Theories of Effects of Stressors on Performance

Stressors have traditionally been considered as having one of two kinds of effect on performance: distraction or arousal. Early research on the effects of what we now consider stressors (e.g., loud noises) assumed a broadly distraction kind of theory. In general, apart from transient effects, such experiments were spectacularly unsuccessful in demonstrating any effects on complex performance - including tests of intelligence, memory, and skill.

Not until the mid-1950s, with the application of information processing concepts to psychology, did theory have much of a part to play in this kind of research. More recent treatments (triggered by the seminal work of Donald Broadbent and his colleagues) has recognized that the effects of stressors may be masked, or compensated for, by the built- in redundancy and strategy options available to the cognitive system.

Broadbent argued that it should be possible to demonstrate the effects of stressors by designing tasks that effectively stretched this regulatory process, for example, by presenting information rapidly and without breaks or by making critical events rare and unpredictable in time and place (e.g., serial reaction and vigilance tasks).

In the distraction theory, environmental events were thought to compete for attention through either their strong stimulus qualities (noise or heat) or their impact on bodily states (causing anxiety and other emotional reactions). In its modern form, the distraction view was developed most fully in Broadbent’s influential filter theory. For example, noise was thought to impair task-relevant operations by capturing selective attention.

This involuntary attention to the noise source interrupted the effective intake of relevant task information and gave rise to processing errors. The distraction theory is best supported by studies of intermittent noise, which impairs performance in the few seconds following each burst. In general, however, the distraction view has been thought to offer a less convincing explanation of the effects of both continuous noise and of other stressors, such as sleep deprivation, not so readily identified with external events.

As an alternative to distraction theory, the arousal theory of stress and performance was developed in the 1960s following the generally accepted view of the day that arousal was a unitary, nonspecific brain process. The application of arousal theory to stress effects was based mainly on the systematic studies of combined effects of stressors carried out in Cambridge, UK.

This made extensive use of the five- choice serial reaction task, in which subjects were required to respond to a continuous stream of lights coming on by tapping one of the five metal plates corresponding to the lights. This task showed impairment under noise and sleep deprivation and improvement when subjects were given incentives to do well.

However, performance under noise improved somewhat when subjects were also sleep deprived, whereas incentives made their effects worse. These interactions between stressors were regarded as supporting the arousal theory of stressors because they appeared to show that impairment could be caused by both understimulation (sleep deprivation) and overstimulation (noise). However, the assumptions concerning the nature of arousal could not be convincingly demonstrated independently of the task itself.

For example, there is no direct evidence that noise is arousing in a physiological sense, except in terms of the transient startle pattern at the onset. Increased arousal under noise is typically found only when people are carrying out cognitive tasks, and then only when they are concerned to prevent performance decrements occurring. In addition, it is clear from developments in physiological theory that arousal is more complex than previously assumed - more specific and linked to task processes. In sum, it has proved to be inadequate as a general theory of effects of stress.