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Reza Azadi, Robert McPeek; Saccadic curvature is gradually modulated by the direction and amplitude of other saccades in a sequence. Journal of Vision 2017;17(10):1277. doi: 10.1167/17.10.1277.
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Although saccades are quite fast and accurate, often their trajectories are not completely straight. Previously we showed that saccades curve away from preceding and following saccades when they are executed as a sequence. However, in those experiments, subjects were instructed to execute two perpendicular saccades. In the present study we binocularly recorded eye-movements in a free viewing search task to asses more natural, voluntary saccade sequences with a wider range of angles and amplitudes. In each trial eight targets (0.8° diameter rings) were presented in random positions and subjects were instructed to find a 0.15° horizontal line, located at the center of one of the targets. For this reason, they needed to foveate the center of the targets one by one. Analysis of saccadic curvature revealed that saccades curved away from their preceding and following saccades. We found a sinusoidal relationship between the angle of two consecutive saccades and their curvature: curvature was maximal when the two saccade vectors were perpendicular, and gradually declined as the angle between the vectors became more acute or obtuse. Moreover saccadic curvature was also modulated by the square root of the amplitude of the preceding and following saccades. Interestingly, saccade curvature was affected not only by the immediately preceding and following movements, but also, to a lesser extent, by movements that were more distant in the sequence. Our results show that for a saccade in a gaze sequence, curvature is systematically influenced by the direction and amplitude of the preceding and following saccades. This effect is strongest for the immediately preceding and following movements. These findings reveal that sequential free viewing saccades are not independent from each other, and are consistent with the idea that sequential saccades are processed concurrently in the oculomotor system.
Meeting abstract presented at VSS 2017
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