Keywords: conditionals, medical discourse, research articles, conference presentations, grammatical norms vs. specialised usage Constructions conditionnelles

The aim of the present study is to examine possible discrepancies between the presentation of a core syntactic construction, the if-conditional, in the theoretical literature and in teaching resources and the way this construction is used in the specialised research discourse of medicine. We focus on three types of differences: differences in the frequency with which the construction is used, differences in the functions it fulfils, and differences in formal features (verb sequences and clause positioning). Two genres are examined: research articles and conference presentations produced by two groups of researchers, native English speakers and non-native (French) authors and speakers. Our analysis reveals some marked divergences between specialised discourse use and what is traditionally presented as the norm. Moreover, the differences observed between the two speaker groups lead us to argue that a more genresensitive and discourse-based approach to syntax is necessary, in order to raise learners" awareness of the linguistic and discursive specificities of their discipline and its associated genres.

Introduction

In recent years, corpus-based and corpus-driven grammars and language studies (e.g. Collins COBUILD 2005;[START_REF] Biber | Longman Grammar of Spoken and Written English[END_REF][START_REF] Hunston | Pattern grammar. A corpus-driven approach to the lexical grammar of English[END_REF] have revealed that language in use often differs significantly from traditional linguistic analyses based on structural units and grammarians" intuitions of language features. Language users constantly make choices in the grammar and lexicon depending on various contextual factors such as the communicative aim and setting, the mode (speech vs. writing), the genre, etc. and these variations have been shown to exhibit systematic patterns. A corpus approach to grammar is particularly relevant to English for Specific Purposes which ever since the outset [START_REF] Barber | Some measurable characteristics of modern scientific prose[END_REF]) has focused on the selective use that disciplinary communities make of the common language in response to their specific epistemic and communicative needs. The process of selection applies not only to the lexis or specialised terminology of the disciplines, but also to the different ways core syntactic constructions are exploited in specialised discourse.

Differences that characterise a specialised use of syntax can be of three kinds: differences in frequency, differences in function, and differences in formal features. Frequency information about grammatical patterns is perhaps the most well-researched aspect in ESP. Certain syntactic constructions are used with a much higher or lower frequency than in general usage. A classic example here would be the much greater use of passives and nominalisations in research articles than in conversation or literature. Less obvious, but equally important, are differences in the functions that a particular syntactic construction may fulfil in specialised discourse. Many common syntactic constructions have multiple functions; it is therefore necessary to see which functions are relevant and which are irrelevant in the specialised discourse at issue. The construction selected for the present study, the if-conditional, is a case in point, as this construction is characterised by a great functional versatility (Dancygier 1998:2). Lastly, syntactic patterns often have several formal variants which are not interchangeable as these subtle distinctions in form are closely linked to semantic nuances. One aim of the study will be to look at which particular formal features of the if-construction are prevalent and why. Some of the differences encountered in specialised syntax use can be attributed to the discipline and others to the genre. During the process of linguistic socialisation into these specialised discourses, both non-native English and novice researchers, if they want to be rhetorically effective, need to master these linguistic and discursive specificities and conventions of their discipline and its associated discourse genres. However, their previous exposure to or training in English does not necessarily prepare them adequately for thisand on occasion may even prove to be negative training that they have to "unlearn" in order to become professionally proficient.

To investigate the nature and extent of this potential discrepancy between theory and practice, we have chosen to restrict ourselves to one scientific discipline, namely oncology, a branch of medicine. We will focus on differences between two medical genres: research articles (RA) and conference presentations (CP) within this one discipline, in relation to the use of a single syntactic construction, if-conditionals. We have selected this particular construction because if-conditionals can be a highly valuable resource in scientific discourse. Their inherent nonassertiveness or "iffiness" (Carter-Thomas 2007) means that they can be used for hypothesizing and hedging. In domains such as medicine where absolute certainty is frequently impossible they therefore enable researchers to retain a certain distance from their claims [START_REF] Salager-Meyer | Hedges and textual communicative function in medical English written discourse[END_REF][START_REF] Martel | Medical discourse: Aspects of author"s comment[END_REF][START_REF] Prince | On hedging in physician-physician discourse[END_REF]. This is particularly true of the clinical investigations analysed here where reasoning is inductive and evidence must be carefully weighed. If-conditionals can also have an important argumentative role, enabling the text producer to set up an alternative argumentative or fictional space to promote research claims, by envisaging alternatives and conceding competing points of view. At the same time results obtained in science, and in medical research in particular, are often established under strictly controlled conditions. Researchers need to carefully delimit the research space and specify the conditions under which the research was carried out. Conditional constructions can play an extremely important role here, in specifying for example the eligibility criteria for patients involved in trials.

Literature on Conditionals

Our aim in the present study is to investigate whether the presentation and analysis of the ifconditional that can be found in a range of language resources corresponds in fact to specialised discourse use. To carry out this comparison, we have drawn on two types of resources: the theoretical literature on conditional constructions on the one hand, and on the other, a selection of teaching-oriented resources, widely used by both teachers and students, namely Toeic manuals, English for Science and Technology (EST) textbooks, and online grammar sites. Details of the teaching resources consulted can be found in Appendix I.

In the abundant literature on conditional constructions, many different typologies have been proposed by philosophers, linguists and grammarians, based on logical or truth implications [START_REF] Lewis | Probabilities of conditionals and conditional probabilities[END_REF], on the conceptual domains or worlds to which the content of the conditional refers [START_REF] Sweetser | From Etymology to Pragmatics[END_REF], or on semantic distinctions [START_REF] Comrie | Conditionals: A Typology[END_REF]. The applicability of these typologies to specialised discourse use proved however to be in most cases problematic.

Classifications of conditional constructions revolving solely around issues of logic and truth are difficult to apply to naturally occurring text. Many uses of conditionals that are unambiguous for speakers in context do not necessarily obey the principles of formal logic, while conversely examples of correct conditional reasoning given in Truth-Functional theory, such as If Paris is the capital of France, (then) two is an even number, are often intuitively unacceptable. As many commentators have noted, natural language also requires some sort of plausible relationship between the two clauses making up the conditional construction. Moreover, while formal logic may be applicable to the use of if-conditionals in mathematics for example, it is largely inappropriate for medicine, an inductive rather than a deductive science, based on observation rather than on abstract logical reasoning.

The influential typology proposed by Eve [START_REF] Sweetser | From Etymology to Pragmatics[END_REF] specifically addresses the nature of the relationship between the two parts of the conditional construction. Sweetser distinguishes conditionals in "content", "epistemic" and "speech act" domains. In the content domain conditional, the relationship between two states of affairs takes place in a socio-physical world and is essentially causal (If Mary goes, John will go).1 . In the epistemic domain the construction links premises and conclusions in a world of reasoning (if she's divorced, (then) she's been married). In the speech act domain, the if-clause justifies or explains the relevance of the speech act performed in the main clause (if I may say so, that's a crazy idea). This typology proved unhelpful for our purposes however. Whilst her content domain category is arguably too encompassing, the other two categories are of limited relevance for our corpus. We found practically no occurrences of the epistemic domain conditionals, the ones closest in usage to the formal logical if-then structure. As for speech-act conditionals, which are relevant primarily to conversation, they are unsurprisingly absent from our monologic data.

Other more functionally based classifications such as that of Anthanasiadou and Dirven (1997) also proved difficult to apply to our medical corpus. A major drawback with this as with many existng classifications is that they are mainly based on decontextualised examples, and are as a result under-specified for disciplinary discourses. The if operator is particularly polysemous and context-sensitive, as is also the case for French si [START_REF] Adam | Variété des usages de SI dans l"argumentation publicitaire[END_REF][START_REF] Bayle | Si polysémique et Si polyphonique[END_REF]) and a fully contextualised approach is in our view essential. Moreover, few analysts tackling if-conditionals seem to have considered the question of genre2 . Given the now widely-recognized impact of genre on the syntactic strategies adopted by writers and speakers, and the importance of genre awareness in achieving mastery of disciplinary discourse, this seemed an important parameter to consider.

When one turns to teaching-oriented resources, further drawbacks are encountered in the way the if-conditional is presented. As in some of the above-mentioned studies, the construction is generally illustrated by decontextualised examples, based moreover on a restricted set of oversimplified rules. The emphasis is invariably on verbal morphology and mainly limited to a presentation of the three so-called canonical conditionals: 1) present + future (If I have time tomorrow, I will call you)3 ; 2) past + "conditional" (If I knew how to drive, I would buy a car); 3) past perfect + "conditional" perfect (If I had been free, I would have gone with you to the movies), with the occasional addition of the "0" sequence of if present + present (If it rains, plants grow). In four out of the seven EST manuals analysed here, for example, the only tense sequences mentioned are the three canonical forms, presented very prescriptively as being all that the student needs to know about this construction: "The conditional form is relatively straightforward so long as the student remembers the sequence of tenses that must be observed" (CW Unit 14; our emphasis). The if present + present sequence is found only in the three OUP textbooks (ELEC, IT, TT), where it is presented as interchangeable with conditional 1 and used to express general rules of the type "If current is passed through a solenoid, a magnetic field is set up" (ELEC).

