Oculomotor capture by transient events: a comparison of abrupt onsets, offsets, motion, and flicker

Attentional and oculomotor capture by some salient visual event gives insight into what types of dynamic signals the human orienting system is sensitive to. We examined the sensitivity of the saccadic eye movement system to 4 types of dynamic, but task-irrelevant, visual events: abrupt onset, abrupt offset, motion onset and flicker onset. We varied (1) the primary task (contrast vs. motion discrimination) and (2) the amount of prior knowledge of the location of the dynamic event. Interference from the irrelevant events was quantified using a discrimination threshold metric. When the primary task involved contrast discrimination, all four events disrupted performance approximately equally, including the sudden disappearance of an old object. However, when motion was the task-relevant dimension, abrupt onsets and offsets did not disrupt performance at all, but motion onset had a strong effect. Providing more spatial certainty to observers decreased the amount of direct oculomotor capture but nevertheless impaired performance. We conclude that oculomotor capture is predominantly contingent upon the channel the observer monitors in order to perform the primary visual task.