Where in the brain does visual attention select the forest and the trees?

Abstract

The perceptual world is organized hierarchically: the forest consists of trees, which in turn have leaves. Visual attention can emphasize the overall picture (global form) or the focal details of a scene (local components). Neuropsychological studies have indicated that the left hemisphere is biased towards local and the right towards global processing. The underlying attentional and perceptual mechanisms are maximally impaired by unilateral lesions to the temporal and parietal cortex. We measured brain activity of normal subjects during two experiments using 'hierarchically' organized figures. In a directed attention task, early visual processing (prestriate) areas were activated: attention to the global aspect of the figures activated the right lingual gyrus whereas locally directed attention activated the left inferior occipital cortex. In a subsequent divided attention task, the number of target switches from local to global (and vice versa) covaried with temporal-parietal activation. The findings provide direct evidence for hemispheric specialization in global and local perception; furthermore, they indicate that temporal-parietal areas exert attentional control over the neural transformations occurring in prestriate cortex.

Schizophrenia Subjects Show Intact Success-Related Neural Activation but Impaired Uncertainty Processing during Decision-Making

“…Specifically, attentional processes that involve sustained, and possibly selective, attention (Coull et al, 1996), switching from task-relevant local to global targets (Fink et al, 1996;Lamb et al, 1989), voluntary attentional control (Hopfinger et al, 2000), and the distinction between taskirrelevant and task-relevant events (Downar et al, 2001;Kiehl et al, 2001;McCarthy et al, 1997) support the view that this area is critical for the extraction and selection of task-relevant information. Moreover, this area has been implicated in inhibitory control in a number of different paradigms (Garavan et al, 1999;Menon et al, 2001;Rubia et al, 2001b;Steel et al, 2001;Doricchi et al, 1997), that is, the allocation of resources to a response that has to compete with a highly overlearned and potentially habitual behavior.…”

The apolipoprotein E gene, attention, and brain function.

“…TMS applied to the parietal cortex produces a neglect-like impairment of contralateral detection during bilateral, but not unilateral, visual stimulation (Pascal-Leone, Gomez-Tortosa, Grafman, & Always, 1994) and also impairs performance on conjunction, but not feature, search (Ashbridge, Walsh, & Cowey, 1997). The role of the parietal cortex in the dynamic scaling of attention is less well established, although there is some supporting evidence from imaging (Fink et al, 1997) and lesion (Robertson, Lamb, & Knight, 1988) studies.…”

“…TMS applied to the parietal cortex produces a neglect-like impairment of contralateral detection during bilateral, but not unilateral, visual stimulation (Pascal-Leone, Gomez-Tortosa, Grafman, & Always, 1994) and also impairs performance on conjunction, but not feature, search (Ashbridge, Walsh, & Cowey, 1997). The role of the parietal cortex in the dynamic scaling of attention is less well established, although there is some supporting evidence from imaging (Fink et al, 1997) and lesion (Robertson, Lamb, & Knight, 1988) studies.Third, the efficiency of the parietal cortex in carrying out these attentional operations depends on basal forebrain activation and the integrity of cholinergic input to the cortex (Everitt & Robbins, 1997;Marrocco & Davidson, 1998;McGaughy, Everitt, Robbins, & Sarter, 2000;Sarter, Givens, & Bruno, 2001;Wenk, 1993). Lesions of the cholinergic basal forebrain by ibotenic acid in monkeys lead to increased attentional disengagement of covert attention, without concomitant effects on memory (Voytko et al, 1994).…”

Picture the difference: electrophysiological investigations of picture processing in the two cerebral hemispheres

“…Finally, the hemispheres also seem to differ in the extent to which they direct attention to global (whole object) or local (object part/feature) aspects of visual stimuli (e.g. [18,24,66]); in general, processing in the left hemisphere seems more directed to local stimulus properties and processing in the right hemisphere to global stimulus properties. Such attentional differences may also underlie observed differences in the hemispheres' abilities to remember information conveyed in pictures: the right hemisphere's memory seems to be more sensitive to global scene organization and coherence, while the left hemisphere seems more proficient at remembering unorganized scenes or incongruent details in scenes [70,71].…”