Interaction of extraretinal eye position signals in a double-step saccade task: psychophysical estimation.

The time course of extraretinal eye position signals (EEPSs) for visually guided saccades made successively with a short intersaccadic interval was estimated on the basis of perceptual errors in localizing a visual 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 depended on the direction of the second saccade. It is suggested that when the second saccade was made in the opposite direction to the first saccade, the EEPS for the first saccade was interrupted before its completion in preparation for the onset of the second saccade. When the two saccades were made in the same direction, the EEPS for the first saccade developed more quickly than in a single-saccade condition. The results are discussed in relation to the findings of recent neurophysiological studies.