century and later mapped out in clinical studies by Jameson and Hurvich ( De Valois, Cottaris, Elfar, Mahon, & Wilson, 2000 ;Jameson & Hurvich, 1955 ;Shevell & Martin, 2017 ). Best depicted in the Derrington-Krauskopf-Lennie (DKL) stimulus space (Figure 1 ), cone-opponency predicts that neurons tuned to either the L-Mo r S-(L+M) pathway will not respond to light whose wavelengths isolate the other ( Derrington, Krauskopf, & Lennie, 1984 ). It is tempting to equate these null responses to the four unique hues of color-opponent theory, in which unique blue, for example, is observed when the “redness ”and“greenness ”of a per-ceived color exactly cancel. But the wavelengths of the unique hues specified by perceptualstudies ( Jameson & Hurvich, 1955 ) only roughly match the wavelengths isolating either cone-opponent pathway ( Wool et al., 2015 ;Wuerger, Atkinson, & Cropper, 2005 ;Xiao, 2014 ), and, more fundamentally, we do not yet understand the mechanisms behind the processing that theanalogy implies ( Mollon & Jordan, 1997 ;Stoughton & Conway, 2008 ;Valberg, 2001 ). That is, how do we get from the single neurons 'chromatic responses to our perception of color? The necessary processing has often been attributed to higher-level brain function ( De Valois & De Valois, 1993 ;Lennie, Krauskopf, & Sclar, 1990 ;M. Li, Liu, Juusola, & Tang, 2014 ; Mehrani, Mouraviev, & Tsotsos, 2020 ;Zaidi & Conway, 2019 ) or yet unidentified higher order mechanisms ( Valberg, 2001 ;Wuerger et al., 2005 ). A central question of color vision research is whether these mechanisms rely on paralle l or modular processing to encode stimulus chromaticity ( Conway, 2009 ;Garg, Li, Rashid, & Callaway, 2019 ;Liu et al., 2020 ;Nauhaus, Nielsen, Disney, & Callaway, 2012 ;Schluppeck & Engel, 2002 ;Shapley & Hawken, 2011 ). If signaling about chromaticity is transmitted w ith information about other visual features, such as brightness, orientation, and spatial frequency, how do these features get teased apart? If not, where is the purported color center of the brain ( Conway, Moeller, & Tsao, 2007 ; Gegenfurtner, 2003 )? Several authors have addressed these questions through combinatorial models that param-eterize the weights of the L, M, and S cones contributing to successive stages of processing(De Valois & De Valois, 1993 ;Gegenfurtner & Ennis, 2015 ;Judd, 1949 ;Mehrani et al., 2020 ; Stockman & Brainard, 2010 ). Though differing in their assumptions of modularity, the theories share a mechanistic framework for the transitio n of single-cell receptive field properties Figure 1. The DKL space maps chromatic stimuli onto a circle with two “cardinal ”axes represent-ing the L-Ma n d S-(L+M) pathways. The excitatory or inhi bitory effect of a stimulus on cone-opponent cells tuned to either pathway can be thought of as a projection of its location in DKLspace onto the relevant axis. Stimuli isolating the two pathways correspond roughly to wavelengthsassociated with the red, green, blue, and yellow unique hues of color-opponent theory, leading tothe common, but mistaken, conflation of chromatic stimulus and color perception. Stimulus space: A geometrical construct in whichchromatic stimuli are represented bythe relative cone responses they yield. Color-opponent theory: Theory of color appearance thatpostulates that the four unique hues — red, green, blue, and yellow —are perceived antagonistically. That is,there is no such thing as a reddishgreen or a bluish yellow. Cone-opponency: Receptive field property of neuronsin the early visual pathway, by whichchromatic stimuli are processedthrough the comparison of therelative L, M, and S cone responses. Network Neuroscience 680Pattern forming mechanisms of color vision Downloaded from http://direct. mit. edu/netn/article-pdf/7/2/679/2118501/netn_a_00294. pdf by guest on 09 August 2024 