Institution: University of California Berkeley
Talk Title: The locus of redundancy masking
Abstract: In redundancy masking (RM), the perceived number of items in repeating patterns is reduced (e.g., perceiving two lines when three are presented). RM has been found with simple (e.g., lines) and complex stimuli (e.g., letters and faces), suggesting that RM occurs at an early stage or multiple stages of the visual processing hierarchy. Here, we investigated whether the neuronal interactions underlying RM occur at a retinal level or higher up in the visual pathways. Observers were presented with arrays of 3, 4 or 5 vertical lines, radially arranged with respect to central fixation in a mirror stereoscope. The lines were presented either ipsilaterally (all lines displayed to the same or both eyes) or contralaterally (lines displayed to different eyes). The center of the arrays was presented at 10º of eccentricity, either to the left or right of fixation along the horizontal meridian for 150 ms. Center-to-center line spacing was set at 0.78º, which was confirmed to be above observers minimum angle of resolution with a Landolt C orientation discrimination task. Results showed RM (i.e., reporting less lines than presented) for all numbers of lines (3, 4 and 5), with the magnitude of RM increasing with the number of lines presented. Crucially, RM was found both for ipsilateral, as well as contralateral presentations. The current results suggest that the locus of RM is at or beyond the site of binocular integration. These findings are a stepping stone to identifying the precise cortical locus or loci of RM. Future psychophysical and neurophysiological research on RM will reveal whether it occurs solely at early stages (e.g., V1, V2), at later stages (e.g., V3, V4), or whether it is a multistage process with several areas playing a key role in giving rise to this type of masking.