Cognitive neuropsychology and the problem of selective attention.

Cognitive psychologists focus on internal mental operations controlling access to consciousness, memory and responding. They are concerned with the way in which central intentions come to affect sensory and memorial processing. The problem of selective attention to visually presented stimuli provides an important model for integrating this approach with an understanding of underlying neural systems. Studies of humans and alert monkeys show that they can attend selectively to eccentric visual locations while maintaining fixation. The occurrence of a target eccentric to fixation induces a disengagement from the current attentional focus, a movement of attention and an engagement of the target. It has been shown that damage to the parietal lobe affects the ability to disengage, while midbrain injury affects the move component. Each hemisphere appears biased toward processing contralateral targets. In order for the posterior visual selection system to operate it must have access to another more general selective attention system not dedicated to visual spatial information. Thus attentional selectivity requires a multilevel hierarchical system with each level viewed as a network of component mental operations. At one level the component operations are dedicated to particular cognitive systems (e.g., visual-spatial) but at higher levels they seem to be general across different cognitive systems (e.g., visual-spatial and language).