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Nilton P. Ribeiro-Filho, Elton H. Matsushima, José A. Da Silva; Angular declination as an exocentric distance cue: some hints for dissociation between perception and action systems. Journal of Vision 2003;3(9):495. doi: 10.1167/3.9.495.
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© ARVO (1962-2015); The Authors (2016-present)
Several studies in the last ten years were devoted to investigate angular declination as an useful visual cue for spatial perception, as assessed by perceptual and visuomotor tasks. Results were not unequivocal, since some of them pointed out that this cue was independent and effective and some others found dependence on interaction with binocular cues. The present two experiments tried to figure out the role of angular declination for exocentric distance perception as assessed by perceptual (verbal report) and visuomotor (visually directed walking) tasks, the first between-subjects factor. Observers (N=40) were asked to verbally judge exocentric distances in depth or to walk toward endpoints of of the same exocentric intervals. In Exp. 1, the exocentric interval was constant (1m) and egocentric distances of this interval varied (1, 2, and 3m). In Exp. 2, the exocentric intervals varied (1, 2, and 3m) and egocentric distance of the interval was constant (1m). The second between-subject factor was angular declination, stimuli were presented either at eye-level (no angular declination), or floor-level. Experimental environment was a dark room and stimuli contained a dim light. Contrarywise to some studies, our data showed strong undershooting for all groups, larger for perceptual performance at eye-level. This may indicate participation of perceptual tendencies, as equidistance tendency. Results also showed that angular declination was not effective as an exocentric distance cue for visuomotor tasks, but was significantly effective for perceptual tasks. Despite the strong deprival of visual cues of our environment, observers' performance was tied to physical distance properties, probably due to angular size cue that varied sistematically with distance. These differences between tasks can be interpreted as different distance processings for perception and for action, supporting hypothesis of dissociation between these two systems.
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