Responses of cells in monkey visual cortex during perceptual filling-in of an artificial scotoma

Weerd, P. D., Gattass, R., Desimone, R., & Ungerleider, L. G.

Nature. 1995 Oct 26;377(6551):731-4.


When we view a scene through one eye, we typically do not see the scotomas created by the optic disc and the blood vessels overlying the retinal surface. Similarly, when a texture field containing a hole is steadily viewed in peripheral vision (artificial scotoma), the hole appears to fill in with the surrounding texture in a matter of seconds, demonstrating that the visual system fills in information across regions where no information is available. Here we show that, in monkeys viewing a similar texture field with a hole, the responses of extrastriate visual neurons with receptive fields covering the hole, increase gradually to a level comparable to that elicited by the same texture without a hole. The time course of these dynamic changes in activity parallels the time course of perceived filling-in of the hole by human observers, suggesting that this process mediates perceptual filling-in.

Contribution to the field

This paper is to date the only one showing a neurophysiological correlate of the Troxler phenomenon. It reveals how mechanisms that maintain figure-ground segregation weaken during maintained fixation. Although not given much prominence in the paper, a stronger version of the activity increases during fixation was shown in the monkey with more stable fixation (i.e., less microsaccades), as opposed to the other monkey who had a less stable fixation behavior (i.e., more microsaccades). This finding foreshadowed the importance of (micro)saccades as a mechanism that gates visual processing, as has become evident in other work many years later from our own group and others.

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