Abstract
When saccading towards a grating that disappears during the eye movement, observers report a short-lived sensation of this target at the saccade goal (Wolf et al, 1980). Our study further characterizes this short-lived percept, examining how its localization can be influenced by a highly dissimilar post-saccadic stimulus. Participants made saccades towards a small, black square. During the eye movement this target was replaced with a white disk that was eight (experiment 1) or ten (experiment 2) times larger. The center of the disk could be situated up to 6° on the right or left of the pre-saccadic target, where the target location fell well outside the disk. Subjects indicated whether they perceived the square inside or outside the post-saccadic disk. In a control condition both stimuli appeared with the same spatio-temporal characteristics but subjects were required to maintain fixation. Overall, participants perceived the stimuli at overlapping locations more often in the saccade than in the fixation condition. Surprisingly, the square was perceived inside the disk even when it was as much as 6° outside. In the fixation condition, the responses were more veridical. This erroneous perception of the target inside the disk can be considered as an instance of trans-saccadic fusion. This is in contrast with previous experiments that failed to observe this phenomenon (eg. O’Regan & Levy-Schoen, 1983) probably because they used complex stimuli. Moreover, this interaction between pre- and post-saccadic stimuli may be related to the classic saccadic suppression of displacement (SSD, Bridgeman et al, 1975). However, unlike the normal SSD case where the similar pre- and post-saccadic targets are seen as one replacing the other, the two targets here differ dramatically and both can be seen. This suggests that the short-lived sensation of the pre-saccadic target might be involved in SSD.
Meeting abstract presented at VSS 2015