Head and eye movements are each facilitated by the offset of a central fixation point in a virtual gap paradigm
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RESEARCH ARTICLE
Head and eye movements are each facilitated by the offset of a central fixation point in a virtual gap paradigm Jason Flindall1 · Aman Sara1 · Alan Kingstone1 Received: 8 June 2020 / Accepted: 11 August 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Eye movements exhibit reduced latencies when the point of fixation is extinguished prior to, or coincident with, the appearance of a peripheral target. Two independent components are responsible for this facilitation. If the offset occurs before target onset, it presents a warning which stimulates response preparation and execution. If offset occurs prior to or coincident with target onset, it triggers the release of fixation-maintenance neurons in the superior colliculus that can delay saccadic responses. While the warning effect facilitates responses regardless of effector, the fixation release effect is thought to be specific to the oculomotor system. Head movements, like saccades, contribute significantly to gaze shifts and may be generated directly by the SC. While head movements have been shown to benefit from the warning effect, it is unknown if, and to what degree, they are affected by the release of fixation-maintenance neurons responsible for inhibiting saccades. To address this issue, we measured head and eye response latencies in a virtual reality-based gap paradigm, turning off the fixation point either 200 ms before (temporal gap condition), coincident with (step condition), or 1000 ms after (temporal overlap/baseline condition) target onset. Our results indicate that head movements, like saccades, are facilitated by both the warning and release components of the gap paradigm. Further, rotational kinematics during gap trials differed significantly from those observed in step and overlap trials (higher, earlier peak velocities). These results are discussed with respect to the theorized structure and organisation of the superior colliculus in humans. Keywords Gaze coordination · Gap effect · Oculomotor system · Kinematics
Introduction When we direct our attention, navigate the world, or respond to an unexpected event, shifts in our attentional focus are typically accompanied by shifts in our gaze. These gaze shifts may be accomplished through independent saccadic eye movements (i.e., eye-in-head movements), or through a highly-coordinated combination of head and eye movements. While we may obviously produce eye movements in the absence of head movements (and vice versa), the degree to which eye and head movements are coordinated during natural, everyday behaviour hints that these two effector systems overlap with respect to their mechanisms of control. Communicated by Melvyn A. Goodale. * Jason Flindall [email protected] 1
Department of Psychology, University of British Columbia, Vancouver, Canada
The degree to which the systems overlap, however, is still largely unknown. One way to probe the interaction of head and eye control systems is through behavioural investigations. The gap effect refe
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