Lukasz Grzeczkowski¹, Martin Rolfs¹; ¹Humboldt-Universität zu Berlin, Germany

Saccades are rapid, ballistic eye movements with stereotypical kinematics: their duration increases linearly with amplitude, while peak velocity saturates exponentially, a relation known as the main sequence. While this relation holds generally true, individual saccades can differ in vigor, moving faster or slower than expected. Previously, we demonstrated that monetary reward for movement speed modulates saccade vigor, irrespective of saccade target location. This manipulation also altered the dynamics of presaccadic shifts of visual attention to the saccade target—before slow saccades, performance at the target rapidly declined. Here, we investigated if the effect of reward on saccade vigor can be specific to certain locations, and if so, if it affects presaccadic attention and visual saliency. In each trial, a cue indicated one of eight potential saccade target locations. A grating then briefly flashed at that location at varying times before saccade, probing presaccadic attention. Participants saccaded to that location, received feedback on their reward, and reported the grating's orientation. In two locations each (which remained constant for each participant), participants received monetary reward when their saccadic peak velocity reached 30% of their fastest or slowest saccades. This manipulation was unknown to the participants, implicitly incentivizing high or low vigor, respectively. Additionally, after each of the three experimental sessions, we measured reaction time and orientation discrimination performance at all locations to assess the saliency of these locations in a fixation task. Results showed that neither saccade kinematics nor presaccadic attention differed as a function of reward location, demonstrating that spatially localized incentives were unable to modulate behavior. However, we found a strong correlation between the peak velocity and presaccadic perceptual performance in the saccade task (R = 0.82). Performance in the fixation task improved across sessions but, again, did not differ between locations demonstrating no selective saliency manipulation by reward.

Acknowledgements: This project has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 research and innovation programme (grant agreement No 865715) and the Heisenberg Programme of the Deutsche Forschungsgemeinschaft (grants RO 3579/8-1 and RO 3579/12-1) granted to MR.