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Leili Soo, Ramakrishna Chakravarthi, Plamen Antonov, Søren Andersen; Suppressive stimulus interactions in visual cortex reflect the critical spacing in crowding. Journal of Vision 2017;17(10):397. doi: 10.1167/17.10.397.
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© ARVO (1962-2015); The Authors (2016-present)
Crowding is a phenomenon in which peripheral object recognition is impaired by the close proximity of irrelevant stimuli. Currently, the neural processes underlying object recognition and its failure in crowding are not well understood. Research examining the neural implementation of visual attention has found that stimulus processing in visual cortex is suppressed by the presence of nearby stimuli. Could the breakdown of object recognition seen in crowding be explained by such flanker induced suppression of target processing in the visual cortex? To answer this question, we assessed cortical processing of a target object as a function of flanker presence and distance to the target while participants performed a target orientation discrimination task. Flankers and targets flickered at different frequencies to elicit steady-state visual evoked potentials (SSVEPs), which allow for the assessment of cortical processing of each of the concurrently presented stimuli. Target identification accuracy and target elicited SSVEP amplitudes decreased with decreasing target-flanker separations. Additionally, we fitted psychometric curves to both behavioral data and target elicited SSVEP amplitudes in order to determine the spatial extent of interference ('critical spacing'). The cortical and behavioral critical spacing estimates closely mirrored each other. Unexpectedly, however, the presence of any flankers, even those far beyond either critical spacing, dramatically decreased SSVEP amplitudes elicited by the target, relative to the unflanked condition. We conclude that suppressive stimulus interactions between targets and flankers in the visual cortex may underlie the perceptual phenomenon of crowding. Further, the finding that flankers far outside the traditional critical spacing can suppress target processing might potentially explain the large variability in observed critical spacing across different experimental conditions if it is the case that behavioral effects are observable only when cortical interference reaches a threshold.
Meeting abstract presented at VSS 2017
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