Spatiotopic priming in visual search

Visual search is faster if the target appears in the same location on consecutive trials than if it appears in different locations. In this study, we investigated how this location priming is affected by eye movements. Subjects were asked to report the orientation of a T-shaped target embedded among L-shaped distracters in a 2 x 4 array. Trials were organized in pairs and subjects had to perform the task while fixating at a red dot. In the first trial of each pair the fixation point was placed on the left side of the screen and on the second trial it was moved to the right side of the screen. Reaction time of the subjects was analyzed to determine if the location priming in visual search follows a retinotopic reference frame or a spatiotopic one. Results showed a non-specific effect of eye movement direction on the reaction time profile: regardless of the location of the target in the first trial, reaction times significantly decreased along the direction of the saccade (p<0.05). To factor out this general effect each location was compared to the vertically aligned control (previously non-target) location having the same horizontal position. Subjects were significantly faster (p<0.05) in finding a target when it was presented in the same spatiotopic location than in the control location with similar eccentricity. There was no significant difference between the reaction time of the subjects for the retinotopic location compared to control (p=0.1). These results suggest that the visual attention maintains a spatiotopic representation for the attended objectʼs location across eye movements.