THE EFFECT OF OCCUPATIONAL IMPACT NOISE ON SENSORIMOTOR PERFORMANCE FRANK PECENKA, Ph.D. Division of Biomechanics Institute of Rehabilitation Medicine New York University Medical Center New York, New York
R ECENT research on the relation between noise and human performance has produced much confusing data. It has been stated that noise has a detrimental effect, no effect, or a facilitating effect. 1.2 Related research expands on the accepted theory that the human body reacts to stress in a predictable way and that loud noise induces a stress reaction.3 It is not at present clear how the effects of noise on different workers can be determined. Noise can be stimulating in certain cases. Some workers not only prefer to work with a higher level of background noise stimulation, but actually work with greater efficiency.4 Evidence is accumulating that noise affects performance of certain kinds of work, such as vigilance tasks, complex mental tasks, tasks that require skill and precision, and those that demand high perceptual capacity.567 Some recent experiments demonstrate that high intensity noise produces irritability, anxiety, and aggressive behavior. Any of these symptoms might diminish required motor performance.8 Literature further documents individual differences in reaction to high-intensity noise, and that, generally, a worker's attention decreases as noise increases.9 Kryter,10 in his recent book on the effect of noise on human performance, questions previous studies that indicated a transient effect of noise on specific tasks. His criticism concerns methodological difficulties, ambiguous interpretations of experimental data, and unusual scoring techniques in the final results. This study attempts to determine the effects of occupational impact noise on the precision and time of unguided hand-motion patterns through quantitative analysis of one aspect of this problem. As a controlled laboraThis research was supported by Training Grant 5-TO1-OH-00103-05 from the National Institute for Occupational Safety and Health, United States Public Health Services, Department of Health, Education, and Welfare.
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tory test of the industrial environment, this study investigates the effect of occuptional impact noise on overall working efficiency and on specific task performance. Grimaldi"1 studied sensorimotor performance under several intermittent noise conditions. The task required guided hand movement. The investigator measured errors, response time, and productivity, and found that performance was poorer under noisy than under quiet conditions in each of these three measures, but his study does not separate the effect on each factor. Chisman12 investigated the effect of continuous industrial noise on the performance time and on the forces exerted in the performance of such unguided fine hand-movement tasks as miniature assembly work, and found that noise significantly affected neither performance time nor the forces exerted in the performance. This study, using modern instrumentation and biomechanically controlled laboratory conditions, investigated the effect of occupational impact noise on unguided hand-motion patterns. Previous research used guided hand movement. Guided hand movements are likely to inhibit the individual's normal motion patterns and to lead to a more restricted feeling when performing forced motion patterns that may result in less efficient work output. Many other applications of unguided hand movement are found in industry, and therefore unguided hand movement was considered of great practical significance. SOURCE OF NOISE
Noise levels in a large electronic assembly plant were found by a factory epidemiological examination to be from 75 dB(A) to 90 dB(A) as measured on the A scale of a sound-level meter. This noise primarily came from a high-speed, shortstroke punch press. Peaks in the noise occurred when several press machines operated simultaneously. Background noise came from activities in other parts of the large factory area. The noise was recorded, using a Sony tape recorder and Shure 55 S dynamic microphone. The following values have been determined for the background noise: peak pressure level: 96.96 dB(A); rise time: less than 5 milliseconds; decay time: 120 milliseconds; impulse duration (from peak to the ambient noise level): 180 milliseconds; and peak level of background noise: 85 dB(A) to 92 dB(A).
Bull. N.Y. Acad. Med.
EFFECT OF NOISE ON PERFORMANCE
TEST CONDITIONS In the study, experimental treatments consisted of three different noise levels: ambient noise of the testing laboratory, 75 dB(A) of occupational impact noise, and 90 dB(A) of occupational impact noise. The first treatment at the ambient noise level of the testing laboratory without occupational impact noise was considered the operational equivalent of quiet occupational noise in an industrial setting. Ambient noise level of the testing laboratory was carefully monitored. If a variation in noise level greater than + 5 dB(A), as measured with a sound level meter with slow meter response, was obtained, the experimental trial was discarded and repeated. The ambient noise level in the laboratory was 55 dB(A), which is considered insignificant. The remaining two noise levels were applied to each subject through earphones. It was assumed that the effects of noise, whether through the earphones or directly from the industrial environment, would be the same. Any effect from the use of earphones was constant and was not measured in this study.
