Lack of Privileged Access to Awareness for Rewarding Social Scenes in ASD

Background:

Reduced social motivation is hypothesised to underlie social behavioural symptoms of ASD (Chevallier et al., 2012). Evidence in support of this theory comes primarily from a) eye-tracking studies that commonly show reduced preferential looking to social compared to nonsocial stimuli, and b) differential neural responses to social rewards in individuals with and without ASD. Nearly all of these studies present stimuli above the threshold of awareness. This leads to an open question of whether such reduced preference for attending to social stimuli is seen if stimuli are presented below the threshold of conscious awareness. Continuous flash suppression (CFS) offers a method to test this possibility. A previous study has shown intact prioritisation of protofacial stimuli in autism using CFS (Akechi et al., 2015). However, this study does not explicitly test the difference between social and non-social stimuli, and uses schematic stimuli that are a) low in ecological validity and b) not rewarding. 

Objectives:

To test whether individuals with and without ASD show earlier detection of social over nonsocial rewarding scenes that are closely matched for low-level stimulus features.. The measured variable is the time it takes for the target stimulus to overcome the interocular suppression induced by a dynamic mask. In line with the reduced social motivation hypothesis, it is predicted that neurotypicals will show a privileged access to awareness for rewarding social scenes, compared to ASD individuals.

Methods:

38 neurotypicals (11 males, mean age = 21.16) and 30 ASD adults (14 males, mean age =37.19) took part in the experiment. On each trial, a rewarding scene (social/nonsocial) was presented to one eye, and a high-contrast mask pattern updating at 10Hz was presented to the other eye. A control condition with inverted version of the same stimuli was similarly presented. Participants were required to indicate which side of fixation they ‘detected anything other than noise’.

Results:

Mean response times were calculated from correct trials. The proportion of incorrect trials was comparable for both the two groups (3.46% for neurotypicals, 3.82% for ASD).

Since the groups were not matched on age, and in light of the known pitfalls of ANCOVA (Miller & Chapman, 2001), data from the two groups were analysed separately using Bayesian analyses (implemented in JASP). In neurotypicals, there was strong evidence for earlier detection of social reward over nonsocial reward stimuli (Bayes Factor [BF] = 839.87; this was not the case for the inverted condition, BF = 0.31). In ASD, there was moderate evidence for a null effect (BF = 0.23; also the case for the inverted condition, BF = 0.20).

Conclusions:

Strong evidence for a privileged access to awareness for rewarding social over nonsocial scenes was observed in neurotypical adults. No such privileged access was seen in ASD individuals, and moderate support for the null model was noted. These results suggest that the purported deficits in social motivation in ASD may extend to early attentional mechanisms.

Figure Legend: 

Cumulative BF for upright social vs. non-social reward stimuli for neurotypicals (left) and ASD (right) individuals.