Low-spatial-frequency bias in context-dependent visual size perception.

Spatial frequency (SF) information is essential for visual perception. By combining a sensitization procedure and the Ebbinghaus illusion, we investigated the effect of SF bias in context-dependent visual size perception. During the sensitization phase, participants were repeatedly presented with low- or high-pass filtered faces or gratings and were asked to discriminate the gender or the orientation of them, respectively. Immediately following the sensitization phase, the Ebbinghaus illusion strength was measured. The results showed that the illusion strength was significantly larger when the prior sensitized images were low-pass filtered relative to when they were high-pass filtered. Moreover, this SF bias was independent of low-level features and the specific content of the filtered images. Our findings extend the understanding of SF bias induced by sensitization in visual domain, and suggest that the processing of context-dependent visual size information is likely to involve magnocellular projections from subcortical areas via low SF channel.