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Frank Durgin, Zhi Li; The large-scale horizontal-vertical illusion produced with small objects. Journal of Vision 2016;16(12):293. doi: 10.1167/16.12.293.
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© 2017 Association for Research in Vision and Ophthalmology.
The comparison of large-scale vertical objects with frontal horizontal extents produces a horizontal-vertical illusion (HVI) that is quite large (e.g., 20% rather than 6%; Chapanis & Mankin, 1967) and that is yoked to the orientation of the ground plane (Klein et al., in press). Here we tested whether a large-scale HVI could be induced in small-scale objects simply by forcing observers to compare their 3D size rather than their 2D projections. We first (N=40) established that we could reproduce both the large-scale and small-scale HVIs using a stereoscopic virtual environment: Horizontal and vertical poles of 4.5-7.5 m viewed at simulated distances of 20-30 m showed HVIs of up to 18% using a method of adjustment, whereas reducing the lengths and viewing distances by a factor of 5 produced HVIs of only about 6% for the same configurations. We next conducted two manipulations to dissociate two different theories of the large-scale effect. To test the Yang et al. (1999) hypothesis that the perceived scale of the object determines the size of the HVI, we embedded normal-size (N=7) or 1/5 scale (N=7) moving avatars into the small-scale scene to modify the perceived sizes of the objects. Although explicit estimates of pole heights were appropriately increased when the avatars were miniatures, this did not increase the HVI, which remained small (M = 6%). However, we were able to produce a large-scale HVI (M=15%) with the same small-scale objects by simply presenting the horizontal and vertical poles at different distances along the ground so that comparisons between 3D sizes rather than 2D projections were required. These results support the hypothesis that the large-scale HVI is due to 20% greater perceptual expansion in angular elevation than in azimuth (Klein et al., in press). The large-scale HVI depends on the visual information used to evaluate length and height.
Meeting abstract presented at VSS 2016
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