David Bourget (Western Ontario)
David Chalmers (ANU, NYU)
Rafael De Clercq
Ezio Di Nucci
Jonathan Jenkins Ichikawa
Jack Alan Reynolds
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Consciousness and Cognition 7 (3):438-453 (1998)
Little is known about distance processing in patients with posterior brain damage. Although many investigators have claimed that distance estimates are normal or abnormal in some of these patients, many of these observations were made informally and the examiners often asked for relative, and not absolute, distance estimates. The present investigation served two purposes. First, we wanted to contrast the use of distance information in peripersonal space for perceptual report as opposed to visuomotor control in our visual form agnosic patient, DF. Second, we wanted to see to what extent her abilities to process distance cues were dependent on binocular vision, in light of Milner et al.'s (1991) observations of preserved stereopsis in DF, and Dijkerman et al.'s (1996) and Marotta et al.'s (1997) observations that her visual guidance of grasping may be particularly dependent on binocular vision of the target. We hypothesized that DF's visuomotor responses would show normal sensitivity to target distance, while her perceptual estimates would not. In the first experiment, we required DF and two age- and sex-matched control subjects to reach out and grasp black cubes placed at varying distances, or to estimate the distance of the cubes from the hand starting position without making a reaching movement. In the second experiment, we required DF and two age-matched control subjects to point as rapidly and accurately as possible to small LED targets which differed in spatial location, under binocular and monocular conditions. The results showed that, relative to the control subjects, DF's grasping movements produced normal peak velocity-distance scaling-when she reached for blocks which varied in depth or pointed to LED targets which were presented at different distances in depth. In contrast, in the cube experiment, her verbal estimates of object distance were poorly scaled, although they improved slightly under the binocular conditions. The results are discussed in terms of current theories of processing streams in extrastriate visual cortex and the distinction between categorical and coordinate spatial processing.
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References found in this work BETA
Melvyn A. Goodale & A. David Milner (1992). Separate Visual Pathways for Perception and Action. Trends in Neurosciences 15:20-25.
A. David Milner (1995). Cerebral Correlates of Visual Awareness. Neuropsychologia 33:1117-30.
H. Chris Dijkerman, A. David Milner & D. P. Carey (1998). Grasping Spatial Relationships: Failure to Demonstrate Allocentric Visual Coding in a Patient with Visual Form Agnosia. Consciousness and Cognition 7 (3):424-437.
R. T. Watson, Elliot S. Valenstein, Alice T. Day & K. M. Heilman (1994). Posterior Neocortical Systems Subserving Awareness and Neglect: Neglect Associated with Superior Temporal Sulcus but Not Area 7 Lesions. Archives of Neurology 51:1014-1021.
Citations of this work BETA
Robert Briscoe & John Schwenkler (2015). Conscious Vision in Action. Cognitive Science 39 (7):1435-1467.
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