The Toeic manuals likewise focus almost exclusively on the three canonicals, as the MCQ format of the Toeic test inherently excludes any "freer" tense combinations. The present+present and past+past ("real in the past") conditionals are each mentioned only once in the four books. On the websites, one finds again a very marked skewing towards the canonical sequences: among the ten sections of Edufind, for example, only one is devoted to the zero conditional, and another to two types of "mixed conditionals". On the Eleaston site, which when consulted (March 2008) contained 51 exercises on if-conditionals, only two focus on "mixed conditionals", one on "past real" conditionals, and a small number contain examples of the "0" conditional, again used to express natural laws and generalisations. While there are passing remarks about the possibility of replacing will/would with other modals depending on the degree of certainty of the outcome, the closed answer format of almost all the quizzes means that formal variants are generally ignored. Several of the teaching resources, however, devote space to the rather literary variants with should/were/had auxiliary inversion (Should the problem arise…) or the past subjunctive were (If I were you…), which do not occur at all in our specialised data.

None of these resources provides any information about the frequency of if-conditionals in general, nor are any possible differences in the relative frequency of the various canonical forms mentioned, though the absence of type 3 in TT, IT and ELEC can perhaps be taken as an implicit indication that this form is less frequent than the others in scientific and technical English.

Concerning clause ordering, the initial position of the if-clause is usually presented implicitly as the default option in all these teaching resources. Almost all the examples and exercises in the EST and Toeic manuals have initial if-clauses (or P-clauses)4 , and when initial Q-clauses do occur, no explanation is given for this alternative order. The only remark made concerns a purely formal feature, punctuation: "If we start a conditional sentence with an 'if' clause, we use a comma before the main clause. However, when we start a conditional sentence with the main clause, there is no need to include a comma" (Target Score:135). On the Edufind and Eleaston websites, where initial if-clauses also largely dominate (75% and 68% respectively), clause ordering often seems determined simply by considerations of screen layout: when the construction is presented as a table or matching exercise, the main or subordinate clause is systematically positioned on the same half of the screen. On the rare occasions when clause order is mentioned in the accompanying explanations, it is presented as an entirely random feature: "The order of the two clauses does not matter" (Eleaston).

The explanations given in these teaching resources about the functions of if-conditionals vary considerably in their terminology, but, as with formal features, they focus on a restricted range. In the three OUP EST textbooks, the main function of the construction is that of expressing the core scientific action-and-effect relation (either real with canonicals 0 and 1, or imagined with sequence 2), while in the three EST textbooks produced specifically for French students (EAST, CW and TS), the semantics of the construction are explicitly linked to the 3 canonicals and expressed as varying degrees of hypothesis. In the Toeic manuals, one finds the same explicit link between a particular form and a specific meaning, though the terms generally used are real/unreal (present or past). The terminology used on the websites is highly varied, not to say confusing, based either on the canonical labels (Type 2, or Second Conditional), semantics (Unreal Past Conditionals), or evenmisleadinglyon truth values (True/Untrue Conditionals). Overall, it seems apparent that these resources pay scant attention to the actual discourse functions of conditional constructions and to their role in building up an argument.

Study data

The data used for this study come from two genres of medical discourse, research articles (RAs) and conference presentations (CPs), both within the field of oncology. Table 1 gives an overview of the data. Gastrointestinal Tract, 22-24 Sept. 1994, Bordeaux, France.

Genre

The research articles subset comprises 60 articles from two leading international journals; all follow the IMRD5 format and can be considered as standard data-based medical RAs. Two author groups are equally represented, with 30 articles by native English-speaking authors (RA-NSE) and 30 by French-speaking authors writing in English (RA-FSE). We made this distinction so as to compare any potential areas of difference in argumentative strategies between the two groups, with a view to developing postgraduate teaching applications for NNS researchers in reading and writing research publications in English.

The second subset, a spoken research genre, comprises 30 research talks delivered at an international conference by the same two author groups, with 15 talks by native speakers (CP-NSE) and 15 by French speakers of English (CP-FSE), again with a view to developing oral/aural applications for NNS researchers.

It should be emphasised that in our search for conditional occurrences, we were only interested in if, the prototypical operator of conditionality in English, and have excluded other conditional subordinators (on condition that, provided that, unless, etc.). We have also excluded occurrences where the subordinate clause is a subject or object clause (and where if is the equivalent of whether), as well as occurrences of as if. However, the study covers both the full if P, Q construction and elliptical P-clauses (such as if necessary), as the latter were relatively common in the data. Having made these adjustments this left us with a total of 433 occurrences: 217 in the RAs, and 216 in the CP subset, for an overall corpus size of just under three hundred thousand words.

Methodology

Given the emphasis on the verb sequences in the literature on conditionals, a first essential step was the examination of the verb forms. It was important not only to see to what extent the traditional EFL paradigm based on the three specific canonical tense sequences was reproduced in our medical data, but also to examine any major differences in the verb sequences preferred in the data-sets. A second formal feature focused on was that of clause order within the conditional sentences. As the initial positioning of P-clauses is usually presented as a norm, we were interested in seeing whether any preferential ordering could be discerned in our medical data, and, if so, whether motivated explanations could be proposed that could act as guidelines for text producers. All the occurrences were classified according to three possible positions of the P clause: initial, medial, or final.

Initial: If you add leucovorin the toxicities are really similar (CP) Medial: This tumor is very amenable if it"s a carcinoma by biopsy to local excision (CP) Final: Patients were eligible for participation if they were 18 years of age or older (RA)

A final formal feature examined in the RA subset was that of the location of the conditional construction within the IMRD sections. It is well-known that there is a strong correlation between the frequency of certain linguistic features and the section of the text [START_REF] Hyland | Hedging in scientific research articles[END_REF][START_REF] Martel | Medical discourse: Aspects of author"s comment[END_REF]. We wished to see whether this was also the case with conditionals.

This formal classification was then completed by an analysis of the functions fulfilled by the conditional constructions in their discourse contexts. We had no predefined analytical categories in mind and instead concentrated on identifying the dominant rhetorical functions in relation to the regularities in the data. Three main functions emerged from this process: Factual, Refocusing, and Discourse Management functionseach subsequently divided into a number of sub-categories.

The Factuals category broadly corresponds to what have often been called course of event, generic or habitual conditionals in other functional approaches [START_REF] Athanasiadou | Conditionality, hypotheticality, counterfactuality[END_REF][START_REF] Ferguson | If you pop over there: a corpus-based study of conditionals in medical discourse[END_REF]) and to the category of real conditions (present or past) often referred to in pedagogical grammars and manuals. However, the term "Factual" seems particularly relevant to scientific discourse, where the facticity [START_REF] Latour | Science in Action[END_REF], or status as fact, of its statements about the natural world is established by observing regularities and correlations, and by carefully defining the conditions under which the facts hold. In clinical medicine, an observational rather than a theoretical science, facticity is important in order to enable protocols and findings to be compared and reproduced. A substitution test of if by when (if [when] X, Y) was used in order to confirm allocation to this category, with the if-operator specifying the exact conditions under which the medical decisions and procedures were carried out, as in example ( 1):

(1) The dose of paclitaxel was reduced by 20% if the patient had Grade 4 neutropenia that lasted >5 days (RA-NSE)

Our Refocusing category comprises occurrences which have a marked argumentative function. To make their claims researchers constantly need to redraw the argumentative boundaries within some type of suppositional or speculative world. This category includes what have often been referred to as unreal or "hypothetical" conditionals in the literature, such as:

(2) If the results of Aoyama et al are confirmed, HFSR might be the most adequate technique to propose (RA-FSE)

as well as modalised recommendations (3) and concessive uses (4).

(3) If the tumor is at a curative stage the operation should be converted to an open surgery (CP-FSE) (4) Even if noncancer deaths did not differ, the presence of concurrent adverse health conditions, or comorbidity, has been shown to increase cancer mortality. (RA-NSE)

In the Discourse Management category we have classified occurrences which serve to instruct or guide readers and listeners in following the development of the text or talk. Ifconditionals can be used to introduce new topics (5) or to instruct readers on where to direct their attention (6):

(5) Now if we go to patients who experienced mucositis toxicity…(CP-NSE) (6) If you look at the crossover versus the non-crossover group, there was a doubling of survival (CP-NSE)

Results

Frequency

As can be seen from Table 1 above, the frequency of if-conditionals varies considerably with genre, ranging from only 0.96/1000w. in the RA to 3 times as many in the CPs (3/1000w.). This corroborates other studies which have found the construction to be more frequent in speech than in writing, both in general and in specialised discourses [START_REF] Ford | Conditionals in discourse: A text-based study from English[END_REF][START_REF] Biber | Longman Grammar of Spoken and Written English[END_REF][START_REF] Ferguson | If you pop over there: a corpus-based study of conditionals in medical discourse[END_REF]. While the difference between the two speaker groups is negligible in the RA (NSE 1.06 vs. FSE 0.85/1000w), it is considerably more marked in the CP, where the native English speakers use the construction twice as frequently as their French-speaking colleagues (NSE 3.85 vs. FSE 1.96), a point we return to later in section 5.4.

