Ambient luminance changes modulate oscillatory properties of the visual system

Abstract

We investigated the effects of ambient luminance changes on neural oscillation dynamics. Brain oscillations, particularly in the alpha range (~10 Hz), are important in determining our percepts. Crucially, ambient luminance changes drastically modulate neural processing. However, the influence of luminance over brain rhythmicity is still not clear. Here, we investigated on 16 subjects the effect of ambient luminance on EEG alpha during spontaneous brain activity at rest (experiment 1) and on 12 subjects during the measurement of the EEG "impulse-response functions" (IRF, or echo function) or the evoked alpha (experiment 2). Results show that during resting, alpha amplitude increased at low luminance (p < 0.001), while luminance changes did not affect alpha frequency. In the second experiment, we found that under low-luminance viewing the IRF amplitude was lower (p < 0.001), and its frequency was slightly faster (p < 0.05). Crucially, the evoked alpha activity behaved differently from the echo function: while evoked alpha and echoes showed a similar amplitude modulation, luminance changes influenced the echo peak frequency but not that of evoked EEG alpha. Finally, we explored the behavioral effects of these modulations in a monocular critical flicker frequency task for 13 subjects (CFF, experiment 3), reporting a facilitatory effect of contralateral dark ambient luminance over temporal thresholds (p < 0.001). Globally, we found that ambient luminance changes affect neural oscillatory dynamics and greatly impact on the occipital alpha expression. These results suggest that the visual system adapts its oscillatory dynamics to fit the environmental light conditions.

Meeting abstract presented at VSS 2017