Browsing by Subject "Postural Control"

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    The Role of Chromaticity in Postural Control
    (2021-09) Rath, Ruth
    I investigated the role of chromaticity in the visual control of standing body sway. In this novel study, I adapted the moving room paradigm—an experimental design that has been widely used in research on the visual control of stance—introducing the unique design element of chromatic lighting variations. Studies relating the control of stance to imposed oscillation of the illuminated environment suggest that, in most cases, postural control is most strongly related to optic flow in the retinal periphery. I asked whether this relation might differ as a function of the chromaticity (color) of light, as, separately, studies on chromatic perception across the visual field also indicate perceptual differences between the retinal center and retinal periphery. Detection and identification of colored stimuli is reported to be best near the fovea and declines in the visual periphery. In particular, the periphery of the retina is more sensitive to blue light than to red light. It has also been reported that some colors appear to move more rapidly than others. I used a within-participants design to expose young adults to the illuminated environment in a moving room, where nearly global optic flow was oscillated in a simple sinusoid pattern in the AP direction relative to observers. Three chromatic conditions were used to illuminate the room (Red vs. Blue vs. Full spectrum), presented in random order. A magnetic motion capture system was used to collect postural data of the head and torso (analyzed separately for movement in the AP and ML axes), in addition to AP movement data of the room. I separately evaluated the spatial magnitude of sway (operationalized as positional variability), and the extent to which body sway was coupled with the movement of the room (using average mutual information). While my experimental design was found to be robust overall—replicating common effects demonstrated in the moving room paradigm—I found no evidence that spatial magnitude of sway, or observer-room coupling differed across chromatic conditions. My study is the first to synthesize and extend differential chromatic perception across the visual field to the domain of perception and action in a moving room paradigm. Color interacts with luminance, form, and motion in ways that are not fully understood, and there are numerous other possibilities for future research investigating the realm of color and its ecological implications.
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    The virtual reality head-mounted display Oculus Rift induces motion sickness and is sexist in its effects
    (2021-06) Munafo, Justin
    Anecdotal reports suggest that motion sickness may occur among users of contemporary, consumer-oriented head-mounted display systems, and that women may be at greater risk. I evaluated the nauseogenic properties of one such system, the Oculus Rift. The head-mounted unit included motion sensors that were sensitive to users’ head movements, such that head movements could be used as control inputs to the device. In two experiments, seated participants played one of two virtual reality games for up to 15 minutes. In Experiment 1, 22% of participants reported motion sickness, and the difference in incidence between men and women was not significant. In Experiment 2, motion sickness was reported by 56% of participants, and incidence among women (77.78%) was significantly greater than among men (33.33%). Before participants were exposed to the head-mounted display system, I recorded their standing body sway during the performance of simple visual tasks. In both experiments, patterns of pre-exposure body sway differed between participants who (later) reported motion sickness and those who did not. In Experiment 2, sex differences in susceptibility to motion sickness were preceded by sex differences in body sway. These postural effects confirm a prediction of the postural instability theory of motion sickness. The results indicate that users of contemporary head-mounted display systems are at significant risk of motion sickness, and that in relation to motion sickness these systems may be sexist in their effects.