Forms

Verb sequences in the RA

The medical RA subset presents a very specific profile of use. The verb sequences used are firstly starkly different from those encountered in the literature on conditionals. The three traditional canonical verb sequences are extremely rare, representing under 5% of the total occurrences in both the NSE and FSE articles (see 3. Other Verb Sequences in the RA These "non-canonical" forms represent overall 95% of the if-conditionals in the data. A minor fraction of these combinations, amongst those classified as "other sequences " in Table 3, are decidedly odd. In (7), for example, the use of the modal might in both the P and Q clauses can almost certainly be attributed to a lack of linguistic expertise by the FSE author(s):

(7) if TGF- overexpression might be required for the initial expansion, the maintenance of the fibrotic lesion might be independent of TGF- action. (RA-FSE) However, the great majority of the non-canonical combinations are appropriate in context and occur with far greater regularity than those in any of the canonical sequences. The most frequent combination in both the FSE and NSE articles, representing globally 48.4% of occurrences, is that of two past tenses:

(8) Patients were eligible if there was evidence of spread of tumor to regional lymph nodes (Dukes" C or tumor, lymph node, metastasis stage III tumor). (RA NSE) Such sequences representing real situations in the past are rarely referred to in the literature on conditionals (see section 2).

The second most frequent verbal form in the medical RA subset, and one also perhaps insufficiently highlighted in the literature, is that involving various types of truncated verb sequence (11.5% of the occurrences). In the RA, conciseness is at premium and the use of reduced verb forms allows a greater economy of style:

(9) (adjuvant therapy allowed if >6 months since completion) (RA-NSE)

The reduced form of the Q clause and the replacement of the verb in the P clause by the mathematical symbol in this particular example represent a considerable gain in concision with regard to the full conditional sentence. However, there is a slight discrepancy here between the two author-sets, suggesting perhaps that the FSE authors are less aware of the usefulness of the various truncated conditional forms.

Verb Sequences in the CP

Canonical forms are slightly more frequent in the CP than in the RA but still only represent 12.5% of the total, a proportion which is once again very different from what the literature and teaching resources lead one to expect (see Table 4). The most common type is canonical 1, used in most cases, however, not for prediction but to describe the speaker"s regular clinical practice, as in the following example:

(10) if it"s a low rectal cancer we"ll do more frequent flexible sigmoidoscopy (CP-NSE)

The quasi-absence of conditional 3 in the two research genres (1 occ. in the RA) is also worth pointing out. This construction is widely-taught, but appears in fact to be irrelevant to the argumentative needs of the specialised discourse studied here, as the researchers would be doing themselves a disservice if they opened up past hypothetical spaces in which a different set of results might have been obtained. Alternatives likely to cast serious doubt on their claims are therefore not raised, obviating the need for canonical 3. The wide variety of other verb sequences, accounting for 87.5% of all occurrences, is shown in Table 5. In strong contrast to the RA, however, where the past + past pattern was the most frequent, it is the present + present pattern which predominates in the CP (31.5% of all occurrences). The function generally attributed to this pattern in EST manuals is that of stating general scientific laws or timeless truths; in the medical CPs studied here, however, it is used, like canonical 1, to describe regular clinical practice, the presentation of personal experience and know-how being a typical feature of the genre:

(11) if tumor is left then we do a postoperative radiotherapy (CP-FSE)

The second largest sequence, present + modal (21.7%) also refers primarily to clinical practice but statements are hedged, reflecting the inherently probabilistic basis of medical knowledge:

(12) if the patient is absolutely inoperable you can try to treat some very superficial T2N0 (CP-FSE)

These two sequences combined account for over half the occurrences. The very high proportion of patterns in the present is probably due to the real-time delivery of the talk, in that speakers prefer the immediacy of the present tense to the distance created by the past, and also to the need to refer constantly to the visuals projected on the screen during the talk.

Two other patterns characteristic of the CP, although seldom pointed out to learners, are the Q-less P-clause and the present + past pattern. The Q-less P-clause, used for slide requests (If I could have the next slide please?), although syntactically incomplete is not pragmatically incomplete in this context, and suffices, as Ford points out, to make a polite request: "A "main" clause seems to be unnecessary …, with the if-clause alone becoming a conventional format for proposing another"s action. " (1997:405). The present + past sequence is used in the CP with the specific role of semiotic management:

(13) now if we look at just some factors, the disease-free survival was less (CP-NSE)

This sequence enables the speaker to manage a smooth transition between the current enunciative space of the talk (the polite invitation in the present tense to look at the slide), to the research or content space of the results obtained in the past (disease-free survival was less…).

Verb

Clause ordering

The initial positioning of if-clauses can only be considered as the norm in the CPs. In the RAs, on the other hand, final P clauses are more frequent than initial P clauses. The tendency towards the final positioning of P clauses is contrary to what is normally presented in the literature as the default positioning but would appear to be a pronounced specificity of the medical RA and characteristic of both author groups (NSE 55%, FSE 52%). Several factors can be seen to motivate this choice. A large proportion of these postposed P clauses in both author groups involve "factual" type conditionals relating to methodology and treatment decisions taken:

Genre

(14) Fine needle aspiration was performed if involvement of inguinal nodes was clinically suspected (RA-FSE: Meth.). ( 15) Patients were eligible for participation if they were 18 years of age or older (RA-NSE:Meth.) In examples such as ( 14) or ( 15) the various defining and criterial uses of P clauses often seem better suited both cognitively and discursively to final positioning. The particular research decisions taken are presented before the precise operational definitions and/or explanations relevant to these decisions. Positioning of the if-clause can also be exploited on occasion for rhetorical effect:

(16) Associations between obliteration rate (OR) and parameters included in the univariate analysis were studied using the chi-square test where variables could be reduced to classes if the counts were >5. If the minimal count was <3, a nonparametric Mann-Whitney test was used. (RA-FSE:Meth.) By alternating the Q-P, P-Q order in these two consecutive sentences, the RA author is thus able to highlight the contrasting methods used in the case of counts >5 and<3. It appears therefore that the emphasis in conditional theory on initial positioning of if-clauses is not only rather misleading but also masks this possible discursive function of the construction. 6In marked contrast to the RA, three-quarters of if-clauses in the CP are initial. Although initial positioning is often presented as a global norm across speech and writing (cf. section 2 supra), it seems more accurate to say that the question of mode plays a predominant role. In real-time processing it is important for speakers to first provide the background for the assertion in Q, by specifying under which conditions it holds, in order to avoid misinterpretation and backprocessing by listeners. They also need to focus the listener"s attention on the referents needed in the subsequent discourse. This "presentational" function of initial if-clauses comes across clearly in many occurrences in the data:

(17) If we look at the toxicities used in some slides before we see that with this schedule we can have less toxicity than with the others (CP-FSE)

As Table 6 shows, the proportion of initial P clauses is identical in the two speaker groups, lending further support to our contention that it is the cognitive constraints of the oral mode which govern initial positioning.

The medial position of P clauses, though rarely mentioned in the literature, is also relatively frequent in the CP (11%), and once again seems to be due to real-time processing factors. Speakers sometimes interrupt the syntactic flow so as to insert in mid-sentence, almost as an afterthought, an if-clause to clarify the condition governing the assertion in Q:

(18) the diameter of the lesions if they"re adenomas tends to be bigger (CP-NSE) This type of syntactic improvisation would usually be eliminated during the writing process.

Functions

In addition to the differences in formal features noted above, the two genres also differ considerably in the preferred functions that if-conditionals fulfil (see 14 (9 occ) Table 7. Functions in the RA and CP

Functions in the RA

The medical RA also presents a very specific profile functionally speaking. What are usually presented as the prototypical hypothetical or predictive functions of if-conditionals are in fact far from "typical" in the medical research article. What predminates instead is a particular type of Factual conditional.

The practical absence of Discourse Management conditionals in the RA should not come as a surprise. All the medical RAs follow the standardised IMRD format, and there is thus no need for any extra meta-discursive signals to guide the reader through the text. The Refocusing type of conditional functions, enabling researchers to make use of the argumentative potential of the construction account for 38% of occurrences. Within this category however, any predictions and hypotheses that do occur are frequently hedged, as envisaging hypothetical alternatives or engaging in speculation is contrary to one of the main objectives of research discourse, namely that of establishing facts.

(19) Also, if preoperative therapy is administered at the time of diagnosis it might be more effective because the metastatic burden may be the smallest at this point. (RA-NSE:Disc.)

