Gazing into spatiotemporal 'known unknowns': the influence of uncertainty on pupil size and saccadic eye movements.

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.