Christophe Pallier

Emmanuel Dupoux

Xavier Jeannin

EXPE: an Expandable Programming Language for On-line Psychological Experiments

This is a preprint a paper published in

When one has to make up a psychological experiment using computerized equipment, there are basically two choices: a) use a general-purpose programming language (C, Pascal, etc.), or b) use one of the special software/freeware packages made for psychological experiments. The first solution is the most general one, but it has several drawbacks. Neither C nor Pascal is very well suited to describe experiments: They force the experimenter to focus on many irrelevant details. More importantly, these languages require a level of programming skills that cannot be expected from the average user, especially if precise timing or synchronization is needed. The second solution, using specialized systems, is simpler and more accessible, especially with systems that provide a graphic interface for the construction of experiments. However, such software is often tied to specific kinds of experiments and imposes rather strict limits on experimental design, stimulus presentation, feedback, etc. For example, it is generally impossible to modify the format of the feedback or to adapt the number or type of trials to the history of subject responses. Another serious problem with these programs is that they are not open and are often tied to a special-purpose hardware (response buttons/audio board).

In this paper, we describe a program that was born five years ago at the Laboratoire de Sciences Cognitives et Psy-Correspondance address: Dr. C. Pallier, Center for Cognitive Science, Rutgers University, New Brunswick, NJ 08903. Email: pallier@ruccs.rutgers.edu C. Pallier was supported by a postdoc fellowship from the Fyssen Fondation; part of this work was also realized while he was a post-doc at the University of Barcelona supported by a Lavoisier Grant from the French Ministry of Foreign Affairs. The audio functions rely on modules programmed by Xavier Jeannin at the LSCP in Paris, and by John Mertus at Brown University. cholinguistique (LSCP, Paris) from our efforts to try to cope with these problems. Our aim was to design a system that had both the power and expandability of programming languages and was as easy to use as the more specialized software. Power was achieved through a scripting system with general-purpose data and control structures. Expansibility was achieved through a modular and open architecture allowing the easy addition of new functions through Borland Pascal Modules. User ease was obtained by designing the language with a maximally simplified syntax and many primitive functions tailored to the needs of experimental testing (trial definition, stimulus presentation, response collection, timing, data saving, etc.).

Thus, EXPE is an interpreter of scripts which is similar in spirit to BASIC. It provides variables, expression evaluation, all the necessary control structures and even subroutines; the BASIC functions "READ" and "DATA" have been enhanced in many ways to allow a compact and legible description of experimental design (more on this subject in the section on Expe's scripts). We want to stress however that it is not a very high level experiment generator in the sense that concepts of experimental blocks or groups are not "hard wired" primitives of the language. Thus, for example, it will not automatically generate a latin square design: the user will have to specify the different groups of subjects and the block order. Nevertheless, most EXPE scripts are usually quite short, and our experience at the LSCP has shown that students can very quickly use it to design and run experiments. Indeed, EXPE has been used extensively in the past four years to prepare and run auditory and visual experiments. It has also been used to test neuropsychological patients.

The hardware requirements have been kept to a minimum: it is a DOS real-mode program, which can run on old PCs with only 640K of memory (though some experiments may require a faster PC to handle the presentation of complex au- Data "Materials" stim1.adf P stim3.adf K stim7.adf D stim2.adf P ... EndData dio or video events). No complex hardware is required for timing and response-time measurements: the response buttons are simple mechanical switches that can be connected directly to the parallel port of the computer. The audio functions rely on the Bliss audio drivers, a system designed by John Mertus at Brown University. This makes EXPE compatible with audio boards for which there exist a Bliss driver1 ; at the LSCP, we use MediaVision's ProAudio Spectrum 16.

The paper is divided into two parts: in the first, we describe the script language and try to convey how easy it is to program new experimental paradigms with it. In the second part, we describe the most unusual aspect of EXPE: the expandabilty of the language through the linkage of Pascal units.

Expe Scripts

Two examples with commentary

In Figure 1, we have provided the script of a simple phoneme categorization experiment: the subject listens to a list of stimuli, and after each one, has to press the key corresponding to the perceived phoneme (it is just a simple example: a real experiment would likely include the instructions for the subject, a training block, and maybe feedback...)

The core of many experiments consists of a series of trials where the only differences are the actual stimuli played in each particular trial. It is convenient to separate the code (i.e., the commands to be executed in each trial) from the data (the description of the stimuli).

In Figure 1, the first block of lines is the code section; the commands enclosed between the "withdata...loopdata" construct will be executed once for each line of data (defined by the "data ... enddata" construct). Within the "withdata...loopdata" loop, #1 refers to the first column of the current line in the data block and hence varies on each pass. So, in the first pass, #1 corresponds to "stim1.adf"; in the second pass it corresponds to "stim3.adf" and so on. #2 corresponds to the second column. If the "database" "Materials" contains 60 lines, the instructions are executed 60 times.

In the example, the whole experiment consists of a single block of uniform trials; each trial starts by the playing of the auditory file the name of which is given in the first column in the current data line ("listen #1"). Then, the file's name, the expected answer, and the subject's response are saved together in the result file ("save #1 #2 readkey"). Finally, the computer waits two seconds before starting the next trial ("wait 2000").

Once this script is written, say in the text file "phondec.pro", entering "expe phondec subjcode" on the DOS command line will launch the experiment. When it is completed, the raw results will be immediately accessible in an ASCII file with four columns: the subject code, the file name, the expected response, and the actual response. Information about the subject and about the date and time of the run are also stored in the result file. It is easy to extract statistics from the result file with programs like "count", "mystat" and "anova" provided in the EXPE package; alternatively the ascii file can be imported into a spreadsheet or in a statistical program.

In data blocks ("databases") containing lists of stimuli, it is good practice to add on each line some information about the category of the stimulus. This information can then be saved with the response of the subject, facilitating easy extraction of the results. It is important to note that databases are not limited to storing stimulus lists. The format inside a database is completely free and the action taken depends on the code section.

For example, we conducted an experiment in which subjects had to perform a click detection while listening to auditorily presented words. Every five to twelve trials, a recognition test was administrated to force subjects to pay attention to the words. In order to achieve this, lines with a special code were interspersed in the stimuli list to instruct Expe to present the subject with an occasional recognition test. An instruction in the main loop branched between a click detection or a recognition test.

The database mechanism is quite powerful. The "result Echo " INSTRUCTIONS FOR EXPERIMENT" Echo "In this experiment, you will be presented first with a target phoneme" Echo "on the screen, then by a spoken word." Echo "Your task is to press the right button if the word contains" Echo "the target phoneme, or the left button if the word does *not* contain it. file" itself is actually a database so that it is possible to access the history of the responses of the subject inside the experiment (for example to compute the mean reaction time in a block). Also, in a given script, there can be several databases, which can be scanned sequentially or in parallel: "withdata...loopdata" loops can be embedded. For example, one database can contain the name of others; this can be used to store the order of experimental blocks: the outer loop controls which list is used, and the inner loops scans through this list.

As a second example, we propose the script of a speeded phoneme detection experiment (see Figure 2). First, the instructions are displayed on the screen. Then, the order of stimulus presentation is randomized (for each subject) with the instruction "shuffle". Inside the loop, the instruction "rttrial 2000 listen..." plays the stimuli and monitors the keyboard and the parallel port for a button or key press during 2 seconds (2000 msec). The reaction time can then be read with the function "rt", and the code of button pressed is accessed with the function "button" (if no button has been pressed, the "button" returns " ''). The entire data line is saved along with the response by the command "save #0 rt button". It is a good idea to save as much information as possible about each trial: it makes things easier for later analyses.

In a given script, several blocks of codes and data can be interspersed freely. Complex designs can be made by embedding "withdata..loopdata" structures at any depth. Conditionals and control structures allow for feedback or trials to depend on the subject's response. A "withdata...loopdata" loop can be interupted before the end of the list, for example if the subject's performance has reached a certain criterion. The next section gives a quick description of capacities of the language.

EXPE's syntax

EXPE's syntax is deliberately minimalist. A program consists in a series of lines where each can be a command line, a data line (appearing between "data" and "enddata"), or a comment (introduced by a percent-sign).

Typically, command lines are executed sequentially, one after another, in the order in which they are encountered. However, some commands allow looping over a block of instructions until a condition is met (we have already seen "withdata...loopdata" but there is also while...endwhile, for...endfor). As in most programming languages, there also are conditional instructions (if..then.endif) that allow execution of some instruction only when a condition is met.

Each command line starts with a command, optionally followed by one or several arguments that can be numbers, strings of characters, variables or other commands. Assignment (":="), standard arithmetic ("+","-", "/", "*") and logical ("and", "or", "xor") operations are special types of commands that take their arguments on their left and right. The standard operator precedence applies, i.e., 3+4*5=23. Commas for arguments and parentheses for expressions are not mandatory (minimalist syntax), but they can be used to make complex expressions more legible.

