Behavioral/Cognitive Hemisphere-Dependent Attentional Modulation of Human Parietal Visual Field Representations

Posterior parietal cortex contains several areas defined by topographically organized maps of the contralateral visual field. However, recent studies suggest that ipsilateral stimuli can elicit larger responses in the right than left hemispherewithin these areas, dependingon task demands.Herewedetermined the effects of spatial attention on the set of visual field locations (the population receptive field [pRF]) that evoked a response for each voxel in human topographic parietal cortex. A two-dimensional Gaussian was used to model the pRF in each voxel, and we measured the effects of attention on not only the center (preferred visual field location) but also the size (visual field extent) of the pRF. In both hemispheres, larger pRFswere associatedwith attending to themapping stimulus comparedwith attending to a central fixationpoint. In the left hemisphere, attending to the stimulus also resulted inmoreperipheral preferred locations of contralat-eral representations, compared with attending fixation. These effects of attention on both pRF size and preferred location preserved contralateral representations in the left hemisphere. In contrast, attentional modulation of pRF size but not preferred location signifi-cantly increased representation of the ipsilateral (right) visual hemifield in right parietal cortex. Thus, attention effects in topographic parietal cortex exhibit hemispheric asymmetries similar to those seen in hemispatial neglect. Our findings suggest potentialmechanisms underlying the behavioral deficits associated with this disorder. Key words: hemispheric asymmetries; retinotopy; visual attentio