Unusual auditory/speech processing in autism spectrum disorder revealed by verbal transformation effects

Abstract

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by an impaired ability to communicate and restricted and repetitive patterns of behavior. Sensory abnormality, a trait included in restricted patterns of behavior, is often observed in individuals with ASD. This study used an auditory illusion called “verbal transformation (VT)” to examine abnormal auditory/speech processing in ASD. In VT, a series of subjective perceptual changes occurs when subjects listen to a repeating word without a pause. The characteristic of VT is that, physically, the stimulus is the same repeated word but the perceptual change differs for each person. In this point, VT could be useful for demonstrating certain ASD traits such as favoring repetition. Twenty-four ASD adults and 24 neurotypical controls listened to three samples of repeated Japanese words for five minutes, and reported their percepts verbally whenever they experienced perceptual changes. As for the number of perceptual changes and that of reported forms, we found no significant difference between the ASD group and controls. However, the phonetic variations of form changes were different, and ASD group showed more phonetic variation than controls. We interpret the results from the viewpoint of unusual adaptation in auditory and/or phonetic processing.