Contrary to many programming languages, the user does not have to pay attention to the argument type: Conversions between numbers, strings or boolean are performed implicitly as needed ("0" is equivalent to 0.0 and to False; however, improper conversions (e.g. 3+"hello") generate a run-time error.).

EXPE also has variables which can be manipulated just as easily as constants. Again, variables have no particular type and can be used as arguments of functions requiring strings or numbers. Variables are especially useful for counting subjects' good and bad responses. Several of our experiments involve adaptative training where the training block ends when a certain performance criterion has been reached. As described above, inside a "withdata...loopdata" loop, "#i" refers to the "i th " item on the current database line. In brief, EXPE takes care of type checking, memory allocation, inputoutput, etc., and allows the user to concentrate on the most important aspect of the research: the execution of the experiment.

Functions for stimulus presentation

We now turn to the specifics of EXPE concerning audio/video output and timing. The simple command "listen <filename>" allows an audio file to be played. There is no limit on the size of audio files: EXPE reads them from the disk and feeds them to the audio board in real-time. Currently, EXPE handles 16 bits Bliss .adf mono and stereo audio files, raw PCM linear 16 bits files, and Windows .wav pcm 8 and 16 bits files. Depending on the hard drive on the computer, loading the file will take a variable amount of time. If playout must start at a very precise time, it is possible to decompose this command in "load <filename>" and "play". "Load" will fill the audio buffers with the beginning of the file and "play" will start the playout immediately (fetching more data on the disk if necessary).

EXPE is not limited to presenting only an entire, prerecorded, audio file: it provides a general audio mixing ta-ble that allows the user to specify millisecond-synchronized sequences of auditory events. The mixing occurs in real-time and allows the user to overlap or gate stimuli, or play some files over the left and others over the right channel. Figure 3 gives a simple example of a stimulus made of two audio sounds played simultaneously, one in the left channel, and the other one in the right channel and amplified by a factor 2. Only the first 1000 msec of each file is played.

By default, the mixing is done in real time. If this exceeds the capacities of the machine (because the hard drive or the CPU is too slow), it is possible to mix the sounds off-line (i.e., before starting playback), into a temporary file, which can be played afterwards.

The current video functionalities are relatively primitive: the basic graphic functions of Borland Pascal are accessible, as is a command to display pictures stored as bitmaps in tiff files. The drawing is done in a hidden page which can be swapped rapidly with the page shown on the screen, allowing measurement of reaction time from the onset of the presentation. However, it is not yet possible to present a visual stimulus in the middle of the presentation of an audio stimulus; we plan a forthcoming version of EXPE in which visual events will be incorporated in the audio mixer, allowing for the possibility of arbitrarily complex sequences of audiovisual events.

With this basic set of instructions, EXPE can handle many current psycholinguistic or neuropsychological experiments that specify a relatively simple sequencing of events. However, experiments requiring the rapid succession of many visual frames (e.g. rapide serial visual presentation), or complex synchronization of audio and video events (cross-modal priming) may not be possible with the basic functions provided. When such a limit is reached, we recommend programming each particular complex stimulus presentation directly in PASCAL and linking it to EXPE code (see the next section about expanding the language).

Another feature worth mentioning is the ability of EXPE to communicate with other hardware or computers through the parallel port or the serial port. For example, for an evoked-potential study, we have been able to link through the parallel port a PC handling the presentation of audio stimuli to another one recording the EEG. The first PC, programmed with EXPE, sent to the second computer codes that were specific and synchronized with each stimulus. In other experiments (head turning), we were able to use the serial port to drive a videotape recorder. The serial port has also been programmed to control a digital audio tape recorder during a naming experiment (the DAT recording the vocal responses of the subject).

Timing and Responses

Control on inter-trial times, feedback duration, etc., is achieved by the functions "clock", "wait" and "waittill". "clock" gives back the time elapsed since the beginning of the experiment. "wait <n>", waits "n" msec, and "waittill <n>" waits until the clock reaches the value "n". For example, to program a series of trials of equal durations, say 4 sec, Length 1000ms Gain 1.0 LEFT audio "file2.adf" 0 Length 1000ms Gain 2.0 RIGHT Enditem Playitem "a:=clock" can be set at the beginning of the trial, and put "waittill a+4000" at the end.

Turning now to the functions that get input from the subject, one can distinguish those recording off-time responses (readkey, readstring, etc.), and those measuring online reaction times. The latter can be achieved with external buttons linked to the parallel port (with millisecond accuracy), or through the keyboard (with less accuracy). For reaction times, the simplest function "RTtrial <deadline> <command>". The reaction time is measured from the real onset of <command> (i.e., first sample output in "listen" or video retrace for video functions). The functions "RT" and "Response" can then be used to access respectively the value of the reaction time and the button (or key) pressed. If no button is pressed before deadline, RT is set to 0. It is sometimes useful to decompose the action of "RTtrial" into more elementary instructions ("EnableResponse", "rtonset := getonset < action >", "LatchResponse") to allow more control in the case of complex sequences of events. By properly connecting a voice key to the parallel port, vocal responses can be used instead of manual ones.

Saving Results

The data recorded by EXPE (subject responses) are saved using the save command. It saves all its arguments, in plain ASCII format, in a memory area which is dumped onto the disk when the experiment ends. User interruptions or runtime errors are caught, and the data are saved on disk before the program exits. Results can be logged onto the same large result .res file, or onto separate files for each subject. In addition, much other information regarding the experiment is saved in the .res file (date, time, experiment duration, type of machine, version of EXPE, etc.). Note that functions that perform the saving, like all other EXPE commands, can be replaced to use different formats.

We now turn to an important feature of EXPE: its capacity for extension.

Expanding EXPE

The limitations of any experimental package are quickly reached by ingenious researchers. Limitations are of two kinds: hardware and software.

As an example of hardware limitation, the user may already have hooked up 10 computers with a particular kind of response button, but the package does not allow for reading out these buttons. EXPE has been programmed in a modular fashion making adaptations to new hardware possible. The pieces of code dealing with the hardware are kept in separate Borland Pascal's units, which means that adapting EXPE to new hardware only involves local changes to these units. For video output, we rely on Borland's BGI drivers. For the audio output, we use the specifications of John Mertus's BLISS drivers, and again EXPE's code is device-independent. Adapting EXPE to new audio boards implies writing up a new BLISS driver (5-6 very low-level functions)2 . Finally, timing and response button are also modular parts of the code. In short, it is possible to adapt EXPE to new input boards or ports. For example, we have used it to command a robot arm (moving objects in a theater designed for baby experiments), or to synchronize a NeuroScan EGG recorder with auditory stimulus presentation.

Software limitations concern, for example, the types of graphic file format the package can display, or the type of audio file it can play. With most experimental software, there is nothing the experimenter can do if he wants to use a format not accommodated by the package. In contrast, EXPE allows new commands to be added to the language very easily. Assuming that the user has the source of a Pascal procedure that does all the necessary work, it is a trivial matter to link this routine with the other functions, resulting in an extension to EXPE's langage.

Consider some examples. If one wants to save the results in a special format adapted to his analyzing tools, a special purpose "save" command can be added to the language. If one has a modular piece of code achieving a very special effect (e.g., self-paced reading), one can link it to expe without too much trouble.

All EXPE's commands are in fact implemented as functions of the type "function myfunction:xvalue;far;" where "xvalue" is a hybrid type defined that allows for transmission of numbers or string of characters. In order to add one (or several) new function(s) to the EXPE language, one must:

1. write a Borland Pascal unit containing the code for this function.

2. add to the initialization section of the unit a line like the following: NewFunc("MYFUNC",myfunction,short-help).

("NewFunc" is part of the interface of a unit called "xcore", which must be included by the unit).

3. add the name of the unit to the list in file named "module.pas" 4. run the batch "make" that invokes bpc to recompile EXPE.

Then, at run-time, keyword "MYFUNC" becomes a new command in the language that can be used within EXPE scripts to call for the desired procedure. It is possible, in a given unit, to add many other commands: the only thing needed in order to add them to the language, is a "NewFunc" statement for each of them. In a nutshell, EXPE is a scripting interface to independently written Pascal functions.

The function written by the user can access the arguments in the script by using the functions "GetStrArg","GetIntArg" or "GetBoolArg". These read the next argument in the current line and convert it to the relevant Pascal type. Syntax, expression evaluation, etc., need not be taken into account since the core of EXPE takes care of such details for the user.

In brief, when the user has written his/her own code into an independent Borland Pascal unit3 , he/she just has to add the name of this module to the list in the file modules.pas and to run "make". This solution has the advantage of allowing the user to distribute his contributions as independent .tpu files. Useful contributions could be incorporated in the standard distribution of EXPE.

Availability

EXPE can be freely downloaded from the internet at the URL http://ruccs.rutgers.edu/pallier. Researchers using it for their experiments are only requested to cite the present paper whenever they report on their work. We provide, along with EXPE, documentation and some tools for preparing experiments and perform data transformations and statistical analyses (including Anovas...). The full package is self-contained and is sufficient to prepare, run, and analyze many psychology experiments.

