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Abstract:
Abstract: Tactile discrimination of grating orientation
activates a parieto-occipital cortical area (Sathian et al.,
NeuroReport, 8:3877,1997) and is impaired by transcranial magnetic
stimulation over this area (Zangaladze et al., Nature,
401:587,1999). In contrast, tactile discrimination of grating
spatial frequency neither recruits nor depends on this area. These
findings may reflect involvement of visual imagery in the
orientation but not spatial frequency task. We investigated this
using the Perky effect, which refers to the disruption of
perceptual performance by a concurrent imagery task. 12 humans
discriminated either the orientation or spatial frequency of
gratings applied to the right index fingerpad. In each session, the
subject performed one tactile task and then visualized gratings
that varied in orientation or spatial frequency while repeating the
corresponding tactile task. Performance on the orientation task was
impaired by concomitant visual imagery. This effect waned with
practice. Performance on the spatial frequency task was generally
unaffected by either simultaneous visual imagery or practice. Our
findings demonstrate a cross-modal Perky effect. The
task-selectivity of the effect is consistent with the notion that
visual imagery is involved in the orientation but not spatial
frequency task. Its decline with practice may account for normal
performance of the blind on tactile discrimination of grating
orientation (Grant et al., Percept Psychophys, in press), despite
normal dependence of this task on visual imagery. Supported by
NEI.
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