Cone Opponency: An Efficient Way of Transmitting Chromatic Information

Tetrachromacy: the mysterious case of extra-ordinary color vision

“…In order to perceive colors, and to discriminate between them, the cone activations from different cone types must be compared. Two independent, post-receptoral channels have been identified for this task [21][22][23][24]. Of particular interest for tetrachromatic vision is the phylogenetically younger, 'red-green' opponent channel.…”

Magno-, Parvo-, and Koniocellular Pathways

“…The LGN layers of each of the three visual pathways have a specific cytoarchitectonic structure. The names of the pathways are derived from these structural characteristics [1,2]. Magnocellular (M) cells have relatively large bodies (lat.…”

“…The receptive fields of such K cells oppose the excitatory input from S cones with the inhibitory input from L and M cones (S-(L + M); bluish-yellowish dimension). K layers also receive inputs from several other cell types which oppose S-cone input to some combination of L and M cone input (+S À ML large bistratified, ÀS + ML large sparse, and two ÀS + ML giant sparse ganglion cells), but their role in color vision is still not fully understood [1,3]. The distinction between the processing of luminance signals (L + M) and the processing of two types of chromatic signals (L-M and S-(L + M)) by geniculate cells had led to their conceptualization as the three orthogonal visual mechanisms.…”

“…As noted in the historical overview, continuous attempts have been made to relate the pathways to the processing of different visual properties: motion processing, form processing, luminance and color processing, and so on. As evidence accumulated it became more and more clear that simple and direct associations between physiological responses and perceptual properties are difficult to establish [1,10,11]. In fact, M, P, and K pathways can only tentatively be treated as wholly separable when it comes to their function: for example, the M pathway contains cells that project information into dorsal cortical areas subserving motion processing, which fits Livingstone and Hubel's model, but it also contains cells that project information into ventral areas subserving object representation [6].…”

“…The view that such "multiplexing" through the L-M channel underlies achromatic vision is based on the fact that P cells are much more numerous than M cells and was initially strengthened by observations of poor spatial acuity of M cells, although recent data showed much smaller differences in M and P cell receptive field center sizes than originally found. In fact, there is an opposing view that strict subcortical segregation of luminance and L-M signals would be beneficial, since it would optimize signal transmission in a noisy, bandwidth-limited system such as primate vision [1].…”