Intact Orientation Perception Bias in Autism Speaks Against the Decreased Divisive Normalization Model

Background: One recent, promising account of Autism Spectrum Disorders (ASD) situates the cause of the disorder in an atypicality in basic neural information processing, more specifically in how activity of one neuron is modulated by neighboring neurons. The canonical neural computation that implements such contextual influence is called divisive (or suppressive) normalization. The account proposes that normalization is reduced in ASD. This idea is inspired by the excitatory/inhibitory imbalance hypothesis of ASD, and by findings of decreased contextual influences in perception and cognition in this population.

Objectives: We tested one fundamental prediction of this model for low-level perception, namely that individuals with ASD would show reduced cross-orientation suppression (leading to an illusory tilt perception).

Methods: 11 young adults with an ASD diagnosis and 12 age-, gender-, and IQ-matched control participants performed a psychophysical orientation perception task with compound grating stimuli. Their illusory tilt perception was derived from psychometric function fits used as a measure of the strength of the divisive suppression by context.

Results: Suppression did not differ significantly between groups, indicating typical divisive normalization in individuals with ASD. In fact, all individuals with ASD showed a considerable orientation bias. There was also no correlation between illusory tilt perception and autistic traits as measured by the Social Responsiveness Scale.

Conclusions: These results provide clear evidence against the decreased divisive normalization model of ASD in low-level perception, where divisive normalization is best characterized. We evaluate the broader existing evidence for this model and propose ways to salvage and refine the model.