Comparison of the color selectivity of macaque V4 neurons in different color spaces

Abstract

Chromatic selectivity has been studied extensively in various visual areas at different stages of visual processing in the macaque brain. In these studies, color stimuli defined in the Derrington-Krauskopf-Lennie (DKL) color space with a limited range of cone contrast were typically used in early stages, whereas those defined in the Commission Internationale de l'Eclairage (CIE) color space, based on human psychophysical measurements across the gamut of the display, were often used in higher visual areas. To understand how the color information is processed along the visual pathway, it is necessary to compare color selectivity obtained in different areas on a common color space. In the present study, we tested whether the neural color selectivity obtained in DKL space can be predicted from responses obtained in CIE space and whether stimuli with limited cone contrast are sufficient to characterize neural color selectivity. We found that for most V4 neurons, there was a strong correlation between responses measured using the two chromatic coordinate systems, and the color selectivities obtained with the two stimulus sets were comparable. However, for some neurons preferring high- or low-saturation colors, stimuli defined in DKL color space did not adequately capture the neural color selectivity. This is mainly due to the use of stimuli within a limited range of cone contrast. We conclude that regardless of the choice of color space, the sampling of colors across the entire gamut is important to characterize neural color selectivity fully or to compare color selectivities in different areas so as to understand color representation in the visual system.

Integration of color, orientation, and size functional domains in the ventral pathway

“…As mentioned in Sec. 1, limited sample sizes are also problematic, especially when, as we have demonstrated, the distribution of color properties is not uniform 41 . This issue becomes worse with the possibility that the specific patterns of functional organization might vary between individual animals.…”

“…The origin of this space represents half-maximal activation along the three axes and is called the adaptation or equal-energy point. Recent electrophysiological studies have verified that the color selectivity in the DKL and CIE spaces are highly correlated for most V4 neurons 41 …”

Theory of neural coding predicts an upper bound on estimates of memory variability.

“…These studies all tested recall of colors chosen from a color wheel (defined as a circle in CIE LAB color space). The dashed black line in Figure 5 (top) corresponds to the average of the maximum standard deviation values obtained in each study (although there is neurophysiological evidence for color tuning in visual cortex, e.g., Conway & Tsao, 2009 ; Sanada, Namima, & Komatsu, 2016 , the limited availability of single-neuron data for color tuning widths, and difficulty mapping between color spaces, means we do not have a prediction for this bound). The results suggest an upper limit at approximately 22° [360°].…”

“…5(top) corresponds to the average of the maximum s.d. values obtained in each study (although there is neurophysiological evidence for color tuning in visual cortex e.g.,Sanada, Namima, & Komatsu, 2016;Conway & Tsao, 2009, the limited availability of single-neuron data for color tuning widths, and difficulty mapping between color spaces, means we do not have a prediction for this bound). The results suggest an upper limit at approximately 22 • [360 • ].…”

A tour of contemporary color vision research

“…Although we can measure neural responses to modulations in cone activity, we do not know what stimuli to use to relate the neural activity to computational mechanisms (Sanada, Namima, & Komatsu, 2016). There is even uncertainty at Marr-Level 1, regarding the computational goal of color: why do we have color vision at all?…”