The effects of post‐saccadic oscillations on visual processing time

Abstract

Aims/Purpose: Saccadic eye movements enable us to search for a target of interest in a crowded scene, or in the case of goal‐directed saccades, to bring the peripheral target to the fovea. Visual information is processed quickly at the end of each saccade, yet precise measurements of the times involved remain controversial. This research investigates the time needed to process visual information at the end of each saccade.Methods: A new psychophysical test makes it possible to measure eye movement response latencies and visual processing times. When the test is used in conjunction with an eye tracker, each component that makes up the ‘integrated saccade latency’ (ISL) time, from the onset of the peripheral stimulus to the correct interpretation of the information carried by the stimulus, can be measured and the discrete components delineated. We measured ISL times in six subjects in response to Landolt ring optotypes of varying contrast presented peripherally at an eccentricity of 8° and also at the point of regard (0°).Results: We show that the time required to process and encode the stimulus attribute of interest at the end of a saccade is longer than that needed to carry out the same task in the absence of an eye movement. Depending on the stimulus contrast, these time durations ranged between 101–120 ms (15%) and 34–48 ms (75%) when eye movements were involved and 57–35 (15%) and less than 25 ms (75%) in the absence of eye movements.Conclusions: The extended visual processing times measured when saccades are involved may be the result of transient loss of spatial resolution caused by eyeball instability during post‐saccadic oscillations. These results explain why stimuli of high luminance contrast yield best performance in visual tasks when eye movements are involved.Acknowledgements: We acknowledge the UK Civil Aviation Authority for their support.