title: Beyond the point of no return: effects of visual distractors on saccade amplitude and velocity.
abstract: Visual transients, such as a bright flash, reduce the proportion of saccades executed, ∼60-125 ms after flash onset, a phenomenon known as saccadic inhibition (SI). Across three experiments, we apply a similar time-course analysis to the amplitudes and velocities of saccades. Alongside the expected reduction of saccade frequency in the key time period, we report two perturbations of the "main sequence": one before and one after the period of SI. First, saccades launched between 30 and 70 ms, following the flash, were hypometric, with peak speed exceeding that expected for a saccade of similar amplitude. This finding was in contrast to the common idea that saccades have passed a "point of no return," ∼60 ms before launching, escaping interference from distractors. The early hypometric saccades observed were not a consequence of spatial averaging between target and distractor locations, as they were found not only following a localized central flash (experiment 1) but also following a spatially generalized flash (experiment 2). Second, across experiments, saccades launched at 110 ms postflash, toward the end of SI, had normal amplitude but a peak speed higher than expected for that amplitude, suggesting increased collicular excitation at the time of launching. Overall, the results show that saccades that escape inhibition following a visual transient are not necessarily unaffected but instead, can reveal interference in spatial and kinematic measures.
authors.affiliation: Center for Mind/Brain Sciences, University of Trento, Trento, Italy; and antimo.buonocore@unitn.it.
authors.forename: Antimo
authors.initials: A
authors.lastname: Buonocore
authors.affiliation: Human Cognitive Neuroscience, Psychology, University of Edinburgh, Edinburgh, United Kingdom.
authors.forename: Robert D
authors.initials: RD
authors.lastname: McIntosh
authors.affiliation: Center for Mind/Brain Sciences, University of Trento, Trento, Italy; and.
authors.forename: David
authors.initials: D
authors.lastname: Melcher
mesh_terms: D000293:Adolescent; D000328:Adult; D006801:Humans; D009433:Neural Inhibition; D011597:Psychomotor Performance; D011930:Reaction Time; D012438:Saccades / Q000502:physiology*
keywords: eye movements; main sequence; saccadic inhibition