Abstract
Previous studies have identified at least two components of chromatic adaptation: a rapid component within a time scale between tens of milliseconds to a few seconds, and a slow component with a half-life of about 10s-30s. The basis of the rapid adaptation probably lies in receptor adaptation at the retina. However, the neural substrate for the slow adaptation remains unclear, although previous psychophysical results hint at the early visual cortex. A promising approach to investigate adaptation effect in the visual cortex is to analyze steady-state visually evoked potentials (SSVEPs) induced by chromatic stimuli, which typically use long durations of stimulation. Here, we re-analyzed the data from two previous SSVEP studies (Chen, Valsecchi & Gegenfurtner, 2017a, 2017b). In these experiments (N = 49 observers in total), SSVEPs were induced by flickering color- or luminance-defined grating stimuli for 150 seconds in each trial. By analyzing SSVEPs with short-window frequency analysis (window size = 4 seconds), we found that chromatic SSVEP responses decreased with increasing stimulating duration and reached a lower asymptote within a minute of stimulation. In line with earlier studies, the luminance SSVEPs did not show any systematic adaptation. The time course of chromatic SSVEPs can be well described by an exponential decay function with a half-life of about 20 seconds, which is very close to previous psychophysical reports (Rinner & Gegenfurtner, 2000; Werner, Sharpe & Zrenner, 2000). This result suggests that slow-phase chromatic adaptation happens already in the early visual cortex. In addition, the current result also provides a guide for future color SSVEP studies in terms of either avoiding or exploiting the adaptation effect.