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Systematic misestimation in a vernier task arising from contrast mismatch

Published online by Cambridge University Press:  06 March 2008

HAO SUN*
Affiliation:
Department of Optometry and Visual Sciences, Buskerud University College, Kongsberg, Norway
BARRY B. LEE
Affiliation:
State Universityof New York, State College of Optometry, New York, New York Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
RIGMOR C. BARAAS
Affiliation:
Department of Optometry and Visual Sciences, Buskerud University College, Kongsberg, Norway
*
Address correspondence and reprint requests to: Hao Sun, Department of Optometry and, Visual Sciences, Buskerud University College, Frogsvei 41, P.O. Box 251, 3603, Kongsberg, Norway. E-mail: [email protected]

Abstract

Luminance signals mediated by the magnocellular (MC) pathway play an important role in vernier tasks. MC ganglion cells show a phase advance in their responses to sinusoidal stimuli with increasing contrast due to contrast gain control mechanisms. If the phase information in MC ganglion cell responses were utilized by central mechanisms in vernier tasks, one might expect systematic errors caused by the phase advance. This systematic error may contribute to the contrast paradox phenomenon, where vernier performance deteriorates, rather than improves, when only one of the target pair increases in contrast. Vernier psychometric functions for a pair of gratings of mismatched contrast were measured to seek such misestimation. In associated electrophysiological experiments, MC and parvocellular (PC) ganglion cells' responses to similar stimuli were measured to provide a physiological reference. The psychophysical experiments show that a high-contrast grating is perceived as phase advanced in the drift direction compared to a low-contrast grating, especially at a high drift rate (8 Hz). The size of the phase advance was comparable to that seen in MC cells under similar stimulus conditions. These results are consistent with the MC pathway supporting vernier performance with achromatic gratings. The shifts in vernier psychometric functions were negligible for pairs of chromatic gratings under the conditions tested here, consistent with the lack of phase advance both in responses of PC ganglion cells and in frequency-doubled chromatic responses of MC ganglion cells.

Type
Research Article
Copyright
Copyright © Cambridge University Press 2008

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