ADAPTATION TO NOISE 



349 



eating data. The installation of a sound- 

 absorbing ceiling in a general office area 

 housing 15 clerks resulted in a 9.2 percent in- 

 crease in efficiency compared with the year 

 previous during which operations and per- 

 sonnel were identical. Bonus figures during 

 the "quiet" year remained consistently above 

 those during the preceding noisy year. 

 Moreover, when the sound-absorbing ceiling 

 was covered with a hard gj'^psum board, re- 

 storing its reverberating quality, the bonus 

 efficiency immediately dropped to an inter- 

 mediate value betweeen the quiet and noisy 

 years, but within two months was approx- 

 imately equal to the level of the quiet year. 

 This suggests that the clerks had readjusted 

 themselves to the higher noise level. At 

 this point the study was terminated due to 

 a reduction in work. 



The data of this Aetna study have never 

 been presented in a way which allows for the 

 calculation of statistical tests of reliabihty of 

 the differences noted. Moreover, the effect 

 of suggestion was not eliminated. It is pos- 

 sible that the clerks may have known the 

 purpose of the study and maj^ unwittingly 

 have exerted greater effort to attain higher 

 levels of production when the acoustic ceiling 

 was installed. The effect of such suggestion 

 has been experimentally demonstrated by 

 Baker (2) for short periods of work. 

 WTiether such suggestion could operate over 

 an extended period of several months is not 

 kno^\^l. 



Adaptation to Noise 



The physiological costs of noise are great- 

 est at the onset of noise and gradually taper 

 off as the noise continues (18, 35, 48). The 

 fact of adaptation shows itself not only in 

 such factors as metabohc rate, digestive dis- 

 turbances and muscle tension, but also in 

 terms of subjective reports of annoyance. 

 The subjects in the English experiment men- 

 tioned above (69) indicated that they could 

 hardly bear the noise in the early experimen- 

 tal sessions, yet at the end they were almost 

 oblivious to it. We have no way of knowing 



whether the changes subjectively reported 

 are traceable to temporarj^ auditory fatigue 

 in the high frequencies which have been 

 demonstrated to be especially annoj'ing or 

 whether the apparent adjustment has some 

 other basis. 



General Fatigue 



It has been repeatedly reported on the 

 basis of cHnical observations that noise con- 

 tributes to general fatigue (3, 4, 16, 32, 46, 

 84). This factor has not been systematically 

 investigated, aside from the work on metabo- 

 hsm reported by Laird (46) and Harmon 

 (32) . Laird reported a 19 percent increase in 

 metabohc rate of typists when they were 

 subjected to undampened office noises com- 

 pared with work in the same space covered 

 with sound-absorbing materials. Harmon's 

 results disagreed with Laird's, but Harmon 

 asked his subj ects to engage merely in men- 

 tal arithmetic in which the muscular com- 

 ponent is obviously sHght, so that metabolic 

 rate could nor be expected to show much 

 change. 



CHnical observations bearing on fatigue 

 take the form of statements such as "stand- 

 ing a watch over a couple of laboring Diesel 

 engines takes more out of a man than when 

 standing watch over a pair of purring tur- 

 bines" (21). A pilot reported, "A person 

 gets much more tired in a noisy plane than 

 he would normally. The physical exertion 

 is not sufficient to warrant this feehng. It 

 must be attributed to the noise which at the 

 end of a long flight leaves my ears ringing 

 and with a definite logy feehng" (23). Fifty 

 percent of 65 instructor pilots in PBY's 

 volunteered the comment that noise con- 

 tributed to unusual fatigue. The existence 

 of such statements drawn from a great va- 

 riety of sources suggests that there may be 

 some validity to the notion — at least it is a 

 hypothesis that merits more systematic re- 

 search than it has so far received. 



Annoyance 

 As indicated above, not all noises of a 

 given loudness are equally annoying. Two 



