(NAS Colloquium) Vision From Photon to Perception (1999) / Chapter Skim
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Spatial integration and cortical dynamics
Spatial integration and cortical dynamics
Pages 59-66
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From page 59... ...
GILBERT, ANTRUDDHA DAS, MINAMI ITO, MITESH KAPADIA, AND GERALD WESTHEIMER The Rockefeller University, 1230 York Avenue, New York, NY 10021-6399 ABSTRACT Cells in adult primary visual cortex are capable of integrating information over much larger portions of the visual field than was originally thought. Moreover, their receptive field properties can be altered by the context within which local features are presented and by changes in visual experience.
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From page 60... ...
The perceptual phenomena obey rules that are consonant with the patterns of connectivity in primary visual cortex, supporting the idea that a major component of the process of spatial integration occurs there. One can characterize a host of processes, referred to as intermediate-level vision, that occur between the discrimination of simple visual attributes, such as orientation, and the identification of complex objects.
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From page 61... ...
If we assumed that connections between the spiking region and the surrounding area of subthreshold activation are reciprocal, the correspondence between the area of the RF surround and the representation of the area of cortical activation suggested that lateral cortical interactions play a part in the extended RF measured with complex visual stimuli. Further evidence for the relationship between the horizontal connections and the cortical columnar architecture is also revealed by the comparison between the optical PS and the optical image of orientation columns (Fig.
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From page 62... ...
2. Functional interactions mediated by horizontal connections visualized in cat visual cortex with optical recording of cortical PS.
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From page 63... ...
The push-pull nature of the surround effects, operating over the cortical sheet, would promote the activation of cells whose RFs are superimposed on a salient contour, and would suppress the activity of cells whose RFs cover a random background. These findings emphasize the nonlinear nature of complex cells in primary visual cortex: the response of these cells in a complex visual environment cannot be predicted from their responses to a single line, presented at different positions and orientations.
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From page 64... ...
The effects illustrated here show the effect of context on the perception of the visual attributes of local features and the underlying facilitatory effect of contours lying outside the classical RF. The psychophysical studies were done in human observers, and the physiological studies were done on superficial layer complex cells in primary visual cortex of alert, fixating monkeys.
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From page 65... ...
5. Short-term plasticity of RF size induced by an artificial scotoma, an occluded area of visual field surrounded by a pattern of lines or random dots.
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From page 66... ...
An important question to be addressed is to differentiate those contextual effects and dynamic changes in RFs that are due to the intrinsic horizontal connections, hence reflechng bottom-up processes, from those that arise from feedback connections, reflecting top-down influences. Though the precise synaptic mechanisms remain to be worked out, the fact that the effects have been observed In primary visual cortex, where much of the detailed functional architecture, connectivity, and RE properties have been worked out In considerable detail, makes accessible an understanding of the mechanisms of higher-order perceptual phenomena.
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