Native Exposure to Sign Language Does Not Attenuate the Social-Cognitive Deficits of ASD

Background: Many studies have investigated the relationship between language development and non-linguistic social cognition, particularly theory of mind (ToM). Two populations in particular have been found to have delays in ToM: the deaf children of hearing parents (Courtin & Melot, 1998; Courtin, 2000; Peterson & Siegal, 1999, 1995; Remmel, Bettger, & Weinberg, 2001) and children with autism spectrum disorders, ASD (Baron-Cohen, Leslie, & Frith, 1985; Happé, 1994). Native-signing children, who are exposed to sign from birth by their deaf parents, show no such delay (Courtin, 2000; Schick, de Villiers, de Villiers, & Hoffmeister, 2007), suggesting that early language exposure is key to ToM development. To date, no research has investigated language and ToM development in native-signing children with ASD. Since the visual modality of sign provides rich opportunities for perspective-taking (Courtin, 2000), might native exposure to a signed language privilege the development of social cognition in children with ASD?

Objectives: To investigate the relationship between language, non-linguistic social cognition (ToM and visual perspective-taking), and non-linguistic spatial cognition (mental rotation) in a novel research population, native-signing children with ASD.

Methods: Sixteen native-signing children with a confirmed ASD diagnosis (12 male, 4 female; M_age = 9.91, SD = 2.43) and 18 typically-developing (TD) native-signing children (8 male, 10 female; M_age = 9.3, SD = 1.77) were tested. Groups were matched for chronological and mental age using the Test of Nonverbal Intelligence (TONI; Brown, Sherbenou, & Johnsen, 2010). Children were tested on the ASL Receptive Skills Test (ASL RST; Enns, Zimmer, Boudreault, Rabu, & Broszeit, 2013), two minimally-verbal social-cognitive tasks: false-belief (Pyers & Senghas, 2009) and visual perspective-taking, and a minimally-verbal mental rotation task (Martin, Senghas, & Pyers, 2013). All responses were coded by a trained coder fluent in ASL and blind to participant group.

Results: Native-signing children with ASD scored significantly lower than native-signing TD children on the receptive language task (ASD M = 85.6, SD = 10.9; TD M = 108.7, SD = 6.3; p <.001), false-belief ToM (ASD M_accuracy = 0.55, SD = 0.35, TD M_accuracy = 0.82, SD = 0.19; p = .01), and visual perspective-taking tasks (ASD M_accuracy = 0.24, SD = 0.4, TD M_accuracy = 0.71, SD = 0.42; p < .01). However, there was no significant group difference in mental rotation (ASD M_accuracy  = 0.75, SD = 0.22, TD M_accuracy  = 0.86, SD = 0.14; p = .23, ns). 

Conclusions: Compared to TD deaf children, deaf children with ASD showed evidence of significant language, ToM, and visual perspective-taking delays, but intact mental rotation skills. Language delays in ASD are thus implicated in the development of social cognition, but not spatial cognition. These results fill gaps in the literature on the role of language in the development of social cognition, and provide additional evidence for deficits in language, ToM, and perspective-taking skills in ASD. We conclude that native exposure to sign is not sufficient to overcome the social-cognitive impairments implicated in ASD, and that signing children with ASD show a similar profile to speaking children with ASD.