Visible Social Interactions Do Not Support the Development of False Belief Understanding in the Absence of Linguistic Input: Evidence from Deaf Adult Homesigners

Abstract

Congenitally deaf individuals exhibit enhanced visuospatial abilities relative to normally hearing individuals. An early example is the increased sensitivity of deaf signers to stimuli in the visual periphery (Neville and Lawson, 1987a). While these enhancements are robust and extend across a number of visual and spatial skills, they seem not to extend to other domains which could potentially build on these enhancements. For example, congenitally deaf children, in the absence of adequate language exposure and acquisition, do not develop typical social cognition skills as measured by traditional Theory of Mind tasks. These delays/deficits occur despite their presumed lifetime use of visuo-perceptual abilities to infer the intentions and behaviors of others (e.g., Pyers and Senghas, 2009; O’Reilly et al., 2014). In a series of studies, we explore the limits on the plasticity of visually based socio-cognitive abilities, from perspective taking to Theory of Mind/False Belief, in rarely studied individuals: deaf adults who have not acquired a conventional language (Homesigners). We compared Homesigners’ performance to that of two other understudied groups in the same culture: Deaf signers of an emerging language (Cohort 1 of Nicaraguan Sign Language), and hearing speakers of Spanish with minimal schooling. We found that homesigners performed equivalently to both comparison groups with respect to several visual socio-cognitive abilities: Perspective Taking (Levels 1 and 2), adapted from Masangkay et al. (1974), and the False Photograph task, adapted from Leslie and Thaiss (1992). However, a lifetime of visuo-perceptual experiences (observing the behavior and interactions of others) did not support success on False Belief tasks, even when linguistic demands were minimized. Participants in the comparison groups outperformed the Homesigners, but did not universally pass the False Belief tasks. Our results suggest that while some of the social development achievements of young typically developing children may be dissociable from their linguistic experiences, language and/or educational experiences clearly scaffolds the transition into False Belief understanding. The lack of experience using a shared language cannot be overcome, even with the benefit of many years of observing others’ behaviors and the potential neural reorganization and visuospatial enhancements resulting from deafness.

Reduced neural selectivity for mental states in deaf children with delayed exposure to sign language

“…While our results suggest that even relatively short delays can delay the development of ToM-selective responses in RTPJ, from our results alone, it is unclear how much linguistic experience is sufficient to overcome this delay or if there is a sensitive period for the impact of linguistic experience on ToM. Prior behavioral studies have found evidence for enduring ToM delays in adults who received access to language after longer delays (i.e., after age 10 years) [91][92][93] , but there is also evidence that ToM delays can resolve with subsequent linguistic experience 33,68,91,94 . Here, we did not observe an enduring effect of delayed access to language on RTPJ selectivity in adults.…”

Reduced Neural Selectivity for Mental States in Deaf Children with Delayed Exposure to Sign Language

“…While our results suggest that even relatively short delays can delay the development of ToMselective responses in RTPJ, from our results alone, it is unclear how much linguistic experience is sufficient to overcome this delay or if there is a sensitive period for the impact of linguistic experience on ToM. Prior behavioral studies have found evidence for enduring ToM delays in adults who received access to language after longer delays (i.e., after age ten years) [91][92][93] , but there is also evidence that ToM delays can resolve with subsequent linguistic experience 33,68,91,94 . Here, we did not observe an enduring effect of delayed access to language on RTPJ selectivity in adults.…”

Is Language Required to Represent Others’ Mental States? Evidence From Beliefs and Other Representations

“…Rather, our evidence comes from adults, who already have fully fledged language abilities a fully fledged theory of mind. The role of language in the development of ToM remains debated, with some arguing that language may be required to form an understanding of false beliefs (e.g., Gagne & Coppola, ; Pyers & Senghas, ; de Villiers, ), while others have found evidence to suggest otherwise, whether from linguistically impaired humans (e.g., Varley & Siegal, ; Varley et al., ) or nonhuman animals (e.g., Krupenye et al., ). Our data, coming exclusively from adults with normal language abilities, is not in a position to inform these debates.…”