Abstract
Saccades are fast eye movements that re-orient gaze direction. While in natural conditions saccades are usually self-paced, in the laboratory saccades are often triggered by appearing targets. The generation of these "voluntary" and "reactive" saccades have been shown to involve partially different cortical pathways. However, saccades of either type confront the visual system with a major challenge since they cause fast image motion on the retina. The visual system counteracts this situation by a neural process called saccadic suppression: During the eye movement the visual sensitivity is strongly decreased. This modulation of neural response properties in the visual pathway starts about 50 ms before the saccade. Thus, an extra-retinal signal, which is generated and projected already during saccade preparation, must be involved in the process of suppression. Since saccade generation differs in voluntary and reactive saccades, timing and nature of this extra-retinal signal and its impact on visual sensitivity might differ, too. In this study, we measured detection thresholds for luminance stimuli that were flashed during the execution of voluntary and reactive saccades and during fixation. Subjects reported if they perceived a probe bar, flashed with luminance values between 0 and 27.4 mcd/m^2 during saccades and 0 and 7.1 mcd/m^2 during fixation. The detection thresholds of each subject in all three conditions was determined as the luminance value at which a psychometric data fit exceeds 50% correct positive responses. We found that the detection threshold was increased during saccade execution compared to fixation and furthermore we found stronger suppression during voluntary vs reactive saccades. This result provides further evidence for partially different networks for the saccade types. Stronger suppression in voluntary saccades could arise from a different composition of the extra-retinal signal that activates suppression or could indicate that the suppression process itself partially differs between voluntary and reactive saccades.
Meeting abstract presented at VSS 2017