Abstract: PURPOSE: Our visual world is rich in color information. The perception of color is commonly described in reference to three color dimensions: hue, saturation or chroma and value or lightness. With hue referring to the peak of the color spectrum, saturation (or chroma) referring to the spread of the color spectrum, and value or lightness referring to the overall intensity of the color spectrum. Previous psychophysical studies on humans have suggested that red (hue) stimuli and those with high saturation have a strong effect on arousal. Electrophysiological studies conducted on both human and non-human primate visual cortices have demonstrated a red dominance in neural responses compared to other colors, but have done so without considering saturation levels. A more recent study looking in primate V1 found a significant effect of the background on responses. Since the gamma (γ) band is often associated with cognitive function such as attention and stimulus awareness in V4, we hypothesized that it might be the saturation of a colored stimulus that drives the power of gamma band activity in color perception rather than the hue of a stimulus.
METHODS: We used linear depth probes to record local field potentials (LFP) and multi-unit activity (MUA) in V4, while presenting isoluminant color stimuli both within responsive fields (RF) and as full field stimuli. We calculated the power spectrum density (PSD) of the LFP signals to six isoluminant hues (red, orange, green, cyan, blue, purple) with varying saturation levels (color distance along the saturation axe of each hue is 0.02 DE in CIE Lu’v’ color space, three to nine levels depending on the gamut).
RESULTS: We found that color patches of all hues induced significantly higher power in both the γ-low (30-50Hz) and γ-high (50-100Hz) bands at higher saturation levels. Furthermore, when comparing different chromatic stimuli at the same saturation level, we observed no specific hue that exhibited a greater γ-band power response.
CONCLUSIONS: High saturation color patches of all hues representing the chromaticity drive a significantly enhanced γ-band response. This increase in γ-band response does NOT depend on the hue of the colored stimulus but rather is dependent on the saturation of the color.

Key words: Color perception, Neural oscillations, Saturation