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A relatively straightforward method of studying the effects of arousal on performance is to manipulate the level of arousal by means of exogenous or external stimulation. Ideally, such stimulation should be intense but non-informative, so that it produces a state of elevated arousal without at the same time attracting attention. In practice, white noise (i.e. a noise consisting of all sound frequencies and resembling hissing) has been far and away the most used exogenous determinant of arousal. There is fairly general agreement that intense white noise produces heightened physiological arousal, and direct evidence in support of this contention was obtained by Berlyne and Lewis (1963), who discovered that moderate intensity white noise produced a significant drop in skin resistance.

The concept of attention has led a rather chequered existence during the history of psychology. It was highly regarded by the introspectionists and armchair theorizers of the nineteenth century, some of whom had important things to say about attention. For example, the following quotation from William James (1980) anticipates a number of later theoretical developments: “If, then, by the original question, how many ideas or things can we attend to at once, be meant how many entirely disconnected systems or processes of conception can go on simultaneously, the answer is, not easily more than one, unless the processes are very habitual; but then two, or even three, without very much oscillation of the mind from one to the next, and no consequent gain of time” (p. 409).

In this book we have considered some of the major effects which such variegated arousers such as anxiety, introversion-extraversion, incentives, time of day, white noise and sleep deprivation have on performance. To what extent are there any general themes running through this gallimaufry of research? One such theme is formed by the Yerkes-Dodson law, which seems to have served as the basis for much of the research endeavour in this area. While we have been at pains to point out that one of the law’s disadvantages is its ability to encompass many different patterns of results with no apparent difficulty, it is nonetheless of interest that it does describe reasonably adequately findings involving extremely heterogenous arousers.

In very general terms, motivation depends on an amalgam of internal and external factors. Thus, for example, the motivational state known as hunger is clearly influenced by internal conditions related to the number of hours of food deprivation and by external stimuli providing visual and olfactory information about food. It is a meaningless question to ask whether motivational states are more affected by external or by internal factors, since the relative importance of each set of factors can vary within extremely wide limits. In addition, of course, internal and external factors typically interact with each other: the incentive value of a bowl of rice is much greater for a starving peasant in Asia than for a bloated member of Western society.

We saw in the previous chapter that one of the major recent developments in the area of attention has been the distinction between attention-demanding processes and automatic processes that do not require attention. There have been at least two other significant shifts in thinking. One is that the original notion of attention as a bottleneck has been replaced by a conceptualization in which attention is regarded as a limited power supply. The basic idea is that attention represents a general purpose limited capacity that can be flexibly allocated in many different ways in response to task demands. The second shift in the status quo ante is that attention is increasingly regarded as constituting only one out of a number of different processing resources.

In this chapter we consider a variety of internal or endogenous factors contributing towards an individual’s level of arousal. It has been claimed that even in the absence of a stimulating environment, some individuals will characteristically be in a more aroused state than others. The dimension of individual differences most frequently referred to in this connection is introversion-extraversion (H. J. Eysenck 1967), the usual assumption being that introverts are chronically more aroused than extraverts.

The concept of anxiety has been used in a bewildering variety of ways by different theorists. While some regard anxiety as a motivational state, others consider it to be an emotion, and still others claim that it combines motivational and emotional components. In spite of these differences of opinion, there would probably be reasonable agreement with the following definition of the anxiety state that was proposed by Spielberger (1972): “Unpleasant, consciously-perceived feelings of tension and apprehension, with associated activation or arousal of the autonomic nervous system” (p. 29).

The emphasis in contemporary approaches to attention and performance, as we saw in the previous two chapters, is very much on theoretical constructs of a cognitive nature. However, it seems probable, both in terms of everyday experience and the relevant experimental evidence, that the physiological state of the organism while engaged in information processing is important and ought to be considered.