Electrical Microstimulation in Macaque Early Visual Cortex Reveals Causal Links to Color Perception

Color perception serves crucial ecological functions in many species. While color coding (e.g., a hue map) has been found throughout the visual pathway, its causal link to perception remains elusive. Here, we trained macaques to perform a color identification task using psychophysical paradigms. In a two-alternative forced-choice (2-AFC) digital task, the animals discriminated between two opponent hues (red vs. green or yellow vs. blue). Microstimulation using a low current (≤50 μA) delivered to the early visual cortex (EVC) frequently biased the animals' perceptual choices toward the preferred hue of the stimulated neurons, indicating a causal influence of local neuronal activity on perceptual decisions. In an analog, eight-category "rainbow" task, microstimulation also induced significant but more variable perceptual shifts. Stronger currents, presumed to introduce more noise, impaired behavioral sensitivity in both tasks, indicating that local neuronal activity is causally necessary for color perception. Our findings provide direct evidence that precise manipulation of the labeled-line chromatic code in the EVC is crucial for producing subjective color perception.