September 2017
Spotlight Summary by Hannah Smithson
Color opponency: tutorial
Human color vision provides a rich testing ground for psychophysical (system-level) and physiological (cell-based) investigations of neural processes. Shevell and Martin – a psychophysicist and a physiologist – present a tutorial on color opponency, and debate what it means to each of them. The format of the paper allows open discussion of points that are often left implicit, or avoided completely, in more formal research papers. What emerges is a clear catalogue of points of convergence and divergence, considered within the context in which each researcher is operating. Opponency, in the broad sense of opposing inhibitory and excitatory elements that can be cancelled or nulled, finds strong empirical support in both physiology and psychophysics. However, although both groups may use the same nomenclature, of “red-green” or “blue-yellow” opponency, they measure different things. Whilst the psychophysicist characterises the relationship between the physical stimulus and colour percepts, but can only infer the underlying biological mechanism, the physiologist maps the relationship between physical stimulus and neural response, but is rarely able to measure the relationship between changes in the neuron’s response and perception. In fact, the surface similarity between the labels adopted by both groups masks an important difference between them: the psychological opponent colors measured in chromatic cancelation experiments do not align with the patterns of color opponency measured in single neurons. Fortunately, there is hope, for both groups have a shared goal of understanding color vision. Threshold-based psychophysical measurements show closer parallels with the physiology, and some psychophysical results, such as those providing evidence for non-linearities in the combination of cone signals, may guide future physiological experiments, particularly now that it is possible to record simultaneously from populations of cells.
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Article Information
Color opponency: tutorial
Steven K. Shevell and Paul R. Martin
J. Opt. Soc. Am. A 34(7) 1099-1108 (2017) View: Abstract | HTML | PDF