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Liu Zhou, Zijiang J. He, Teng Leng Ooi; The intrinsic bias influences the size-distance relationship in the dark. Journal of Vision 2010;10(7):60. doi: 10.1167/10.7.60.
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© ARVO (1962-2015); The Authors (2016-present)
A dimly-lit target in an otherwise dark environment is perceived as located at the intersection between its projection line from the eye and an implicit slant surface (intrinsic bias) (Ooi et al, Nature 2001). To investigate if the intrinsic bias affects the size-distance relationship, observers used a perceptual matching task to report the perceived size of a dimly-lit target (0.75deg) at multiple locations (1.5–6.75m and 0 or 0.5m above the floor). Based on the matched metric size and physical angular target size, we derived the perceptual target location (perceived target direction is veridical in darkness). We found the derived perceptual target locations form a profile of a slanted surface, resembling the intrinsic bias. This indicates the intrinsic bias supports size perception in the dark. We then used a blind-walking-gesturing-size-estimation task to measure the judged target location and judged target size. In this task, observers walked blindly to traverse the perceived target distance, gestured its perceived height and indicated its size. From the indicated target sizes we derived the perceptual target distances, and compared these with the measured distances. We found a reliable correlation between the two distances, suggesting the intrinsic bias is responsible for both perceived size and distance in the dark. Finally, we investigated the effect of knowledge of target size on judged location. Using the blind-walking-gesturing task, we measured observers' judged location of the dimly-lit target in the dark when they either had, or had no, knowledge of the physical target size. We found knowledge of the physical target size (2.5cm) improves the accuracy of the judged target locations. Altogether our findings reveal that in the reduced cue environment where the intrinsic bias dictates our perceptual space, there exists a lawful relationship between perceived size and distance, which reflects the uniqueness of our perceptual world.
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