Temporal dynamics of normalization reweighting.

Researchers studied how the brain processes repeated visual information in 220 people, including some with autism. They found that when the same visual patterns are shown repeatedly, the brain adapts by changing how it responds within 2-5 seconds. Importantly, people with autism showed the same brain responses as people without autism, suggesting their visual processing works similarly in this specific area.

This study examined how neural suppression in visual cortex changes over time using EEG measurements from 220 participants across three experiments. Researchers found that when visual stimuli are presented repeatedly, suppression between them strengthens within 2-5 seconds of stimulus onset. This 'normalization reweighting' was observed in primary visual cortex and occurred for both monocular and dichoptic visual arrangements. Importantly, the study found no significant differences in this reweighting process between individuals with high versus low autistic traits or between those with and without autism diagnoses, challenging theories that propose fundamental inhibition/excitation differences in autism.

Findings suggest that basic visual adaptation mechanisms function typically in autism, which may inform understanding of sensory processing differences. Results do not support theories of widespread inhibition/excitation imbalances in autism, at least for this specific visual process.

Study focused on a specific visual processing mechanism and may not generalize to other sensory or cognitive processes. The autism-related findings are based on trait measures and diagnostic status rather than detailed clinical assessments. Sample size for the MEG experiment was relatively small (N=20).

For decades, neural suppression in early visual cortex has been thought to be fixed. But recent work has challenged this assumption by showing that suppression can be reweighted based on recent history; when pairs of stimuli are repeatedly presented together, suppression between them strengthens. Here we investigate the temporal dynamics of this process using a steady-state visual evoked potential (SSVEP) paradigm that provides a time-resolved, direct index of suppression between pairs of stimuli flickering at different frequencies (5 and 7 Hz). Our initial analysis of an existing electroencephalography (EEG) dataset (N = 100) indicated that suppression increases substantially during the first 2-5 seconds of stimulus presentation (with some variation across stimulation frequency).

We then collected new EEG data (N = 100) replicating this finding for both monocular and dichoptic mask arrangements in a preregistered study designed to measure reweighting. A third experiment (N = 20) used source-localized magnetoencephalography and found that these effects are apparent in primary visual cortex (V1), consistent with results from neurophysiological work. Because long-standing theories propose inhibition/excitation differences in autism, we also compared reweighting between individuals with high versus low autistic traits, and with and without an autism diagnosis, across our three datasets (total N = 220). We find no compelling differences in reweighting that are associated with autism.

Our results support the normalization reweighting model and indicate that for prolonged stimulation, increases in suppression occur on the order of 2-5 seconds after stimulus onset.