Using evidence accumulation modelling to quantify the relative contributions of spatial attention and saccade preparation in perceptual tasks

A typical way to investigate the relationship between spatial attention and the programming of an eye movement is with a dual-task. Here, participants simultaneously make an eye movement in one direction and discriminate a target at the same or a different location. Results of these tasks consistently find that performance is best at the goal of an upcoming eye movement. It is less clear, however, the extent to which spatial attention can shift independently of the programmed saccade. In this paper, for the first time, we use an evidence accumulation model to examine this longstanding question. Specifically, across two studies, we quantify the relative contributions of spatial attention and saccade preparation in a perceptual dual-task. Our results establish that there is a unique and measurable effect of spatial attention away from the saccade goal, and, interestingly, that the relative magnitude of this effect varies by cue type. There is a larger influence of spatial attention when a peripheral rather than a central cue is employed. We suggest that these results support the claim that each form of orienting is mediated by a distinct underlying mechanism.