Comparisons between electrophysiologically and psychophysically determined contrast sensitivity functions in humans.
Item
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Title
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Comparisons between electrophysiologically and psychophysically determined contrast sensitivity functions in humans.
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Identifier
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AAI9605582
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identifier
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9605582
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Creator
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Conte, Mary Maddalena.
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Contributor
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Advisers: James Gordon | Vance Zemon
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Date
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1995
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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 | Psychology, Experimental | Psychology, Psychometrics
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Abstract
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The spatial contrast sensitivity function (CSF) is a psychophysical measure of the minimum amount of contrast needed to detect the presence of spatial stimuli. It provides information about contrast perception over a range of spatial frequencies and is used as a measure of overall visual performance. In addition, it has become an important clinical tool for evaluation of pathological losses of visual function. The conventional method of measuring the CSF requires concentration and an active judgment by the observer and thus can yield unreliable results in patient populations. An objective measure that requires minimal cooperation from the patient would be indispensable. Primary among objective measurements of the CSF has been the visual evoked potential (VEP). However, a controversy exists over how well or poorly an evoked potential measure of contrast sensitivity in humans correlates with standard psychophysical measures. The purpose of this study was to quantitatively compare psychophysically derived contrast sensitivity functions with those derived from steady-state visual evoked potentials using a systems analysis approach.;Stimuli included vertical sinusoidal gratings of several spatial and temporal frequencies and contrasts. Gratings were temporally modulated sinusoidally in an appearance-disappearance manner. In the psychophysical experiments, the method of adjustment was used to collect two types of contrast detection thresholds. Observers were instructed to adopt two separate criteria for setting contrast: (1) to adjust contrast until the spatial pattern was just visible, and (2) to adjust contrast until the temporal flicker was just visible. In this way, separate pattern and flicker thresholds were obtained. Visual evoked potentials were recorded to these same stimuli modulated at 6.27 Hz at ten contrast levels ranging from 0.01 to 0.48. Fourier analysis of the VEP yielded fundamental (F1) and second harmonic (F2) response components. Amplitude and phase of these response components were plotted as functions of contrast for each spatial frequency tested. Contrast sensitivities were derived from these VEP data according to several criteria and were then compared to the psychophysically determined sensitivities. VEP criterion measures derived from amplitude or phase data alone yielded CSFs similar to those derived from amplitude and phase data combined. For one observer, a CSF derived from the second harmonic (F2) response correlated highly {dollar}(r\sp2 = 0.99,\ p < 0.05){dollar} with the psychophysical pattern CSF over the entire spatial frequency range. However, a consistent evoked potential correlate of the psychophysical functions was not observed across observers. For spatial frequencies above 3.6 cycles/degree, there was good agreement between VEP and psychophysical CSFs, regardless of the harmonic component used for the analysis. Results are discussed in terms of underlying cortical processing and clinical applications of VEP contrast sensitivity derivation techniques.
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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.
