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BELL SYSTEM TECHNICAL JOURNAL 



Fig. 2- 



-Typical hearing test record as it would appear when illuminated 

 from underneath. 



spends closely to that for zero hearing loss on the 2A Audiometer.* 

 Hence hearing losses given here are comparable in magnitude with 

 audiometric measurements. 



The range of the test is shown in Table 1, which gives the hearing 

 loss corresponding to each test step.^ The range covered is 62 db in 

 the first four columns and 48 db in the last. 



' Some confusion has been occasioned by referring to the audiometer zero as normal 

 hearing. Actually it is supposed to represent average normal hearing, where normal 

 hearing refers to a range about the average value. If an individual has a hearing 

 loss, his hearing is not necessarily abnormal. The amount of hearing loss which 

 should be considered abnormal is discussed in a later section. 



^ The hearing loss values given in Table 1 correspond to the actual tone levels in 

 the test. Throughout this paper it is assumed that the threshold of an individual 

 lies between the last level at which he correctly records the number of tones and the 

 first level at which he does not, and in computing mean values the loss is reckoned 

 mid-way between these two levels. 



