A PSYCHOPHYSICAL INVESTIGATION OF TRANSIENT AND SUSTAINED MECHANISMS IN HUMAN VISUAL MASKING.
Item
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Title
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A PSYCHOPHYSICAL INVESTIGATION OF TRANSIENT AND SUSTAINED MECHANISMS IN HUMAN VISUAL MASKING.
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Identifier
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AAI8302554
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identifier
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8302554
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Creator
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SCHENKEIN, JOYCE BARBARA.
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Contributor
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Ivan Bodis-Wollner | Mitchell L. Kletzman
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Date
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1982
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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 threshold of an 8.3 msec sinusoidal test grating was measured as a function of its onset asynchrony (SOA) with respect to a 725 msec mask of 2.6% contrast and the same spatial frequency (5, 4 or 6 c/d). The test grating was either in the same spatial phase as the mask, or laterally displaced by 180(DEGREES).;Large "primary" peaks occurred with mirror-like symmetry in time at small (25 msec) asynchronies from mask onset and offset. The timings (but not the magnitudes) of these peaks were phase-dependent suggesting that spatial phase is processed in a temporal way.;The same SOAs associated with a primary peak to gratings in one spatial phase, were associated with troughs, or facilitation for gratings of the opposite spatial phase. Peaks and especially troughs decreased in magnitude as spatial frequency increased. The fact that the primary peaks occurred at short latency and that their amplitudes decreased with spatial frequency suggest that they represent transient neural responses.;At longer (40-100 msec) delays and on opposite "sides" of the temporal edge from the primary peaks, were smaller "secondary" peaks. The magnitudes and delays of these peaks increased with spatial frequency suggesting the importance of sustained neural mechanisms.;To test this theory, monocular masking thresholds of 5 and 4 c/d test gratings were measured following 3 min adaptation to low contrast (1-4%) counterphase (TA; transient adapting) or stationary (SA; sustained adapting) gratings of the same spatial frequency (5 or 4 c/d). Adaptation was either in the same or contralateral eye.;TA altered detection at both spatial frequencies whereas SA affected only 4 c/d. SA DECREASED whereas TA INCREASED all masking peaks, suggesting that the sustained system ordinarily masks, whereas the transient system ordinarily enhances test detection. SA reduced the primary and secondary peaks by the same magnitude indicating that sustained influences at these different SOAs are equal. However, TA, raised secondary peaks more than primaries, indicating unequal transient influence at these SOAs. Ipsilateral and contralateral effects were identical after SA ONLY, suggesting that the sustained system is binocular whereas the transient system is predominantly monocular.
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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
