Impact of lacking a language model[edit]
Studies by Deanna Gagne and Marie Coppola of perspective-taking abilities in adult home signers reveal that home signers do not pass experimental false-belief tasks, despite having visual observation of social interaction. False-belief understanding, integral to the development of theory of mind, requires language experience and linguistic input. Further study of these adult home signers indicates that home signers show precursor abilities for theory of mind, such as visual perspective taking.[22][23]
Lack of conventional language for numbers has been shown to affect numerical ability. In comparison to unschooled hearing and signing deaf individuals, adult home signers do not consistently produce gestures that accurately represent cardinal values of larger sets and do not exhibit effective use of finger counting strategies.[24] Further study indicates home signers are able to recall gestures used as nouns, verbs, and adjectives, but they show poor number recall, which worsens as numbers increase.[25]
Cross-cultural comparisons[edit]
Syntactic structure is similar between groups of home signers in different cultures and geographical regions, including word order preferences and complex sentence usage. For example, home sign systems of children in Turkey and the United States exhibit similar patterns in sentence-level structure.[20]
Certain gestures, such as pointing, head shaking, and shrugging, share similar meanings throughout cultures. Young children shake their heads to indicate negation before they express negative meanings through language. However, most young children use the head shake as an initial marker of negation, and replace it with speech or manual signs once language is acquired. Children using a home sign system do not have exposure to a structured language, and therefore do not replace the head shake with manual signs until language is acquired.[15]
Home sign systems differ across cultures in terms of gesture use by hearing caregivers. Compared to American mothers, Chinese mothers show more similarity in gesture form (handshape and motion) and syntax with systems used by their deaf children. In comparing narratives from Chinese and American deaf children, home signing children produce culturally appropriate narratives. Variability between home signers are group internal, with different individual home signers having their own set of gestures for the same type of object or predicate.[1][18]