Redundancy masking and the compression of information in the brain
The visual world is inherently complex, presenting far more information than a human visual system can process in full. To manage this overload, the visual brain employs several mechanisms. One mechanism that possibly contributes to the reduction of information is redundancy masking (RM): the reduction of the number of perceived items in repeating patterns. For example, when three identical lines are presented in the periphery, observers often perceive only two. The underlying neural mechanisms of RM remain unclear. Here, we use steady-state visual evoked potential (SSVEP) to examine whether redundancy-masked items are neurally suppressed or integrated with neighboring items. Three identical arcs (quarter-circles; 0.44{degrees} line width) were presented in the periphery (eccentricities: 17.3{degrees}, 19.5{degrees}, and 21.7{degrees}), each tagged with a unique frequency. Participants maintained central fixation, monitored via a gaze-contingent control, and reported the number of arcs they predominantly perceived after each 10s trial. We analyzed baseline-corrected amplitudes at each tagged frequency and calculated signal-to-noise ratios (SNRs) for fundamental and intermodulation (IM) components, separating trials by behavioral responses (RM: 2 items perceived, non-RM: 3 items perceived). Fundamental frequency comparisons revealed that the outer arc elicited higher SSVEP responses than the inner and middle one under RM, with no significant differences between arcs under non-RM. However, fundamental frequency SNRs did not differ between RM and non-RM perceptions. When we compared IM SNRs, the middle and outer arc's combination was significantly higher during RM compared to non-RM, suggesting increased neural integration between them. These results indicate that RM involves a loss of conscious access to visual information, yet corresponding neural signals are not entirely suppressed. Instead, the neural signatures we found suggest the integration with neighboring elements across space and time. We suggest that redundancy-masked items - although unavailable for conscious report- are still observed in the neural signatures of RM.