SUMMARY OF RESEARCH 



351 



attempt to develop screening tests for this 

 purpose. Part of the reason for this defi- 

 ciency lies in the difficulty of developing re- 

 Uable measures of annoyance. Investiga- 

 tors have reported that subjective reports of 

 annoyance vary from time to time and from 

 individual to individual in what appeared to 

 be unpredictable ways unrelated to the char- 

 acter of the exposure noise. 



It has been suggested further (a) that 

 those people with initial hearing defects 

 might be less susceptible to noise annoyance 

 or (b) that they are more susceptible to noise 

 annoyance. A German study (68) reports 

 the effects of exposure to sounds of 100 db for 

 180 seconds, with audiometric measures 

 taken before and 15 seconds after exposure. 

 The investigator found that ears with 

 chronic inflammation are more sensitive to 

 noise than ears in healthy condition. Thus, 

 persons showing especially a thickening of 

 the mucous membranes on account of 

 chronic middle ear inflammation must be 

 considered especially liable to the detrimen- 

 tal effects of noise. 



W. H. Wilson (98) suggested a screening 

 technique which involved exposure to a tone 

 of 2048 cycles at 80 db for eight minutes. 

 One minute following exposure a complete 

 audiogram was taken and compared with the 

 pre-exposure audiogram . This was repeated 

 for each ear. Subjects were examined prior 

 to beginning their basic firing on both pistol 

 and rifle ranges. In no instance were the 

 subjects known to have gone out on the 

 range sooner than five days after the above 

 tests. Between the firing and the next au- 

 diometric study there was a minimum lapse 

 of 13 and a maximum lapse of 35 hours. It 

 was predicted that those showing an audi- 

 tory loss of 10 db or greater in the pre-firing 

 tests as a consequence of exposure to 2048 

 cycles would show a hearing loss on their re- 

 turn from the firing range at a later date. 

 Thirty out of 108 tested fell in this category. 

 Of these, 25 did show such a loss compared 

 with their pre-firing tests. Of the 78 men 

 who did not show initial auditory fatigue, 14 



showed a significant decrease in acuity on 

 return from the firing range. Seven days 

 later 26 of the original 39 men who showed 

 hearing losses at the end of firing were re- 

 tested, and 16 of these still showed some 

 hearing loss (the rest of the original 39 had 

 been sent to other posts). 



While this attempt at predicting suscep- 

 tibihty to noise trauma is not definitive, it 

 is sufficiently encouraging to warrant further 

 investigation with exposure to other types of 

 noise and with some variations in basic pro- 

 cedures. 



An attempt to use simulated battle noises 

 for the selection of emotionally stable in- 

 fantry men resulted in the conclusion that 

 such exposures were not an important sup- 

 plement to other screening devices (35). 

 However, since this study was concerned 

 with selecting emotionally stable men and 

 not those least susceptible to noise effects, it 

 cannot be looked upon as a negative finding 

 from the latter standpoint. 



One attempt to circumvent the deleterious 

 effects of noise on communication involved 

 the training of pilots to understand voice 

 communication in the presence of noise. In- 

 telMgibility scores were compared between 

 initial and final tests with control and ex- 

 perimental groups (experimental groups be- 

 ing exposed to noise inserted in the commu- 

 nication system). In general, practice with 

 noise was advantageous (14). 



Summary of Research 



Many of the studies on the effects of noise, 

 especially those which appeared before 1930, 

 are difficult to evaluate because of unstand- 

 ardized descriptions of noise levels and 

 frequency characteristics. This is not a 

 reflection on the investigators, but was 

 rather due to the lack of agreement on ter- 

 minology and inadequate measuring in- 

 struments. Unquestionably, over-all noise 

 levels of 110 db and higher are potentially, if 

 not actually, harmful to the auditory func- 

 tions, especially if the noise is long continued 

 and high frequencies predominate. Al- 



