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Abstract Expectation of a future stimulus increases the preparedness to act once it actually appears and results in reduced latency of the appropriate motor response. Real world events are uncertain both spatially and/or temporally but this uncertainty could itself be expected. In the presence of both expected spatial and temporal uncertainty, which one should be prioritized by the motor system could depend on the context. Therefore, we investigated the relative weight of expected spatial and temporal uncertainty during the preparation of a saccadic eye movement. A reaction time task was used with a variable foreperiod between a warning and an imperative visual stimuli. Expected temporal and/or spatial uncertainty associated with the stimulus was cued. We found that before imperative stimulus onset, pupil dilation increased with expected temporal uncertainty but was unaltered by spatial uncertainty. After imperative stimulus onset, both types of expected uncertainty affected saccade latency. Maximum eye velocity was modulated by expected spatial uncertainty only. In conclusion, expected temporal and spatial uncertainty do not have the same impact on preparation and execution of a motor response. There could be a prioritization of the relevant information as a function of the evolving expected uncertainty context during the task.

Abstract Expected surprise, defined as the anticipation of uncertainty associated with the occurrence of a future event, plays a major role in gaze shifting and spatial attention. In the present study, we analyzed its impact on oculomotor behavior. We hypothesized that the occurrence of anticipatory saccades could decrease with increasing expected surprise and that its influence on visually-guided responses could be different given the presence of sensory information and perhaps competitive attentional effects. This hypothesis was tested in humans using a saccadic reaction time task in which a cue indicated the future stimulus position. In the ‘no expected surprise’ condition, the visual target could appear only at one previously cued location. In other conditions, more likely future positions were cued with increasing expected surprise. Anticipation was more frequent and pupil size was larger in the ‘no expected surprise’ condition compared with all other conditions, probably due to increased arousal. The latency of visually-guided saccades increased linearly with the logarithm of surprise (following Hick’s law) but their maximum velocity repeated the arousal-related pattern. Therefore, expected surprise affects anticipatory and visually-guided responses differently. Moreover, these observations suggest a causal chain linking surprise, attention and saccades that could be disrupted in attentional or impulse control disorders.