Anmol Kaur¹, Cheryl Olman; ¹University of Minnesota

The brain integrates different cues and information to perceive the world, but disruptions to these cues can lead to confusion about size and depth. For example, two objects with the same angular size that appear to occupy different portions of the visual field will also activate different areas of V1 (Murray, Boyaci, & Kersten, 2006). The psychophysical approach of measuring spatial frequency (SF) sensitivity allows us to determine if the size illusion (“ball in the hall”) provides behavioral evidence for modification of the structure of neuron receptive fields, rather than just the amplitude of their responses, by feedback related to size perception. The present study examined the effect of feedback on SF tuning. Participants detected grating patterns inside two discs differing in perceived size for 5 different SFs (4, 6, 8, 12, 16) with two conditions (context or no-context). A mixed-design ANOVA was conducted to evaluate the effects of SF and location on contrast detection thresholds in the context condition. A significant main effect of SF was found at the Participant:SF level indicating that contrast detection thresholds varied significantly with SF. A paired t-test revealed that the average threshold (N=10) between the Top and Bottom locations was higher for spatial frequencies of 6 cycles per degree and above, and statistically significant at 6 and 8 cpd. These findings suggest that the SF response for the Top ball is shifted to the left relative to the Bottom ball. The findings demonstrate that perceived size influences SF tuning, supporting the role of feedback in modulating neural processing in V1. This result provides behavioral evidence for the modulation of neuron receptive fields by feedback related to contextual size perception, aligning with theories of predictive coding explaining how the brain integrates spatial and contextual cues to resolve discrepancies in size and depth perception.