Attention to One or Two Features in Left or Right Visual Field: A Positron Emission Tomography Study

Abstract

In human vision, two features of the same object can be identified concurrently without loss of accuracy. Performance declines, however, when the features belong to different objects in opposite visual fields. We hypothesized that different positron emission tomography activation patterns would reflect these behavioral results. We first delineated an attention network for single discriminations in left or right visual field and then compared this with the activation pattern when subjects divided attention over two features of a single object or over two objects in opposite hemifields. When subjects attended to a single feature, parietal, premotor, and anterior cingulate cortex were activated. These effects were strongest in the right hemisphere and were, remarkably, unaffected by the direction of attention. In contrast, direction of attention affected occipital and frontal activity: right occipital and left lateral frontal activity were higher with attention to the left, whereas right lateral frontal activity was higher with attention to the right. When subjects identified two features of the same object, parietal, premotor, and anterior cingulate activity was enhanced further, predominantly this time in the left hemisphere. Again, there was no direction sensitivity. Direction-sensitive activation of lateral frontal cortex also was increased. Finally, when subjects divided their attention over opposite hemifields, activity in the direction-sensitive occipital and frontal regions fell to a level midway between those seen during exclusively leftward or rightward attention. Thus, the behavioral efficiency with which we attend to multiple features of a single peripheral object is paralleled by enhanced activity in structures generally active during peripheral selective attention as well as in structures that depend on the specific direction of attention, most notably lateral frontal cortex. In addition, in the direction-sensitive regions, dividing attention over hemifields causes a compromise pattern between the extreme levels obtained during unilateral attention.

Interdependence of Nonoverlapping Cortical Systems in Dual Cognitive Tasks

“…Previous studies have also reported a decrease in activation in a sensory area when a second computational demand was placed on the same area or on another area (Rees et al, 1997;Vandenberghe et al, 1997). For example, the amount of activation in V5 associated with the perception of irrelevant moving dots was smaller during the performance of a more demanding visual word judgement task (deciding whether it had two syllables) than during a less demanding task (whether it was in uppercase) (Rees et al, 1997).…”

“…Several previous neuroimaging studies have examined dual tasks that activate cortical regions that overlap in the two tasks, such as a visually presented verbal task that was performed in the presence or absence of a visual distractor (Rees et al, 1997), or a related task that contrasted attention to single vs multiple visual objects (Vandenberghe et al, 1997). The results of such studies generally show that the activation associated with a given task decreases when a second task, drawing on the same cortical area, is being performed concurrently (Klingberg and Roland, 1997).…”

A decrease in brain activation associated with driving when listening to someone speak

“…However, the results are different for tasks that involve two concurrent streams of thought. The activation in the regions that are activated by each of the tasks when they are performed alone typically decreases from the single task to the concurrent dual-task situation, presumably because of the competition for the same neural resources (Klingberg and Roland, 1997;Rees et al, 1997;Vandenberghe et al, 1997). Moreover, the rostral anterior cingulate becomes involved in concurrent dual tasks (Dreher and Grafman, 2003).…”

Divided versus selective attention: Evidence for common processing mechanisms

“…Prefrontal, posterior parietal and premotor cortical areas were more activated by divided attention to two stimulus dimensions than by selective attention to each separate dimension (Corbetta et al, 1991a;Vandenberghe, et al 1997;Rees et al, 1997;Herath et al, 2001;Loose et al, 2003;Nebel et al, 2005;Weerda et al, 2006;Johnson and Zatorre, 2006). Enhanced activity in the anterior cingulate cortex (ACC) has also been reported, although, where performance accuracy was not equated, this may be explained by differences in error processing and response uncertainty between the selective and divided attention conditions (Carter et al, 1998;Botvinick et al, 1999).…”

“…When participants concurrently discriminated two stimulus features, left superior parietal, left frontal and temporal activations exceeded the summed activity in the single discriminations (Vandenberghe et al, 1997). Analyses were restricted to stimuli presented in the left hemifield.…”