Auditory Perceptual Capacity Is Superior in Autism

Background:  

Autism Spectrum Disorder (ASD) has an intriguing profile of both deficits and abilities. Individuals show enhanced pitch discrimination (e.g. Bonnel et al 2003), higher rates of absolute (‘perfect’) pitch compared to general population (Miller, 1999) and often find seemingly innocuous sounds distressing. In 2013, altered sensory processing was added to the diagnostic criteria for the condition (APA, 2013). It is essential to find ways to reduce auditory distraction and the negative impact that auditory stimuli have on individuals with ASD.

Objectives:  

This study used two behavioural experiments to examine whether an increased capacity for processing sounds in ASD could be underlying both the negative and positive aspects of this behaviour. 

Methods:  

16 autistic adults and 16 neurotypical adults took part in the study. In Experiment 1, an inattentional-deafness paradigm was used. Participants listened to a scene containing characters preparing for a party and were asked to concentrate on a conversation between two women in order to answer subsequent questions. Halfway through, an additional male character walked through the scene, continually repeating ‘‘I’m a gorilla’’. After the scene, participants were asked whether they heard anything unusual.

Experiment 2 examined the limits of auditory capacity in ASD by measuring detection of a critical stimulus (CS) under various levels of perceptual load. In this task, increased capacity would manifest as more task-relevant processing and enhanced task performance. Participants were asked to detect a target sound (dog/lion) among varying numbers of non-target sounds (other animals). Binaural sound recordings were used to position auditory components on an imaginary semi-circle in front of the head. A car noise (the CS) was also present on 50% of the trials, in positions that lay on an imaginary semi-circle of greater eccentricity than the animal sounds. Participants were asked to indicate which target was present (e.g. lion or dog) and whether the CS was present or absent on that trial.

Results:  

In Experiment 1, 50% of autistic participants detected the ‘gorilla’, whereas only 12.5% of neurotypical controls did (p = 0.022). This suggests that autistic individuals process more irrelevant information from the auditory scene; evidence of increased perceptual capacity.

In Experiment 2, controls showed a significant reduction in detection sensitivity to the CS as the auditory load of the central task increased. In the ASD group, detection rates of the CS were significantly higher overall, and as auditory load of the central task increased rates did not drop to the same extent as for neurotypical controls .

Conclusions:

The experiments demonstrate that autistic people were better at detecting additional unexpected and expected sounds, suggesting that they have increased auditory perceptual capacity relative to non-autistic controls.  

This offers an explanation for the auditory superiorities seen in autism (e.g. heightened pitch-detection). Somewhat counter-intuitively, this same ‘skill’ could result in the sensory overload that is often reported – which subsequently can interfere with social communication. These findings have important practical implications and could be used to develop intervention programs to minimise the distress that is often seen in response to auditory stimuli.