A behavioral and electrophysiological study of the comparison of size-discrepant shapes.

An experiment was performed to find an electrophysiological correlate of the way objects of different sizes are perceived as identically shaped. The subjects were presented with pairs of geometrical figures and were instructed to decide whether the two polygons of a pair were identical in shape regardless of size. In addition to event-related potentials (ERPs), reaction times and error rates were recorded. Reaction times increased approximately linearly with increasing size ratios. The subtraction between the ERPs of 'test' and 'control' conditions showed two main activities: a positivity localized on the occipitotemporal scalp areas in the 200-450 ms range, and a negativity localized on the posterior scalp areas in the 500-750 ms range. These different results were discussed with respect to size ratio.