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

Mina Gheiratmand, Tim Meese, Kathy Mullen

Research output: Contribution to journalArticlepeer-review


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.

Original languageEnglish
Article number2
Number of pages13
JournalJournal of Vision
Issue number1
Publication statusPublished - 1 Feb 2013

Bibliographical note

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)


  • color vision
  • contrast
  • cortex
  • isoluminance
  • orientation
  • psychophysics
  • vision


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