William JAMES once wrote, "Every one knows what attention is. It is the taking possession by the mind, in clear and vivid form, of one out of what seem several simultaneously possible objects or trains of thought. Focalization, concentration, of consciousness are of its essence. It implies withdrawal from some things in order to deal effectively with others" (James 1890: 403-404). The study of selectivity in information processing operations, of "withdrawal from some things in order to deal effectively with others," has its modern origins in the 1950s with BROADBENT's Perception and Communication (1958). Loosely speaking, much of this work may be taken as research into "attention," though problems of selective information processing of course need not be identical to James's first-person view of selective consciousness or awareness.

In fact many aspects of selectivity must contribute to the organization of any focused line of activity. At any given time, the person is actively pursuing some goals rather than others. Some actions rather than others bring those goals closer. Some parts rather than others of the sensory input are relevant and must be examined or monitored. The general state of alertness or drowsiness is also often considered an aspect of "attention." In Perception and Communication, a single selective device was used to handle many different phenomena: selective listening, loss of performance with long work periods, impairments by loud noise, and so forth. When the theory was updated in Decision and Stress (1971), data from many experimental tasks already required a substantially more complex approach, with a variety of distinct selective mechanisms. Modern work seeks to understand both separate aspects of processing selectivity and their relations.

Selective perception in a variety of modalities has been particularly well investigated. Experiments on selective listening in the 1950s dealt with people listening to two simultaneous speech messages. First, these experiments showed limited capacity: People were often unable to identify both messages at once. Second, they showed conditions for effective selectivity: People could identify one message and ignore the other providing the messages differed in simple physical characteristics such as location, loudness, or voice, but not when they differed only in content. Third, these experiments showed the striking consequences of efficient selection: A person listening to one message and ignoring another would subsequently be able to report only the crudest characteristics of the ignored message, for example, that it had changed from speech to a tone, but not whether it had been in a familiar or an unfamiliar language.

All three points have received much subsequent study. As an example of the many things learned regarding limited capacity, experiments with mixed visual and auditory stimuli show that the major limit on simultaneous perception is modality-specific: One visual and one auditory stimulus can be identified together much better than two stimuli in the same modality (Treisman and Davies 1973). Regarding the control of stimulus selection, experiments show the joint influence of top-down (task-driven) and bottom-up (stimulus-driven) considerations. Top-down influences are important when a person is specifically instructed to pay attention just to objects in a certain region of a visual display (selection by location), objects having a certain color or other property (selection by object feature), or objects of a certain category (e.g., letters rather than digits) (von Wright 1968). Selection by location (spatial attention) has been particularly well studied (Posner 1978). Irrespective of the task or instruction, however, stimulus factors such as intensity (Broadbent 1958) or sudden onset (Jonides and Yantis 1988) also contribute to the choice of which stimulus is processed. Long practice in considering a certain stimulus relevant or important will also favor its selection, as when one's own name attracts attention in a crowded room (Moray 1959). Regarding the results of efficient selection, finally, experiments have detailed what differs in the processing of attended and ignored stimuli. Often, very little can be explicitly remembered of stimuli a person was asked to ignore, even though those stimuli were perfectly audible or visible (Wolford and Morrison 1980). In contrast, indirect measures may suggest a good deal of hidden or unconscious processing; for example, an ignored word previously associated with shock may produce a galvanic skin response even while subjects fail to notice its occurrence (Corteen and Dunn 1974). The nature and duration of such implicit processing of unattended material remains a topic of active debate, for example, in the discussion of IMPLICIT VS. EXPLICIT MEMORY.

These studies reflect general questions that may be asked of any selective process. One is the question of divided attention, or how much can be done at once. Another is the question of selective attention, or how efficiently desired stimuli can be processed and unwanted stimuli ignored. Experiments measuring establishment of a new selective priority concern attention setting and switching. The complement to switching is sustained attention, or ability to maintain one fixed processing set over an extended time period.

