Second, sign languages use the geometrical properties of the signing space to realize morphosyntactic, semantic, and pragmatic categories in the three-dimensional signing space ( Engberg-Pedersen, 1993 Padden, 1998 Aronoff et al., 2005 Pfau and Steinbach, 2016 Steinbach and Onea, 2016). First of all, sign languages employ various articulators such as the hands, the upper part of the body, the head, and the face to express grammatical features simultaneously. van Herreweghe and Vermeerbergen, 2012 Orfanidou et al., 2015). Nevertheless, sign languages retain some modality-specific properties that may impact the linguistic structure and the cognitive processes underlying the perception and production of signed communication and that have an influence on the handling of sign language data (cf. 1 In addition, psycho- and neurolinguistic studies with non-impaired and impaired deaf signers show that sign languages access the same neural networks involved in auditory speech processing, albeit with some concrete modality-specific features ( Poizner et al., 1987 Emmorey, 2002, 2003 Corina and Knapp, 2006 Campbell et al., 2008 Corina and Spotswood, 2012 Dye, 2012 Woll, 2012). Although the two modalities clearly differ in the production and perception of communicative signals, the underlying linguistic structures seem to be very similar across both modalities ( Meier, 2002, 2012 Sandler and Lillo-Martin, 2006). Sign and spoken languages use two different modalities, the visual-gestural modality of sign languages and the oral-auditory modality of spoken languages. In addition, we discuss the complementarity of theoretical approaches and experimental studies and show how the interaction of both approaches contributes to a better understanding of sign languages in particular and linguistic structures in general. The special combination of the challenges discussed in this article seems to be a specific facet empirical research on sign languages is faced with. While some of these challenges also pertain to (some varieties of) spoken languages, other challenges are more modality-specific. These challenges are related to the socio-linguistic status of the Deaf community and the larger variability across signers within the same community, to the social status of sign languages, to properties of the visual-gestural modality and its interface with gesture, to methodological aspects of handling sign language data, and to specific linguistic features of sign languages. In this article, we address specific challenges that arise in judgment data elicitation and experimental studies of sign languages. By contrast, the impact of modality on linguistic data elicitation and collection, corpus studies, and experimental (psycholinguistic) studies is still underinvestigated. The impact of modality on the grammatical structure and linguistic theory has been discussed at great length in the last 20 years.

Natural languages come in two different modalities. 2University of Göttingen, Göttingen, Germany.

1ICREA-Pompeu Fabra University, Barcelona, Spain.

Sign language for all done