Conclusion

EXPE provides an expandable, intuitive, but powerful scripting language for experiment construction. Although we do not wish to review all existing experimental packages, the most powerful of these packages (MEL, PSYSCOPE) also have underlying script-like languages. In these packages, however, such script-like languages are machine-oriented, and are normally not programmed directly by the user. Rather, a menu-driven or graphics interface guides the user in the specification of the experiment. Such specification is used to generate the appropriate script code which is then fed into the experiment engine. This approach has the advantage that users do not need to do any programming to implement an experiment.

However, it is typically the case that graphic or menudriven interfaces have intrinsic limitations in the complexity and range of designs or protocols that they can express. For instance, the interface may not allow the user to modify the format of the feedback messages, or to schedule trials that depend on the history of subject responses. Indeed, the user-interfaces are often more restrictive and less powerful than the underlying scripting language. Yet, when the user wants to get around these limitations, he/she has to abandon altogether the user-interface and cope with an unfriendly machine-oriented scripting system. EXPE lacks a "high-level" interface: Users cannot enter, in menus or through a graphic interface, parameters such as SOA, or numbers of trials in a block. On the other hand, the scripting language has been designed to be human readable and to minimize the burden of programming. Still, the fact that using EXPE requires a basic understanding of instructive programming may be a drawback for a certain class of users. Also, in comparison with the above-mentioned packages, it should be mentioned that a library of scripts for common experimental paradigms is not available.

In summary, here are what we conceive as advantages of EXPE:

1. It provides specialized commands and structures for stimulus presentation and response recording. The audio functions are especially powerful, allowing for the playing of files of unlimited size, and for mixing several files in real time (which is useful, for example, for dichotic experiments).

2. Compared with languages such as C or Pascal, users do not have to learn to use a compiler. The language is much more similar in spirit to BASIC, and is thus simpler to master. Users can use their favorite word processor to write scripts, and, at any time, they can get on-line help on expe's commands by calling "expe -?".

3. It is open-ended: If necessary, "power users" can add new functions by programming them in Borland Pascal and linking them to EXPE.

4. It can be used freely: The license allows users to make an unlimited number of copies.

Figure 1 .

 1 Figure 1. Example of a phoneme categorization script

Figure 2 .

 2 Figure 2. Example of a phoneme detection script

Figure 3 .

 3 Figure 3. Mixing two audio files Defitem audio "file1.adf" 0 Length 1000ms Gain 1.0 LEFT audio "file2.adf" 0 Length 1000ms Gain 2.0 RIGHT Enditem Playitem

  " Echo Echo "Respond as soon as you have heard the target phoneme." readkey

	Shuffle trials	;randomizes the trial order
	WithData trials
	Wait 1000		;wait one second
	Cls			;clear the screen
	WriteXY 38 12 #1	;display the target phoneme
	Wait 1000		;wait another second
	Cls			;clear the screen
	Wait 500		;wait 500ms
	RtTrial 2000 Listen #2 ;make a timed response trial with
				;deadline 2000ms
	Save	#0 button rt	;save the trial characteristics and responses
				;feedback for slow and wrong responses:
	If button=='˜' WriteXY 20 20 "Too Slow !"	;no button press
	If button!='˜' and (button!=#3) WriteXY 20 20 "Wrong Response"
	LoopData
	Data trials	;target-phoneme stimulus-file desired-response
	P	sheep.adf 1
	M	glop.adf 2
	D	disk.adf 1
	K	pump.adf 2
	...
	EndData

Bliss drivers and tools are available at ftp://jam.cog.brown.edu.

However, this does not mean that this is an easy task: the structure of Bliss drivers requires the use of assembly language. And the programmer must not be afraid of dealing with the DMA and other capricious beasts.

There is also the possibility to link C code to Pascal, but with an important restriction: no functions of the C run-time library can be used. Future use of dll may solve this problem.


Christophe C Pallier
email: pallier@lscp.ehess.fr

Núria Sebastián-Gallés

Emmanuel Dupoux

Anne Christophe

Jacques Mehler

Nuria Sebastian-Gallés

Perceptual adjustment to time-compressed speech: A cross-linguistic study

des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

The persistence of intelligibility despite great changes in background noise, talker's voice, speech rate, dialect, etc. has to be part of any reasonable account of speech perception. How is it that speech perception remains so amazingly accurate under these changing circumstances?

Possibly, the answer lies with the listener's processing apparatus that has been devised to compensate for the input's instability. When listening conditions are not too degraded, the compensation seems almost instantaneous and effortless (see [START_REF] Miller | Effects of speaking rate on segmental distinctions[END_REF], for a review of adaptation to changes in speech rate). Under more inordinate conditions, such as listening to a heavy foreign accent in a noisy conference room, a larger time frame is required for adaptation to be complete (for adaptation to synthetic speech, see [START_REF] Schwab | Some effects of training on the perception of synthetic speech[END_REF]. The purpose of the present study is to expand our understanding of such compensation processes and to raise questions about speech perception from that perspective.

Past studies have used artificially compressed speech to quantify the way in which the speech processing system deals with variations in speech rate. Predictably, these studies have found that intelligibility decreases as compression rate increases [START_REF] De Haan | The relationship of estimated comprehensibility to the rate of connected speech[END_REF][START_REF] Foulke | Review of research on the intelligibility and comprehension of accelerated speech[END_REF][START_REF] Heiman | Word intelligibility decrements and the comprehension of time-compressed speech[END_REF][START_REF] Schmitt | Variable speech control vs. Varispeech: Does newer mean better[END_REF]. Likewise, over the course of exposure to such signals, subjects' performance tends to improve [START_REF] Mehler | Temporal information processing in the nervous system: Special reference to dyslexia and dysphasia[END_REF][START_REF] Voor | The effect of practice on the comprehension of worded speech[END_REF]. After 10-15 sentences, performance reaches a plateau.

To explain this improvement in performance, several mechanisms can be advanced, ranging from low-level adjustments in the processing of acoustic properties to the use of ad-hoc highlevel strategies to improve the integration of information in memory systems. Our experiments investigate whether these adjustments involve the systems that map the acoustic information onto the proper lexical representations. If the results of these investigations reveal that adapting to compressed speech involves these systems, then studying this adaptation is bound to help us understand speech perception at large.

Recent research comparing speech perception across varied linguistic settings indicates that speakers of different languages rely on processes that are specific to their maternal language. [START_REF] Mehler | The syllable's role in speech segmentation[END_REF] and [START_REF] Cutler | A language specific comprehension strategy[END_REF] have shown that French and English subjects behave in conflicting ways when they have to find a string of phonemes that coincides with the first syllable of a word. Such observations have led these authors to conclude that it is the specific phonological properties of each one of the languages that induces the use of different properties to map sounds to meaning. In other words, speakers of French, a language with clearly marked syllabic structures and fixed accent, use syllables to initiate lexical processes while speakers of English, a language with ambisyllabicity and contrastive stress, adopts a different strategy.

The above conclusions have been substantiated by research conducted in other languages with a wide variety of experimental procedures [START_REF] Bradley | The status of the syllable in the perception of Spanish and English[END_REF][START_REF] Cutler | The syllable's differing role in the segmentation of French and English[END_REF][START_REF] Cutler | The monolingual nature of speech segmentation by bilinguals[END_REF][START_REF] Otake | Mora or syllable? Speech segmentation in Japanese[END_REF][START_REF] Pallier | Attentional allocation within syllabic structure of spoken words[END_REF][START_REF] Sebastian-Gallés | Contrasting syllabic effets in catalan and spanish[END_REF][START_REF] Zwitserlood | The role of the syllabe in the perception of spoken Dutch[END_REF]. From these studies, it emerges that the nature of accent, the number of vowels, the extent to which the language relies on vowel reduction, etc. are all factors which influence how the acoustic signal is exploited to identify lexical candidates. If these conclusions are correct, then the perceptual adjustments to compressed speech in a given language might be of little or no use when another language is presented, under similar conditions, unless the languages are treated alike at some early processing stage. Accordingly, studying adaptation across languages would help us understand the way in which acoustic information is processed by speakers in general and how language diversity may influence such processes.

Before becoming entangled in such issues, however, it is judicious to establish the possible contributions of the above-mentioned levels to habituation to fast speech. If most of the adaptation is due to either very low-level acoustic mechanisms or to very late high-level postlexical procedures, the interest in using this experimental procedure would be rather limited. On the basis of various observations, though, we can dismiss the belief that low-level acoustic processing plays an extensive role in this adaptation. For instance, Dupoux & Green (in press) have shown that once subjects have adapted to compressed speech, their performance remains unaffected by a change in speaker (male to female). This result suggests that while adaptation is specific to compressed speech, it occurs at a level sufficiently abstract so that talker-specific acoustic information only plays a minor role. What about the view that it is very late, high-level processes that are responsible for most, if not all, of the observed adaptation effects? Little data can be advanced to respond to this question. However, there are easy experiments that could provide us with a clear answer to that question. For instance, if the adaptation takes place at a late (post-lexical) level, it should be driven by lexical or semantic variables; accordingly, one might expect that speakers will show transfer only after they adapt to a language they understand. Indeed, it would follow that adaptation would be impossible to a language that subjects cannot understand.

