INDEPENDENT ON AND OFF PATHWAYS IN HUMANS UNDERLIE ASYMMETRIES IN BRIGHTNESS AND DARKNESS PERCEPTION.
Item
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Title
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INDEPENDENT ON AND OFF PATHWAYS IN HUMANS UNDERLIE ASYMMETRIES IN BRIGHTNESS AND DARKNESS PERCEPTION.
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Identifier
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AAI8801775
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identifier
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8801775
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Creator
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WELCH, JANET SUSAN.
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Contributor
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James Gordon | Vance Zemon
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Date
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1987
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Language
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English
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Publisher
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City University of New York.
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Subject
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Psychology, Physiological
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Abstract
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ON and OFF pathways have been found in many vertebrate species, including man. ON cells respond to increments in light, OFF cells respond to decrements in light. ON and OFF pathways have been found to differ morphologically, physiologically, and pharmacologically. It has been hypothesized that ON and OFF pathways mediate the perception of brightness and darkness, respectively. There is some psychophysical evidence of differences in human perception of brightness and darkness, suggesting differences in the properties of the ON and OFF pathways.;Novel positive- and negative-contrast stimuli were designed in order to selectively emphasize responses from ON and OFF pathways. The responses to these stimuli were measured by recording visual evoked potentials (VEPs), electrical responses from the visual cortex. The amplitudes and phases of the first four harmonic components of the VEP response were obtained by using Fourier analysis. The results revealed differences in the responses to positive- and negative-contrast stimuli, suggesting asymmetries in the ON and OFF pathways. The spatial tuning of the two pathways appears to be different; the spatial tuning of the OFF pathway may be finer than that of the ON pathway. At the higher spatial frequencies (check sizes of 5 to 9 minutes of arc), higher amplitude responses were reliably found for negative-contrast stimuli than for positive-contrast stimuli. The temporal tuning curves in response to positive- and negative-contrast stimuli are similar in shape but different in magnitude of response; negative contrasts elicited higher amplitude VEPs over the range of temporal frequencies tested. Contrast experiments also revealed higher amplitude responses to negative contrasts. Therefore, it appears that the OFF pathway has finer spatial tuning and greater contrast gain than the ON pathway. The techniques used in this research, as well as the results found, may be useful in delineating human perception of brightness and darkness.
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Type
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dissertation
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Source
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PQT Legacy CUNY.xlsx
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degree
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Ph.D.
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Program
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Psychology
