INTERACTION OF EXTRARETINAL EYE POSITION SIGNALS IN A DOUBLE-STEP SACCADE TASK - PSYCHOPHYSICAL ESTIMATION

The time course of extraretinal eye position signals (EEPSs) for visua lly guided saccades made successively with a short intersaccadic inter val was estimated on the basis of perceptual errors in localizing a vi sual target flashed between the two saccades. The EEPSs for the first and the second saccades were shown to interact in a specific way when the intersaccadic interval was short. The pattern of interaction depen ded on the direction of the second saccade. It is suggested that when the second saccade was made in the opposite direction to the first sac cade, the EEPS for the first saccade was interrupted before its comple tion in preparation for the onset of the second saccade. When the two saccades were made in the same direction, the EEPS for the first sacca de developed more quickly than in a single-saccade condition. The resu lts are discussed in relation to the findings of recent neurophysiolog ical studies.