The research we report here has two main goals. First, to establish whether high-level processes (lexical and semantic) are essential to explain adaptation to compressed speech. Second, to evaluate if phonological information plays a role in the adaptation to compressed speech. To attain these goals we have carried out four experiments through which we explore how monolingual and bilingual speakers adjust to compressed speech in different languages. Specifically, two language pairs have been chosen: Catalan-Spanish and French-English. The choice of the first pair is justified for two reasons: first, the fact that these two languages have comparable phonological properties and that speakers of these languages seem to rely on similar speech perception routines [START_REF] Sebastian-Gallés | Contrasting syllabic effets in catalan and spanish[END_REF], and second, our easy access to a large Catalan-Spanish bilingual community. The second pair, French-English, was selected because these two languages rely on different representations [START_REF] Cutler | The syllable's differing role in the segmentation of French and English[END_REF][START_REF] Cutler | The monolingual nature of speech segmentation by bilinguals[END_REF] or, at least, on representations that are much more distant from one another than those of Catalan and Spanish and also because of the ease of finding a bilingual population.

If semantic processing plays a major role in the adaptation to compressed speech, then bilinguals (both Catalan-Spanish and French-English) ought to transfer the adaptation secured with one language onto the other one. In contrast, if phonological variables are a primary factor in determining adjustment, the phonological proximity of the languages will be a determinant factor. If this is the case both bilingual and monolingual subjects should show transfer between Spanish and Catalan, while neither bilingual nor monolingual French-English subjects should show it.

General Methodology

In the experiments reported below, we presented subjects with a set of habituation sentences in one language (8 or 10 sentences) followed by a set of compressed test sentences in the same language or in another language. In both the habituation and test phases, after hearing each sentence, subjects were asked to write down all they could recall and these responses were scored in terms of number of recalled syllables. In a previous study, we have found that scoring in terms of words or syllables did not lead to contrasting results [START_REF] Mehler | Temporal information processing in the nervous system: Special reference to dyslexia and dysphasia[END_REF]. Using number of recalled syllables instead of recalled words also allowed us to score the performance of speakers exposed to a foreign language. The dependent variable was the percentage of recalled syllables as a function of type of habituation, which is subjected to between-subject and within-item comparisons. Because of the between-subject design of the experiments, care was taken to make sure that the test sentences were presented under similar listening conditions for all the groups. Moreover, subjects in the different pairs of languages were taken from the same population and assigned randomly to one of the experimental groups.

The compression rate, which varies from study to study, had been adjusted for each study so that initial performance was between 30% and 70% of syllables correctly recalled. This was done to avoid ceiling or floor effects. The materials were recorded and digitised at 16kHz (16bits quantization), and compressed using the PSOLA algorithm [START_REF] Charpentier | Diphone synthesis using an overlap-add technique for speech waveforms concatenation[END_REF]. The program operates by first labelling the signal at each consecutive pitch period. Unvoiced portions of speech are blindly labelled into chunks equal to the size of the mean pitch period. Next, adjacent pitch periods are averaged in the time domain according to a scheme that depends on the compression rate. The averaging window is slightly longer than the width of each pitch period with vanishing smoothing functions on either side. The end result is a signal with fewer pitch periods than the original. For example, a signal compressed at a 50% compression rate will end up with only half the number of pitch periods as the original signal. However, since the information is averaged across adjacent pitch periods and not simply deleted, the signal retains many of the brief acoustic events like release bursts that are important to phonetic perception.

Experiment 1: Spanish-Catalan Bilinguals

Spanish and Catalan are two Romance languages which have quite similar phonologies. They both are syllable-timed languages with lexical stress. Even though they differ in several phonological dimensions (for instance, Catalan is a language with vowel reduction, while Spanish is not), they seem to rely on similar processing strategies [START_REF] Pallier | Attentional allocation within syllabic structure of spoken words[END_REF][START_REF] Sebastian-Gallés | Contrasting syllabic effets in catalan and spanish[END_REF]. All in all, it seems reasonable to conjecture that the procedures for mapping acoustic information onto lexical representations ought to be quite similar in the two languages. Consequently, if phonological representations participate in the process of adaptation to compressed speech, this adaptation ought to transfer from one language to the other. method Materials and Procedure.

Fifteen Spanish sentences and fifteen Catalan sentences, matched for meaning and length in syllables, were selected (see Appendix). Ten sentences in each language (matched) were chosen as "habituation" sentences; the five other were chosen as "test" sentences. All sentences were then recorded from two female bilingual speakers of Spanish and Catalan, digitised and compressed at 38% of their original duration.

There were six experimental groups. Three groups had test sentences in Catalan and three others had test sentences in Spanish. In the "Different Language" condition, two groups of subjects received the habituation sentences in a different language from that in the test sentences. In the "Same Language" condition, two other groups of subjects listened to test and habituation sentences in the same language but spoken by a different speaker. Finally, the "Control: condition consisted of two other groups of subjects who listened only to the experimental sentences.

Subjects were tested individually in a soundattenuated room. Sentences were presented through a tape recorder (TASCAM PORTA ONE), binaurally over headphones.

Subjects

Forty-eight bilingual Catalan-Spanish subjects were assigned to each of the Same Language groups and another forth-eight subjects to each of the Different Language groups. Twenty-eight subjects were assigned to each one of the Control groups. In all, two hundred and forty eight subjects were tested. All subjects were highly proficient in both Spanish and Catalan and spoke daily both languages with equal fluency. They were all first and second year undergraduate students of the University of Barcelona. They received course credits for their participation in the experiment.

Results

A global analysis of variance with language of the test sentences (Spanish or Catalan) and experimental condition (same language, different language and control) was performed. The two main effects are significant. Subjects are more accurate in reporting the experimental sentences in Spanish than in Catalan (F(1,242)=39.7, p<.0001) and there are also differences between the three experimental groups (F(2,242)=41, p<.0001). However, the interaction between the two factors is not significant (F(2,242)=1.58, p=.21). Means for each experimental group are displayed in table 1. Planned comparisons of means shows that there are statistically significant differences between the three experimental condition. The Control Groups differs from both the Same Language (t(150)=10.36, p<0.0001) and the Different Language groups (t(150)=8.05, p<0.0001). The Same Language and Different Language groups also differ significantly from each other (t(190)=2.86, p<0.005).

_________________________

Insert Table 1 here _________________________

Discussion

Highly compressed speech in Catalan or in Spanish can be used by proficient bilingual speakers to improve their performance when they are exposed to one or to the other language. Moreover, once the subjects adapt to one of the languages, they benefit from such an adaptation when they are switched to the test sentences in the other language. Indeed, the performance of the Different Language group was significantly better than that of the Control group. Nevertheless, the transfer was not perfect, since the Same Language and Different Language groups differ significantly from each other.

It is however difficult to attribute the crosslinguistic transfer exclusively to phonological factors. Indeed, the bilingual subjects were equally fluent in both languages and they had an excellent understanding of the sentences in both languages. It could be then that adaptation to fast rates is taking place at the syntactic/semantic level (that is, subjects who adapt are able to quickly derive a high-level representation under temporal pressure), in which case, cross linguistic transfer would occur whenever subjects understand the two languages at hand. The next experiment was designed to assess the possible contribution of semantic information to the adjustment processes.

Experiment 2: Spanish Monolinguals

In this experiment, monolingual Spanish subjects were tested with the same sentences as those that were used in experiment 1, with one difference: they always received the test sentences in Spanish. If the adjustment mechanism is mainly driven by semantic structures, no transfer from Catalan should be observed given that monolingual subjects do not understand Catalan.

Method

Materials and Procedure.

The same experimental procedure and materials as in the previous experiment was employed. The three groups received the test sentences in Spanish; the Different Language group habituated to Catalan and the Same Language group habituated to Spanish, while the Control group heard only the Spanish test sentences. Subjects were asked to write down the sentences even during the habituation phase. For the Different Language group subjects were asked to do a transcription as best they could of the Catalan habituation sentences.

Subjects were tested in a quiet room in groups of two, though they could not see each other. Sentences were presented over headphones with the same equipment as in the previous experiment.

Subjects

Subjects were college students at a Madrid school who volunteered to take the experiment. None of them knew Catalan. Special care was taken in selecting subjects without any significant previous exposure to Catalan (e.g., spending summer holidays in Catalan-speaking regions). There were 12 subjects in each of the groups, for a total of 36 subjects.

Results

An analysis of variance was performed on the mean percentage of correct syllables reported for the test sentences (see Table 2). The effect of experimental condition ("Same Language" vs. "Different Language" vs. "Control") was highly significant (F(2,33)=22.9; p<.001). Comparisons of means showed that there were no differences between the "Same Language" and "Different Language" groups (t<1), but that these two groups were different from the "Control" one ("Different Language" vs. "Control": t(21)=2.06, p=.05; "Same Language" vs. "Control": t(21)=2.37, p=0.03).

