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668 JEROME R. COX, JR. anticipated that in the near future, however, standardized selections of every speech will be available. This will greatly enhance the usefulness to industry the speech audiometer, since by measuring the threshold of hearing for every!, speech, it is possible to make some estimate of the listener's practical abili| hear correctly everyday speech. f M. RELATION BETWEEN THE THRESHOLDS FOR PURE TONES AND SPE: . Because of the complications introduced by the variety of causes of hel loss and by the variations in the shape of the audiogram, there is no method! precisely predicts an individual's "hearing for speech" directly from his pure| audiogram. In addition, different kinds of speech tests rank hearing impair*1 differently. Therefore, it is impossible to make this computation with accurac: each individual. However, a simple rule may be used to obtain the relatioij most often holds between the thresholds for pure tones and speech. The lac ability to hear speech at threshold is highly correlated with the average d| pure-tone hearing losses at 500, 1000, and 2000 c.p.s.18 Thus, the hearing l--'"' decibels at these three frequencies are added and the total divided by 3 to estimated "hearing loss for speech." ^ The fact that only the three frequencies 500, 1000, and 2000 c.p.s. ar in this computation does not necessarily mean that sounds above 2000 c.pl unimportant in the understanding of speech. It is the high correlation betwee' average of the three pure-tone hearing losses and the "hearing loss for speech allows us to bypass the details of the very complicated-.matter_QLha^LWMU: stand speech. N. AUDIOMETRIC PROGRAMS It is extremely important that industrial audiometric programs be und' supervision of a competent otologist whenever one is available. Manyi?- may arise that require his medical judgment, and his testimony about the? of the audiometric program may be extremely valuable in any future litigSg' The training of the personnel who actually carry out the audiometric m should be' approved or supervised by the otologist. Sueh personnel may.a: a technician, a nurse, an audiologist, or the plant physician. A mut-uallyM to^l^$^iSTc_pFoce3m^Kp^3"bg_developed"mdT^bl|piye.d--?ig0r-jtu|i| duresi'Should^B^set up for. the proper care of thbse^whose audiogram|||| unusual susceptibility to noise or those who show symptoms of any ofTilL other kinds of hearing impairment. Advice about audiometric program^ --obtaifild^Stti-tlierStibcQmmittee- on Noise. in. Industrv of the Committe' ' --"--S' u R. Carhart, Speech reception in relation to pattern of pure-tone loss, J. Spcm orders, 11, 97 (1946) NOISE AND THE CONSERVATION OF HEARING 669 fopllrvation of Hearing of the American Academy of Ophthalmology and ^yngology.18 O, HEARING IMPAIRMENT Sere are many disorders that can affect the hearing apparatus. Traditionally disorders are grouped according to whether they occur in the sound-conductIfparatus (outer and middle ear) or in the remainder of the system (cochlea, ft|y. nerve, and central nervous system). The former group are called con- ||||*disorders and the latter have variously been called perceptive, nerve, or |8|l$r disorders. In order to emphasize the different character and the impor- mlljTdaisborldeer7s. of the central nervous system, this group has been listed sepa- TABLE 7 Hearing Impairments and Their Causes Bjders of the sound-conducting apparatus. Obstruction of the ear canal by: feExcess wax or foreign bodies. r |fSwelling from bacterial or fungus infection, particularly in hot, wet climates. jM6vement of the drum membrane and the osBicular chain hindered by: Extreme displacement of the drum membrane and the ligaments of the ossicular i| chain caused by barometric changes that occur when the Eustachian tube is closed ufsiyelling from an adenoid infection or a cold may produce closure). swihM or pus in the middle ear.________ i of acarlike, fibrous tissue called "adhesions" that tend to increase in number 1 Bize as a result of repeated middle ear infections. Jig Otosclerosis, an abnormal bonelike growth on the stapes that begins just after ^adolescence and becomes progressively worse. Ikfnage to drum membrane or ossicular chain as a result of: -lExplosion or a blow on the head. ||||@hronic infection. Removal by a surgeon to halt the spread of infection. Borders of the auditory receiving apparatus. *'mifunctioning of the cochlea as a result of: i 4 ylfjni&re's disease, a transient disorder that is usually characterized.by attacks of ffijizinese, ringing in the ears;'and1 loss <if'Me ability un<ter^S'^i!ys'^)^!wlie& jjunda are,heard. Ssfbtary causes that produce a permanent and sometimes progressive. hearing.loss I' V' . ' ; (continued) ||uiries may be sent to the Director of Research, Sub&ftmittee- on- ||||Sonnie Brae, Los Angeles, Calif; In'addition to providing:' advice td*i|!dust^vbn S^wPb..r.o...K...r..a..m....s...?...^..t.h...e..i.r..8..u...h..d...Q....m....f.h..i.t..a...a.--iHatg3as>M----n:un-mni--ogunCT e fiiV <.liu 1 lOTtlfflBfm 1----- ffiddta relating hearing loss to noise exposure. This, work is directed toward increasing Ifljbf the effects, of noise. Groups interested in contributing audiometric..data should he Subcommittee for information on recommended procedures and standardized cards ting data. 1.1 fi U \v*' j