Inhibition of return in the oculomotor decision process: Dissociating visual target discrimination from saccade readiness delays.

Saccades toward previously cued or fixated locations typically have longer latencies than those toward novel locations, a phenomenon known as inhibition of return (IOR). Despite extensive debate on its potential function, it remains unclear what the role of IOR in the oculomotor decision process is. Here, we ask whether the effect on eye movement planning is best characterized as a delay in visual target discrimination or as a reduction in readiness to execute the movement (saccade readiness). To evaluate this question, we use target-distractor tasks with clear speed-accuracy trade-offs. Simultaneously cueing both the target and distractor (or neither) we find longer latencies at the cued locations. Despite this delay in latencies, accuracy improves in line with the speed–accuracy trade-off curve (Experiment 1). This suggests that while visual target discrimination can progress unimpeded, saccade readiness is reduced. Based on this reduction in readiness we predict that the more saccades rely on visual target discrimination, the less their destination will be affected by inducing IOR. Indeed, after cueing either the target or an onset distractor (Experiment 2), short-latency, stimulus-driven, saccades are strongly biased away from the cued location, while the destinations of longer latency goal-driven saccades are affected only minimally. The fact that primarily stimulus-driven saccades are affected by inducing IOR is interesting as it can explain why the spatial bias associated with IOR is not consistently found. (PsycInfo Database Record (c) 2020 APA, all rights reserved) Public Significance Statement—This study provides a novel insight into how the planning of upcoming eye movements is impacted by prior attentional shifts. It is a well-established fact that saccades (rapid eye movements) toward previously cued or fixated locations are delayed, a phenomenon known as inhibition of return. However, we find that despite the delay in the execution of saccades, visual discrimination of peripheral targets is unaffected by cueing. Further evaluation shows that it is the destination of eye movements that are considered stimulus-driven (those drawn toward salient locations) that are primarily affected. Together, this suggests that the role of inhibition of return in ocular movement planning is mostly limited to biasing observers away from previous salient events, and is not, what was generally thought, a general foraging facilitator in search. (PsycInfo Database Record (c) 2020 APA, all rights reserved)