The high number of factual functions in the RA corpus can thus be related to this need to establish facticity in scientific texts. While it is true that reference to Factual conditions in scientific texts is usually addressed in EST manuals (cf. section 2), reference is invariably only made to factual conditions in the present, expressing some type of generalisation or timeless truth. In our medical RAs, the great majority of factual if-conditionals involve the past + past pattern and refer to specific pieces of research accomplished by the author and colleagues, rather than to the statement of any general truths.

(20) If 10% or more of the malignant nuclei were stained, the slide was scored as negative (RA-NSE:Meth)

Functions in the CP

As in the RA, the Refocusing function accounts for one-third of if-conditionals; the other two functions, however, are distributed very differently between the two genres.

Factuals are less common in the CP (41% vs. 61% in the RA), no doubt because most Factuals occur in the Methods section of the RA, a section that is much shorter and less detailed in the CP -audiences come to hear "breaking news" and fresh results, so established methods are very quickly glossed over.

The function that marks the real specificity of the CP genre however is Discourse Management. Whereas we found only one occurrence in the 60 RAs, there are 56 in the 30 CPs (i.e. >100 times as many). Two factors can be adduced to explain this difference. Firstly, the structure of conference presentations is more variable from one speaker to another than that of the RA. The absence of a template therefore makes it necessary for speakers to guide their audience through the talk by signalling its organization. Moreover, as various analysts of lengthy expository monologues have pointed out, organizational markers are necessary in this type of discourse in order to chunk the continual verbal flow into manageable segments and mark topic boundaries [START_REF] Rilling | Lexical phrases as organisational markers in academic lectures: A corpusand computer-based approach to research and teaching[END_REF][START_REF] Thompson | Text-structuring metadiscourse, intonation and the signalling of organisation in academic lectures[END_REF]. If-conditionals are one of the preferred means to do this; in Rilling"s study of university lectures, for example, of the nine most frequent 4-word topic shifters, four are if-conditionals. A typical example from our data is:

(21) If we now go on to discuss the other problem, that is the local recurrence problem, this is a serious problem (CP-NSE)

Another reason for the large number of discourse management if-conditionals is linked to the fact that scientific speakers" need to manage concurrently two kinds of semiotic spacesthe verbal space, or spoken commentary, and the visual space, or what is projected onto the screen. As the latter is an integral part of the scientific content, the two spaces need to be connected by intratextual references for the discourse to be cohesive (Young 1990:91). Ifconditionals have the advantage of giving a suitably polite directive to the audience, not threatening to the listener"s negative face. These various discourse management uses of if-conditionals have received little attention in the teaching literature on conditionals7 .

NSE /FSE differences

As several of the tables shown above indicate, in addition to the differences between genres, there are also some interesting divergences in the way the two speaker groups use ifconditionals in specialised discourse. This section discusses the most significant differences observed.

NSE /FSE differences in the RA

In the RA, there are overall few notable differences concerning the forms of if-conditionals in the two author groups. In both sets of articles final positioning of P clauses is preferred and recourse to the three canonical conditionals is very rare (see Tables 2 &6). Both groups instead frequently use the combination of two past tenses in order to describe real situations in the past. In the FSE subset there are however slightly more verb sequences involving two present tenses or the present + modal sequence than in the NSE subset. This discrepancy can be related to the slightly higher proportion of refocusing type conditionals in the FSE subgroups.

As Table 7 illustrates, although discourse management functions are conspicuously absent in both author groups, there are some differences with regard to the distribution of the refocusing and factual functions. Factuals, even if predominant in both author groups, are more widely used by the NSE authors than by their FSE counterparts. Refocusing conditionals, on the other hand, are more exploited by the FSE authors than by the NSE authors (46% & 32% respectively), particularly with the contrastive and concessive uses, where one invariably finds two present tenses:

(23) If the results are encouraging for T2 lesions, the rate of local failure with RT [radiotherapy] … for T3 lesions remains >20%. (RA-FSE:Disc.) (24) Even if these local failures are surgically salvageable in most patients, they are certainly not trivial events and, in some cases, may have a deleterious impact on survival. (RA-FSE)

These differences can be related not only to a certain amount of language interference (French si has a wider range of values than English if) but also to the potential influence of different national academic writing styles. Lack of space prevents us from examining this issue here in detail but in a previous study contrasting the use of French si and English if in the medical research article (Carter-Thomas 2007), French authors were seen to make greater use of the refocusing and manoeuvring capacity of the conditional operator si in argumentation and it is therefore possible that this trait is also carried over to their research writing in English.

The differences in the distribution of functions between the two author groups is also reflected in the distribution of if-conditionals across the RA IMRD sections. Although if-conditionals occur with a similar frequency in both author groups (see Figure 1) the occurrences are not distributed in the same way over the RA sections. As is well-known there are considerable differences in communicative function from one section of the research article to another [START_REF] Swales | Genre Analysis[END_REF][START_REF] Swales | Research genres[END_REF]. In particular a sharp distinction is maintained between the research data and its interpretation. In the NSE group the majority of occurrences are in the more descriptive Methods and Results sections (67%), as opposed to only 27% of occurrences in the Discussion section. Those of the FSE authors also contain a substantial number of occurrences in the Methodology section (46%), but they also contain an almost equally high percentage of occurrences in the more polemical Discussion sections (44%), reflecting the greater recourse to refocusing functions of if-conditionals noted above and exploitation of the construction"s argumentative potential.

NSE /FSE differences in the CP

The need for syntactic structures that are adapted to the specific communicative requirements of the conference presentation genre is not always fully apprehended by the FSE speakers, leading to much greater differences between the two speaker groups than those observed in the RA. This is to some extent understandable as in the CP no hard and fast rules, or even models that can be analysed and then imitated, exist.

A first major difference between the two speaker groups concerns the frequency with which they use if-conditionals in their talks: though overall if-conditionals are three times more frequent in the CP than in the RA, this is mainly due to the NSE speakers who use the construction twice as frequently as FSE authors do (NSE: 3.8/1000w. vs. FSE: 1.9/1000w.).

Or, to put it differently, the ratio of if-conditionals in the CP compared to the RA is 4:1 in the case of NSE, and only 2:1 for FSE. When switching from a written to an oral mode of presentation, the French speakers do not differentiate as radically as the American speakers do in their choice of preferred syntactic patterns. This confirms our earlier findings on other syntactic constructions such as the passive, extraposition, pseudo-clefts and inversion (Carter-Thomas & Rowley-Jolivet 2001; Rowley-Jolivet & Carter-Thomas 2005): in all cases, the constructions characteristic of written scientific discourse are more prevalent in FSE talks, while those characteristic of speech are much less in evidence.

There are also some notable differences with regard to the three main functions of ifconditionals in the two speaker subsets. Although Factual functions are exploited in the same proportion in both groups, the FSE researchers make greater use proportionally speaking of the Refocusing functions (NSE 28%; FSE 45%), reflecting the greater recourse to the argumentative capacity of refocusing if-conditionals noted previously among FSE RA writers. The most striking difference however is in the Discourse management function, that is, ifconditionals used to signal the structure of the talk and to direct the audience"s attention, as in:

Now if we look at some other series…. It is heavily used by the NSE speakers (47 occ., representing 31% of all if-conditionals in their talks), but only sparsely by the FSE speakers (a mere nine occurrences; see Table 7). It would appear that this pragmatic use of the ifconditional is largely unfamiliar to the latter group, no doubt in part because it is granted so little attention in EFL manuals. Given its important discourse functions in the CP, this raises the possibility that their talks may be less clearly signposted and with less attention paid to politeness strategies. EFL learners are generally taught logical link-words and set expressions on the other hand, therefore, I will now move on to my second point, etc.to structure their discourse. However, many if not most of these do not occur at all in our data, in either speaker group. Incorporating some explanations of the more pragmatic uses of conditionals, within a generally more genre-sensitive approach to English syntax, would prepare learners more completely for the reality of disciplinary discourse use they are likely to encounter.

Conclusions

This study of the frequencies, functions and forms of if-conditionals in two medical research genres has highlighted several interesting features of specialised discourse use. We have seen firstly that if-conditionals are overall much more frequent in the spoken than in the written genre. This tallies with the findings of several studies comparing if-conditionals in speech and writing in general, so on this point specialised discourse is not noticeably different.

Several of the formal features of the construction, however, diverge markedly from what the theoretical and pedagogical literature present as the norm. Whereas if-conditionals are invariably presented in the literature with the P-clause in initial position, this is by no means the case in the medical RA. On the contrary, initial positioning seems to be attributable to modal factors such as the constraints of cognitive processing in speech rather than being a characteristic feature of the construction itself. We have also noted that certain verb sequences in if-conditionals are highly genre-specific, with the RA being characterised by the past + past pattern and to a lesser extent truncated forms. In the CP, the present + present sequence dominates, while two additional patternspresent + past and the Q-less P-clauseappear motivated by the semiotic and pragmatic parameters of the genre. Most importantly for teaching applications, we have seen that the emphasis in EFL/EST manuals on the three "canonical" verb patterns is largely irrelevant to the research discourses of medicine. In both the RA and the CP, these patterns represent only a fraction of all verb forms used in the construction8 .

