Sensitivity to Emotional Stimuli in Autism Spectrum Disorder: The Effect of Emotional Images On Time Perception

Background:  

Temporal judgments can be distorted by the emotional content of stimuli. In the temporal bisection task the duration of an emotionally expressive face is overestimated compared to a neutral facial expression (e.g. Droit-Volet et al., 2004). It is hypothesized that this effect is driven by stimulus-induced increases in arousal, which speed the rate of an ‘internal clock’ that meters time. To date, performance on this task has not been explored in individuals with autism spectrum disorder (ASD). If individuals with ASD show overestimation of emotional stimuli then it would suggest that their implicit responsiveness to emotional cues is intact. However, the absence of the effect would indicate an atypical response to emotion.

Objectives:  

(1) To establish whether temporal judgements in individuals with ASD or those with a high degree of self-reported autistic traits are modulated by the emotional salience of stimuli. (2) To see whether such effects are specific to emotional facial expression or generalise to other emotional images.

Methods:  

Study 1 tested 85 undergraduate students, who also completed the Autism Quotient (AQ) questionnaire (Baron-Cohen et al., 2001). Study 2 tested 20 adults with an ASD and 26 comparison participants, matched on age and IQ. Participants were presented with the classic time bisection task in which they learnt two reference durations, one ‘short’ (400 ms) and one ‘long’ (1600 ms). During the testing phase they were presented with a variety of stimuli of intermediate durations and had to classify them as either more similar to the short or the long references. In two conditions, temporal judgements were assessed for face stimuli (angry, happy, fearful and neutral faces) and a selection of natural images (snarling dog, puppy, spider and flower) that varied in emotional salience. 

Results:  

As expected, participants in Study 1 overestimated the duration of fearful and happy faces compared to the neutral face, and overestimated the duration of the snarling dog and puppy compared to the flower. However, these effects did not correlate with self-reported autistic traits. In Study 2 the group with ASD overestimated the duration of both the emotional face and natural images compared to neutral face and flower.

Conclusions:  

Individuals with ASD and individuals from the general population both with low and high levels of autistic traits show an implicit response to emotional stimuli, which is manifest in the overestimation of duration. Further, this effect is found both for human faces and for images of the natural world. The data do not suggest a fundamental insensitivity to the arousing content of either facial or natural images in ASD. These findings have implications for understanding how emotional stimuli are processed in ASD and for better delineating typical and atypical aspects of emotion processing in ASD.