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Brian P. Dyre, Kelli T. Kludt, Lisa R. Fournier; The effects of color coding and attentional selection on perception of heading with transparent optical flow. Journal of Vision 2002;2(7):510. doi: 10.1167/2.7.510.
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© ARVO (1962-2015); The Authors (2016-present)
Superimposing two transparent, radially-expanding optical flow fields with distinct foci of expansion (FOE) produces systematic misperception of one's heading direction (Dyre, Richman, & Fournier, 2000, ARVO). We examined whether coding flow fields in distinct colors mediates this misperception pre-attentively or through attentional selection. Observers viewed simulations of translation through two independently-moving rigid volumes of randomly spaced dots. The heading directions specified by the judged and non-judged flow fields (FOE and FOE') were separated horizontally by 0–16 deg. Some displays had red dots assigned to one flow field and green dots to the other; other displays had red and green dots mixed across both flow fields. Exp. 1 provided no instructions about the colors of the dots; Exp. 2 instructed observers to attend all the dots, or just the red or green dots, but provided no information about color assignment. Observers reported the perceived direction of FOE and whether they perceived one coherent flow field or two transparent flow fields. Separations <- 4 deg. most often resulted in coherent motion; those > 4 deg. most often produced transparent motion. Neither color assignment nor attentional instructions affected the number of flow fields perceived. Repulsion errors of the perceived FOE direction away from FOE' accompanied transparent motion. Color assignment alone did not affect repulsion errors, but directing attention to one flow field unique in color significantly increased repulsion errors and even produced repulsion errors for trials where coherent motion was perceived. In contrast, for trials where attention was directed to both flow fields and coherent motion was perceived, heading errors of attraction toward FOE' occurred. These results suggest that misperception of heading with transparent optical flow is due to both motion contrast and induced motion, and that attentional selection by color enhances the contribution of induced motion.
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