The linguistic study of sign languages is relatively recent compared with spoken language linguistics. Not until the mid-twentieth century did linguists show that sign languages obey linguistic principles in a way that separates them from mere pantomime and gesture. Because the linguists involved in this endeavour were working predominantly in the Western world, the bulk of the early research was carried out on American Sign Language and a handful of European sign languages, such as French, British, German and Danish. This work revealed that signed and spoken languages share basic linguistic properties at the levels of phonological, morphological and syntactic structure, but that modality does play an important part in shaping how that linguistic structure is expressed.

Concentrating on a small number of languages did not, however, allow linguists to determine how much variation exists across sign languages. Some have argued that the visual-gestural modality has a homogenising effect on sign languages, leading to less variation overall compared to what is found across spoken languages. Moreover, sign languages are relatively young, which affects the amount of variability (Meier Reference Meier2000). The hypothesis that there is less variation among sign languages can be tested only by broadening the range of sign languages studied. Indeed, since the late 1990s there has been a greater interest in studying sign languages from non-Western countries, such as Hong Kong, Lebanon, Jordan, Nicaragua, Ghana and Brazil, and it is becoming clear that these languages show more variation than was initially predicted.

Visible variation: Comparative studies on sign language structure is a collection of papers from a European Science Foundation Exploratory Workshop, focusing on descriptions of lesser researched sign languages and comparisons at different levels of linguistic structure. The authors demonstrate convincingly that being able to compare a much broader set of sign languages opens up an exciting new avenue of typological research – one which promises to give us a better understanding of the similarities and differences not only between different sign languages, but more generally between signed and spoken languages.

In their introductory chapter, ‘Can't you see the difference? Sources of variation in sign language structure’, the editors, Pamela Perniss, Roland Pfau & Markus Steinbach, set out the ways in which different sign languages are able to differ from one another. In so doing, they provide an introduction to sign language phonology, morphology and syntax in a way that is readily accessible to linguists unfamiliar with sign language structure. With respect to phonology, different sign languages vary in their handshape inventories, the size of their signing space, the extent to which they make use of mouthings to accompany signs, and the extent to which the non-dominant hand can be deleted from signs. In morphology, the correspondences between classifier handshapes and their referents are conventionalised in different ways across languages, and only some languages have classifiers that mark gender. The paradigms of plural pronouns vary with respect to the degree of indexicality, the number and type of plural pronouns that exist, and the types of plural inflection. Variation is most striking, however, within syntax, and shows up in constituent order, the use of agreement auxiliaries, sentential negation, question-formation, relative clauses and the use of signing space.

Subsequent chapters in this volume explore some of these sources of variation in more detail. Chapter 2, by Marie A. Nadolske & Rachel Rosenstock, is entitled ‘Occurrence of mouthings in American Sign Language: A preliminary study’. Greater research focus is being directed to the role that the mouth plays in sign languages, which makes sense, as deaf people look at each others' faces rather than each others' hands when they communicate. Visual forms represented on the mouth have a range of functions: the mouth can provide adverbial information to the manual sign, or it can disambiguate a manual sign which may mean two things on its own. There is, however, anecdotal evidence that American Sign Language (ASL) users do not use their mouth for disambiguation as much as European signers do, which has been attributed to sociolinguistic reasons. Nadolske & Rosenstock compare signers in different genres of signing and are able to demonstrate greater use of the mouth than previously described. As the authors note, this is a preliminary study with a small data set, and more research should be carried out to substantiate their findings.

In chapter 3, ‘Do all pronouns point? Indexicality of first person plural pronouns in BSL [British Sign Language] and ASL’, Kearsy Cormier describes how pronominal pointing can become less visually iconic. Pointing is a problematic area for sign linguistics because it resembles gesture. Cormier provides an in-depth linguistic analysis of how pronouns in two sign languages have moved away from pointing directly at people and towards conventionalised and more abstract forms. The data were collected through elicitation using written English, which may have been problematic due to language-mixing. Cormier's study reveals differences between the two sign languages in the extent to which signers used inclusive and exclusive pronominal pointing.

The next two chapters deal with negation, and both reveal that the strategies used for negation in sign languages are very similar to those used in spoken languages: namely, negative particles, negative suffixes (even though suffixes generally are not widely used in sign languages) and split negation. In contrast to spoken languages, sign languages also make use of non-manual markers of negation, e.g. a headshake or head turn. In chapter 4, ‘Negation in Jordanian Sign Language: A cross-linguistic perspective’, Bernadet Hendriks describes the diverse manual negators used in Jordanian Sign Language – a neutral negator, three emphatic negators, an apologetic negative interjection and three different negative existentials – each with a subtly different meaning. Hendriks shows that in contrast to many Western sign languages, manual negators play a more important role than non-manual markers. For example, while British Sign Language allows a headshake on its own to negate a sentence, this is not possible in Jordanian Sign Language, where headshakes and other non-manual markers, while common, are not obligatory, and have to be paired with a manual marker.

