Cortical evoked potentials as indicators of auditory-visual cross-modal association in young adults

Auditory evoked potentials (AEPs) were studied from scalp locations Cz and Oz on 37 adults aged 20-22 years during sensori-sensorial association of a weak sound (S) and a strong flash of light (L). After sound alone repetition (habituation), S-L association modified AEP: first, it caused a generalized orienting response expressed as increasing of Cz and Oz amplitude AEPs. Then, this pattern gave way to an activation limited to the Oz lead: the increase of amplitude was then concomitant with shortened latencies when compared to sound-alone-habituated responses. Inter-individual differences were observed since these occipital modifications were recorded only on 26 subjects. The other 11 subjects did not exhibit any occipital modifications following S-L association. For them, the main modification was a strong decrease of Cz AEP induced by S-L association. These two groups also differed in their capacity to ignore irrelevant stimuli which is higher in the first group (AEP amplitude habituation with sound-alone repetition) than in the second one (no AEP habituation).