SUBJECTS FOR THE STUDY The volunteer subjects for the study were 12 right-handed, physically healthy women between 20 and 40 years old. Righthanded subjects were chosen because of the task-board design. The age range helped to eliminate the physiological effects of aging as a factor in the response of subjects to noise, and this age range represented that most likely to be found in an industrial setting in which precision work is performed. Volunteers were screened to exclude those who could not learn the tasks in a maximum of one and one-half hours or who could not pass an audiologic examination. From an initial pool of 40 volunteers, 18 were selected for learning ability, and this group was further reduced by audiologic examination to the final sample of 12. These 12 women, who came from an employment agency or from the staff of a university hospital, had the following regular occupations: secretary (5), actress (1), optical mechanic (1), respiratory therapist (1), baby sitter (1), student (2), and unemployed
(1). EQUIPMENT DESCRIPTION AND TEST PROCEDURE A triaxial kinesiometer was used to monitor the hand movements. Data
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for velocity and acceleration were generated for the motion in each of the three planes, and the vector sum of the three components of velocity was also produced. Sound was supplied by playback from a tape recorder, while the levels were monitored and set by a sound-level meter. A multichannel strip chart recorder (Beckman Dynograph) displayed and recorded the contact of the hand-held cylinder and task-board holes and the vector sum of the velocity components. A digital computer (PDP 8/e-I) was programmed for precision time measurements and to print out the tabulated time data. Audiometer testing was performed using Beltone 15 CX equipment. The task board was a flat surface containing a series of individual holes in which a cylinder could be mated. The subject held a plastic cylinder with a metallic conductor attached to the bottom. The equipment recorded when this conductor contacted a conductor either at the top or the bottom of each hole. The complete task included the hand movements of eight motion patterns in four directions (left to right, right to left, far to near, and near to far). In every direction there were two reaches: short (or 10-inch) and long (or 20-inch) distance. The specific holes were chosen so that hand movements could be executed in the coronal and midsagittal planes. The task consisted of six identical hand movements for the short (10inch) distance or six identical hand movements for the long (20-inch) distance for all four directions. The eight motion patterns made a total of 48 hand movements, and these 48 hand movements were performed three times for each run. Therefore, one run consisted of 144 hand movements of short and long distances in all four directions. The first two hand-motion tasks started at the left side of the task board from the starting hole Si toward terminal hole 1 or 2. The same procedure was repeated from right to left, from far to near, from near to far. After the completion of the 144 hand movements at the ambient noise level came a three-minute break. The 144 hand movements were then repeated at the 75 dB(A) of occupational impact noise level followed by another three-minute break. The 144 hand movements were once again repeated, this time at 90 dB(A) of occupational impact noise level after which came a break of 10 minutes. The procedure described above was repeated three times. Each hole had electrical contacts near the top and the bottom to sense the proximity of the contact cylinder to the hole. A properly performed task required that the cylinder be placed in the terminal hole without first Bull. N.Y. Acad. Med.
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touching the top contact, which required greater hand-movement precision and control than the situation in which the top of the terminal holes was touched first. Electrical contacts at the top and bottom of each hole in the task board were connected to the strip-chart recorder for a graphic record and to the digital computer to measure the time of each hand-motion pattern. MEASUREMENT OF THE PRECISION OF UNGUIDED HAND-MOTION PATTERNS
The subject placed the cylinder in the appropriate starting hole at the beginning of each hand-motion pattern. When the subject first touched the starting hole with the cylinder, the completed circuit sent an electrical signal to the recorder. Ability to seat the cylinder in the terminal hole without first touching the upper side of the hole was taken as a measure of precision of unguided hand-motion patterns. A Beckman Dynograph recorder visually indicated the performance of each hand-motion pattern simultaneously throughout the experiment. The strip-chart recorder ran at 1 cm./second to allow direct one-to-one measurement of all component times with an accuracy of + 5 milliseconds and this served as a check against the digital computer (see below). From the strip-chart recorder it was possible to observe how many times the subject touched the upper side of the terminal hole (called the "errors" of performance) during the experiment. By subtraction of errors from the total number of hand motions, the number of successes was obtained. The number of errors was obtained and used for later statistical computation. The maximum number of successful hand movements for a given task was limited to six. MEASUREMENT OF TIME OF UNGUIDED HAND-MOTION PATTERNS
