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Converging levels of analysis in the cognitive neuroscience of visual attention.
Philosophical Transactions of the Royal Society B., 353, 1307-1317.
Year of publication:
Fundamental aspects of the problem of attention include limited processing capacity, top-down control, and object integration. These are considered in the context of the distributed brain activity that is engendered by visual input. Four illustrative sets of experiments are described. The first experiments concern divided attention within and between sensory modalities in normal human behaviour. In the within-modality case it is hard to identify two separate perceptual targets presented close together in time. No such restriction is seen between modalities. The second set of experiments measures distinct aspects of attentional impairment following human brain lesions. The results implicate bilateral reductions in processing speed as well as lateral attentional bias in the deficits following parietal lesions; lateral biases, indeed, may be a very general consequence of unilateral brain damage. The third set of experiments uses functional imaging to measure lateralized brain activity during focused attention to left or right. The most conspicuous result is activation of lateral frontal cortex ipsilateral to the direction of attention. An important component of lateral attentional control may be frontal inhibition of the unattended side. The final experiments measure attentional modulation of single neuron activity in the visual cortex of the monkey. Results show widespread suppression of response to unattended or nontarget stimuli. Task-specific patterns of neural priming are associated with instructional cues indicating which object or location the animal should attend in a forthcoming display. The results suggest a highly distributed view of attentional functions in the brain. In contrast to conventional views, attention is not the province of any one part of the sensorimotor network. Instead it is a state developing as a single, selected object gains dominance throughout that network, making its different properties available together for control of behaviour.