Space- and object-based attention components were examined in neurologically normal and parietal-lesion subjects, who detected a luminance change at 1 of 4 ends of 2 outline rectangles. One rectangle end was precued (75% valid); on invalid-cue trials, the target appeared at the other end of the cued rectangle or at 1 end of the uncued rectangle. For normals, the cost for invalid cues was greater for targets in the uncued rectangle, indicating an object-based component. Both right- and left-hemisphere patients showed costs that were greater for contralesional targets. For right-hemisphere patients, the object cost was equivalent for contralesional and ipsilesional targets, indicating a spatial deficit, whereas the object cost for left-hemisphere patients was larger for contralesional targets, indicating an object deficit.

Although clinical evidence of spatial attention deficits, such as neglect and extinction, is typically associated with lesions of the right temporal-parietal junction, recent evidence has suggested an important role for the superior parietal lobe. Two groups of patients, selected for lesions at the temporal-parietal junction including the superior temporal gyrus (TPJ group), or for lesions involving the parietal but not the superior temporal region (PAR group), performed cued-target detection tasks in 2 experiments. An extinction-like response time pattern was found for the TPJ but not the PAR group. In addition, both groups were able to use expectancy information, in the form of cue predictiveness, suggesting that separate mechanisms mediate exogenous and endogenous processes during attention shifts.

Three experiments investigated the identification or localization of a letter that was displaced from the fixation point by 1 degree-3 degrees. The subject's task was to identify a fixated letter and identify (Experiment 1) or localize (Experiments 2 and 3) the displaced letter. On uncued trials, the displaced letter could appear at any of eight locations on any of three rings surrounding the fixated letter; on cued trials, the ring containing the displaced letter was specified. The results indicated that cuing improved subjects' identification and localization of the displaced letter. Invalid cuing (Experiment 3) produced costs comparable in magnitude to the benefits. The distance of the target from the cued ring determined cost, but costs were unaffected by the appearance of a target within the presumed beam of attention. It was proposed that attention should be viewed as a general, rather than feature-specific, resource that can be voluntarily allocated to multiple regions of the visual field.

Five experiments investigated the role of attention in identifying global and local targets in hierarchically structured patterns. Hierarchical patterns were presented at a variable stimulus onset asynchrony (SOA) either after a cue (4 arrows or shaded boxes) or after no cue. Targets occurred at the cued level 80% of the time and at the uncued level 20%. On uncued trials, target level probability was .5. Global cues produced benefits for both global and local targets over SOA on cued trials. Local cues produced benefits only for local targets. For uncued trials, responses favored local targets overall when interspersed with locally cued trials but favored global targets when interspersed with globally cued trials. The role of an attentional window and discrete distribution of attention over global and local levels of hierarchical patterns are discussed.

Four experiments examined the effects of inhibition of return on endogenously generated and visually guided saccades. In Experiments 1-3, subjects responded to a peripheral target by making either a prosaccade (toward the target) or an antisaccade (toward the field opposite the target). Prior to the appearance of the target, one of the two equiprobable target locations was activated by presenting a peripheral precue (Experiments 1 and 2), or by executing an endogenous saccade in response to a central precue (Experiment 3). In Experiment 1, the eyes remained fixed when the cue appeared; in Experiment 2 subjects made a saccade to the peripheral cue, and returned their eyes to the centre before the target appeared. In both experiments, saccade latencies were longer for targets appearing at the precued location for both prosaccade and antisaccade tasks. In Experiment 3, saccade latencies were longer for targets appearing at the precued location only in the prosaccade task; no effect of the precue was obtained in the antisaccade task. These results suggest that endogenously generated saccades activate both an inhibition of target detection and a motor alternation bias. Experiment 4 showed that inhibition of return generated by a peripheral precue increased the latency for a subsequent endogenous saccade (from a central, arrow target) toward the precued location. Inhibition of return may affect perceptual processing and also produce a motor alternation bias dependent upon whether it is activated exogenously or endogenously. Posner and Cohen (1984;Posner, Cohen, & Rafal, 1982) observed that when attention is summoned by a luminance change (brightening or dimming), the initial facilitation of detection at the stimulated location is succeeded, within a few hundred ms, by an inhibition of detection at the same location. This phenomenon, which they called inhibition of return, has since been demonstrated in numerous studies which have revealed much about its properties