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Abstract:
Neuropsycological evidence indicates that the perception of
three-dimensional object shape based on shading gradients can be
preserved in the face of impaired ability to perceive object shape
from line drawings (Humphrey et al., 1996). Such results suggest
that different cognitive/neural mechanisms may be involved in
extracting shape information from shading cues than from contours.
We tested this hypothesis by asking whether viewing grayscale novel
objects (compared to their scrambled versions) would activate the
same cortical regions within individual subjects as viewing line
drawing versions of the same objects (compared to their scrambled
versions). Functional MRI images were obtained with echo-planar
surface coil imaging at 3T. In a passive viewing task, four out of
four subjects analyzed individually showed largely overlapping
activations in lateral occipital cortex for i) 3-D grayscale
objects vs. their scrambled versions and ii) line drawing objects
versus their scrambled controls. A similar pattern of activations
was observed in three out of three subjects performing a"1-back"
matching task to ensure attention to all stimulus types. These
results suggest that a region in the lateral occipital cortex
(presumably within area "LO" described by Malach et al., 1995) is
involved in extracting and/or representing abstract descriptions of
object shape independent of the image properties used to define
that shape (i.e., lines versus shading).
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