_________________________ Insert Table 2 here

_________________________

Discussion

Monolingual Spanish subjects adapted with Catalan sentences perform better than Control subjects. Subjects in this experiment profit similarly from listening to Catalan or Spanish during the habituation phase.

It is important to note that the monolingual Spanish subjects were unable to understand the compressed Catalan sentences presented during the habituation phase. The average number of correctly reported syllables was 15%, and mostly correspond to function words that are very similar in the two languages. The bilingual subjects tested in Experiment 1 reported over 75% correct syllables on these same sentences. Yet, both bilinguals and monolinguals benefited equally from the presentation of Catalan when tested with Spanish (if anything, the monolinguals seemed to benefit more, since their performance for Catalan habituation was no different from that of Spanish habituation). This clearly indicates that understanding is not essential for adaptation to take place. Hence, the transfer of adaptation observed between Catalan and Spanish cannot be due to adjustments taking place at high levels of processing. It has to be at a shallow processing level, presumably before lexical access.

It could be that subjects adapt to fast signals, whether or not these signals are in their language, and maybe whether or not they are linguistic signals at all. There are reasons to doubt that such low level effects might account for our findings. Indeed, this explanation should predict that any two pairs of languages should show adaptation. In fact, [START_REF] Altmann | Factors affecting adaptation to time-compressed speech[END_REF] failed to observe transfer from French to English, or the reverse, on monolinguals of either of these languages. The finding that certain pairs of languages show transfer while others do not is important, because it would suggest that adaptation is relying not on raw acoustic properties, but rather on linguistic (presumably phonological) ones. Languages that share many phonological properties might show more transfer than languages that are more phonologically distant. However, before going into these issues, one has to assess whether the failure of English-French transfer is real.

There is unfortunately one procedural difference between the Altmann and Young study and our Experiments 1 and 2: during the habituation phase, we required subjects to write down what they heard, whereas this was not the case in the Altmann and Young study. Since understanding compressed speech in a foreign language is so difficult, subjects may simply fail to pay attention to the sentences in the habituation set and wait for the test sentences in their native language.

The next experiment was design to try and replicate Altmann and Young's results using English/French bilingual subjects. An additional measure we adopted was that our subjects were required to write down both habituation and test stimuli.

Experiment 3: French-English Bilinguals

Speakers of English and speakers of French may rely on different properties to encode speech. Vowel reduction, an important property for English, is almost non-existent in French. Syllables, in contrast, play a greater role in the representation of French than in that of English. These two languages are thus much more phonologically distant than are Spanish and Catalan.

In this experiment, bilingual French-English subjects were tested and, as in experiments 1 and 2, were asked to write down as much as they could recall of the habituation and the test sentences. If the failure to obtain any transfer between French and English is due solely to a lack of attention during the habituation phase, then transfer should be observed in experiment 3. On the other hand, if the explanation of the results lies with the differences in phonologically-related processing, the pattern of results obtained by Altmann and Young should be replicated in experiment 3.

Method

Materials and Procedure.

Sixteen sentences in French were constructed and matched to 16 sentences in English; sentences in English and French had the same number of words and syllables and were translations of one another. The sixteen sentences in French were split in two groups, A and B, and the English sentences were also split into two corresponding groups, A and B. Half of the subjects started with sentences in group A and switched to B in the other language while the other half started with sentences in group B and switched to A in the other language. This resulted in four groups of Subjects. A-French going to B-English; B-French going to A-English; A-English going to B-French and B-English going to A-French. Subjects were tested in groups of five in a classroom with the sentences played over two loudspeakers. After each sentence was played, subjects were asked to write down all that they could recall. Sentence were recorded by a bilingual Female speaker and were compressed with the PSOLA algorithm as above. The sentences were compressed to 40% of their initial duration.

Subjects

Sixty eight bilingual student subjects (seventeen in each group) were tested in their school in the outskirts of Paris. The school, the Lycee International caters to students who are bilinguals and who want to pursue high-school studies in both languages in parallel. The students were selected after consultation with their teachers and after an evaluation of their performance in each language. They were fluent in both languages, they had no foreign accent in either, and they had practised both languages continuously since the age of three. They were 16 to 18 years old at the time of testing.

Results

In Table 3 we present the results for subjects' performance on sentences before and after adaptation to the other language. The design allowed us to compare exactly the same sentences before and after adaptation, though presented in different groups of subjects.

_________________________

Insert Table 3 here _________________________ We conducted an ANOVA on number of syllables correctly reported in the different conditions. A global analysis included the four groups as a between-subjects factor and change (before vs. after) as a within-subject factor. None of the main factors introduced a significant effect. The only significant effect was an interaction between groups and change, F(1,64)=287, p<.0001 This interaction was due to the fact that French sentences produced better recall rates than English sentences. A t-test performed on the French sentences revealed no significant difference between before and after change. Similarly, performance on English sentences was not significantly different before and after change.

Discussion

The pattern of results observed in this experiment shows that bilingual French-English subjects do not benefit from listening to sentences in English when they are tested in French or vice-versa. We can thus conclude that understanding the language to which one is exposed is not sufficient for adaptation to compressed speech to extend to sentences in one's native language. This complements experiment 2 which demonstrated that understanding was not necessary for adaptation to take place. Together, these results suggest that adaptation does not rely on lexical processes. The data is compatible, however, with the notion that adaptation occurs at a phonological level, one that involves processing strategies that are linked to one's native language. If this is true, we expect adaptation to transfer across languages with similar phonological properties. Phonologically speaking, Dutch and English have much more in common than French and English. For instance, both have been described as stresstimed languages while French has been classified as a syllable-timed language [START_REF] Abercrombie | Elements of general phonetics[END_REF].Yet, there are differences between English and Dutch, for example, with respect to the distinctive status of vowel length and the salience of retroflex consonants in Dutch. All the same, we predict that English monolinguals, trained with compressed Dutch, will perform better than if trained with French. Our next experiment was designed to evaluate this prediction.

Experiment 4: Monolingual English Subjects

This experiment contrasts the effectiveness of exposure to French, Dutch and English, respectively, on the performance of native speakers of English.

Method

Materials and procedure

We first selected 5 English sentences, 18 to 19 syllables long, to be used as test items (see appendix). We then selected 10 sentences in Dutch, in French, and in English for use as habituation items. These sentences were selected from a multilingual corpus of sentences gathered at the LSCP by Thierry Nazzi. Thus it was possible to equate the number of syllable and, approximately, the mean duration of the habituation sentences across languages (averages=18 syllables and 3.4 seconds). In a given language, all habituation sentences were spoken by the same speaker. The 5 test sentences were also pronounced by a single speaker.

We compressed the test sentences to 40% of their original duration, and the habituation sentences to 50%. These rates were chosen on the basis of a pilot test to avoid ceiling or floor performance. The compressed sentences were recorded on DAT tapes, in four lists: (1) one comprising only the five test sentences ("No habituation" condition); (2) one with 10 English habituation sentences followed by the 5 English test sentences; (3) one with 10 French sentences followed by the 5 English test sentences; (4) one with 10 Dutch sentences followed by the 5 English test sentences. Each sentence was preceded by a tone followed by 2 seconds of silence to allow subjects to focus their attention. After each sentence, subjects had 30 seconds to write down what they had heard. They were encouraged to write down as much as possible, even in the foreign language conditions; moreover they were told that the last five sentences were in English. There were four groups of subjects, each assigned to one of the lists.

Subjects

Seventy-five English native speakers were tested at the Centre for Speech and Language and the Cognitive Development Unit in London. 18 were assigned to the "Dutch habituation" group, and 19 to the three other groups.

_________________________

Insert Table 4 here _________________________

Results

A one-way anova with the factor Group revealed that different habituation yielded different performance (F(3,71)=3.68, p=0.016). A comparison of means showed that only the 'English' group differed significantly from the others. Planned t-tests comparing the Dutch with the French and English groups revealed only marginally significant effects (F(1,35)=2.77 p=.10 (two-tailed) for Dutch vs. French and F(1,36)=2.12 p=.15 for Dutch vs. English).

Discussion

This experiment confirms the finding of Experiment 3: listening to compressed French does not help to process compressed English. On the other hand, subjects habituated to compressed Dutch display an improvement in performance which is half the one yielded by English. The effect is small and the differences not quite statistically significant (although with a onetailed hypothesis, the French vs. Dutch comparison has p=0.05). Unfortunately, it was impossible for us to test more subjects. More subjects might have given us stronger results. Nonetheless, this experiment has served to confirm previous observations and has uncovered a trend that upholds our hypothesis that adaptation is a function of the similarity between languages at the prelexical level.

