Preferences for visible white sclera in adults, children and autism spectrum disorder children: implications of the cooperative eye hypothesis

Visible white sclera (i.e., the opaque white outer coat enclosing the eyeball) is a uniquely human trait. An explanation for why such coloration evolved has been put forward by the Cooperative Eye Hypothesis (Kobayashi and Hashiya, 2011; Kobayashi and Kohshima, 1997, 2001; Tomasello et al., 2007), which states that visible white sclera evolved to facilitate communication via joint attention and signaling of gaze direction. Therefore, we hypothesized that viewers comprised of both typically developing children and adults would show reliable preferences for stimuli with visible white sclera. However, because autism spectrum disorder (ASD) individuals have impaired social cognition and show gaze aversion, we also hypothesized that ASD children would show no consistent preference for eyes with visible white sclera. We tested these hypotheses by obtaining participants' preferences across six sets of stuffed animals, identical but for the manipulation of eye size, eye color, and presence of visible sclera. Both hypotheses were supported. In addition to providing evidence consistent with the Cooperative Eye Hypothesis, our results also suggest that eyes and gaze serve a central role in social cognition. Furthermore, our results from ASD children have practical applications for therapeutic practices and evidence-based interventions.