The neurobiology of visual attention is a particularly active topic of current research. In the primate brain, visual information is distributed to a network of specialized cortical areas responsible for separate visual functions and dealing partially with separate visual dimensions such as shape, motion and color (Desimone and Ungerleider 1989). Taken together, these "visual areas" cover roughly the posterior third of the cerebral hemispheres. Recordings from single cells in several visual areas of the monkey show weak or suppressed responses to stimuli that the animal is set to ignore (Moran and Desimone 1985). Measurements of gross electrical activity in the human brain, and associated changes in local cerebral bloodflow, similarly suggest greater responses to attended than to unattended stimuli (Heinze et al. 1994). Damage to one side of the brain weakens the representation of stimuli on the opposite side of visual space. Such stimuli may be seen when they are presented alone, but pass undetected when there is concurrent input on the unimpaired side (Bender 1952). All these results suggest that concurrent visual inputs compete for representation in the network of visual areas (Desimone and Duncan 1995). Attended stimuli are strongly represented, while responses to unwanted stimuli are suppressed.

Complementary to selective perception is the selective activation of goals or components of an action plan. Here, too, errors reflect limited capacity, or difficulty organizing two lines of thought or action simultaneously. Everyday slips of action, such as driving to work instead of the store, or stirring coffee into the teapot, are especially likely when a person is preoccupied with other thoughts (Reason and Mycielska 1982). Practice is again a key consideration. Although it may be impossible to organize two unfamiliar activities at once, familiar behavior seems to occur automatically, leaving attention (in this sense) free for other concerns. Indeed, familiar actions may tend to occur "involuntarily," or when they are currently inappropriate. Again everyday action slips provide clear examples: taking a familiar route when intending to drive elsewhere, or taking out one's key on arrival at a friend's door (James 1890). A laboratory version is the Stroop effect: Naming the color of a written word suffers substantial interference from a tendency instead to read the word itself (Stroop 1935). Such results suggest a model in which conflicting action tendencies compete for activation. Practice increases an action's competitive strength.

Disorganized behavior and action slips occur commonly after damage to the frontal lobes of the brain (Luria 1966). Disorganization can take many forms: intrusive actions irrelevant to a current task, perseverative repetition of incorrect behavior, choices that seem ill-judged or bizarre. A major question is how action selection develops from the joint activity of multiple frontal lobe systems. A more detailed treatment is given in ATTENTION AND THE HUMAN BRAIN.

To some extent, certainly, it is appropriate to consider different aspects of "attention" as separate. To take one concrete example, it has been amply documented that there are many distinct forms of competition or interference between one line of activity and another. These include modality-specific perceptual competition, effector-specific response competition, and competition between similar internal representations (e.g., two spatial or two verbal representations; see Baddeley 1986); though there are also very general sources of interference even between very dissimilar tasks (Bourke, Duncan, and Nimmo-Smith 1996). Each aspect of competition reflects a distinct way in which the nervous system must select one set of mental operations over another.

At the same time, selectivities in multiple mental domains must surely be integrated to give coherent, purposive behaviour (Duncan 1996). It has often been proposed that some mental "executive" takes overall responsibility for coordinating mental activity (e.g., Baddeley 1986); for example, for ensuring that appropriate goals, actions, and perceptual inputs are all selected together. At least as attractive, perhaps, is an approach through self-organization. By analogy with "relaxation" models of many mental processes (McClelland and Rumelhart 1981), selected material in any one mental domain (e.g., active goals, perceptual inputs, material from memory) may support selection of related material in other domains. The description of top-down control given earlier, for example, implies that goals control perceptual selection; equally, however, active goals can always be overturned by novel perceptual input, as when a telephone rings or a friend passes by in the street. Whichever approach is taken, a central aspect of "attention" is this question of overall mental coordination.

See also

-- John Duncan


Baddeley, A. D. (1986). Working Memory. Oxford: Oxford University Press.

