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Tomoya Nakamura, Ikuya Murakami; Common-onset visual masking reduces a simultaneous tilt illusion. Journal of Vision 2020;20(11):450. https://doi.org/10.1167/jov.20.11.450.
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Common-onset visual masking occurs when a sparse mask appears together with a target but remains after its offset. Several previous studies suggest that later sustained signals, possibly involving perceptual awareness of the target, are disrupted in this situation. On the other hand, the sustained signals are considered to integrate contextual information from surrounding space. Here we investigated how the contextual information about orientations of remote surroundings interacts with common-onset masking. We compared a repulsion effect of a simultaneous tilt illusion between simultaneous and delayed mask offset conditions. In the simultaneous offset condition, a target Gabor patch having a vertical grating and a surrounding four-dot mask were briefly flashed and disappeared together. In the delayed offset condition, the mask appeared together with the target, but remained there for 0.3 s after the target disappeared. This condition was suitable for common-onset visual masking to occur, but we optimized stimulus parameters so that the target was never rendered completely invisible. In both conditions, eight tilted Gabor patches were arranged circularly around the target, serving as inducers for the tilt illusion. Observers were asked to indicate whether they perceived the target patch as tilted clockwise or counter-clockwise from the vertical. The repulsion effect was estimated as how many degrees the target patch appeared to be tilted away from the orientation of the inducers. We found that the repulsion effect occurred in both conditions but was smaller in the delayed offset condition than in the simultaneous offset condition. In contrast, discriminability of target orientation did not differ. It was also confirmed that the decrease of repulsion was not fully explained by the appearance of a subjective upright square seen in the four-dot mask. We suggest that the remaining mask can disrupt contextual modulation by surrounding space, while leaving low-level visual features of the target intact.
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