Arousal

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n.

The act of arousing, or the state of being aroused.

Whatever has associated itself with the arousal and activity of our better nature.

Hare.

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The state of being prepared for action. The intensity of arousal ranges from deep sleep to extreme excitement. Heightening of arousal is brought about by stimulation of the sympathetic nervous system and an increase in secretion of the hormones adrenaline and noradrenaline. As the body becomes prepared for action, the electrical activity of the brain changes; sweating becomes more profuse; muscle tension, heart rate, and metabolic rate all increase; and some blood is diverted from the gut to the skeletal muscle. Exercise psychologists have established that there is an optimal state of arousal above and below which a person underperforms (see catastrophe theory). Excessive levels of arousal can be very uncomfortable and are better referred to as anxiety.

The state of general preparedness of the body for action. It varies along a continuum ranging from deep sleep to extreme excitement. The term arousal is sometimes used synonymously with alertness and interchangeably with anxiety, although the latter is more correctly confined to situations of high arousal accompanied by unpleasant sensations. Arousal involves the activation of various organs under the control of the autonomic nervous system, especially the reticular activating system. The degree of arousal is reflected by a number of physiological indicators including blood pressure, electroencephalograph brain wave patterns, galvanic skin reaction, heart rate, muscle tension, and respiration rate. Biochemical indicators include concentrations of adrenaline and noradrenaline in the blood. There is not a perfect correlation between these indicators. Different sports have different optimal arousal levels. The relationship between arousal and performance is often described by the inverted U-hypothesis. This hypothesis is based on the assumption that arousal is unidimensional, but there is evidence that there are two or more arousal systems in the brain. Some workers distinguish between psychological arousal (the readiness of an individual to respond to stimuli) and physiological arousal (as indicated by heart rate, sweating, etc.). See also catastrophe theory.

Arousal differs from attention in that it involves a general rather than a particular increase (or decrease) in perceptual or motor activity. There can, however, be quite specific 'arousal', such as sexual arousal. General arousal is mediated by a diffuse neural system, centred in the brain stem, which not only sets a level from sleep to wakefulness (and sometimes over-arousal) but also provides moment-to-moment changes of arousal which are usually appropriate to the prevailing situation, or task in hand. A great deal is known of the neurology of arousal (Milner 1971), especially in the amygdala.

Subtle moment-to-moment changes of arousal are experienced, for example, while driving a car, arousal immediately increasing with any small unexpected event or situation. It has been suggested that fatigue results from over-arousal, the blurring of perception perhaps being due to raised 'neural noise', or increased randomness of neural signals (which may also occur in ageing) in over-arousal. Experiments conducted on vigilance during the Second World War found that radar operators and others looking out for infrequent signals or events rapidly became inefficient as their level of arousal dropped — errors or misses increasing in as short a time as half an hour. This loss of arousal in repetitive or boring situations (though it also occurs in the stress and danger of battle) can be distinguished experimentally from fatigue.

Arousal has been related to stress; indeed stress may be over-arousal. There is an optimal level of arousal, which has been thought of as following an inverted 'U', for performing a task. But the performance of skills at low arousal differs from that when arousal is 'over the top' of optimal arousal; this suggests that the arousal function is not truly U shaped. Errors under conditions of under-arousal tend to be omissions while over-arousal tends to lead to errors of commission or overcorrection.

Learning is improved with increase of arousal — again up to an optimum level, when over-arousal becomes associated with distractions of various kinds (Bills 1927; Sherwood 1965). There is considerable evidence that long-term but not short-term recall is improved with increased arousal. This is presumably because the laying-down of memory traces is more efficient, perhaps with more cross-associations for future reference, for learning while arousal is high. Many people learn to control and optimize their arousal level when working or studying, by varying the task, or perhaps with the aid of music, or (not to be recommended!) smoking. There is little point in working when arousal falls close to the level of sleep.

(Published 1987)

Bibliography
• Bills, A. G. (1927). 'The influence of muscular tension on the efficiency of mental work'. American Journal of Psychology, 38.
• Broadbent, D. E. (1971). Decision and Stress.
• Crawford, A. (1961). 'Fatigue and driving'. Ergonomics, 4.
• Milner, P. (1971). Physiological Psychology.
• Sherwood, J. J. (1965). 'A relation between arousal and performance'. American Journal of Psychology, 78.
• Welford, A. T. (1976). Skilled Performance: Perceptual and Motor Skills.

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