Abstract
Saccadic eye-movements enable us to rapidly direct our high-resolution fovea onto relevant parts of the visual world. However, while we can intentionally select a location as the target for a saccade, the wider visual scene also influences the executed movement. In the presence of multiple objects, eye-movements may be "captured" to the location of a distractor object, or biased towards the intermediate position between objects (the "global effect"). Here we examined how the relative strengths of the global effect and visual object capture changed as a function of saccade latency and the separation between items. Importantly, while many previous studies have failed to give explicit instructions to observers, we instructed our participants either to saccade to a specified target object or to the midpoint between the two stimuli. This allowed us to examine how the explicit movement goal influenced the tendency for saccades to terminate at target, distractor, or intermediate locations. Using a probabilistic mixture model, we found evidence that both visual object capture and the global effect co-occurred at short latencies and declined as latency increased. As separation between the objects increased, capture came to dominate the landing positions of fast saccades, with reduced global effect. Critically, instructions substantially altered the distribution of saccade landing points, even at the shortest latencies. By comparing the model fits across the two tasks we could separately estimate the proportion of saccades unwantedly captured by either global or stimulus locations. This allowed us to dissociate the two different types of automatic capture from the influence of goal-directed processes. Overall, these results suggest that previous studies may have overestimated the role of automatic processes in determining saccade endpoints by confounding the influences of stimulus capture, global effect, and goal-directed processes on saccade landing distributions.
Meeting abstract presented at VSS 2017