Effect of inter-stimulus interval (ISI) on the average amplitude of the auditory and somatosensory N1 and P2 waves.

<p><i>y</i> axis: amplitude (µV); <i>x</i> axis: ISI category. Both in the auditory and in the somatosensory modality the ISI had an opposite effect on the auditory and somatosensory N1 and P2: at shorter ISIs, the N1 displayed significantly larger amplitudes while the P2 displayed significantly smaller amplitudes. Error bars represent the variance across subjects (standard error of the mean). Asterisks highlight ISI categories in which the average peak amplitude was significantly different from the peak amplitude at the category ‘100–200 ms’ (* p<0.05; ** p<0.01).