Academic journal article Attention, Perception and Psychophysics

Effects of Gaze on Vection from Jittering, Oscillating, and Purely Radial Optic Flow

Academic journal article Attention, Perception and Psychophysics

Effects of Gaze on Vection from Jittering, Oscillating, and Purely Radial Optic Flow

Article excerpt

In this study, we examined the effects of different gaze types (stationary fixation, directed looking, or gaze shifting) and gaze eccentricities (central or peripheral) on the vection induced by jittering, oscillating, and purely radial optic flow. Contrary to proposals of eccentricity independence for vection (e.g., Post, 1988), we found that peripheral directed looking improved vection and peripheral stationary fixation impaired vection induced by purely radial flow (relative to central gaze). Adding simulated horizontal or vertical viewpoint oscillation to radial flow always improved vection, irrespective of whether instructions were to fixate, or look at, the center or periphery of the self-motion display. However, adding simulated high-frequency horizontal or vertical viewpoint jitter was found to increase vection only when central gaze was maintained. In a second experiment, we showed that alternating gaze between the center and periphery of the display also improved vection (relative to stable central gaze), with greater benefits observed for purely radial flow than for horizontally or vertically oscillating radial flow. These results suggest that retinal slip plays an important role in determining the time course and strength of vection. We conclude that how and where one looks in a self-motion display can significantly alter vection by changing the degree of retinal slip.

Although multiple senses contribute to the perception of self-motion, visual and vestibular information appear to dominate this experience (Dichgans & Brandt, 1978; Gibson, 1966; Howard, 1982). Vision is able to detect both constant and accelerating self-motions from the optic flow presented to our moving eyes (Berthoz, Pavard, & Young, 1975; Dichgans & Brandt, 1978; Johansson, 1977; Lishman & Lee, 1973). By contrast, the vestibular system of the inner ear is able only to detect self-accelerations, on the basis of the inertia of the fluid in the semicircular canals and otolith organs (Dichgans & Brandt, 1978). Most explanations of how these two senses interact in the perception of self-motion are based on the notion of sensory conflict (see Oman, 1982; Reason, 1978; Reason & Brand, 1975; Zacharias & Young, 1981). For example, it has long been known that there can be substantial delays in the onset of visually induced illusions of self-motion (known as vection; Melcher & Henn, 1981; Teixeira & Lackner, 1979; Wong & Frost, 1981; Young, Dichgans, Murphy, & Brandt, 1973; Zacharias & Young, 1981). Sensory conflict theories propose that such delays occur because salient visual-vestibular conflicts are generated when stationary observers are first exposed to a visual self-motion display, since they expect to be accelerated up to the speed represented by this display, but the vestibular stimulation that normally accompanies such a self-acceleration is absent (e.g., Zacharias & Young, 1981). These theories predict that the initially salient visual-vestibular conflict will fade rapidly when the optic flow simulates constant velocity self-motion (because little or no vestibular input is expected in this situation) and that, after a short time, compelling vection will be induced. If, on the other hand, the optic flow simulates large and frequent changes to the speed and direction of self-motion, it is predicted that salient visual-vestibular conflicts should persist and prevent the induction of compelling vection.

Sensory conflict accounts of self-motion perception have recently been challenged by findings that compelling vection can be induced in situations thought to generate significant and sustained visual-vestibular conflicts (Palmisano, Burke, & Allison, 2003; Palmisano, Gillam, & Blackburn, 2000). The jittering and nonjittering displays used in these studies all contained the same radial flow component, which simulated constant-velocity forward self-motion in depth, and were thus expected to generate only transient visual-vestibular conflict in stationary observers. …

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