Measuring the Value of Social Stimuli in Autism Spectrum Disorders

Background: An increased preference for non-social over social stimuli is reported in autism Spectrum Disorders (ASD). A recent theory describes this in terms of reduced motivation to engage with others (Chevallier, Kohls, Troiani, Brodkin, & Schultz, 2012). However, there are currently few simple behavioural ways to test this claim or to quantify social motivation in individuals with or without ASD.

Objectives: In this study we aimed to develop a method to measure social motivation and determine if the behavioural preference for social / non-social stimuli differs between people with and without ASD.

Methods: We used a simple behavioural paradigm called Choose-a-movie (CAM) that measures preference for social versus non-social stimuli in adolescents and adults with and without ASD. On each trial, participants chose which of two movies to watch, and must consider their movie preferences against the amount of effort (key-hits) required to see a movie. Three different movie categories were compared: movies of adult actors with direct gaze, adult actors with averted gaze, and non-social movies of object rotating on a table. Each trial presented two movies from these categories.

In experiment one, 40 adolescents with ASD and 40 age/IQ matched typical adolescents completed the CAM paradigm with one set of paired stimuli (i.e. direct gaze versus object movies). In experiment two, 29 adults with ASD and 24 age/IQ matched typical adults completed the CAM paradigm with three sets of paired stimuli: a) direct gaze versus objects, b) averted gaze versus objects, c) direct versus averted gaze movies. 

Results: The results from experiment one showed that adolescents with ASD tended to invest more effort to watch object/ non-social movies than to watch direct gaze social movies. In experiment two, adults with ASD showed a significantly reduced preference for direct gaze social movies than matched comparison group. They invested more effort to look at the object/non-social movies than direct or averted gaze social movies. When presented with two social movies (direct versus averted gaze), typical adults preferred to view direct gaze movies but adults with ASD showed no preference between these categories. 

Conclusions: Together, these studies show differences in the value associated with social stimuli between adults and adolescences with and without ASD. Both adults and adolescents with ASD value non-social stimuli more than matched adults and adolescents without ASD. These data provide a precise quantification of social motivation, and advance our understanding of how value of social engagement may differ between those with and without ASD.