It is clear that learners who have been led to believe that only these forms exist and that they can be used in all circumstances will be ill-equipped for either producing or processing medical research discourse. This discrepancy is undoubtedly linked to the incompatibility between the rhetorical aims of the medical research genres and the habitual semantics of the "canonical" forms, namely prediction, supposition, and counterfactuality. The functions fulfilled by if-conditionals in our corpus appear on the contrary to be very genre-specific. Each of the two genres makes preferential use of a particular function: Factuals in the RA and Discourse Management in the CP. These preferences are rhetorically motivated, in that they correspond in each case to the communicative and argumentative needs of the genre in question.

At several points in this study, however, we have noted differences between the native English writers/speakers and their French counterparts. In the RA, the FSE group differs from the NSE by a rather different distribution of if-conditionals over the RA sections and greater use of the Refocusing function. While some of these differences can perhaps be attributed to interference from French or to different writing styles, others, we would contend, are linked to the way such common syntactic patterns as the if-conditionals are generally presented to learners. The much lower frequency of if-conditionals in the FSE CPs, for example, can probably be attributed to a lack of awareness of the pragmatic and discourse management functions of the construction.

Our study has brought to light some important discrepancies between the general theory and rather prescriptive rules found in learner manuals on if-conditionals on the one hand, and specialised discourse practice on the other. If teaching oriented resources give a misleading or incomplete picture, learners may be unfamiliar with certain verb patterns and functions, and therefore risk either misunderstanding certain usages or being less rhetorically effective themselves in the different genres they need to master. Teaching if-conditionals using decontextualised examples, or focusing on purely logical and abstract meanings, without taking into account the specific requirements of the genre and discipline, can even be counterproductive.

What is needed is a more genre sensitive approach to such common syntactic constructions as the if-conditional. This includes familiarising learners therefore with the specificities of the syntactic patterns they are likely to meet when reading, writing or speaking the discourse of their specialised communities. If a more genre-sensitive and discoursal approach to syntax is taken, learners will be more aware of the linguistic and discursive specificities of their discipline and its associated genres and therefore more adequately prepared to take part in the life of their discourse communities.

Online grammar resources

The following websites were consulted (March 2008):

1. <http://eleaston.com> Section Grammar > Verbs > Conditional 2. <http://www.edufind.com> Section verbs and verb tenses > sub-sections on if-sentences and the conditional

( 22 )

 22 If you look at the number of patients that were treated, … (CP-NSE)

Figure 1 .

 1 Figure 1. Comparative distribution of if-conditionals by section in the NSE and FSE RAs

Table 2 .

 2 Table 2 below). It is clear that any novice or NNS author, who has been led to believe that such forms are the norm, will therefore be illprepared for this reality of discourse practice. Canonical verb sequences in the RA Our RA subset reveals instead a variety of other verb sequences. The most frequent of these are given inTable 3:

	Verb sequence	NSE	FSE	All RAs
	Canonical 1	2	0	2
	Canonical 2	4	3	7
	Canonical 3	1	0	1
	All canonical forms (1,2,3)	7	3	10 (4.6%)
	Other combinations	112	95	207 (95.4%)
	Verb sequence	NSE	FSE	All RAs
	Present + present	9	12	21
	Present + modal	9	15	24
	Present + past	2	4	6
	Modal + other	5	2	7
	Past + past	61 (51.2%) 44 (44.9%) 105 (48.4%)
	Past + modal	4	1	5
	Past perfect + past	4	2	6
	Truncated verb sequences 17 (14.2%) 8 (8.1%) 25 (11.5%)
	Other sequences	1	7	8
	All non-canonical forms	112	95	207
	Table

Table 4 .

 4 Canonical verb sequences in the CP

	Verb sequence	NSE	FSE	All CPs
	Canonical 1	13	5	18
	Canonical 2	8	1	9
	Canonical 3	0	0	0
	All canonical forms (1,2,3)	21	6	27 (12.5%)
	Other combinations	131 (86.2%) 58 (90.6%) 189 (87.5%)

Table 5 .

 5 Other verb sequences in the CP

	sequence	NSE	FSE	All CPs
	Present + present	45	24	69
	Present + modal	29	18	47
	Present + past	13	0	13
	Modal + other	11	2	13
	Past + past	6	0	6
	Past + modal	4	0	4
	Q-less P-clause	13	2	15
	Truncated verb sequences	6	7	13
	Other sequences	4	5	8
	All non-canonical forms 131 (86%) 58 (90.6%) 189 (87.5%)

Table 6 .

 6 Clause ordering in the RA and CP

		# Occ.	Positioning (%)
			Initial Medial Final
	RA	217	43.3	3.2 53.4

  Table 7).

		Factuals % Refocusing % Discourse %
	All RAs	61	38	1
	NSE	68	32	0
	FSE	53	46	1
	All CPs	41	33	26
	NSE	41.5	28	30.5 (47 occ)
	FSE	41	45

All examples in this paragraph are from Sweester 1990.

See however[START_REF] Ferguson | If you pop over there: a corpus-based study of conditionals in medical discourse[END_REF],[START_REF] Facchinetti | Conditional constructions in modern English legal texts[END_REF] and[START_REF] Rowley-Jolivet | A genre study of if in medical discourse[END_REF] for recent analyses of ifconditionals conducted from a genre perspective.

3 All examples taken from<http://eleaston.com>

In much of the theoretical literature on conditionals, the subordinate if-clause is termed the P-clause and the main clause the Q-clause.

Introduction, Method, Results, Discussion, the usual format of the research article.

The respective ordering of the P and Q clauses also fulfills a vital role in information structuring. The initial section of the sentence will usually be the site of what the enunciator intends to be interpreted as given or topical information (Carter-Thomas & Rowley-Jolivet 2001). In a conditional construction, an initially occurring "if' acts as a signal to the receiver to provisionally accept a set of circumstances denoted by the P clause as backcloth to a new state of affairs expressed in the Q clause. Lack of space prevents us however from developing these aspects further here.

Among the teaching resources consulted, the only one to mention the "politeness" function of if-clauses, with ellipsis of Q and a passing allusion to the influence of the spoken mode, is IT: "We use the action part of ifsentences, especially in spoken English, to give instructions in a polite way. The effect part is assumed."(IT, 70)

To assess whether this is a discipline-specific feature or more generally characteristic of research discourse, it would be interesting to compare the quasi-absence of canonical verb sequences in medicine with texts from another discipline such as law, in which if-conditionals are known to be common[START_REF] Facchinetti | Conditional constructions in modern English legal texts[END_REF].

Appendix I: Corpus of teaching resources on the if-conditional


Cyprien Pindat
email: pindat@lri.fr

Emmanuel Pietriga
email: emmanuel.pietriga@inria.fr

Olivier Chapuis
email: chapuis@lri.fr

Claude Puech
email: claude.puech@inria.cl

Drilling into Complex 3D Models with Gimlenses

Keywords: CR Categories: H.5.2 [Information Interfaces and Presentation]: User Interfaces -Graphical user interfaces-[I.3.5]: Computer Graphics-Computational Geometry and Object Modeling Detail-in-Context, Lenses, Multi-scale Visualization

Figure 1: Exploring the CAD drawing of a car engine. The three Gimlenses provide detailed views of different constituent parts of the engine, at different magnification levels and with varying orientation, while revealing their location inside the global 3D model. a) Context view. b) Magnified side view of a knot behind, and thus originally hidden by, the cylinder head cover. c) View fully revealing a poppet valve in-context from a different angle than the main view, with d) another Gimlens configured so as to provide a low-angled point of view on the valve.

Introduction

Three-dimensional computer modeling has become an essential activity in many domains: the movie industry, medicine, scientific visualization at large, and the automotive, aerospace and electronics industries, which sometimes rely on 3D modeling throughout the design and production chain (Computer-Aided Design and Manufacturing). Processing and graphics rendering capabilities now make it possible to model and visualize extremely complex datasets on widely varying types of displays: desktop workstations featuring one or multiple screens, ultra-high-resolution wall-sized displays [START_REF] Nancel | Mid-air pan-and-zoom on wall-sized displays[END_REF], and virtual reality environments such as CAVEs [START_REF] Sandin | The cave: audio visual experience automatic virtual environment[END_REF]]. For instance, Boeing's 777 airliner was entirely modeled using CAD software, resulting in a very complex and dense 3D scene featuring more than 350 million polygons [START_REF] Dietrich | Exploring a boeing 777: Ray tracing large-scale cad data[END_REF]]. Highly-detailed models of the entire human anatomy, of complex mechanical components and even entire cities are now available, usually for a price given the difficulty of creating such datasets.

