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A binocular site for contrast-modulated masking.

Harris, Julie M and Willis, Alexandra (2001) A binocular site for contrast-modulated masking. Vision Research, 41 (7). pp. 873-881. ISSN 00426989

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Abstract/Description

Contrast-modulated (CM) gratings, composed of two luminance-modulated sinusoids of similar spatial frequency, mask the detection of test sinusoids at the difference frequency. However, the mechanism underlying masking by CM gratings remains poorly understood. In this paper, we aimed to determine whether the masking of 1 cycle deg−1 LM test gratings by a 1 cycle deg−1 beat (formed from a pair of carriers at 8 and 9 cycles deg−1) occurs in monocular channels or after the site of binocular combination, or both. Threshold elevations for the detection of a 1 cycle deg−1 test grating were obtained for a number of stimulus conditions, including: (1) dichoptic CM (both 8 and 9 cycles deg−1 mask components presented to one eye, with the 1 cycle deg−1 test grating to the other); (2) dichoptic variant (8 and 9 cycles deg−1 mask gratings presented to separate eyes, with the 1 cycle deg−1 test grating presented to one eye); (3) binocular CM (all mask and test gratings presented to both eyes). As a control, masking magnitude was also measured for LM mask gratings of similar frequency (1 cycle deg−1) and effective contrast (3%) to that of the beat. For both LM and CM masks, the dichoptic condition yielded threshold elevations that were similar or greater than the binocular condition. When 8 and 9 cycles deg−1 mask components were presented to separate eyes (the dichoptic variant condition), no beat pattern was visible and no elevations in detection threshold occurred. The results demonstrate that, like LM masking, detection of a target in the presence of a CM mask does not involve purely monocular mechanisms. Further, that the site of CM masking must occur beyond the stage at which monocular matching for stereopsis takes place. This is consistent with other studies which suggest that dichoptic masking is contingent on stereo matching, and thus occurs relatively late in the hierarchy of binocular visual processing.

Item Type: Article
Print ISSN: 00426989
Electronic ISSN: 1878-5646
Uncontrolled Keywords: Dichoptic; Binocular; Masking; Contrast-modulation
University Divisions/Research Centres: Faculty of Health, Life & Social Sciences > School of Health and Social Sciences
Dewey Decimal Subjects: 600 Technology > 610 Medicine & health > 612 Human physiology
Library of Congress Subjects: R Medicine > RE Ophthalmology
Item ID: 2241
Depositing User: RAE Import
Date Deposited: 04 Apr 2008 11:34
Last Modified: 28 Aug 2013 11:57
URI: http://researchrepository.napier.ac.uk/id/eprint/2241

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