 2-Class Classification	4-Class Classification
	SVM	57.5%	31.3%
	Naïve Bayes	55.0%	32.5%

Table 6 .

 6 Classification accuracies of blink number + GSR frequency power

	Classification Algorithm 2-Class Classification	4-Class Classification
	SVM	71.5%	53.6%
	Naïve Bayes	75.0%	50.0%