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6. STRESS
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6.1 Effect of Environmental Stress upon Performance
6.1.1 Performance in Continuous Noise (Forster, Grierson, Poulton) (Project No. 4)
Forster and Grierson (48) have performed a series of experiments which cast doubt on the previously held view that loud noise produces a narrowing of the attentional field. A new look by Poulton (167) at experiments on continuous noise suggests that the deterioration in performance in continuous noise may be due to the masking of either acoustic cues, or inner speech,both of which may normally be used in quiet. If so, prevention of the deterioration in performance is a simple psychophysical problem of making the cues audible, or substituting adequate visual cues.
6.1.2 Fatigue in Junior Hospital Doctors (Carpenter, Edwards, Poulton)
Our results indicate that for brief periods doctors can compensate for loss of sleep, provided they are sufficiently awake to appreciate the importance of what they are doing. But dull routine tasks are likely to suffer from loss of sleep. Long hours of work were not found to degrade performance unless they involved loss of sleep (180).
6.1.3 Physical Disturbances (Carpenter, Edwards, Poulton, D.C.V. Simmonds)
These studies include Poulton's work on steady and gusty winds of moderate strength and on the vibration produced by low-frequency noise (174; 179), work by Carpenter on the bang and sudden change in weight on firing a simulated missile from the shoulder, and the work by Simmonds and Poulton on the spontaneous rotary shake which occurs in holding a camera with a heavy long-focus lens (183). In all cases the physical disturbances interfered with precise motor skills. But this may in some cases be compensated for by the increase in behavioural arousal which the physical disturbance also produces. In the low-frequency noise, performance was reliably better on a 30-minute 5-choice tapping task, and also on a 30-minute visual vigilance task, than in the control condition. Advice has been given on methods of reducing camera shake, and on the design of the control systems of Army and Navy missiles which have to be aimed manually.
6.1.4 Transfer Bias in the Interaction of Noise and Heat (Edwards, Poulton)
In an experiment by Poulton and Edwards on the interaction of noise and heat (174), there were four conditions: noise by itself, heat by itself, noise combined with heat, and a control condition without noise or heat. In a design where the same subject was tested in all four conditions the only observed effect was a decrement in heat. When subjects were tested in only one condition however both noise and heat tend to improve performance. Within-subject designs are suspect since they give rise to transfer between conditions (177).
6.1.5 Bias in Subjective Judgments (Poulton)
Subjective judgments of the effects of stress sometimes contradict the results of tests of performance. In addition to bias by transfer, Poulton has described seven distinct biases in quantitative subjective judgments. Ways of avoiding the bias have been suggested (173).
6.1.6 Development of a Cognitive Test Battery (Baddeley, Lewis, Thomson, Wing)
The APU has traditionally been concerned with the measurement of human performance under stress. This interest continues although it is not at present a major research area. A test of semantic processing is being developed by Baddeley, Lewis and Thomson which allows an estimate of the speed at which the subject can access information in long-term memory. So far this has been tested using alcohol as a stressor and has proved to be sensitive (2). Lewis and Baddeley are continuing to provide a battery of tests for use in the Royal Naval Physiological Laboratory trials on deep oxyhelium diving. It is already becoming clear that reliable impairment occurs at 1000 feet, a depth at which it has previously been claimed that performance is unaffected.
6.1.7 Diver Performance and Selection (Baddeley, Godden)
In addition to our work with the Royal Naval Physiological Laboratory, Godden and Baddeley have been involved in two projects on divers. The first was concerned with context dependent memory in divers. We showed that material learnt in one environment (on land or under water) was much better recalled in that environment than in the alternative context. When memory is tested by recognition, no such effect occurs (58). An extension of this work showed that learning a manual skill on land could actually impair its performance under water is compared to a control group which has no pretraining. Implications for diver training are obvious.
We have just completed the first stage of a Department of Employment sponsored project with Stirling University on the selection of trainee divers. The final report includes a detailed description of the range of jobs undertaken by commercial divers involved in both inshore harbour works and offshore North Sea oil diving. Divers entering the three officially recognised training schools within the UK were given a range of tests, and are currently being followed up to study the relationship between test performance and subsequent diving career (10).