To determine the effects of occupational impact noise on performance time, the time for each hand-motion pattern was measured by the digital computer, which could easily evaluate the time for relatively small handmotion patterns. The time measurement was activated by a contact cylinder sensing input and output, respectively, from the starting hole to a designated terminal hole and back to the starting hole. Measurement of the time of hand-motion patterns was programmed on a digital computer capable of recording electrical impulses in milliseconds, and it was possiVol. 55, No. 3, March 1979
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TABLE I. MEANS AND STANDARD DEVIATIONS OF ERRORS CLASSIFIED ACCORDING TO NOISE LEVELS (ERRORS IN MEAN NUMBERS)
Ambient noise 1 2 X (n=3) SD
75 dB(A) 3 4 SD X(n=3)
90 dB(A) 5 6 SD X(n=3)
1 2 3 4 5 6 7 8 9 10 11 12
39 22 20 25 26 25 35 26 25 26 24 30
33.00 52.00 49.30 51.00 17.00 56.30 55.00 47.00 13.70 66.30 55.00 50.30
4.00 7.21 6.43 18.19 16.52 7.57 9.34 4.36 4.73 8.62 11.53 4.51
48.00 52.00 56.00 54.70 9.70 55.30 58.00 53.30 13.00 64.30 56.30 50.00
14.00 8.08 16.82 20.31 4.73 12.50 3.61 8.96 3.61 11.15 13.32 7.81
34.30 62.00 57.00 65.00 16.00 63.70 56.70 45.00 21.30 69.70 58.00 51.70
6.35 14.93 15.72 21.17 4.58 13.58 16.07 14.11 7.10 12.70 3.00 15.31
ble to determine response time by measuring the elapsed time of transporting the cylinder from the starting hole to the terminal hole as indicated before. A printout from the computer numerically displayed time data pertinent to each run of the unguided hand-motion patterns. From these data a total of six hand motions, the average time per task, was computed for statistical evaluation. EXPERIMENTAL PROCEDURE
Each subject was tested individually in one session. At the beginning of each session the subject was familiarized with the project, signed a consent form, and completed the personal questionnaire. Each subject underwent examination by a staff otorhinolaryngologist, including a hearing test, to determine eligibility for the study. These examiniations were also repeated after the experimental procedure. Hearing sensitivity was considered normal if thresholds were 20 dB13 or below for the frequencies 125, 250, 500, 1,000, 2,000, 4,000, 6,000, and 8,000 Hz as measured with a standard audiometer, Beltone 15 CX. Temporary or permanent hearing loss is a remote possibility in experiments involving noise exposures and, as a precaution, the intensity and duration of noise exposures in this experiment were at levels considered completely safe.14 Bull. N.Y. Acad. Med.
EFFECT OF NOISE ON PERFORMANCE
TABLE II. MEANS AND STANDARD DEVIATIONS OF TIME FOR PERFORMANCE CLASSIFIED ACCORDING TO NOISE LEVELS (TIME IN SECONDS) 90 dB(A) 75 dB(A) Ambient noise 1 2 3 4 6 _ 5 SD X (n=3) SD X (n=3) X (n=3) SD 1 2 3 4 5 6 7 8 9 10 11 12
39 22 20 25 26 25 35 26 25 26 24 30
81.707 72.623 61.683 56.186 63.070 62.503 66.700 62.016 48.510 62.273 53.043 62.726
8.846 9.733 8.655 9.003 21.184 1.749 14.179 9.301 4.714 3.412 5.312 3.596
77.936 70.046 61.683 61.486 64.806 62.950 61.056 55.640 48.733 55.351 51.630 60.656
3.920 3.879 4.736 3.497 1.443 1.128 5.008
75.556 64.783 56.753 60.403 65.013 59.480 72.087 64.946 51.486 56.656 51.650 58.083
4.007 4.570 6.279 11.221 21.576 3.975 3.722 17.098 5.876 3.921 8.106 4.135
5.217 0.280 6.321 9.136 9.695
Means and standard deviations of errors as a function of noise conditions are shown in Table I. Differences between means by inspection of the data can be summarized as follows: Mean errors among subjects in the ambient noise condition differ greatly. Mean errors progressively increase when the occupational impact noise increases to 75 dB(A) level in six of 12 subjects. Mean errors are more pronounced at the 90 dB(A) level in 10 of the 12 subjects. The effect of occupational impact noise is especially marked when increased to 90 dB(A). The overall means for errors for occupational impact noise conditions compared to ambient noise conditions for the total experiment is as follows: 45.5 mean errors at ambient noise level, 47.6 mean errors at 75 dB(A) level, and 50.03 mean errors at 90 dB(A) level. These apparent differences in the effect of occupational impact noise suggest that occupational impact noise increases motor performance errors as noise levels increase. Mean time of the performance for all subjects is included in Table II. Mean time of performance with 75 dB(A) of occupational impact noise was 2.83% shorter than the mean time for the ambient noise condition. Mean time for 90 dB(A) of occupational impact noise was 2.18% less than the mean time for the ambient noise condition. Hence, subjects slightly tended to perform the task faster but less precisely under the 75 dB(A) and Vol. 55, No. 3, March 1979
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