Abstract
Studies on the interaction of visual attention and saccadic eye movements argue in favor of an obligatory coupling of saccade goal and focus of visual attention (e.g., Deubel & Schneider, 1996). In a similar fashion, Khurana and Kowler (1987) proposed a coupling of visual attention and the target of smooth pursuit eye movements. The current study investigated whether exogenous and endogenous attention shifts (Posner, 1980) are possible during smooth pursuit eye movements. Subjects foveated a stationary fixation cross (fixation conditions) or a moving cross (smooth pursuit conditions). An exogenous or endogenous cue indicated the location of the upcoming discrimination target (symbols “E” and mirror “E”) with a probability of 80%. The difference in discrimination performance between valid and invalid cue conditions was taken as a measure of visual attention. The discrimination target was either stationary or moved at the same velocity as the pursuit target. Stationary discrimination targets in space were stationary on the retina with eye fixation, but not with smooth pursuit and vice versa for moving targets. Effects of exogenous and endogenous cueing were about the same size for fixation and pursuit conditions. Further, it did not matter whether the discrimination target was stationary or moving. However, retinal motion of the discrimination target influenced smooth pursuit gain. Pursuit gain decreased when the discrimination target was stationary in space and moved across the retina, but not when it moved with the pursuit target and was approximately stationary on the retina. The reduction of pursuit gain with the onset of the discrimination target was present for exogenous and endogenous cues, but it occurred earlier in the exogenous than in the endogenous condition (∼150 ms vs. ∼350 ms after discrimination target onset). The results suggest that the coupling of visual attention to the target of a smooth pursuit eye movement is not as strong as has been proposed.
Supported by the Deutsche Forschungsgemeinschaft (DFG KE 825/3-1 and 825/4-1,2).