Effects of inter-stimulus interval on perceived locations of successively flashed perisaccadic stimuli.

We investigated the perceived locations of two stimuli flashed successively near the time of saccade execution in a dark room. The inter-stimulus interval (ISI) between the flashes ranged from 80 to 240 ms. The results show that when the ISI was 120 ms or shorter, perceived locations of the flashes interacted with each other so that the perceived distance between them was equal to the distance between these flashes on the retina. When the ISI was 240 ms, this interaction was weak. These results suggest two hypotheses. Firstly, the relation of retinal locations of flashes is a strong cue for perceiving the flash locations when the ISI is shorter than about 120 ms.Secondly, the process of perceiving or memorizing a flash location requires some time. Therefore, the perceived location of the succeeding flash affects that of the preceding flash when the ISI as shorter than about 120 ms.