As their real-world counterparts, complex 3D models are difficult to inspect, because they are made of numerous distinct parts assem- Cyprien Pindat, Emmanuel Pietriga, Oliver Chapuis, and Claude Puech. 2013. Drilling into complex 3D models with gimlenses. In Proceedings of the 19th ACM Symposium on Virtual Reality Software and Technology (VRST '13). c ACM, 2013. This is the author's version of the work. It is posted here by permission of ACM for your personal use. Not for redistribution. The definitive version will be published in VRST '13, October 6 -8 2014, Singapore. http://doi.acm.org/10.1145/2503713.2503714 bled together into dense scenes that generate a lot of visual occlusion. Constituent elements will often partially occlude or even fully surround one another, and can also have widely varying sizes (e.g., an airplane's wings compared to a bolt). Quickly identifying elements of interest, getting detailed views of those elements from different perspectives, putting them in a broader spatial context, and relating them to other elements are all challenging tasks. Often, several designers will be working collaboratively on these datasets, requiring support for merging their work into a single assembly: detecting and understanding conflicts such as, e.g., intersecting parts due to problems of scaling and positioning.

These different tasks involve setting up multiple cameras and manipulating them to inspect elements from different angles and at different scales, as well as changing the visibility settings of elements that lie in the line of sight between the observer and the objects of interest. Those interactions are tedious to perform and cause significant distraction.

We introduce Gimlenses (Figure 1), a multi-view, detail-in-context visualization technique that enables users to navigate complex 3D models by drilling holes into the outer layers of a model to reveal objects that are buried, possibly deep, into the scene. The geometry of those holes gets constantly adjusted so as to guarantee the visibility of objects of interest from the parent view. Gimlenses can be cascaded and constrained with respect to one another. They provide synchronized, complementary viewpoints on the scene at different scales and from different angles, enabling users to inspect distinct parts simultaneously, facilitating their understanding, inspection and comparison [START_REF] Plumlee | Zooming versus multiple window interfaces: Cognitive costs of visual comparisons[END_REF]].

Related Work

Gimlenses build upon work in multi-scale visualization, 3D navigation and smart visibility techniques for CAD.

Multi-scale Visualization

Gimlenses are essentially detail-in-context representations, providing multiple simultaneous points of view on the 3D model at different scales. Gimlenses are categorized as an overview+detail technique [START_REF] Cockburn | A review of overview+detail, zooming, and focus+context interfaces[END_REF]]: they relate one or more detailed views, called focus regions, into a larger, less detailed contextual view of the dataset. Multi-scale techniques apply either to 2D visualization, e.g., [START_REF] Carpendale | A framework for unifying presentation space[END_REF], 3D visualization, e.g., [START_REF] Carpendale | Extending distortion viewing from 2D to 3D[END_REF]], or both [START_REF] Pietriga | Representationindependent in-place magnification with sigma lenses[END_REF]. Some techniques use spatial distortion to achieve a smooth integration of the focus in the surrounding context [START_REF] Carpendale | A framework for unifying presentation space[END_REF], possibly adapting the focus' shape to the underlying geometry [START_REF] Pindat | Jellylens: content-aware adaptive lenses[END_REF], while other techniques achieve this integration through a combination of spatial distortion, alpha blending and dynamic parameter adjustments according to user input [START_REF] Pietriga | Representationindependent in-place magnification with sigma lenses[END_REF]. Gimlenses are more specifically drawing upon the DragMag [START_REF] Ware | The Drag-Mag image magnifier[END_REF], a technique that offsets the magnified view and visually relates it to the corresponding region in the context view using simple line segments.

In the realm of 3D multi-scale visualization, Carpendale et al. [START_REF] Carpendale | Extending distortion viewing from 2D to 3D[END_REF]] transposed the general focus+context approach [START_REF] Cockburn | A review of overview+detail, zooming, and focus+context interfaces[END_REF] based on spatial distortion to 3D data cubes. The technique guarantees the visibility of particular cells in a cube by moving and resizing the surrounding ones. The concept was generalized to arbitrary meshes using an energy grid optimization model [START_REF] Wang | Feature-preserving volume data reduction and Focus+Context visualization[END_REF]. The technique only magnifies objects in-place, though, and does not address the problem of visibility in dense scenes. Magic Volume Lenses [START_REF] Wang | The magic volume lens: An interactive focus+context technique for volume rendering[END_REF] provide in-place magnification and can reveal some details hidden behind outer layers, but the detailed view is necessarily oriented according to the context view, and magnification factors are severely limited by both the spatially-distorted transition and problems of quantization [START_REF] Appert | Highprecision magnification lenses[END_REF] due to the single focus region. The DragMag technique mentioned earlier was also transposed to 3D in [START_REF] Plumlee | Integrating multiple 3d views through frame-of-reference interaction[END_REF], providing users with a multi-window detail-in-context visualization technique that somewhat resembles ours. However, the technique was designed for navigating in oceanic data, i.e., relatively flat 3D scenes compared to car engines or layered models of the human anatomy. Thus the technique does not deal with problems of visual occlusion typically encountered in complex, dense 3D scenes.

Magic Lenses [START_REF] Bier | Toolglass and magic lenses: the seethrough interface[END_REF] are lenses that are used to modify the rendering of objects seen through them. The concept is very generic and powerful. Examples more closely related to our work are lenses that render, e.g., a wireframe version of the original object. Originally designed for 2D graphics, Magic Lenses were later extended to work with 3D graphics [START_REF] Viega | 3D magic lenses[END_REF][START_REF] Ropinski | Real-time rendering of 3D magic lenses having arbitrary convex shapes[END_REF].

3D Navigation

Numerous techniques have been designed to make navigation into 3D environments more efficient than when using the usual pan, zoom and rotate functions found in most 3D user interfaces, using different metaphors such as that of a flying vehicle. [START_REF] Tan | Exploring 3D navigation: combining speed-coupled flying with orbiting[END_REF]] combine speed-coupled flying with orbiting. McCrae et al. [Mc-Crae et al. 2009] adapt the travel speed of the flying vehicle in a space-scale-aware manner using a cubemap technique to enable navigation in multi-scale environments. Navidget [START_REF] Hachet | Navidget for easy 3D camera positioning from 2D inputs[END_REF]] is a gesture-based interactive widget that enables users to get a preview from a different perspective on the scene before actually repositioning and reorienting the main camera to match this new point of view. Another way to ease navigation is to constrain camera movements to object dependent surfaces [START_REF] Khan | HoverCam: interactive 3D navigation for proximal object inspection[END_REF] or authored surfaces [START_REF] Burtnyk | Stylecam: interactive stylized 3d navigation using integrated spatial & temporal controls[END_REF].

Smart Visibility

Smart Visibility originates from static technical illustrations [Viola and Gröller 2005]. It aims at conveying the most information possible using a single, often static illustration by unveiling its most important parts. Smart visibility techniques are based on cutaway views [START_REF] Feiner | Cutaways and ghosting: satisfying visibility constraints in dynamic 3D illustrations[END_REF][START_REF] Li | Interactive cutaway illustrations of complex 3D models[END_REF]], ghostedviews [START_REF] Bruckner | Illustrative context-preserving volume rendering[END_REF]Viola et al. 2005;[START_REF] Kruger | Clearview: An interactive context preserving hotspot visualization technique[END_REF][START_REF] Correa | The occlusion spectrum for volume classification and visualization[END_REF][START_REF] Correa | Visibility histograms and visibility-driven transfer functions[END_REF] or spatial rearrangement [START_REF] Li | Automated generation of interactive 3D exploded view diagrams[END_REF][START_REF] Mcguffin | Using deformations for browsing volumetric data[END_REF]]. [START_REF] Burns | Adaptive cutaways for comprehensible rendering of polygonal scenes[END_REF] propose adaptive cutaways that adapt their geometry to guarantee the visibility of predefined parts of interest. While some of these techniques do make it possible to interactively select the main point of interest to be revealed [START_REF] Li | Interactive cutaway illustrations of complex 3D models[END_REF][START_REF] Li | Automated generation of interactive 3D exploded view diagrams[END_REF]], these are still aimed at producing static illustrations. They do not provide a true solution for exploring complex 3D scenes.

Gimlenses are conceptually related to the 3D occlusion management techniques surveyed in [START_REF] Elmqvist | A taxonomy of 3D occlusion management for visualization[END_REF], and more specifically to the x-ray category of tools: perspective cutout [Coffin and Hollerer 2006], x-ray tunnels [START_REF] Bane | Interactive tools for virtual x-ray vision in mobile augmented reality[END_REF], and the looking glass from [START_REF] Looser | Through the looking glass: the use of lenses as an interface tool for augmented reality interfaces[END_REF]. Such techniques also provide solutions for revealing hidden parts of a 3D scene, as do Gimlenses. However, those techniques are used in addition to a 3D navigation technique, which increases the burden put on users, who have to handle both navigation and visual occlusion management conjointly but sequentially. On the contrary, Gimlenses integrate occlusion management with 3D navigation, automatically revealing the focused part of the scene to the observer. This integration facilitates exploration no matter the type of display, but is especially useful in contexts where input capabilities are limited or where interaction is more challenging than on a desktop workstation such as, e.g., wall-sized displays operated from a distance or via a touchsensitive surface. Another distinctive feature of Gimlenses compared to earlier work are their capacity to get coordinated and cascaded, as detailed in Section 3.6.

