Abstract
The previous research reporting on the influence of stimulus contrast on eye movements showed decreasing latency in saccadic onset with increasing contrast of a visual stimulus, however considering only horizontally-oriented saccades. The current study targeted the latency of reflexive saccades to a Gabor patch (GP) presented at horizontal and vertical locations in three eccentricities (2°, 6.5°, 11°) to 12 participants. The selected spatial frequencies (SF) were 0.8, 1.4, 2.2, 4.3 cpd (cycles per degree), and the contrast ranged from 0.03 - 66%. The experimental procedure considered a GP appearing for maximum time of 0.5s (or disappeared as the gaze position exceeded the fixation area - 1°) randomly either above, below, left or right relatively to a central fixation mark. The monocular gaze position was captured by an infra-red eye tracker. The GP had a constant size of 1.4°, while its contrast was managed by the QUEST+ adaptive psychometric procedure, upon an outcome, whether a respective saccade towards the stimulus was detected or not. The QUEST+ was applied for each of the four tested locations individually. First the 95th percentile of the timing was sought for each location and SF individually over the three eccentricities, while applied Friedman’s test showed no significant effects of the SF and location χ2(15) = 2.1; p=0.52, χ2(15) = 2.1; p = 0.55 and χ2(15) = 1.2; p = 0.75 for each of them. However, we found exponentially decreasing latency with increasing contrast in both horizontal and vertical directions from approximately 0.48s to 0.30s (R2all > 0.74). Furthermore, the comparable trend was found for other tested percentiles as well (25%, 50%, 75%). In conclusion, we propose the possibility to adjust the presentation time of a visual stimulus accordingly to its parameters for better time performance in visual field-specific visual performance testing using reflexive saccades.