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Jing Xing; Why Are Visual Images Not Blurred with Lateral Excitation?. Journal of Vision 2004;4(8):777. doi: 10.1167/4.8.777.
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Long-range excitatory lateral interactions between neurons have been reported in the visual cortex. It is suggested that the excitatory interactions bind and link different parts of the cortical representation of a visual image. However, lateral excitation can result in blurring object boundaries of an image. In this report we showed psychophysical evidence that lateral excitation is constrained by the boundaries. Using a contrast-matching task, we measured the effect of surround gratings on the perceived contrast of a central grating patch. Surround gratings enhanced the perceived contrast of the central stimulus when the central contrast was higher than the surround contrast. This enhancement effect increased with the size of the central stimulus. On the other hand, the enhancement effect did not vary with the size of the surround and the distance between the central and the surround stimuli. Moreover, varying the orientation and spatial frequency of surround gratings had little effect on the amount of enhancement. These results suggest that enhancement is gated by but not directly exerted by surround stimuli. We proposed that lateral excitation occurs within a stimulus and does not spread between different stimuli in suprathreshold visual tasks. Such interactions can regularize an image without blurring the boundaries.
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