Gimlens

Gimlenses provide users with multiple, possibly coordinated, detail-in-context views on 3D scenes that provide support for the deep exploration of complex layered models at different scales. We first describe the interface's main features. Then we explain how holes are drilled into the model to guarantee the visibility of objects of interest while preserving context. The following section introduces more advanced features: automatic orientation constraints and lens cascading. We conclude with implementation details and performance figures, followed by a discussion of current limitations and future work.

Main Interface Components

As in all focus+context techniques, the purpose of the main viewport is to provide users with an overview of the scene. This viewport, which we call the context view (Figures 1-a and 2-a), can be freely rotated, panned and zoomed using conventional techniques adapted to the display platform.

From this context view, users may instantiate multiple Gimlenses that can then be used to drill into the model (Figure 1). Each Gimlens is composed of four main elements: the view window, the object selector, the lens proxy and the cone-shaped cut. The view window (Figure 2-b) is an independent viewport that users can freely move and resize. It contains the detailed view that corresponds to the lens' focus region. The object selector, symbolized by a blue ring (Figure 2-c), identifies the current object of interest in the model, focused on by the lens. The object selector and view window are visually linked together by two line segments, called tethers in [START_REF] Ware | The Drag-Mag image magnifier[END_REF]. While this set of elements is sufficient to relate the detail and context views in 2D visualizations, additional information has to be conveyed to users to achieve full 3D linking [START_REF] Plumlee | Integrating multiple 3d views through frame-of-reference interaction[END_REF] of views. This is especially important in the case of scenes that contain numerous layers and closely clustered parts and pieces, as those are prone to occluding one another, making it even more challenging for users to get a good sense of spatial orientation.

The lens proxy (green cone in Figure -2-d) indicates the orientation of the Gimlens. The cone is oriented such that its axis is aligned with the line of sight of the corresponding Gimlens, its tip oriented towards the observer. The cone is rendered as an opaque, smoothly shaded object with lighting effects to help users evaluate its orientation in the scene. To help them evaluate its position in the scene, the cone is blended with the elements of the model that should actually occlude it, as illustrated in Figure -1-c (red cone).

Finally, as users inspect objects in the scene by repositioning the Gimlens (Section 3.2), we perform a cone-shaped cut (Section 3.5) to guarantee the visibility of the object of interest from the context view by drilling into the model all the way down to this object (Figure 2, outlined yellow cuts into the cylinder head cover and beyond). We further enhance the readability of this representation by outlining the object of interest both in the view window and in the context view (knot with green outline, Figures 2-b and2-c).

Repositioning a Gimlens

There are multiple ways to reconfigure the point of view of a Gimlens on the model. Users can grab the object selector (blue ring, Figure 2-c) and drag it in the context view. As the Gimlens' focus point slides on the surface of the model, following the object selector, the viewing frustum gets adjusted accordingly, depending on some properties detailed later (automatic orientation constraints). The object of interest gets updated as soon as the focus point falls on another object.

Users can also make the lens orbit around the object of interest by dragging the lens proxy (green cone, Figure 2-d) around it. Finally, the Gimlens' viewing frustum can be reconfigured by freely rotating, panning and zooming the lens' viewport using dragging, as when reconfiguring the context view. The controls should be mapped to input device buttons in a consistent manner between the two types of viewports.

Drilling into the Model

The set of interactions described above make it possible to inspect the outside of complex 3D models, but are of little use when inspecting the inside of those models. Many models, including CAD drawings of engines or planes, 3D maps of buildings and plants, or layered representations of the human anatomy are composed of large amounts of objects, many of which are inside other objects.

A foundational feature of Gimlenses is that they let users drill into the model supporting its exploration and allowing for fast access to objects that are buried, possibly deep, into it. Users can iteratively The technique's name is inspired by the word gimlet, a tool for drilling small holes, mainly in wood. Cuts are shaped as truncated cones whose axis is oriented from the object of interest to the observer's eye. The cone itself is invisible, but hides every object that intersects it. If an object only partially intersects the cone, the geometrical intersection between the two shapes is computed and only the part that falls within the cone is made invisible. The cone's geometry depends on the size of the object of interest, on the position of the focus point on this object (determined by the position of the selector -blue ring -on the object), and on the viewing frustums of both the context view and Gimlens. Being truncated, the cone has a top and a base, which we call the near and far bases in reference to the near and far clipping planes of a viewing frustum. The near and far bases are located close to the observer and close to the object of interest, respectively.

An interesting property of the cone is that the size of cuts decreases as the parts being cut are located deeper into the model. No matter the projection considered (perspective or orthogonal), this helps users get a better sense of how deep the focus point is, as they can always see how many layers got cut to get to the object of interest. To further emphasize this, we outline the surfaces that resulted from intersecting the cone with the parts that originally overlapped it (yellow strokes in all figures).

Cuts are also performed in the Gimlens viewport, coupling the near base to the apex of the lens' viewing frustum so that the object of interest always remains visible no matter how the former gets positioned. However, this behavior is not always desirable. For instance, when instantiating a Gimlens to inspect the intersection between the surfaces of two distinct parts in the model, the cut cone would hide one of those surfaces, hence hiding an important piece of information, as illustrated in Figure 3. Cuts performed inside the lens' view window can thus be toggled on/off.

Adjusting Depth

We designed an interaction technique based on the above drilling method, that enables users to navigate inside a 3D model by successively drilling holes into it starting from the outer layer. On a desktop workstation, the technique is operated with the mouse wheel. In other environments, such as virtual reality platforms or wall displays, the corresponding actions have to be mapped to a linear continuous input control channel on one of the available interaction devices. Invoking the technique on the current part of interest (on which the selector lies) cuts out a hole in it and moves the focus point on the surface below, that was just revealed by the cut. Users can also climb back, filling the holes previously cut in reverse order, with the focus point and object of interest getting updated accordingly. The cut cone automatically adjust its geometry, following the focus point controlled with the cursor. Figure 4 illustrates this process.

Gimlenses keep a history of what parts got cut, allowing the user to drag the focus point from one part of interest to the next and drill down iteratively. This navigation method can be seen as an easy way of toggling the visibility of the successive parts that the focus point falls on during the drilling process, except that each part's visibility is only affected locally around the line of sight so as to better preserve context.

Optimizing Cuts

Cuts are an essential features of Gimlens. They enable navigating inside models and act as visual cues that help situate objects of interest within the model. A good navigation experience depends on guaranteeing a good visibility of the focus point from the lens, on the readability of the depth cues and on the predictability of the interface's behavior, and on the performance in terms of frame rates. All of these factors depend on the shape of the cut.

Before opting for a truncated cone shape, we experimented with a content-aware dynamically adapting cut shape similar to the technique presented in [START_REF] Burns | Adaptive cutaways for comprehensible rendering of polygonal scenes[END_REF]. The cut was adapting to the geometry of the Gimlens's current object of interest. Our intuition was that by adapting the shape of the cut to the shape of the content, we would optimize the portion of the scene to be cut, thus preserving more context information, in the same spirit as JellyLenses [START_REF] Pindat | Jellylens: content-aware adaptive lenses[END_REF], which dynamically adapt the shape of a fisheye to optimize the focus, context and distorted regions to provide more relevant focus+context representations. But an informal evaluation performed in our laboratory revealed that users preferred to interact with cuts that always had a cone-based shape. The cut shape radically changing its geometry depending on the geometric characteristics of the various objects of interest was found to be disturbing, as it was both unstable and unpredictable.

Good rendering performance is also essential to achieve a good user experience. Our prototype is based on a rasterization rendering method. The cut is implicitly defined by a piece-wise function that we compute for each fragment of primitives resulting from the rasterization. We note p the position of the focus point in eye-space coordinates, and m the position of the fragment being processed. We define x, the projection of the fragment on the cone's axis, and y, the distance of the fragment to the cone's axis as follows:

x = dot(m, p) p , y = m × p p
The near base, with a radius of S, controls the wideness of the aperture. A large base favors the visibility of what is inside the cut, but does so at the expense of the context since more of the model gets hidden. Users can control this parameter, but we have found a base radius that corresponds to roughly 25% of the main viewport's size to yield a good compromise between cut visibility and context preservation. We note n the distance from the near base to the camera's position. If a fragment is situated closer to the camera than the near base, i.e., if x < n, it gets discarded if:

y < S * x/n.
The far base is positioned at the focus point. f , its distance from the observer in eye space coordinates, is equal to p . Its radius, s in eye-space coordinates, is computed automatically, so that the object of interest can fully fit within the cone, with some tolerance.