Bender, M. B. (1952). Disorders in Perception. Springfield, IL: Charles C. Thomas.

Bourke, P. A., J. Duncan, and I. Nimmo-Smith. (1996). A general factor involved in dual task performance decrement. Quarterly Journal of Experimental Psychology 49A: 525-545.

Broadbent, D. E. (1958). Perception and Communication. London: Pergamon.

Broadbent, D. E. (1971). Decision and Stress. London: Academic Press.

Corteen, R. S., and D. Dunn. (1974). Shock-associated words in a nonattended message: a test for momentary awareness. Journal of Experimental Psychology 102:1143-1144.

Desimone, R., and L. G. Ungerleider. (1989). Neural mechanisms of visual processing in monkeys. In F. Boller and J. Grafman, Eds., Handbook of Neuropsychology, vol. 2. Amsterdam: Elsevier, pp. 267-299.

Desimone, R., and J. Duncan. (1995). Neural mechanisms of selective visual attention. Annual Review of Neuroscience 18:193-222.

Duncan, J. (1996). Cooperating brain systems in selective perception and action. In T. Inui and J. L. McClelland, Eds., Attention and Performance XVI. Cambridge, MA: MIT Press, pp. 549-578.

Heinze, H. J., G. R. Mangun, W. Burchert, H. Hinrichs, M. Scholz, T. F. Munte, A. Gos, M. Scherg, S. Johannes, H. Hundeshagen, M. S. Gazzaniga, and S. A. Hillyard. (1994). Combined spatial and temporal imaging of brain activity during visual selective attention in humans. Nature 372:543-546.

James, W. (1890). The Principles of Psychology. New York: Holt.

Jonides, J., and S. Yantis. (1988). Uniqueness of abrupt visual onset in capturing attention. Perception and Psychophysics 43:346-354.

Luria, A. R. (1966). Higher Cortical Functions in Man. London: Tavistock.

McClelland, J. L., and D. E. Rumelhart. (1981). An interactive activation model of context effects in letter perception: Part 1. An account of basic findings. Psychological Review 88:375-407.

Moran, J., and R. Desimone. (1985). Selective attention gates visual processing in the extratriate cortex. Science 229:782-784.

Moray, N. (1959). Attention in dichotic listening: affective cues and the influence of instructions. Quarterly Journal of Experimental Psychology 11:56-60.

Posner, M. I. (1978). Chronometric Explorations of Mind. Hillsdale, NJ: Erlbaum.

Reason, J., and K. Mycielska. (1982). Absent-minded? The Psychology of Mental Lapses and Everyday Errors. Englewood Cliffs, NJ: Prentice-Hall.

Stroop, J. R. (1935). Studies of interference in serial verbal reactions. Journal of Experimental Psychology 18:643-662.

Treisman, A. M., and A. Davies. (1973). Divided attention to ear and eye. In S. Kornblum, Ed., Attention and Performance IV. London: Academic Press, pp. 101-117.

von Wright, J. M. (1968). Selection in visual immediate memory. Quarterly Journal of Experimental Psychology 20:62-68.

Wolford, G., and F. Morrison. (1980). Processing of unattended visual information. Memory and Cognition 8:521-527.

Further Readings

Allport, D. A. (1989). Visual attention. In M. I. Posner, Ed., Foundations of Cognitive Science. Cambridge, MA: MIT Press, pp. 631-682.

Norman, D. A., and T. Shallice. (1986). Attention to action: willed and automatic control of behavior. In R. J. Davidson, G. E. Schwartz, and D. Shapiro, Eds., Consciousness and self-regulation. Advances in research and theory, vol. 4. New York: Plenum, pp. 1-18.

Pashler, H. (1997). The Psychology of Attention. Cambridge, MA: MIT press.

Posner, M. I., and S. E. Petersen. (1990). The attention system of the human brain. Annual Review of Neuroscience 13:25-42 .