A parametric fMRI study of overt and covert shifts of visuospatial attention

Michael S. Beauchamp, Laurent Petit, Timothy M. Ellmore, John Ingeholm, James V. Haxby
NeuroImage. 2001-08-01; 14(2): 310-321
DOI: 10.1006/nimg.2001.0788

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1. Neuroimage. 2001 Aug;14(2):310-21.

A parametric fMRI study of overt and covert shifts of visuospatial attention.

Beauchamp MS(1), Petit L, Ellmore TM, Ingeholm J, Haxby JV.

Author information:
(1)Laboratory of Brain and Cognition, National Institute of Mental Health,
Bethesda, Maryland 20892, USA.

It has recently been demonstrated that a cortical network of visuospatial and
oculomotor control areas is active for covert shifts of spatial attention (shifts
of attention without eye movements) as well as for overt shifts of spatial
attention (shifts of attention with saccadic eye movements). Studies examining
activity in this visuospatial network during attentional shifts at a single rate
have given conflicting reports about how the activity differs for overt and
covert shifts. To better understand how the network subserves attentional shifts,
we performed a parametric study in which subjects made either overt attentional
shifts or covert attentional shifts at three different rates (0.2, 1.0, and 2.0
Hz). At every shift rate, both overt and covert shifts of visuospatial attention
induced activations in the precentral sulcus, intraparietal sulcus, and lateral
occipital cortex that were of greater amplitude for overt than during covert
shifting. As the rate of attentional shifts increased, responses in the
visuospatial network increased in both overt and covert conditions but this
parametric increase was greater during overt shifts. These results confirm that
overt and covert attentional shifts are subserved by the same network of areas.
Overt shifts of attention elicit more neural activity than do covert shifts,
reflecting additional activity associated with saccade execution. An additional
finding concerns the anatomical organization of the visuospatial network. Two
distinct activation foci were observed within the precentral sulcus for both
overt and covert attentional shifts, corresponding to specific anatomical
landmarks. We therefore reappraise the correspondence of these two precentral
areas with the frontal eye fields.

Copyright 2001 Academic Press.

DOI: 10.1006/nimg.2001.0788
PMID: 11467905 [Indexed for MEDLINE]

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