Abstract
Goal: Microsaccades (MS, fixational eye movements < 1°) enhance perception by preventing retinal adaptation and increase resolution, but for briefly presented stimuli, they can blur the image and impair performance. Here, we investigated the timecourse of MS frequency during a visual discrimination task with exogenous (involuntary) attention cueing; specifically, how MS rates would vary across the trial sequence according to task events in both the attention and neutral conditions. Methods: Observers performed a 2AFC orientation discrimination task, following a neutral or an attention cue. Four Gabor patches appeared simultaneously at 4 isoeccentric locations (6.4° eccentricity) and observers discriminated the orientation of the target, indicated by a response cue. Task difficulty was equated by adjusting stimulus contrast. Fixation was monitored: right eye position was monitored with an Eyelink 1000 eye-tracker; if observers made a >1° saccade away from central fixation the trial was cancelled and repeated. A standard velocity-based detection algorithm was used to detect microsaccades (Engbert & Kliegl, 2003). Results: Covert attention increased accuracy and shortened reaction time. MS kinematics followed the main sequence, the higher the peak velocity the greater the amplitude. MS rates systematically varied across the trial; they were highest during the intertrial period, monotonically decreased from fixation through the (neutral or 100% valid attention) cue until stimulus onset, and rebounded in the response interval. The MS main sequence, rate and temporal dynamics were similar in both the attention and neutral conditions. In both cases, saccades were very scarce between cue onset and stimulus offset. Conclusions: During a temporally predictable visual discrimination task, in both neutral and attention conditions, observers systematically exhibited MS suppression in anticipation of an upcoming stimulus, likely because greater fixation stability benefits perception of brief stimuli. These results provide further support for the tightly linked relation between oculo-motor behavior and perception across time.
Acknowledgement: NIH NEI R01-EY027401