348 



NOISE 



Stevens and others (85, 86) concluded 

 that exposure to airplane noise at 115 db for 

 continuous seven-hour periods repeated over 

 16 experimental days distributed over four 

 weeks had no effect on tasks labeled coordi- 

 nated serial pursuit, serial disjunctive reac- 

 tion time, card sorting, rotary pursuit, code 

 translation tests, and monocular distance 

 judgments. Measurements on five subjects 

 of metabolic rate, respiration rate, speed of 

 visual accommodation, saccadic movements, 

 bodily sway, hand steadiness, frequency of 

 reversible prospective, and speed of dark 

 adaptation all gave highly variable results 

 from subject to subject and from time to 

 time, apparently unrelated to noise condi- 

 tions. It was therefore concluded that these 

 tests gave inconclusive results on the effects 

 of noise. On the other hand, a coordinated 

 serial reaction time task requiring subjects 

 to direct a beam of light along an opaque 

 pathway by means of airplane controls 

 showed approximately a five percent decre- 

 ment (statistically significant) in the speed 

 and accuracy with which the task was per- 

 formed. This result, the investigators sug- 

 gest, might be an artifact of certain minor 

 auditory cues present during the "quiet" pe- 

 riods but masked by the noise, or of the fact 

 that the subjects set their own pace on this 

 task and worked near the hmit of their ca- 

 pacity. 



A series of laboratory studies conducted 

 in England (69), in which the noise condi- 

 dions are not completely described, showed 

 that the effects of noise on a simple motor 

 task (placing pegs in a moving peg board) 

 gave results that were difficult to interpret. 

 Two subjects had nine percent fewer misses 

 with noise and two other subjects had 71 per- 

 cent more misses. The authors recognize 

 that they did not adequately control practice 

 effects that might in part account for some of 

 the discrepancies noted. Regular, recurring 

 movements tended to be more disturbed by 

 irregularly presented noise than by noise 

 synchronized with the movements. Mental 

 tasks, such as a number setting test in which 



the individual operated levers to obtain a 

 particular combination of numbers, showed 

 a small adverse effect. Speed of operations 

 was diminished, although, with continued 

 exposure, the adverse effect of noise was less 

 noticeable. Subjective reports suggested 

 that noise was more distracting in mental 

 rather than on simple motor skills. 



A Russian report (5, seen only in ab- 

 stract) suggests that visual efficiency is ad- 

 versely affected by a 20- to 30-minute expo- 

 sure to engine noise at 105 to 110 db. 



Three field studies of the effect of noise on 

 production (94, 95, 97) have agreed in show- 

 ing a small decrement in output that seemed 

 traceable to the noise factor. However, all 

 of these are open to methodological criti- 

 cisms and cannot be accepted wholly at their 

 face value (3). Weston and Adams (94), 

 examining the output of weavers over a 26 

 weeks' period during which the workers wore 

 ear defenders on alternate weeks, showed an 

 output gain of one percent while wearing ear 

 defenders. Since the output was largely con- 

 trolled by loom speeds and could not in itself 

 vary greatly, a more reveahng statistic was 

 the increase of operators' speed during the 

 five minutes per hour when the weavers were 

 tying knots or making other adjustments. 

 This work, under the control of the opera- 

 tors, increased in speed about 12 percent 

 when wearing ear defenders. A somewhat 

 comparable study (95) done by the same 

 authors under similar circumstances showed 

 a 3§ percent advantage in output and a 13| 

 percent improvement in speed. However, 

 great variabifity from month to month was 

 shown in speed of operations, which sug- 

 gested important uncontrolled factors influ- 

 enced the data. The second study, in con- 

 trast to the first, employed two groups of 

 workers, one of which wore ear defenders and 

 the other did not. The equivalence of these 

 two groups initially was never demonstrated. 



The third important field study (50, 97) 

 was done at the Aetna Life Insurance Com- 

 pany, in which bonus figures, reflecting the 

 efficiency of employees, were used as the indi- 



