Chicken broccoli rice casserole1/22/2024 In this case, an assumption that objects and texture elements (such as the bricks that compose the walls of the room) remain the same physical size (and the same distance) conflicts with the stereo/motion parallax cues. The situation in which stereo/motion parallax cues are apparently suppressed is when the room expands around them as they walk across it (the center of expansion is the cyclopean point) so that as objects get farther away, they also get larger. Indeed, in our apparatus, subjects can detect the change in size of the room when they walk through a virtual wall from a small room into a large room, using only stereo/motion parallax cues. The relative disparities and equivalent motion parallax signals change by a factor of 4 (i.e., a 300% increase, substantially above a detection threshold of 10–20% for disparity increments McKee, Levi, & Bowne, 1990) hence, they should be readily detected. The impression of a stable scene is equally strong when the floor and ceiling are removed, showing that it is not simply because people assume a constant eye height (Ooi, Wu, & He, 2001). The subjective reports of people in the expanding room are that they are surrounded by a stable room, although its dimensions (as specified by stereopsis and motion parallax) change greatly in all directions (up to fourfold in this experiment) as they walk across the room. This is probably because the visual system computes quite different parameters depending on the task, rather than the effect being due to reweighting of cues (Bradshaw, Parton, & Glennerster, 2000 Glennerster, Rogers, & Bradshaw, 1996 Tittle, Todd, Perotti, & Norman, 1995). Varying the task has been shown to alter subjects' responses even when the reliability of available cues remains the same. It has also been shown that training can influence the relative weighting applied to visual and haptic cues (Atkins, Fiser, & Jacobs, 2001). Nevertheless, it is possible to change the weight applied to different cues in a matter of seconds (Triesch, Ballard, & Jacobs, 2002) by changing the reliability of those cues. It has been argued that this combination may be “mandatory” for cues within one sensory modality because subjects appear to be unable to access the information from individual visual cues, at least for discriminations close to threshold (Hillis, Ernst, Banks, & Landy, 2002). There is a growing consensus that when several sensory cues contribute to a percept such as the 3D shape of an object, the combination process is well described by a weighted linear summation of cues in which the weighting of each cue is determined by its reliability (Backus, Fleet, Parker, & Heeger, 2001 Buckley & Frisby, 1993 Jacobs, 2002 Johnston, Cumming, & Landy, 1994 Johnston, Cumming, & Parker, 1993 Landy, Maloney, Johnston, & Young, 1995 Richards, 1985 Taylor, 1962 Young, Landy, & Maloney, 1993 for recent quantitative analyses, see Hillis, Watt, Landy, & Banks, 2004 Knill & Saunders, 2003). In either case, subjects appear not to have direct access to stereo/motion parallax cues. This can be explained by assuming that subjects remap the relationship between stereo/motion parallax cues and perceived size or that they develop strategies to change their criterion for a size match on different trials. However, for stereo/motion parallax feedback, performance in many conditions became worse such that, paradoxically, biases moved away from the point reinforced by the feedback. For texture-based feedback, the pattern of responses was consistent with observers weighting texture cues more heavily. Because of feedback, observers were able to adjust responses such that fewer errors were made. Subjects were given feedback about the accuracy of their size judgments, where the “correct” size setting was defined either by texture-based cues or (in a separate experiment) by stereo/motion parallax cues. As the subject walked, the room expanded or contracted, although subjects failed to notice any change. Subjects compared the size of two objects, each visible when the room was of a different size. We determined whether the integration of stereopsis/motion parallax cues with texture-based cues could be modified through feedback. In an immersive virtual reality environment, subjects fail to notice when a scene expands or contracts around them, despite correct and consistent information from binocular stereopsis and motion parallax, resulting in gross failures of size constancy (A.
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