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Abstract:
Abstract: A predominant view holds that distinct spatial
representations underlie action-based and perception-based
indications of spatial relations. In this view, action-based
responses are mediated by a dorsal (occipito-parietal) neural
pathway and perception-based responses by a ventral
(occipito-temporal) neural pathway. Some evidence suggests that the
dorsal stream is further specialized for processing egocentric
distances. However, egocentric distance perception is rarely tested
systematically in neurological patients, so neuropsychological
support for this view is scant. To investigate this issue, we
tested a patient (JW) whose performance on previous tests was
consistent with selective ventral stream damage that spared dorsal
stream processing. We collected verbal reports of distances (15-50
cm), which presumably could be impacted by ventral stream damage,
and open-loop manual pointing indications of distances, which are
thought to engage dorsal stream processing. Targets were viewed
monocularly or binocularly under well-lit viewing conditions. JW's
verbal and pointing responses were highly consistent, appropriately
scaled, and unaffected by viewing condition. The results indicate
that perception-based and action-based indications of egocentric
distance under these conditions are mediated by a common spatial
representation, but do not rule out an anatomical dissociation of
spatial processing. Future testing of JW will compare verbal and
manual indications of exocentric relations and include kinematic
analysis of manual responses.
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