Applied Ergonomics 1978, 9.2, 101-103

Psychomotor performance: the effects of continuous noise and augmented feedback

C. Mackay, T. Cox and G. Freeman

Stress Research, Department of Psychology, University of Nottingham

An experiment is reported which tests the hypothesis, put forward by Poulton (1976a, b) that the detrimental effects of noise are due to the masking of auditory feedback. The results of the experiment showed that noise impaired the performance of a tracking task both in the presence and absence of task-related auditory feedback. These findings are contrary to Poulton's predictions.

Introduction

Recently, Poulton (1976a and b) has forcefully argued that coatinuous nobe affects performance in two ways. First, it may Improve performance by increasing arousal. Second, it may impair performance by masking task-related auditory feedback and, in some tasks, inner speech. These postulates are counter to the orthodox view that noise leads to over-arousal which in turn causes a decrease in performance (see, eg, Broadbent, 1971 ; Kalmeman, 1973). In a subsequent reply to Poulton's ideas, Broadbent (1976) whilst accepting the possible detrimental effects of masking, has reasserted the claim that noise can lead to over-arousal and thus to a decrement in performance.

In two of his papers, Pouiton (1976a and 1977) has referred to work carried out at Nottingham (Simpson, Cox and Rothschild, 1974). This work was concerned with the effects of glucose loading and noise upon pursuit rotor performance. Poulton concluded that the detrimental effect of noise reported in this experiment must be due to the masking of augmented feedback in the noise (80 dBA) condition. The augmented feedback, he suggests, is caused by the clicks produced from the electronic relays as the subject leaves and acquires the target. He believes that these clicks must be audible in quiet (50 dBA) conditions. However, he did not consider that the authors also reported that the noise induced impairment in performance could be attenuated by the oral administration of a small quantity of glucose. Glucose administered before tracking, under the quiet condition, led to an impairment in performance. The existence of this interaction effect (glucose x noise) makes it unlikely that Poulton's explanation could be to t~y adequate. Part of the original experiment has thus been replicated in a way which attempts to test out Poulton's hypotheses, because of their bearing on these results, and because of their theoretical importance and practical significance.

Experimenllal dedln An independent group dedgn was chosen in order to

eliminate transfer effects. Two factors were of interest; noise (50, 66 and 90 dBA) and feedback (feedback and no feedback). A third factor, period wit l~ task (lst, 2nd and 3rd successive 5 rain period) was also studied to examine any differential effects of noise or feedback at different stages within the task. Time on target (TT) and deviations from target (DEV) were taken as measures of performance. Seven subjects were randomly assigned to each of six groups.

Subjects 42 male undergraduate (non-psychology) students

participated voluntarily in the experiment. They were all by their own report in good health. Those with visual or auditory defects were excluded. All subjects were tested at the same time of day (9.00 am-12.00 am).

Experimental task

As far as possible the experimental task and procedure followed those used in the original experiment (q.v.) The experimental task used was a stellate pursuit-rotor manufactured by Forth Instruments. The track width was 20 mm and the stylus diameter was 4 ram. The speed of rotation of the light to be tracked was kept constant at l0 roy/rain, giving an overall distance/time requirement of 0-14 m/s. The task lasted for 15 rain with both time-on-target and deviations being recorded continuously on Grason-Stadler/Aim Bioscience programming modules. Cumulative scores for time-on-target and deviations were taken after each 5 mill period. Subjects used their preferred hand for tracking.

Continuous 'white' noise was generated by a Campden Instruments Type C1530 White Noise generator and controlled by a Type A64 Advance Instruments step attenuator. Noise

0003-6870/78/0902-0101 $01.00 ~) 1978 11~ Business Press Applied Er|lonomi~ June 1978 101

was presented to the subjects via headphones. Headphone noise levels were standardised using a Briiel and Kjaer sound level type 2205. The pursuit rotor and noise generator were housed separately in a cubicle. The programming apparatus was kept outside the cubicle at a distance of about 3 m. During the course of the experiment the door of the cubicle was kept closed to prevent any sounds from the programming apparatus being overheard by the subject. Wires connecting the apparatus were passed through a small hole (of approximately 25 mm diameter) drilled into the side of the cubicle.

