Abstract
It is well-established how visual stimuli and self-motion in laboratory conditions reliably elicit retinal-image-stabilizing compensatory eye movements (CEM). Their organization and roles in natural-task gaze strategies is much less understood: are CEM applied in active sampling of visual information in human locomotion in the wild? If so, how? And what are the implications for guidance? Here, we directly compare gaze behavior in the real world (driving a car) and a fixed base simulation steering task. A strong and quantifiable correspondence between self-rotation and CEM counter-rotation is found across a range of speeds. This gaze behavior is “optokinetic”, i.e. optic flow is a sufficient stimulus to spontaneously elicit it in naïve subjects and vestibular stimulation or stereopsis are not critical. Theoretically, the observed nystagmus behavior is consistent with tracking waypoints on the future path, and predicted by waypoint models of locomotor control - but inconsistent with travel point models, such as the popular tangent point model.
Highlights
MethodsThe test track and simulator experiments were designed to be as similar as possible, within practical limitations
If stereoscopy or vestibular sensations are critical to organizing the oculomotor strategy for these compensatory eye movements (CEM), the correlation will only be observable in real driving - or at least it will be much attenuated in the simulator. It is immediately clear in both experiments that the horizontal gaze position pattern (Fig. 3) shows optokinetic nystagmus (OKN) with pursuit-like slow phases (SP, gaze rotating right to left in a clockwise right-hand turn) and saccadic quick phases (QP, gaze jumping left to right)
It is commonly thought that in richer naturalistic tasks visual stability in part rests on the same or similar SEM mechanisms working in synergy with each other
Summary
The test track and simulator experiments were designed to be as similar as possible, within practical limitations. The main points of difference were: (i) for maximal experimental control in the simulator the driver’s speed was controlled by the computer. We did not have the equipment to place speed under experimenter control at the test track, and the drivers themselves controlled the speed. (ii) the curve radius was bigger in the simulator (where it is safe to use higher speeds) and (iii) there were some visual differences to the layout of the simulated path (explained in detail below). Upon arrival the participants were debriefed as to the purpose of the study, and they signed an informed consent form for the publication, and the use of the collected data for scientific purposes
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