Timing of concurrent visual stimuli determines modulation of saccadic amplitude

Moritz Feil, Meinrad Abegg, Mathias Abegg
2018 Journal of Vision  
The temporal relation of competing visual stimuli may determine the corresponding oculomotor response. In this study we systematically varied the temporal coincidence of two conflicting stimuli and investigated saccades that were elicited from such stimuli. We varied the time of presentation of two identical spatially separated stimuli between 0 and þ165 ms and measured the amplitude of the saccade elicited by these stimuli using infrared eye tracking. In the first experiment, all stimuli were
more » ... , all stimuli were shown for 36 ms only. In the second experiment, stimuli remained on the screen until the subsequent stimulus appeared, whereas in the third experiment all stimuli were removed after saccade onset. Up to an interstimulus interval of 82 ms, we found a significant shift of the saccadic endpoint toward the location of the second stimulus as compared to saccades toward the first stimulus alone. The strongest saccadic bias was observed if a stimulus was shown 36 ms after or before another stimulus. In contrast, time intervals longer than 82 ms elicited saccade adaptation-that is, the saccadic landing point gradually moved toward the second location over time. In more than 99% of trials, the second stimulus appeared before the saccade reached its endpoint. The timing of a conflicting stimulus determines the associated saccadic response: Simultaneous presentation of two stimuli results in a saccadic endpoint at an averaged intermediate position, short interstimulus intervals result in a strong shift of the saccadic endpoint toward the location of the second of two consecutive stimuli, and longer interstimulus intervals elicit saccade adaptation. The timing of two stimuli thus is associated with distinct processes, which complement each other in order to provide an optimal oculomotor response. Citation: Feil, M., Abegg, M., & Abegg, M. (2018). Timing of concurrent visual stimuli determines modulation of saccadic amplitude. Apparatus The subjects were seated 60 cm (50 cm for Experiment 2) away from a screen with their head immobilized by a chin and forehead rest. A 20-in. CRT monitor (ViewSonic G220fb) with dimensions of 1,024 3 724 pixels and a refresh rate of 85 Hz was used for all experiments. The room's luminance was kept constant
doi:10.1167/18.11.8 fatcat:4hiy2hbnezbflb2up27voq6vm4