Generation of feedback

Poulton suggests that augmented feedback is presented to the subject in the form of audible clicks emanating from the electronic relays in the modules of the programming apparatus. In 'quiet' conditions the subject can hear these clicks and so, it is suggested, they aid his performance. In the present experiment the programming modules were kept well away from the subject to prevent this happening in the no feedback group. However, in the feedback groups, 'clicks', identical to those produced from the relays, were superimposed over the sound of the noise. These clicks were generated by taking the output from the electronic probe and feeding it into a capacitor (value 0.047/aF) connected in parallel with a 1MI2 resistor. As the probe left or acquired the light a sharp click was produced in the headphone. Although it was not possible to produce a constant click/noise ratio over the three noise levels all subjects in the feedback conditions reported hearing the clicks.

Procedure

At the start of the experiment the subject was shown the pursuit rotor and the principles of operation explained. He was asked to track the fight around the stellate target using a stylus, until told to stop. Each subject was given a short time (1 rain) to practice tracking, the relevant experimental condition was then imposed. At the end of the experiment subjects in the no-feedback conditions were asked what they had heard apart from the noise. One subject reported hearing clicks. His data were discarded. All subjects in the feedback condition reported hearing clicks and all but one realised that the clicks represented target acquisition.

Results

Mean time on target scores and number of deviations showing the effects of the two variables of interest are shown in Fig. 1.

Analysis of variance of the time on target scores showed that increasing noise brought about an impairment of

~ rformance in terms of decreased time on target scores ( Noise (2, 36 = 4.06, p< 0.05) and an increased number of deviations (FNoise (2, 36) = 3.75, p< 0.05). There was no significant effect of the feedback condition. A successive improvement in performance at each stage during the task was shown for both time-on-target (Fperiods (2, 72) = 4.11, p< 0.05) and deviations (Fperiod s (2, 72) = 13.23, p< 0.01).

There was a trend for the no-feedback group to be worse at 90 dBA than the corresponding feedback group on both of the dependent variables. However, analysis using the t-test revealed that those differences were not statistically reliable.

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Fig. 1

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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FT C~..~ / / i

N o i s e level (dBA)

The effects of noise arid flicilack on mean time on target scores (T and t04id tkiel) and deviations D and broken lines). Feedback = F, No Feedback : F .

Discussion

Poulton's (1976) paper makes three predictions for the outcome of the present experiment. First, noise should lead to either no effect or an improvement in performance. Second, his paper suggests that introducing augmented feedback, in the form of clicks, should lead to an improvement in tracking performance as in the Reynolds and Adams (1953) experiment. The third prediction is that performance in the quiet with feedback should be reliably better than performance in the no-feedback high noise condition. This prediction describes what Poulton assumes is occurring in the Simpson, Cox and Rothschild (1974) experiment. Performance in high noise was worse than in the quiet because the feedback present in the quiet (FI~) is not present in high noise (F~I). Analysis of the data shows, quite clearly, that the first two predictions are not the case. In fact, as with the previous experiment (Simpson, Cox and Rothschild, 1974) noise leads to an impairment in performance. The second prediction was also not borne out. Although there was a slight tendency for feedback to improve performance, overall, there was no reliable effect of this variable. Comparison of the two relevant groups (feedback,quiet vs no-feedback -noise) shows that although there is some support for the third prediction, the overall pattern of the results renders it redundant. We can now say that the detrimental effect of noise in the Simpson, Cox and Rothschild (1974) experiment was not due to masking of auditory feedback, but to some other effect of noise.

Poulton has stated that reported degradations in psychomotor performance observed in conditions of noise are always due to masking of auditory feedback. The present experiment suggests that, unless information is available concerning the effect of noise and feedback together, it would be unwise to accept his statement.

