Figure 2. Auditory evoked potentials at the Cz location in the presence or absence of light.

EEG activity evoked at the Cz location (referred to both mastoids) by an auditory stimuli alone (green), by blue light exposure alone (blue), or light and sound simultaneously (bimodal, red). In order to isolate the modulatory effect of light on auditory evoked potentials, we compared the bimodal trials to the mathematical sum of both the auditory and light alone trials (black line). Horizontal bars correspond to results of the permutation statistics between the bimodal trials and sum of both trials alone (probability values as on the lateral vertical color bar). The difference is significant whenever the color is not dark blue. In the 500ms condition (left panels), each auditory stimulus was preceded by 350ms of light and terminated simultaneously with light extinction, while in the 2s condition (right panels), each auditory stimulus was preceded by 1850ms of light and terminated simultaneously with light extinction. In the 2s condition, all three participants showed significant differences between the bimodal trials and the sum of both trials alone, while in the 500ms condition only participant 2 presented marginal (but significant) differences (see text for details).

See Supplemental Figure S2 for detailed behavioral results.