A detailed an alysis was mad e of th e response characteristic s of single cells in th e lat eral geniculate nucleus of the macaqu e monkey. Th e goa l was to understand how the se cells cont rib ute to th e proc essing of visual information. Dat a were an alyzed from a representative sa mple of 147 cells, whose respons es to eq ua l-energy spectra (prese nte d as diffuse flash es of monocbromatic light) were record ed at three radiance levels. On the basis of th eir responses, th e cells were di vided int o two ge nera l classes : (a) spect ra lly nonopponent cells which respond to all wavelengths with either an increase or decr ease in tiring rat e, (h) spec t ra lly opponent cells (ab out two-th irds of th e sa mple) which respond with a n increase in firing ra te to so me parts of the spect rum an d a dec rease to ot her par ts. Four typ es of op ponent cells were found : (i) red excita tory and gree n inh ibit ory (+ R-G), (ii) gre en excitatory an d red inhibitory (+G-R), (iii) ye llow excita tory a nd blu e inhibitory (+ Y-11), (iv) blu e excita tory and yellow inhibito ry (+ ll-V). Co mpa risons with psychoph ysical dat a ind icat ed that nonopp oncnt cells transmit brightness inform a tion ; opponent cells , however, carry inf ormation ab out color, th e hu e of a light being det ermined by th e relat ive responses of the four types. The sa tura tion of spec t ra l light s appears to be related to th e differences in respo nses of opponent and nonopp onent cells.

Hue and saturation scaling were used to measure the appearance of spectral lights as a function of stimulus size for nine loci across the horizontal retinal meridian. At a given locus, each hue (R, Y, G, and B) grew as a function of stimulus size up to some asymptotic value. The parameter values of Michaelis-Menten growth functions fitted to the hue data were used to derive the sizes of the so-called perceptive fields of the hue mechanisms. The fields for all mechanisms increased with eccentricity, and this increase was greater on the temporal than on the nasal retina. By increasing stimulus size it was possible to achieve fovealike color vision to eccentricities of 20 deg. However, even the largest stimuli failed to produce fully saturated hues at 40 deg. The retinal size scales of the four hue mechanisms were not the same; those for R and B were similar, and these mechanisms had the smallest perceptive fields everywhere. The perceptive fields of the hue mechanisms at all loci were larger than anatomical estimates of the sizes of retinal receptive fields.

Hue and saturation of spectral lights were measured (direct scaling) in the fovea and at 45 degrees in the periphery; all lights were of equal photopic retinal illuminance (1200 trolands). At each retinal location both large and small targets were used. As shown by previous studies, small peripheral targets appear desaturated and of uncertain hue, except long wavelengths which appear red. However, if target size is increased, saturation increases and a full range of hues is seen; the hue functions for large peripheral targets are comparable to foveal ones for very small targets. From a modified form of color matching, it was concluded that the color deficiency in the periphery is more tritanlike than deutanlike; this is strengthened by the observation, that, for small peripheral targets, hues are generally apportioned between two hue categories and the change from one to the other is at about 580 nm.