OBJECT-CENTERED ATTENTIONAL BIASES IN THE INTACT BRAIN

By simulating neglect-like effects in neurologically intact observers, we evaluated whether normal attentional allocation can be object cent ered. In a series of three experiments, observers detected a small gap on the left or right side of a configuration presented in either the left or right visual field. The figures were positioned so that on dif ferent trials, the left and right sides would fall in the same retinot opic, hemispatial, and environmental location. Thus, only the location with respect to an object-centered frame varied. We found opposite pa tterns of bias within each visual held: For figures in the left visual field, left gaps were detected better than right gaps, whereas in the right visual field the opposite pattern was evident. Control conditio ns indicate that these biases are not due to masking from eccentric co ntours and depend on the left and right segments being united into a s ingle form. These results indicate that opposing orientational biases of the left and right hemispheres can operate within an object-centere d frame in the normal brain. This evidence converges with patient stud ies and single-unit electrophysiology to reveal the importance of a re latively late, abstract locus for visual selection.