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T. L. Ooi, K. A. May, P. J. Gunther, Z. J. He; Prism adaptation effects on absolute distance judgment. Journal of Vision 2001;1(3):5. doi: 10.1167/1.3.5.
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The visual system accurately computes absolute distances by using a variety of depth-cues on the ground surface in combination with other intrinsic cues, such as the angle of declination (Sedgwick, 1986; Philbeck & Loomis, 1997; Wu et al, 2000). While the intrinsic cues are often constant, certain deviant situations can destabilize them. Here, we explored how judged absolute distance is affected by wearing a pair of 10 PD base-up prisms, which effectively causes the visual space to be tilted away from the observer, thence altering the angle of declination. We also explored how two different modes of prism adaptation [i) walking while navigating obstacles; ii) throwing beanbags while standing stationary to minimize optic flow information] serve to recalibrate one's distance judgment. For each mode, prism adaptation was maintained for 15 minutes. Absolute distance judgments were measured with the blindfolded walking paradigm (Thomas, 1983) in three conditions: 1) without prism: baseline; 2) with prism: pre-adaptation; 3) without prism: post-adaptation. Compared to baseline, observers underestimated absolute distance in condition 2 and overestimated absolute distance in condition 3. Interestingly, these general results were obtained for both modes of prism adaptation, indicating the role of a multimodal adaptation mechanism for absolute distance judgment. It also points to the possibility that adaptation occurs at the site where horizontal direction, which is used to define the angle of declination, is determined.
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