Cues to the relative spatial locations of visual targets presented in the dark

Abstract

Information about eye position is used to make accurate saccades to stimuli in the environment. This study addressed the question of whether eye position is used in making perceptual judgments of the relative spatial locations of two successively presented visual targets. Subjects sat in a completely darkened room with their heads immobilized in a chin rest. A fixation light appeared straight ahead of the subject and was extinguished for a period of time between 1–30 seconds (dark interval duration). Subjects were instructed to keep their eyes directed at the remembered fixation location throughout the dark interval. At the end of the dark interval, a target light was presented for 1 ms in either the same physical or retinal location as the fixation point. Subjects responded whether the target light was in the same or different location as the fixation location. Eye position was monitored throughout the trial and confirmed that the eyes strayed away from the fixation location during the dark interval. If subjects are able to keep track of their eye position, then they will answer “same” only when the target light falls on the same physical location as the fixation light. Results indicate that as dark interval duration increased, subjects relied on retinal error information to make their response — they responded “same” when the target light fell on the same retinal location as the fixation light. This suggests that subjects are not able to monitor changes in eye position in the absence of visual cues.