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Heather L. Jenkin, Richard T. Dyde, Michael R. Jenkin, Laurence R. Harris; The perceived direction of “up” measured using shape-from-shading in a virtual environment.. Journal of Vision 2004;4(8):384. doi: 10.1167/4.8.384.
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© ARVO (1962-2015); The Authors (2016-present)
The direction of “up” is a fundamental property of visual perception and is created from information arising from several sources including the direction of gravity, orientation of the body and visual polarity cues. Cognitive strategies based on knowledge of natural laws, such as the expected direction of sunlight or the direction in which dropped objects fall, can also contribute. Here we assess the use of a wide-field virtual environment to generate a perceived up direction that differs from that defined by gravity and body orientation. In the absence of competing cues, observers assume that illumination comes from above. A shaded disc is experienced as most convex when its brightest segment is perceived as uppermost and this orientation can therefore be taken as a measure of perceived up. Observers sat in the Immersive Virtual environment at York (IVY) formed by six rear-projection screens that fully surround the viewer. On each screen a view of an 8′× 8′×16′ room, with the correct perspective for the viewer, was presented stereographically using shutter glasses. The roll angle of this virtual 3D room was varied between +/− 90 degrees from vertical. For each room orientation the observer adjusted the orientation of a flat, virtual, shaded disc that floated in front of them, until it appeared maximally convex. For room orientations within approximately 35 degrees of upright the perceived direction of “up” was heavily influenced by the orientation of the surrounding virtual room. The pattern of responses within this range could be modeled as the weighted sum of vectors corresponding to the direction of gravity, orientation of the body and the orientation of the visual environment. For larger tilts other factors seemed to influence the observers' judgements. Earlier studies have shown that real rotated and tilted rooms manipulate the perceived direction of up. The IVY wide-field virtual environment has a similar effect for small roll angles (+/−35 degrees) but not for larger angles.
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