Orientation-specific surround suppression is not alleviated by voluntary attention

Abstract

The perception of a stimulus is modulated by the spatial interactions in the visual field as well as by the behavioral goals of the perceiver. We examined the interaction between two kinds of modulation of contrast perception: the allocation of voluntary visual spatial attention and stimulus-driven orientation-specific surround suppression (OSSS). OSSS is the reduction in the perceived contrast of a target that occurs when a collinear grating is placed adjacent to the target. In non-human primates, attention has been shown to relieve surround suppression in neuronal firing rates. We asked whether allocation of voluntary attention would counter the perceptual effects of OSSS. We tested 16 observers in a two-interval forced-choice task. In each trial, participants viewed two gratings, each embedded in a surround annulus on opposite sides of the fixation, followed by a single isolated grating in one location and were instructed to indicate which of the intervals contained the higher contrast at that location. At the beginning of each trial, one location was cued and the judgment was more likely to be performed at that location (70% valid). The point of subjective equality (PSE) was determined for valid/invalid/neutral cue trials and for collinear/orthogonal surround conditions. Replicating previous results, we found that OSSS reduced the perceived contrast of the embedded grating when a collinear surround grating was present, relative to an orthogonal surround (F_1,14=27.5, p<0.05). We found that allocation of voluntary attention did not affect the PSE (F_1,14=0.18, p=0.68). The slope of the psychometric curve was significantly shallower in the invalid cue cases (F_1,14=6.0, p<0.05) and also for the collinear, relative to the orthogonal, surround condition (F_1,14=7.6, p<0.05). Taken together, these results suggest that while OSSS affects both perceived contrast and sensitivity, voluntary attention only affects sensitivity. In addition, attention does not seem to relieve the perceptual effects of OSSS.

Meeting abstract presented at VSS 2013