Unlike spoken languages, sign languages of deaf communities use mainly visual-gestural modality (i.e., hands, torso, face and eye gaze) for communicative expressions. This project investigates to what extent using visual-gestural modality shapes sign language structure and its development in children . To do so comparisons of such structures between  unrelated sign languages (e.g., Turkish and German Sign Languages), respective spoken languages (e.g., German, Turkish), and non-linguistic gestural expressions of hearing  adult and child speakers in these countries will be conducted. These comparisons will reveal which aspects of sign language expression and their development are attributable to modality-specific properties and which aspects are shaped by general design features of language.