It is interesting to note the absence of any main effect due to auditory feedback in the present experiment. Reynolds and Adams (1953) presented a click to their subjects when they had completed a continuous period of time on target. Before the start of that experiment, subjects

102 Applied Ergonomics June 1978

were told that they would hear a click when they reached a given level of performance. In the present experiment subjects were not told they would hear clicks or what any clicks might represent. However, all subjects heard the clicks, and, apart from one individual, correctly interpreted their meaning. It is therefore difficult to use subject 'ignorance' as an explanation of the lack of auditory feedback effects. The subject can see quite clearly however when the tip of the stylus leaves the moving light. Perhaps subjects do not, need this visual feedback to be augmented by auditory feedback. It is also possible that the type of auditory feedback presented is inappropriate; a continuous sound which always operated when the subject was on target would probably be a more powerful method for maintaining or increasing performance.

References

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

Broadbent, D.E. 1976 Applied Ergonomics, 7.4,231-235. Noise and the

details of experiments; a reply to Poulton

Kahneman, D. 1973 "Attention and Effort", Englewood Cliffs, New

Jersey: Prentice-Hall

Poulton, E.C. 1976a Applied Ergonomics, 7.2, 79-84. Continuous noise

interferes with work by masking auditory feedback and inner speech

Poulton, E.C. 1976b Aviation, Space and Environmental Medicine,

November, 1193-1204. Arousing environmental stresses can improve performance, whatever people say

Poulton, E.C. 1977 Psychological Bulletin, 84.5,977-1001. Continuous

intense noise masks auditory feedback and inner speech

Reynolds, B., and Adams, J.A. 1953 Journal of Experimental Psychology, 45, 315-320.

Motor performance as a function of click reinforcement

Simpson, G.C., Cox, T., and Rothschild, D.R. 1974 Ergonomics, 17, 481-487. The effects of noise stress

on blood glucose levels arid skilled performance

A note on the masking of acoustic clicks

E.C. Poulton

The experiment by Mackay, Cox and Freeman (1978) provides a convincing demonstration of the detrimental effect of masking by continuous noise. In the amplified click condition the clicks can be heard even in the 90 dB(A) noise, although they are partly masked by the noise. Thus if anything performance is better in this condition than in the unamplified click condition.

In the unamplified condition the clicks picked up by the headphones must be from the action of the counter which records the number of times the stylus leaves the star shaped target track. The people are not told in advance to listen for the clicks, and on questioning at the end only one person reports them. But if they were told to listen for the unamplified clicks, presumably people would report them in the control 50 dB(A) noise. Thus the control condition is an example of the now well established phenomenon of perception without awareness, or subliminal perception (Nisbett and Wilson, 1977). The unamplified clicks must be completely masked by the 90 dB(A) noise.

In both conditions performance is worse with masking from the 90 dB(A) noise than in the control 50 dB(A) noise. For the two conditions combined the effect of the masking is reliable statistically. This is in line with the conclusion

that noise does not degrade performance in the absence of masking (Poulton, 1977). In prolonged dull tasks where arousal is low, noise may reliably improve performance if masking is not a problem (Poulton, 1976).

References

Mackay, C., Cox, T., and Freeman, G. 1978 Applied Ergonomics, 9.1,101-103. Psychomotor

performance: the effects of continuous noise and augmented feedback,

Nisbett, R.E., and Wilson, T. De C. 1977 Psychological Review, 84, 231-259. Telling more

than we can know: verbal reports on mental processes.

Poulton, E.C. 1976 Aviation, Space and Environmental Medicine, 47,

1193-1204. Arousing environmental stresses can improve performance whatever people say.

Poulton, E.C. 1977 Psychological Bulletin, 84, 977-1001. Continuous

intense noise masks auditory feedback and inner speech.

Applied Ergonomics June 1978 103