THE TIME COURSE OF TEMPORAL SUMMATION AT VARIOUS BACKGROUND LUMINANCES.
Item
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Title
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THE TIME COURSE OF TEMPORAL SUMMATION AT VARIOUS BACKGROUND LUMINANCES.
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Identifier
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AAI8120763
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identifier
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8120763
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Creator
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SHAH, PRERNA M.
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Contributor
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Mitchell L. Kietzman
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Date
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1981
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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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The present study evaluated changes in threshold luminance of a brief test flash superimposed spatially and temporally onto a subliminal conditioning flash. Parameters studied were background luminance, conditioning-flash duration and delay between the onsets of the conditioning and test flashes. The common purpose was to investigate excitatory effects within the visual system that were created by the subliminal conditioning flash, evaluated at various times during its exposure.;A four-channel Maxwellian view optical system was used to present the conditioning and test flashes, superimposed at 6(DEGREES) 30' along the right horizontal meridian of the right eye. The test flash was a 30' circular target of 5 msec duration; the conditioning flash was a 30' circular target with a duration of either 10 msec, 20 msec, 40 msec or 80 msec. All four conditioning flashes were equated for their energy content. The conditioning flash and test flash were spatially superimposed onto a 40(DEGREES) adapting field of either -3.0 log mL, 0.0 log mL or 2.0 log mL luminance. The test flash was temporally superimposed at five different delays from the onset of the conditioning flash; the temporal delays were either 0%, 25%, 50%, 75% or 100% of the respective conditioning-flash duration. A descending method of adjustment was used to obtain all threshold measurements. Two observers were tested extensively.;The data were analyzed to display the magnitude and time course of temporal summation. The magnitude of temporal summation was the difference in the test-flash thresholds presented with and without the conditioning flash. The time course of temporal summation was the change in the magnitude of temporal summation at various onset delays between the test and conditioning flashes.;The results were: (1) Increased background luminance and conditioning-flash duration decreased the magnitude of temporal summation, particularly at the shortest and longest delay intervals. (2) Increased background luminance and conditioning-flash duration also altered the time course of temporal summation such that lower background luminances and shorter conditioning flashes produced a flat function, while higher background luminances and longer conditioning flashes produced a non-monotonic function. (3) The non-monotonic function obtained at higher background luminances and longer conditioning flashes was symmetrical and "U"-shaped; maximum summation always occurred at the middle of the conditioning-flash duration (at 50% onset delay interval).;Results indicate that the temporal parameters of the visual system are altered by varying the level of adaptation. The neural mechanisms underlying the phenomenon of temporal summation and the effect of background luminance on temporal summation are discussed.
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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
