PHYSICAL CHARACTERISTICS 01- AUDITION 



57 



sounds so ncarl>- alike that no existing physical apparatus can separate 

 them. The binaural feature adds a sense of orientation with respect 

 to a source and uniform sensitivity for sounds approaching from differ- 

 ent directions. The abnormal auditory sense may be regarded as 

 lacking niore or less in (a) range of sensation (frequency and intensity) ; 

 (b) quality of sensation in various regions of the range; (c) the bi- 

 naural sense. Apparatus and methods have been developed by means 

 of which the outstanding features of these functions can be measured 

 and to a limited extent compensated for. 



2. Minimum Audibility. Fig. 1 shows a plot of the logarithmic 

 average of minimum audible pressure on 72 normal ears taken through- 



1000 JOOO 



rREOuCNCY 



5000 10000 JOOOO 



50000 10000» 



AUPITORY 5EN5AT10N AREAS 



out a range of frequency from 60 to 4,0C0 cycles.^ Both the intensity 

 and frequency scales are logarithmic. Although all skew errors in the 

 determination of the average curve have not been eliminated, an 

 investigation has shown that they are so small as not to affect the 

 utility of the curve for the purpose of measuring deafness. Among 

 the errors which obviously tend to raise this curve might be men- 

 tioned, noise in the observing room, abnormality of hearing, lack of 

 attention, and low mentality of the observer. Care was taken to 

 reduce these errors to a minimum without actually making separate 



'This curve has already been pubhshed; The Frequency Sensitivity of Normal 

 Ears, by H. Fletcher and R. L. Wegel, Proceedings pf the National Academy of Sciences, 

 January, 1922, and Physical Review, June, 1922. 



