The P300 amplitude of the event-related brain potential indicates changes within a frame-of-reference.

The starting point of this study was the fact that investigations in the frame-of-reference research were mostly performed on the behavioural level. The present study aimed at studying behaviour of P300 amplitude of the event-related brain potential in a frame-of-reference investigation. Ten healthy volunteers participated in the investigation. Test material consisted of horizontal bars of different lengths presented successively on a screen. Each bar (serial stimulus) was preceded by a prestimulus (anchor) of constant length. Each serial stimulus was to be evaluated according to a 9 step rating scale. There were no significant differences in the overt length judgements of the serial stimuli depending on the 3 different anchor lengths. However, the mean P300 amplitude increased with growing dissimilarity between the length of the anchor and serial stimulus length. Thus, it is assumed that the adaptation level on the internal dimension of stimulus length, which was assumed to be influenced by the anchor stimuli, led to the different behaviour of P300 amplitude.