Abstract
Perceptual atypicalities are a widely acknowledged but poorly understood feature of autism. We demonstrate here a striking violation of one of the most adaptive psychophysical computations - Weber's law - in high-functioning individuals with autism. JNDs based on the best-fitting psychometric functions were measured for size visual judgments (Exp. 1), weight haptic discrimination (Exp. 2), and illusive perception of weight (brightness-weight illusion; Exp. 3). Results for the typically developed group confirmed Weber's law, demonstrating a linear increase in JNDs with intensity, resulting in constant fractions across intensities. The results for the ASD, in contrast, showed no scaling of JNDs with intensity; instead, fractions decreased linearly with intensity. In striking contrast to its consistency in typical perception, Weber's law does not hold for visual and haptic perception in autism. These robust modulations in psychophysical computations, demonstrated for different domains of perception, suggest a modality-independent, low-level mechanism driving altered perception in autism.
Highlights
Autism Spectrum Disorder (ASD) refers to a group of neurodevelopmental disorders of yet unknown etiology
The results show that perception in autism, in both the visual and haptic domains, does not adhere to Weber’s law
The recording of incoming changes in absolute metrics may lead to the sensory overload often reported in these individuals (e.g., O’Donnell et al, 2012)
Summary
Autism Spectrum Disorder (ASD) refers to a group of neurodevelopmental disorders of yet unknown etiology. Hypersensitivity to sensory stimuli and biographical reports about the apparent lack of habituation to stimuli with repeated exposure (Gerland, 1997Grandin, 1992), the lack of contextual interference (e.g., Foxton et al, 2003), and findings demonstrating that perceptual representations remain close to the input (e.g., Hadad et al, 2017) all suggest difficulties using past experiences to derive expectations of incoming sensory signals; they suggest reduced auto-calibration of the perceptual system to its environment (Pellicano and Burr, 2012) We asked whether this reduced calibration in autism is evident at early stages of encoding during which sensitivity to changes in incoming stimulus is calibrated based on the immediate standard stimulation. Experiment three extended the investigation to conditions where JNDs scale with the perceived rather than the physical intensities
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