Blobs versus bars:psychophysical evidence supports two types of orientation response in human color vision


The classic hypothesis of Livingstone and Hubel (1984, 1987) proposed two types of color pathways in primate visual cortex based on recordings from single cells: a segregated, modularpathway that signals color but provides little information about shape or form and a second pathway that signals color differences and so defines forms without the need to specify their colors. A major problem has been to reconcile this neurophysiological hypothesis with the behavioral data. A wealth of psychophysical studies has demonstrated that color vision has orientation-tuned responses and little impairment on form related tasks, but these have not revealed any direct evidence for nonoriented mechanisms. Here we use a psychophysical method of subthreshold summation across orthogonal orientations for isoluminant red-green gratings in monocular and dichoptic viewing conditions to differentiate between nonoriented and orientation-tuned responses to color contrast. We reveal nonoriented color responses at low spatial frequencies (0.25-0.375 c/deg) under monocular conditions changing to orientation-tuned responses at higher spatial frequencies (1.5 c/deg) and under binocular conditions. We suggest that two distinct pathways coexist in color vision at the behavioral level, revealed at different spatial scales: one is isotropic, monocular, and best equipped for the representation of surface color, and the other is orientation-tuned, binocular, and selective for shape and form. This advances our understanding of the organization of the neural pathways involved in human color vision and provides a strong link between neurophysiological and behavioral data.

Publication DOI:
Divisions: College of Health & Life Sciences > School of Optometry > Optometry
College of Health & Life Sciences > Clinical and Systems Neuroscience
College of Health & Life Sciences
College of Health & Life Sciences > School of Optometry > Centre for Vision and Hearing Research
Additional Information: Creative Commons Attribution Non-Commercial No Derivatives License Funding: Canadian Institutes of Health Research (CIHR) [MOP-10819]; Engineering and Physical Sciences Research Council grant (UK)
Uncontrolled Keywords: color vision,contrast,cortex,isoluminance,orientation,psychophysics,vision,Ophthalmology,Sensory Systems
Publication ISSN: 1534-7362
Last Modified: 17 May 2024 07:09
Date Deposited: 11 Jan 2013 08:24
Full Text Link: http://www.jour ... 13/1/2.abstract
Related URLs: http://www.scop ... tnerID=8YFLogxK (Scopus URL)
PURE Output Type: Article
Published Date: 2013-02-01
Authors: Gheiratmand, Mina
Meese, Tim (ORCID Profile 0000-0003-3744-4679)
Mullen, Kathy

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