General discussion

The results reported in these four experiments show that comprehension of compressed speech can improve when subjects are exposed to compressed sentences in other languages; yet, not every language will help. Habituation to either Spanish or Catalan improves comprehension of sentences in the other language. In contrast, prior habituation to French does not improve comprehension of English nor does exposure to English help comprehension of French. Habituation to Dutch tends to facilitate processing of English. One could prima facie hypothesize that this effect would require the subjects' comprehension of the habituation language. In fact, Spanish and Catalan have a greater lexical overlap than English and French, or English and Dutch.

Our experiments, however, suggest that when cross-linguistic adaptation to compressed speech is observed, it remains robust regardless of whether subjects understand the habituation sentences or not. Indeed, while bilingual speakers of Spanish and Catalan improve their performance on the test sentences when they are habituated to the other language, monolingual speakers of Spanish who do not understand Catalan improve as much as the bilinguals do. A similar trend of improvement was observed for English speakers exposed to compressed Dutch, a language which they do not understand. Conversely, bilingual speakers of French and English who do understand both languages nevertheless fail to show adaptation from one language to the other. Therefore, without denying that comprehension may augment adaptation, we have to invoke some other properties to explain why it is that the recollection of compressed sentences is enhanced from prior exposure to certain other languages, regardless of whether the subjects understand them or not.

The finding that adaptation to compressed speech arises without comprehension is compatible with the study by Altmann and Young which showed that subjects exhibit a significant improvement in the processing of compressed sentences after listening to sentences composed of non-words. Moreover, the finding that adaptation to compressed speech shows transfer for some language pairs and not for others, suggests that low-level tuning to acoustic properties of fast speech might not be crucial. Again, this is compatible with the study by Dupoux and Green showing transfer of adaptation when different speakers utter the habituation and test sentences (replicated in our Experiments 1, 2 and 4). What we are looking for, then, is a set of properties more abstract than acoustics, which are language-specific, but that do not require comprehension. Such properties as these can of course be found at the level of phonology. In fact, a growing body of data suggests that speech perception involves a processing level that encodes the phonological properties of linguistic sounds in a language-specific way (Otake & Cutler, 1996;[START_REF] Otake | Mora or syllable? Speech segmentation in Japanese[END_REF]. This processing level, which has been called "pre-lexical", would mediate between the lexical level and the acoustic/phonetic level. The observed adjustments to compressed speech are consistent with the data from many studies on the role of pre-lexical properties on processing. Indeed, different languages use more or less similar pre-lexical representations. Why is it that Spanish and Catalan show reciprocal adjustments? Because both languages rely on syllables and on an accent that falls, roughly, in the penultimate syllable of open class words. While subjects may or may not understand the compressed sentences, they exploit these regularities in the signal. When they switch to the test sentences, these adjustments prove to be useful. Likewise, why is it that French and English do not show such reciprocal adjustments? Because French relies on syllables and on an accent that always appears in the last syllable of every open class word. English does not show an equal reliance on syllables, but instead highlights strong vs. weak syllables in its pre-lexical representations [START_REF] Cutler | The role of strong syllables in segmentation for lexical access[END_REF].

The experiments reported suggest that the study of adaptation to compressed speech may help us to classify languages in terms of their sound patterns. In the same manner in which phonemes can be organized into a matrix of features that can predict perceptual confusions [START_REF] Miller | An analysis of perceptual confusions among some English consonants[END_REF], natural languages may fit into natural classes that can be equally organized into a similarity space. Future studies will show whether this is the case.

The long pathway that leads to the sea is really pretty.

The dog is an animal that is in general always adorable.

The discussion is always centred on the problems of the economy.

He takes the bus to accompany his wife to the dentist.

My grand-parents were born only two years before the great war.

The young girl sleeps in the old hotel near the park.

The old man has a certain experience of these good wines.

The music on the radio is too modern for my cousin.

The product invented by this little man is toxic and lethal.

Each morning the young priest reads ten pages of the bible.

The minister has a great interest for all the new projects.

Test sentences in French

La troupe de comédiens a joué une parodie sur les députés.

Les appartements dans cet immeuble sont trop bruyants pour mes parents.

Le policier poursuit le voleur sur le toit de la banque.

Le groupe de joueurs qui vient est sûrement le plus important.

Le jeune docteur a dit que tes deux bras sont cassés.

Le long chemin qui mène à la mer est vraiment joli.

Le chien est un animal qui est en général toujours adorable.

La discussion est toujours centrée sur les problèmes de la sécurité.

Il prend le bus pour accompagner sa femme chez le dentiste.

Mes grand-parents sont nés presque deux ans avant la grande guerre.

La jeune fille dort dans le vieil hotel près du parc.

Le vieil homme a une certaine habitude de ces bons vins.

La musique à la radio est trop moderne pour ma cousine.

Le produit inventé par ce petit homme est toxique et mortel.

Chaque matin, le jeune prêtre lit dix pages de la bible.

Le ministre a un grand intérêt pour tous les nouveaux projets.

Experiment 4

Having a big car is not something I would recommend in this city.

Trade unions have lost a lot of their influence during the past ten years.

The library is opened everyday from 8 am to 6 pm.

They didn't hear the god news until last week on the visit to their friends.

The government is planning a reform of the education programme.

  Cutler, Mehler et al. have argued that French and English depend on contrasting pre-lexical representations. These differences in the pre-lexical representations generate different behaviours in a fragment detection task. In related studies, Sebastian-Gallés et al. have shown that Spanish and Catalan Subjects behave in a fragment detection task as if they used similar pre-lexical representations for both languages. In other experiments, Otake et al. show that speakers of Japanese have different pre-lexical representations from those used for any of the above Indo-European languages.

Table 1 .

 1 Mean percent recalled syllables from compressed Spanish and Catalan sentences for Catalan/Spanish bilingual subjects as a function of previous habituation.

	Habituation	Spanish Sentences	Catalan Sentences	Average
		Mean SE	Mean SE
	Nothing	66% 1.5	57%	2.1	61%
	Same language	91% 1.1	78%	1.3	85%
	Different language	83% 1.8	76% 1.6	80%

Table 2 :

 2 Mean percent recalled syllables from compressed Spanish sentences for monolingual Spanish subjects as a function of previous habituation.

Table 3 .

 3 Mean percent recalled syllables (and standard-error) from compressed French and English sentences for French/English bilingual subjects as a function of preceding habituation.

	French sentences	English sentences	Mean
	Mean	SE	Mean	SE

Table 4 :

 4 Mean percent recalled syllables (and standard-error) from compressed English sentences for monolingual English subjects trained with different languages.

	Habituation	English Sentences
		Mean SE
	None	52.1% 3.7
	English	65.2% 3.7
	French	50.3% 3.5
	Dutch	58.1% 3.1

Acknowledgements:

This research was supported by grants from the Human Frontier Science Program, the Human Capital program of the EEC, the Franco-Spanish Exchange Program for 1993-1995, and the Fyssen Foundation. The first version of this paper was written while Christophe Pallier was a post-doc at the Rutgers Center for Cognitive Science, NJ. We thank Peter Golato for help in data gathering, William Marslen-Wilson and Suzanne Howard at the Center for Speech and Language at Birkbeck College, and John Morton at the Cognitive Development Unit, MRC, for letting us use their facilities to test English subjects (Exp.4).

Appendix: Materials for Experiments

Experiment 1 and 2:

Test sentences in Spanish Le dije que volviera antes del mes de julio.

Cerro la puerta poco a poco para no despertar a su hija.

Esta silla es mucho mas comoda que la otra.

Estas atletas han sido las ganadoras de la ultima carrera.

Empezo a pintar hace tres meses.

Test sentences in Catalan

Li vaig dir que tornes abans del mes de juliol.

Va tancar la porta poc a poc per a no despertar la seva filla.

Aquesta cadira es molt mes comoda que l'altre.

Aquestes atletes han estat les guanyadores de la darrera cursa.

Va comencar a pintar fa tres mesos.

Experiment 3

Test sentences in English

The group of comedians has staged a parody of the parliament.

The apartments in this building are too noisy for my parents.

The policeman chased the burglar on the roof of the bank.

The group of players that comes is surely the most important.

The young doctor has said that both your arms are broken.


Christophe Pallier

Angels Colomé

Núria Sebastián-Gallés

The influence of native-language phonology on lexical access: exemplar-based vs. abstract lexical entries

This study uses medium-term auditory repetition priming to investigate word recognition processes. Highly fluent Catalan-Spanish bilinguals whose first language was either Catalan or Spanish were tested in a lexical decision task involving Catalan words and non-words. Spanishdominant individuals, but not Catalan-dominant individuals, exhibited repetition priming for minimal pairs differing in only one feature that was non-distinctive in Spanish (e.g. / ¢¡ ¤£ ¦¥ / vs. / ¨ § ©£ ¥ /), thereby indicating that they processed them as homophones. This finding provides di- rect evidence both that word recognition uses a language-specific phonological representation and that lexical entries are stored in the mental lexicon as abstract forms.

