Ângela Gomes Tomaz¹, YuYi Lu¹, Dennis M. Levi¹, Bilge Sayim²; ¹Herbert Wertheim School of Optometry & Vision Science, University of California Berkeley, ²Cognitive and Affective Sciences Lab (SCALab), UMR CNRS 9193, University of Lille, Lille, France

In redundancy masking (RM), observers perceive fewer items than presented in repeating patterns (e.g., perceiving two lines when three are presented). Previous research has found RM for both simple (e.g., lines) and complex stimuli (e.g., faces) indicating that it might occur at multiple stages of visual processing. Here, we investigated whether RM occurs from retinal level neuronal interactions or higher up in the visual pathways. Twenty observers were presented with 3, 4 or 5 lines (0.04° width, 1° height), both monocularly and binocularly, in a mirror stereoscope. In the binocular presentation, lines were presented ipsilaterally (i.e., all to the same eye) and contralaterally (i.e., some lines to the right eye and others to the left eye). The center of the line array was set randomly at +10° or -10° of eccentricity along the horizontal meridian. Lines were radially aligned with respect to central fixation and presented for 150ms. Center-to-center line spacing was 0.78°, and confirmed with a Landolt C orientation discrimination task to be above the observers’ minimum angle of resolution at the experimental eccentricity. Observers were instructed to report the number of lines perceived. Results showed that observers reported fewer lines than presented for all numbers of lines revealing RM. The (absolute) magnitude of RM increased with the number of lines presented. Importantly, RM was found both for ipsilateral, as well as contralateral presentations suggesting that its locus is at or beyond the site of binocular integration. However, bigger deviations than expected for contralateral presentations suggest that other factors (e.g., contralateral suppression, binocular rivalry) may be playing a role in the findings. Future psychophysical and neurophysiological research on RM will reveal the precise cortical locus – or loci – of RM.

Acknowledgements: Supported by a grant from the National Eye Institute awarded to Dennis Levi (R21EY030609) and an NIH institutional training grant (T35EY007139).