In chapter 5, ‘On the syntax of negation and modals in Catalan Sign Language and German Sign Language’, Roland Pfau & Josep Quer discuss cross-linguistic variation with respect to headshakes in two sign languages in which a headshake is an obligatory negation marker. In Catalan Sign Language, the headshake can be associated with just the manual negator, but in German Sign Language, it has to be associated with, at a minimum, the manual negator and verb sign. However, both languages pattern alike with modal verbs: modals cannot be negated only by a headshake; instead, a special cliticised or suppletive negative form of the modal has to be used. Pfau & Quer argue that this pattern can be accounted for by the negative markers occupying different positions within the Negation Phrase (NegP), but that in both languages negated modals undergo obligatory movement to a higher modal functional head (Mod).

In chapter 6, ‘Real data are messy: Considering cross-linguistic analysis of constituent ordering in Auslan [Australian Sign Language], VGT [Flemish Sign Language], and ISL [Irish Sign Language]’, Trevor Johnston, Myriam Vermeerbergen, Adam Schembri & Lorraine Leeson deal explicitly with a methodological problem that is likely to have worried the reader during previous chapters – that of small participant numbers. Compounding the difficulty of recruiting large enough numbers of participants for research studies is the fact that sign language performance/knowledge is more varied than is the case for spoken languages: most signers are non-native (only 5–10% of deaf children are born to deaf parents). The question then arises whether studies should recruit just native users. However, in so doing, they would ignore a lot of the variability that is present in the population of sign language users.

A further related issue is that of contact with the majority, spoken language. This point comes up in Hendriks's contribution in chapter 4. A backwards head tilt is used amongst hearing people in many Mediterranean countries as an informal way of saying ‘no’. Although it is also used by deaf people, Hendriks argues that it does not have grammatical status in Jordanian Sign Language, unlike in Greek and Turkish Sign Language. The issue of language contact is also raised in chapter 7, ‘Cross-linguistic comparison of interrogatives in Croatian, Austrian, and American Sign Languages’, by Ninoslava Šarac, Katharina Schalber, Tamara Alibašić & Ronnie B. Wilbur. Croatian and American Sign Languages each have a manual marker for polar questions, which is probably borrowed from the surrounding pedagogical sign systems of Signed Croatian and Signed English.

In chapter 8, ‘The expression of modal meaning in German Sign Language and Irish Sign Language’, Annika Herrmann considers how modality influences the expression of modal meanings in sign languages compared with spoken languages. After a too-lengthy description of modals in German, we learn about how the face is used to express modal meanings. Herrmann's study of modals in both sign languages was motivated by looking for spoken language equivalents in the two sign languages. A better method might have been to start within the sign languages and discover first what meanings are expressed, before making the comparison with German or English.

In chapter 9, ‘Reported action in Nicaraguan and American Sign Languages: Emerging versus established systems’, Jennie Pyers & Ann Senghas focus on a particularly pervasive device in sign languages – referential shift. Referential shift is a device used in extended discourse (akin to, for example, She said, ‘I need more paint’). The nice twist to this chapter is that the authors track the use of referential shift across two languages that have very different ages. Nicaraguan Sign Language is only twenty-five years old and in older signers of the language (those who created it in the 1970s), the gestural origins of the language are still evident. Using cleverly designed experiments, the authors were able to elicit different types of referential shift, involving both the use of the whole body and the restricted sign space in front of the signers at waist level. Younger signers use less explicit strategies to mark reference shift and are more consistent in their use of this aspect of the grammar.

Chapter 10, ‘Grammaticalisation of auxiliaries in sign languages’, by Markus Steinbach & Roland Pfau, highlights an area of language where modality has a clear impact. Whereas auxiliaries in spoken language have the primary function of encoding tense, agreement and mood, many sign languages have auxiliaries which instead express subject and object agreement. These auxiliaries are grammaticalised from a variety of sources, such as concatenated pronouns, nouns and verbs. This again contrasts with spoken languages, where verbs are the most common source of grammaticalisation into auxiliaries. Steinbach & Pfau argue that this modality-specific pattern is grounded in the spatial properties of agreement in sign languages. Furthermore, they raise (albeit in a footnote) an additional methodological problem in the study of sign language variation, namely, that diachronic changes, e.g. grammaticalisation paths, are difficult to trace when the language has no written record. Fortunately, the lexical item that is the source of a particular grammaticalisation process frequently coexists with the grammaticalised form. However, one cannot help but wonder what valuable insight into sign language change has been lost through the lack of records. This makes the corpora that are currently being created of sign languages all the more valuable. The linguists who follow us in the next few decades will have a resource at their fingertips that we sorely miss currently.

In the final paper, chapter 11, ‘The possible range of variation between sign languages: Universal Grammar, modality, and typological aspects’, Annette Hohenberger brings the reader back to the issue of possible variation between sign languages, this time from a more theoretical perspective. She urges a unified approach to studying cross-linguistic variability in sign languages, within a generative grammar framework. It is, of course, an empirical question as to whether Universal Grammar provides good coverage of the typological data.

What is likely to strike the reader of this volume most strongly is that much of what is found typologically in signed languages is also found in spoken languages, and therefore that the research endeavour set out in this volume is likely to shed just as much light on spoken languages as on sign languages. It is a shame that manual phonology and prosody are not included in the book. Nevertheless, the number and variety of languages studied as well as the diversity of language structures covered is impressive, and makes us very enthusiastic for the future of cross-linguistic sign language research. For all those who are intrigued by the human mind's remarkable capacity for language, this book will be a rewarding read.