Correctly perceiving and producing the sounds of a second language is a very difficult task, as evidenced both by widespread anecdotal evidence and by a number of formal studies (see Strange 1995 for a review). Problems of this kind are observed even in those who have been exposed to the second language for considerable periods of time and who have therefore had plenty of opportunities to learn its sounds [START_REF] Flege | Age constraints on second-language acquisition[END_REF][START_REF] Mack | Consonant and vowel perception and production: Early English-French bilinguals and English monolinguals[END_REF]Pallier, Bosch, & Sebastián-Gallés, 1997a;[START_REF] Sebastián-Gallés | On-line processing of native and non-native phonemic contrasts in early bilinguals[END_REF]. It has been suggested that our nativelanguage phonological system acts as a "sieve", filtering out the properties in the speech signal that our first language (L1) system cannot properly accommodate [START_REF] Polivanov | La perception des sons d'une langue étrangère[END_REF]Trubetzkoy, 1939Trubetzkoy, /1969)). However, the ease with which foreign sounds are perceived varies; the degree of difficulty depends on the perceived phonetic similarity between L1 and L2 sounds [START_REF] Best | A direct realist view of cross-language speech perception[END_REF][START_REF] Flege | Second language speech learning: Theory, findings and problems[END_REF]. Similar, but not identical, L2 sounds and L1 phonemic categories are particularly difficult to perceive. Among the best known examples of this are the problems that Japanese listeners experience in distinguishing English /r/ and /l/ phonemes, which are both mapped to Japanese /l/ [START_REF] Goto | Auditory Perception by normal Japanese adults of the sounds "l" and "r[END_REF][START_REF] Mcclelland | Understanding failures of learning: Hebbian learning, competition for representational space, and some preliminary experimental data[END_REF]. Here we consider the consequences for lexical representations when L2 learners have difficulties in creating separate phonetic categories for certain L2 sounds. It is reasonable to expect that a minimal pair of L2 words differing only in one phoneme contrast (i.e. This research was supported by Spanish MEC research Grant PB97-977 and Catalan Government research grant GR00083. Special thanks are due to Anne Christophe and Albert Costa for constructive comments on previous versions of this paper. We also thank Anna Capdevila for her help in preparing the materials. A preliminary report of this study was given at the Sixth Eurospeech meeting (Budapest, Hungary), September 1999.

"rock"-"lock") will be represented in the same way by L2 learners who do not possess the /r/-/l/ contrast. Indeed, if both L2 phonemes are assimilated to the same L1 phoneme, then the two words become homophones.

Previous research in L2 phonemic perception has not addressed this issue; to date, studies in the field have focused on phonemic perception per se. Participants typically have to decide consciously whether a given speech sound corresponds to a given category (e.g. an identification task), or matches another speech sound (e.g. a same-different task). In fact, several studies have shown that the acoustic-perceptual system does not lose its ability to perceive the acoustic differences between non-native contrasts [START_REF] Mann | Distinguishing universal and languagedependent levels of speech perception: Evidence from Japanese listeners' perception of English [l] and [r][END_REF][START_REF] Miyawaki | An effect of linguistic experience: The discrimination of [r] and [l] by native speakers of Japanese and English[END_REF][START_REF] Werker | noun)), cel-zel (sky-zeal), sonazona (sounds (verb)-zone), calces-calzes (panties-cups) Common contrasts capa-cava (cape-wine cellar), tia-dia (aunt-day), sogasoda (rope-soda), pala-bala (shovel-bullet), gala-cala (full dress-cove), pot-bot (pot-boat), gata-bata (cat-dressing gown), gol-bol (goal-bowl[END_REF]. The fundamental difference between native (skilled) and non-native (less-skilled) speech perception mechanisms seems to lie in the fact that the former focus their attention on a more abstract (linguistic) level than the latter. This would seem to suggest that the difficulties L2 learners encounter with some foreign contrasts have an attentional, rather than a perceptual, origin [START_REF] Flege | Second language speech learning: Theory, findings and problems[END_REF][START_REF] Jusczyk | From general to language-specific capacities: the WRAPSA Model of how speech perception develops[END_REF][START_REF] Lively | Training Japanese listeners to identify English /r/ and /l/ III. Long-term retention of new phonetic categories[END_REF][START_REF] Mayberry | The long-lasting advantage of learning sign language in childhood: Another look at the critical period for language acquisition[END_REF]. In these circumstances, it is not a priori impossible that some of this acoustic/phonetic information might percolate into the lexicon. Likewise, it is conceivable that bilinguals, despite their lack of sensitivity to certain L2 contrasts when performing certain (conscious) phonemic perception tasks, might be sensitive to the same contrasts when identifying words. In fact such a possibility would be consistent with models of the lexicon in which words are stored directly as concrete exemplars. Models of lexical representation can be distinguished on the basis of their representational format. Some models propose that words are represented in the lexicon in the form of abstract phonological representations [START_REF] Mcclelland | The TRACE models of speech perception[END_REF][START_REF] Norris | Shortlist: A connectionist model of continuous speech recognition[END_REF]. According to others, word-forms are stored in the brain in the form of detailed acoustic traces [START_REF] Goldinger | Words and voices: Implicit and explicit memory for spoken words[END_REF][START_REF] Goldinger | Words and voices: Episodic traces in spoken word identification and recognition memory[END_REF][START_REF] Klatt | Speech perception: A model of acousticphonetic analysis and lexical access[END_REF][START_REF] Klatt | Lexical Representations for Speech Production and Perception[END_REF][START_REF] Pisoni | Some thoughts on "normalization" in speech perception[END_REF].

Proponents of the "acoustic trace" theory claim that word recognition involves a "direct" comparison between the memorized acoustic pattern and that elicited by the current acoustic signal. Each word is associated to many acoustic tokens and word recognition consists in finding the nearest match in a vast collection of word-forms. Experimental evidence supporting this view has shown that participants are very sensitive to non-linguistic surface cues in word recognition tasks, such as speaker's voice [START_REF] Goldinger | Words and voices: Episodic traces in spoken word identification and recognition memory[END_REF][START_REF] Schacter | Auditory priming: Implicit and explicit memory for words and voices[END_REF]see Pisoni, 1996 for a review). As discussed above, previous research on second language speech perception has shown that the speech perceptual system does not lose its capacity to perceive correctly the acoustic properties of the speech signal because of the acquisition of the first language phonological system, and thus it is able to acoustically perceive new non-native contrasts. If word-forms are stored in the mental lexicon in an acoustic format and perception of L2 contrasts preserves this information, the episodic view of the mental lexicon predicts that instances of L2 minimal pairs will not share the same acoustic-lexical representation, and, accordingly, they should not be processed as homophones. The model in which words are represented as abstract phonological entities proposes the opposite. In this model, the acoustic speech stream is coded as a normalized, language-specific phonological representation (which may consist of features, phonemes, syllables or a combination of these). This prelexical phonological representation is used for matching with lexical representations. Whenever a pair of L2 phonemes are assimilated to the same L1 phoneme, their representation will become identical at the prelexical level: the L1 phoneme will be used for coding both L2 speech sounds. Consequently, two L2 words which differ only in such a contrast will receive exactly the same lexical representation, in which the L1 phoneme takes the place of both L2 phonemes. Therefore, the two L2 words would be functionally homophones.

In previous studies [START_REF] Bosch | First and second language vowel perception in early bilinguals[END_REF][START_REF] Bosch | La estructura interna de las categorías fonéticas: percepción de vocales e identificación de prototipos en catalán y español[END_REF]Pallier et al., 1997a;[START_REF] Sebastián-Gallés | On-line processing of native and non-native phonemic contrasts in early bilinguals[END_REF] we identified two groups of highly skilled Spanish-Catalan bilinguals with a comparable (if not fully equivalent) command of both languages at the lexical level, but who show significant differences in the phonemic representations of the two languages. Spanish and Catalan are two Romance languages that differ at the segmental level, both in their vowel and consonant repertoires. Spanish has five vowels: /a/, /e/, /i/, /o/ and /u/, and Catalan has eight: /a/, /e/, / /, /i/, /o/, /¡ /, /u/ and /¢ /. Spanish does not have voiced fricatives in their phoneme repertoire, but has unvoiced fricatives that do not exist in Catalan (such as / £ / and /x/). Catalan has both voiced fricatives (such as /z/ and /¤ /) and unvoiced fricatives (some of the latter not appearing in Spanish, such as /z/). In these experiments it was observed across a wide range of tasks that most Spanish-dominant bilinguals fail to perceive Catalan contrasts that do not exist in Spanish (e.g. the vowel contrast /e/-/ε/). In these studies, all participants had been born in Barcelona (Spain) or in its metropolitan area (where both languages are spoken), had received the same bilingual education, and were currently extensively exposed to both languages. The basic difference between the groups was that Spanish-dominant bilinguals had been raised in a monolingual Spanish environment before attending kindergarten while Catalan-dominant bilinguals had been raised in monolingual Catalan environments.