Additional constraints are enforced, so as to make sure that the far base does not get larger than the near base (which would not make sense) and that the cone's angle does not get larger than 20 • . Fragments between the near base and the far base, i.e., for which n < x < f , get discarded if: To avoid sharp edges at the far base, we make the far base round by extending it with a spherical shape that gets merged with the truncated cone. Fragments behind the far base (f < x) get discarded if:

y < (x -n) * s f -n + (f -x) * S f -n
(x -(f -s * (S -s) f -n ), y) < s * ( (S -s) f -n , 1)
Finally, small parts that lie within the cut cone but are not causing significant obstruction should not be hidden, as they will often provide interesting contextual information. Our technique takes the size of a part that falls in the cone into consideration before deciding whether to hide it or not. If the part is big enough to fully occlude the object of interest, we apply the full cut. Otherwise we just make a small hole into it to reveal the focus point when it lies precisely on the line of sight, as illustrated in Figure 2.

Combining and Cascading Lenses

Multiple Gimlenses can be instantiated simultaneously to provide users with different perspectives on the 3D model: different locations, different scales, and different angles. This is useful, e.g., when comparing multiple parts of a model, such as two knots inside an engine. Gimlenses can be created for both, the user then drilling towards each knot, adjusting the view and then orbiting these two objects of interest.

Gimlenses can also be cascaded, in a way somewhat similar to what PolyZoom does for 2D maps [START_REF] Javed | Polyzoom: multiscale and multifocus exploration in 2d visual spaces[END_REF]. Cascaded lenses A second Gimlens gets instantiated to look at an object that lies in the cut cone of the first lens, causing a conflict. The portion of this object that lies near the focus point of the second lens gets rendered translucently.

share the same focus point. They enable users to easily get multiple views on the same object of interest at varying scales and from different angles. Figure 5 gives an example. A user wishes to inspect a steal pipe in an air distillation plant. She cascades several Gimlenses, that give her points of view on the region of interest at different scales.

Instantiating multiple lenses can lead to conflicts if the focus point of one lens lies on a part of the model that got cut while drilling with another lens. To resolve this sort of conflict, our technique renders the portion, centered on the first focus point, of the object that is the source of the conflict using alpha blending to make it translucent.

The part is thus revealed, without hiding the second focus point. See Figure 6.

Automatic Lens Orientation and Coordination

Gimlenses let users define orientation constraints between cascaded lenses. Lenses constrained in this way automatically update their orientation as the focus point is updated. This spares users the burden of having to reorient each camera to get the desired angle on the object of interest as the focus point gets moved, a process that is quite tedious to perform manually. We define three orientation constraints that enable different behaviors.

Figure 7 illustrates the potential of this feature. The first lens is set up with a Pivot constraint, that maintains the camera position in-place as it pivots around to follow the focus point. This is particularly useful when exploring the inside of cavities. The two other lenses are set up with a Parent orientation constraint. This means that their orientations are defined relative to the one of their parent lens (the first lens). With these constraints set up, as we slide the focus point along the teeth from left to right, the lenses automatically move along and rotate, maintaining views from both inside and outside the patient's mouth without the need for users to make any adjustment themselves.

When inspecting the interface between two surfaces, users can select the Surface constraint, that will preserve the view orientation relative to the orientation of the surface's normal at the focus point.

During relocation of the focus point, or when changing the context view's viewing frustum, Gimlenses will automatically adjust the camera to preserve the view orientation on the surface, again sparing users the burden of manually adjusting the lens' cameras.

As the focus point jumps from one polygon to the next, Surface orientation constraints might cause the view in the lens to change abruptly. To avoid this, we smoothly animate the transition over 100ms.

Implementation

We implemented our prototype in C++ using OpenGL. The implicit definition of the cone cut is written with GLSL in a fragment shader.

Fragments falling inside the cut cone are discarded. Those intersecting its surface are outlined in yellow, and those falling outside are kept in the pipeline.

Changing the focus point or adjusting the viewing frustum of the context view requires casting rays into the scene to find all intersections with model parts. To ensure an interactive frame rate even with complex models, we make use of a space-partitioning data structure to optimize the ray casting. In our implementation, we currently use an AABB (axis-aligned bounding box) tree data structure.

As summarized in

Discussion and Future Work

We presented a multi-view, detail-in-context technique for navigating complex 3D scenes. As demonstrated throughout the article, the technique can prove useful in a variety of domains: for inspecting an industrial CAD model of a car engine, for exploring an anatomi-cal representation of the human head, or walking through a 3D map of an air distillation plant.

The datasets we experimented with provided separate geometrical descriptions of each element in the model. Gimlenses can be applied in a straightforward manner in such cases, as the scene is already segmented into meaningful objects. Unfortunately, this is not the case for all datasets. For instance, if we consider the polygonal meshes generated from 3D scans of scenes such as art pieces or even entire cities, those can reach a high degree of complexity due to the very nature of the scene that was scanned and the precision of the technology now available to achieve such scans. These are good candidates for exploration with Gimlenses. However, those datasets are not segmented into meaningful components, and it would be necessary to pre-process them before they could be explored with our technique. Another option would be to design interaction techniques that would let users define their own segmentation in an easy way, either declaratively or by demonstration. The resulting segmentation could then be used as input by Gimlenses. We are faced with the same segmentation issue when considering volumetric datasets. Moreover, in this case, users might want to explore the fundamental, primitive elements of the data: the voxel. This would require extending Gimlenses to support the per-voxel inspection of the dataset. All considerations related to such segmentation of the scene into meaningful objects, however, are beyond the scope of this work.

Another aspect that requires further work is the mapping of Gimlens parameters to user interface controls. While the mapping to a wheel-equipped mouse or even a gesture-enabled trackpad for a laptop or desktop workstation is straightforward, the mapping to the more exotic input devices typically used in CAVEs or when interacting with wall-sized displays (motion tracking, mid-air pointing device, etc.) requires more thinking. This, however, highly depends on the available devices and their capabilities as well as, to some extent, on the application-dependent mappings already in place. In the particular case of CAVEs, additional challenges will arise, as the lens windows' position should be adapted automatically to match observers' position and orientation in the scene.

Finally, another potential area for improvements is that of graphics rendering. Currently we apply the same rendering technique to all lenses and to the context view. But as views might serve different purposes, enabling different rendering strategies, as Magic Lenses do [START_REF] Wang | The magic volume lens: An interactive focus+context technique for volume rendering[END_REF], or even simply enabling users to easily change lighting conditions to emphasize some features of the data, would be useful improvements.

Figure 2 :

 2 Figure 2: A Gimlens magnifying a knot deep inside a car engine. Context view (a); Gimlens view window (b), object selector (c), proxy (d).

Figure 3 :

 3 Figure 3: A Gimlens verifying the surface intersection between a connecting-rod and the camshaft. (a) Enabling the cut reveals the object of interest during exploration but hides its neighbors. (b) Disabling the cut enables users to see both parts.

Figure 4 :

 4 Figure 4: Illustration of how the drilling technique behaves. (a) The focus point lies on the frontmost part. This part gets drilled into, revealing the other parts behind it. (c) The focus point gets slid on the parts visible from the observer's perspective (colored red) and, finally, (d) cuts through the second layer (d).

Figure 5 :

 5 Figure 5: Exploring an air distillation plant. Three Gimlenses are cascaded to magnify a steal pipe. (a) shows a view from the left to better situate the focused part within the shed, (b) and (c) apply magnification successively. (d) and (e) magnify a distinct part of the plant.

Figure 6 :

 6 Figure 6: Exploring a brain. (a) A first Gimlens gets instantiated and delves deep inside the head, hiding several objects in the process. (b)A second Gimlens gets instantiated to look at an object that lies in the cut cone of the first lens, causing a conflict. The portion of this object that lies near the focus point of the second lens gets rendered translucently.

Figure 7 :

 7 Figure7: Three Gimlenses combined to explore the inside of the maxillary dental arcade of a patient using different orientation constraints. Dragging the single focus point that controls all three lenses updates all views automatically, providing complementary perspectives on the successive teeth (1,2,3).

Table 1

 1

		, we achieve interactive frame rates for
	all models demonstrated in this article. Performance figures were
	gathered on a HP Z-series 800 PC equipped with an nVidia Quadro
	4000, and an Intel Xeon E5-1650 CPU running at 3.20GHz. The
	framebuffer size was set to 1920x1080 (running fullscreen on a Full
	HD monitor). The technique could be made to scale further by
	coupling it with state-of-the-art computer graphics techniques that
	can render extremely complex 3D polygonal scenes.
	Model	Million triangles	1 Gim. / 2 Gim. (fps)
	Air Plant	1600	15 / 10
	Car Engine	266	57 / 40
	Head	58	63 / 45

Table 1 :

 1 Performance (Frame-rates)