Effects of Luminance Contrast on the Color Selectivity of Neurons in the Macaque Area V4 and Inferior Temporal Cortex

Abstract

Appearance of a color stimulus is significantly affected by the contrast between its luminance and the luminance of the background. In the present study, we used stimuli evenly distributed on the CIE-xy chromaticity diagram to examine how luminance contrast affects neural representation of color in V4 and the anterior inferior temporal (AITC) and posterior inferior temporal (PITC) color areas (Banno et al., 2011). The activities of single neurons were recorded from monkeys performing a visual fixation task, and the effects of luminance contrast on the color selectivity of individual neurons and their population responses were systematically examined by comparing responses to color stimuli that were brighter or darker than the background. We found that the effects of luminance contrast differed considerably across V4 and the PITC and AITC. In both V4 and the PITC, the effects of luminance contrast on the population responses of color-selective neurons depended on color. In V4, the size of the effect was largest for blue and cyan, whereas in the PITC, the effect gradually increased as the saturation of the color stimulus was reduced, and was especially large with neutral colors (white, gray, black). The pattern observed in the PITC resembles the effect of luminance contrast on color appearance, suggesting PITC neurons are closely involved in the formation of the perceived appearance of color. By contrast, the color selectivities of AITC neurons were little affected by luminance contrast, indicating that hue and saturation of color stimuli are represented independently of luminance contrast in the AITC.

Neurons in the inferior temporal cortex of macaque monkeys are sensitive to multiple surface features from natural objects

“…Thus, selective responses of IT neurons to surface images of natural objects were constructed not simply by inheriting the response properties from the preceding areas but by gradual and hierarchical processing in the ventral pathway. Some changes in response properties along the ventral pathway have been reported (Tanaka et al 1991; Kobatake and Tanaka 1994; Denys et al 2004; Rust and DiCarlo 2012; Goda et al 2014; Namima et al 2014), and the present results revealed that information derived from the surfaces of natural objects is also processed in a hierarchical manner.…”

Representation of Perceptual Color Space in Macaque Posterior Inferior Temporal Cortex (the V4 Complex)

“…We considered the responses of each cell to the low-luminance and high-luminance stimuli in the hue-matched subset, to match the high- and low-luminance stimulus sets used in the analysis by Namima et al (2014). For each cell, for each luminance set, we calculated a selectivity index = 1 − (minimum response)/(maximum response), where responses are the raw mean firing rates of the cell in response to the luminance set.…”

Color tuning of neurons in face patches of macaque inferior temporal cortex

“…In doing so, we found that 25% of face-selective neurons in both ML and AL had significant color-tuning responses, and the whole population was significantly biased towards L>M colors (Figure 6), supporting the hypothesis. The color selectivity of face cells was weaker than the selectivity observed in color-biased domains of posterior inferior temporal cortex (Bohon et al, 2016) and anterior temporal cortex (Komatsu et al, 1992;Namima et al, 2014). As those other studies show, neurons located within color-biased domains identified independently by fMRI typically have narrow (i.e.…”