This study explored lexical access in the group of Spanishdominant bilinguals, who are nevertheless extremely fluent in Catalan. Their performance was compared with that of a Catalan-dominant group of Catalan-Spanish bilinguals. We selected the repetition priming task as a suitable tool for studying the format of lexical representations. In this paradigm, participants are asked to perform lexical decisions on lists of stimuli, some of which appear twice. When a word is encountered for a second time, participants respond more rapidly than when it occurs the first time. If the repeated stimulus is a non-word, no difference is recorded in participant decision times. Therefore, this task is considered to tap lexical information. For our bilingual population, the crucial comparison rests on minimal pairs of Catalan words which differ in only one Catalan-specific contrast, such as /¥ §¦ ©¢ /-/¥ ©¢ / (meaning "granddaughter" and "clean", fem).

Catalan-dominant bilinguals would be expected to process these words as being quite distinct (which indeed they are) and to show no facilitation for the second word of a pair. The Spanish-dominant participants, on the other hand, would be expected to exhibit one of two behaviors: either they would behave in exactly the same way as the Catalan dominants (no facilitation for the second word), or they would behave as if the words were real homophones (as much facilitation as for a repetition).

In our experiment, participants were asked to perform an auditory lexical decision task on lists that contained minimal pairs of Catalan words, comprising three Catalan-specific contrasts. As already mentioned, previous research has shown that Spanish-dominant bilinguals have difficulty in perceiving these contrasts (Pallier et al., 1997a;[START_REF] Sebastián-Gallés | On-line processing of native and non-native phonemic contrasts in early bilinguals[END_REF]: /e/-/ε/, /o/-/ó/ and /s/-/z/. Thus, for example, the Catalan word /¥ ©¢ / (meaning "clean" f.) was followed lower down the list by the stimulus /¥ §¦ ©¢ / (meaning "granddaughter"). If these pairs of Catalan words, such as /¥ ©¢ /-/¥ ¦ ¢ /, are stored in the mental lexicon as ho- mophones, Spanish-dominant bilinguals should treat /¥ §¦ ©¢ / as a repetition of /¥ § ¢ /, while Catalan-dominant bilinguals should treat them as separate phonological lexical entries.

Method

Material

The stimuli were Catalan words and pseudo-words. Fortyeight words forming twenty-four minimal pairs based on phonemic contrasts specific to Catalan were included, as well as sixteen words forming eight minimal pairs based on contrasts that exist both in Spanish and in Catalan (see appendix). In addition, sixty-four Catalan pseudo-words were created that formed thirty-two minimal pairs following the same patterns as the preceding words. Finally, 152 words and pseudo-words were also included to serve as filler items. Four counterbalanced lists of 280 stimuli were created in the following way: In each list, one member of each minimal pair appeared (e.g. /¥ §¦ ©¢ / from /¥ ¦ ¢ /-/¥ ©¢ /) and was fol- lowed, 8 to 20 items further down in the list, either by the other item in the minimal pair (e.g. /¥ ¢ /), or by itself (e.g. /¥ ¦ ¢ /). The members of a given minimal pair appeared in the same positions in all four lists, but were counterbalanced across the lists.

Procedure

The participants were tested individually in sound attenuated booths. The presentation of the stimuli was fully controlled by Hewlett Packard personal computers, equipped with Pro-Audio 16 sound cards. Auditory stimuli were presented through Sennheiser HMD224x headphones with an ISI of 2.5 seconds. The experimental situation was controlled by the program EXPE [START_REF] Pallier | EXPE: an expandable programming language for on-line psychological experiments[END_REF].

Participants

Sixty-four undergraduate Psychology students from the University of Barcelona participated in the experiment in exchange for course credits. All were fluent bilingual speakers of Spanish and Catalan. Half were born in Catalanspeaking families, and half were born in Spanish-speaking families. All participants had learnt their second language (either Spanish or Catalan) from an early age (in the latest case beginning at the age of six).

Results

We defined a "repetition effect" as the reaction-time decrease between the first and the second occurrences of an item (condition "same") or between the occurrences of an item and its counterpart in a minimal pair (condition " minimal pair"). Reaction times to the second occurrence were subtracted from the reaction time to the first, therefore a positive value means a repetition effect. The average "repetition effects" are plotted on Figure 1, as a function of the following factors: Language dominance of the participants (Catalan vs. Spanish), Condition (same vs. minimal pair), Contrast type (Catalan-specific vs. Common contrast) and Lexical status (Words vs. Pseudo-words). The 95% confidence intervals displayed are based on the subject-based Anovas, but the item-based Anovas lead to the same conclusions concerning significance. These figures reveal significant repetition effects only for words in the condition "same" for both populations and, in the condition "minimal pair", only in the Spanish-dominant group for the Catalan-specific contrasts. These analyses are corroborated by the fact that the Condition × Language interaction, restricted to words, was significant for Catalan-specific contrasts (interaction in Figure 1 A: F1(1,56)= 4.2, p<.05; F2(1,21)= 4.2, p=.05), but not for Common contrasts (interaction in figure 1 B: both Fs<1). There was no effect of Repetition on the pseudowords.

Analyses performed on absolute reaction times revealed a main effect of Lexical status (with RTs to pseudowords be-ing 60 msec slower than RTs to real words (F1(1,56)= 57.7, p<.001 and F2(1,56)= 6.6, p<.05). The effect of Language Dominance was not significant (Catalan-Dominant: 921 ms SD=83 and Spanish-Dominant: 945 ms SD=114). Nor did error analyses yield any significant results.

Discussion

The results of this experiment revealed clear-cut processing differences between the populations of participants tested. More specifically, both groups exhibited a repetition effect for a "Same" repetition, but not when a minimal change intervened between the first and the second occurrence of an item. The crucial test condition involved minimal pairs of Catalan words that differed only in one contrast that was not present in Spanish (e-, o-¡ , s-z). In such cases, Spanish native speakers showed a repetition facilitation of the same amplitude as that observed for a real repetition. In contrast, the Catalan-dominant bilinguals did not show any repetition effect for these minimal pairs. It should be stressed, however, that the Spanish-dominant bilinguals achieved a high performance in the lexical decision task with Catalan words: their reaction times and error rates were not significantly different from those of Catalan natives. In short, our experiment shows that some pairs of Catalan words are processed as homophones by Spanish-dominant bilinguals, even though they master Catalan very well and their performance on a lexical decision task in Catalan is equivalent to that of natives. We can conclude, therefore, that although Spanish bilinguals master the Catalan lexicon, their lexical representations differ from those of native Catalans.

The implications of these results are twofold. First, the data presented here show that the lack of sensitivity to difficult L2 phonemic contrasts is not due to the particular properties of the tasks employed in L2 phoneme perception experiments, but that this lack of sensitivity extends into the way L2 words are represented in the mental lexicon. If listeners have difficulties in perceiving an L2 phonemic contrast, they will represent L2 word pairs with that contrast as homophones.

Second, the present data contribute to the on-going debate concerning the general format of the mental lexicon. Contrary to the predictions of the episodic view of the mental lexicon, and in agreement with abstractionist models, instances of L2 minimal pairs have been processed as homophones. Yet, one possible way for episodic models to account for the present data would be to assume that words are stored in an acoustic format ("language-free"), but that the metric of comparison depends on the language of the listener. Therefore, bilingual speakers would perceive speech sounds (acoustically) in the two languages in the same way, but how this information is retrieved in the brain would differ in the way the different acoustic parameters are employed. Following these notions, episodic models could postulate that lexical representations in Catalan and Spanish dominant listeners would not differ (they would contain both linguistic and non-linguistic information), but the way this information is retrieved from the lexicon would be language-dependent. Though this is not an impossible scenario, this theory would have to explain a number of complex points before it could be accepted. For example, it has to explain how the retrieval mechanism, very sensitive to acoustic properties of the input (such as changes in speakers' voice, see [START_REF] Goldinger | Words and voices: Episodic traces in spoken word identification and recognition memory[END_REF] remains insensitive to massive acoustic properties of the speech signal in the second language; i.e., it has to account for how, in spite of mastering a second language lexicon (reaction time and error rates differences were not significant in the two populations under study), the metric of comparison of Spanish dominant listeners does not change to conform to Catalan (second language) properties.

To conclude, the fact that Spanish-dominant bilinguals processed Catalan-specific minimal pairs as homophones favors the view that lexical representations consist of abstract language-specific phonological representations. In addition, it seems that this abstract phonological code, once acquired, is hard to modify. Even though the Spanish-dominant bilinguals in the experiment had had at least 15 years of exposure to Catalan at the time of testing, and had attained a high degree of performance in Catalan, they had not been able to learn the Catalan-specific contrasts. The results also suggest that although acoustic information may be available to the speech perception system, it does not percolate into the lexicon.

Figure 1 .

 1 Figure1. Repetition effect as a function of language, condition, contrast type and lexical status. Panels: a.) words with catalan-specific contrasts; b.) words with common contrasts; c.) pseudowords with catalan-specific contrasts; d) pseudowords with common contrasts (error bars show 95% conf. intervals)