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Denis Schluppeck, Stephen A. Engel; Color Opponent Neurons in V1: A Review and Model Reconciling Results from Imaging and Single-Unit Recording. Journal of Vision 2002;2(6):5. doi: 10.1167/2.6.5.
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The signals in visual cortex that ultimately give rise to color perception remain poorly understood. Controversy has particularly surrounded one aspect of color’s encoding in the visual system—opponent processing in primary visual cortex. Early single-unit studies suggested that V1 contains relatively few color-opponent neurons. Neuroimaging measurements, however, have suggested that such neurons might be relatively numerous. Here, we reconcile these apparently discrepant results and conclude that V1 contains relatively large numbers of color-opponent neurons. We first review results from each method and find that most neuroimaging studies provide evidence of substantial color opponency in V1, and that despite apparent controversy, most single-unit studies agree that relatively large numbers of V1 neurons show some sort of color opponency. To reconcile the results from different techniques more formally, we used electrophysiological data to predict the outcomes of neuroimaging experiments. We simulated the expected fMRI response in V1 to spatial patterns of different color, based on the neurons’ properties, as reported in Johnson, Hawken, and Shapley, (2001). The simulated responses to stimuli used in Engel, Zhang, and Wandell, (1997) agree well with the actually observed fMRI results. The model identifies several factors that led to the apparent discrepancy between techniques, and makes testable predictions about how these factors influence the magnitude of color-opponent signals. fMRI and single-unit data converge to show that large numbers of color-opponent neurons exist in V1.
Note. This table summarizes results from imaging of color vision. The fourth column indicates how details about the stimuli were reported: using cone contrast calculations (cone), CIE coordinates (CIE), or “–“, when no details were given. The last column indicates, whether the results from the study are consistent with relatively large numbers of color-opponent neurons in V1 (++), show likely color-opponent signals with a possible contribution by S cones (+), are inconclusive (?), or whether the report did not allow any inferences to be made about opponency in V1 (–).
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