392 



Scientific Proceedings (131) 



190 (2150) 



A new auditory test apparatus. 



By A. G. POHLMAN and F. W. KRANZ. 



[From the St. Louis University and Wallace Clement Sabin Labo- 

 ratory of Acoustics, Geneva, Illinois.] 



Practically all tests on the location of deafness are made by 

 comparing the acuity of hearing as found by use of the tuning 

 fork by air transmitted sound with that determined by applying 

 the stem of the fork to the head bones. The disadvantages of 

 the tuning fork test are both of a physical and physiological na- 

 ture. No two forks are alike nor can the activation of any fork 

 be expressed in terms of absolute or even reproducible units. It 

 is also quite impossible to establish the threshold of audition 

 either by the distance through which a fork is heard or in the 

 case of bone transmission, by the length of time a given fork is 

 heard when applied to the head. Scientific work on the problem 

 of auditory acuity demands first of all that a standard method 

 of measurement of acuity by air transmission be adopted. It is 

 also essential that a new type of apparatus be devised which shall 

 replace the tuning fork for the determination of minimum audi- 

 bility for bone transmitted sound. Such an apparatus must 

 fulfill several requirements. It must be possible to deliver the 

 energy to the bone in a series of graded intensities. It must also 

 be so arranged that the stimulus may be exhibited at a given 

 pitch and a given intensity for an indefinite period of time. It 

 must be capable of accurately reproducing any given intensity. 

 Finally, for clinical purposes it must be easily transported, stand- 

 ardized and practically fool-proof. 



Such a piece of apparatus has recently been developed at the 

 Riverbank Laboratory. In its refined form, the range of inten- 

 sities available will be sufficient to test subjects of all grades of 

 acuity of hearing. The clinical type of instrument is portable 

 and may be connected with any lamp socket on the ordinary 

 sixty cycle alternating current. Standardized reproducible in- 

 tensities may be obtained both for air and bone transmitted 

 sound at 60 and 120 p.p.s., the vibrating elements being actuated 

 electromagnetically. It is hoped that this device will serve the 

 otologist as an accurate instrument for diagnostic purposes in 

 the field in which the low pitch tuning fork is now used. 



