VISUAL EXTINCTION AS A SPATIOTEMPORAL DISORDER OF SELECTIVE ATTENTION

STUDIES of normal behaviour have shown that the process of selection t akes a finite time, one measure of which is the attentional dwell time , that is the period of interference produced by one attended stimulus on a subsequent one. Here we investigated the time for selection in F B, a neurological patient suffering from a visuospatial disorder of at tention (unilateral extinction). FB was asked to identify two letters displayed in rapid succession either to the left (damaged), or to the right (intact) visual hemifield. By varying the interval between stimu li, we measured how long the first letter continued to interfere with accuracy on the second-that is the first letter's attentional demand o ver time. The results showed that the process of selection has an abno rmal duration in the affected visual field, being at least twice as lo ng as in the intact field. We suggest that the slowed visual processin g for the contralesional object may contribute to the competitive bias against that object which is the hallmark of unilateral extinction. ( C) 1998 Rapid Science Ltd.