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Philip O'Herron, Rudiger von der Heydt; Persistence of the neural border ownership signal indicates short-term memory in perceptual organization. Journal of Vision 2007;7(9):310. doi: 10.1167/7.9.310.
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© ARVO (1962-2015); The Authors (2016-present)
The responses of neurons in visual cortex generally decay rapidly after the stimulus is turned off. To study persistence of figure-ground organization we studied border ownership (BO) selective neurons in situations where a figure-ground display changed to an ambiguous display. Cells were recorded in macaque V2 under behaviorally induced fixation. A square figure with one side centered in the receptive field (giving a particular BO assignment) was presented for 0.5s and followed by 1s presentation of an ambiguous edge - a contrast border that appeared behind a circular aperture. The local contrast in and around the receptive field remained constant. We measured the duration of the BO signal (the difference in firing rates between conditions with the two initial sides of figure). We found that during the ambiguous edge presentation, the BO signal decayed slowly, with a time constant of around 600 ms. In contrast, when, after the same initial display, the figure was flipped to the opposite side, the signal reversed quickly, with a time constant of 30 ms. Controls in which the colors of figure and ground were alternated rapidly during the initial display showed that the persistence of the BO signal was not due to an afterimage. When the display was switched to ‘figure’ again after the ambiguous edge period, the BO signal assumed the corresponding value rapidly, as observed for figures flipping sides. In summary, in the absence of figure-ground cues, the BO signal persists with slow decay, but it is reset quickly when new figure-ground information is presented. These features indicate a mechanism of short term storage, which may contribute to the stability of figure-ground organization despite the rapid fluctuations that characterize the retinal image in normal vision.
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