Attention is an executive process by which inputs are selected for processing. It describes the means by which humans and animals can identify and process important environmental events in a sustained manner, while ignoring others which are irrelevant. The term is used in a number of different ways, because attention is not a single process. For instance, selective, divided and sustained forms of attention have been identified in humans. SELECTIVE ATTENTION is sometimes also called focused attention. It refers to the ability to detect and analyse a specific portion of the information available to the senses, while ignoring the rest. DIVIDED ATTENTION pertains to the concurrent processing of more than one input. SUSTAINED ATTENTION is required for continuous performance of a task which is not under automatic control. It is sometimes used synonymously with VIGILANCE, although this can be misleading: vigilance is better defined as the constant detection of rare and unpredictable events, which is not something demanded by every continuous performance task.
Many paradigms have been designed to provide a perspective about the way in which people maintain an alert state and detect, orient to and process sensory signals (Posner & Peterson, 1990). These typically involve auditory tasks such as DICHOTIC LISTENING and shadowing, or VISUAL SEARCH tasks. Each can be modified to measure selective or divided attentional processes: in listening/shadowing tasks the subject can be instructed to focus on one or both streams of information; in visual tasks divided attention may be achieved by using a number of salient cue points which require simultaneous monitoring through COVERT ORIENTING. Measurement of shifts in attention are also possible. In cued visual tasks, the increase in response time to a target following an inappropriate cue is a measure of the time required to disengage attention. The WISCONSIN CARD-SORT TEST provides a way of investigating the attentional importance given to different dimensions of stimuli and the ease with which we shift between them. Sustained attention is typically measured in experiments which involve continuous decisions about target stimuli, or alternatively by testing the resistance of performance to a distraction. Although the data-processing components of each task may be very different, the combination of paradigms can discover whether attentional processes are common to all.
Some attentional paradigms have been successfully modified for animal subjects (Robbins, 1998). For instance, the FIVE-CHOICE SERIAL REACTION TIME TEST measures sustained and divided attention in rats, as they continuously monitor and respond to the presentation of a light in one of five possible locations, for the delivery of a small food reward. Selective attention can also be investigated in this task by including random bursts of white noise amongst the visual stimuli. Paradigms specifically designed to investigate divided attention include those which require monitoring of simultaneously presented visual stimuli, and more recently the performance of concurrently presented conditional discriminations in the auditory and visual domains. The roles of the INTRADIMENSIONAL SHIFT and EXTRADIMENSIONAL SHIFT have been successfully investigated in a modification of the Wisconsin card-sort test for PRIMATES.
Just as attention is not a unitary process, it has been shown that it is not carried out by one particular region of the brain, but by a network of systems which interact with specific stimulus-response processing systems (Posner & Peterson, 1990). Within this network, certain regions have been ascribed specific functions through the use of LESION techniques in animal studies and the development of sophisticated human brain scanning techniques such as POSITRON EMISSION TOMOGRAPHY and MAGNETIC RESONANCE IMAGING. For instance, the SUPERIOR COLLICULUS is likely to have responsibility for movement of visual attention through its involvement in eye movements. The lateral pulvinar of the THALAMUS and the posterior PARIETAL CORTEX have been highlighted as crucial for the engagement and disengagement of attention respectively. The PREFRONTAL CORTEX has been shown to be required for making successful extra-dimensional shifts. In addition, the neurochemistry of attentional processes is beginning to unfold. Forebrain CHOLINERGIC and brainstem NORADRENERGIC systems which innervate the cerebral cortex are thought to be involved in aspects of accuracy, while the brainstem cholinergic, SEROTONERGIC and noradrenergic systems may enhance sensory awareness by their enhancement of the excitability of thalamic relay neurons. The NIGROSTRIATAL DOPAMINE SYSTEM titrates MOTOR READINESS. The discovery that attention can be broken down into distinct neurochemical and neuroanatomical components has supported its investigation within the context of disease states. For instance, the parietal lobes have been linked particularly closely with attentional neglect (see NEGLECT SYNDROME), the frontal lobes have been associated with perseverative deficits in SCHIZOPHRENIA, and attentional deficits in patients with ALZHEIMER’S DEMENTIA have been attributed to a loss of forebrain ACETYLCHOLINE.
Posner M.I. & Peterson S.E. (1990) The attention system of the human brain. Annual Review of Neuroscience 13:25–42.
Robbins T.W. (1998) Arousal and attention: psychopharmacological and neuropsychological studies in experimental animals. In The Attentive Brain, ed. R.Parasuraman, pp. 189–220, MIT Press: Cambridge MA.
WENDY L.INGLIS
This is the complete article, containing 808 words
(approx. 3 pages at 300 words per page).
