ILLUSTRATIONS OF AUDITORY SIGNALS 



205 



frequencies; i.e., the acoustic energy is the 

 same for any frequency if the voltage across 

 the earphone is the same. Other phones 

 tend to produce much more energy at one 

 frequency than at others: they have a 

 peaked response. If the resonance peak of 

 the earphones corresponds to the signal fre- 

 quency, then the earphone is essentially a 

 band-pass filter, and discrimination should 

 be better with the peaked earphones than 

 with the flat earphones. The experimental 

 tests showed that discrimination actually 

 was better with the peaked phones, although 

 the improvement was not as much as when 

 the narrow-band-pass filter was used. The 

 practical conclusion of this experiment was, 

 then, that distortion-producing phones are 

 better for this particular type of signal than 

 flat-response phones. 



Special Instruments 



Expanders. Other experiments were even 

 more specific, in the sense that they were 

 only tests of particular pieces of equipment 

 which might be used with radio range instru- 

 ments. One of these special gadgets was a 

 signal expander — a device which amplifies 

 large signals more than it amplifies small 

 signals. Thus it should make differences in 

 signal strength more different, and improve 

 discrimination. The tests showed that dis- 

 crimination actually was improved, and 

 demonstrated the feasibility of the particular 

 instrument. 



Pitch Modulators. Another device tested 

 was one which translated intensity differ- 

 ences into frequency differences. The tests 

 showed that pitch discrimination was better 

 than intensity discrimination at favorable 

 S/N ratios, but was not as good when the 

 signal was appreciably less intense than the 

 noise. 



Summary of Radio Range Experiments 



The experiments on the radio range signal 

 are illustrations of the kinds of research 

 done on the simplest type of auditory signal. 

 Only simple discrimination is required, and 



much of the research was concerned solely 

 with factors which affect the intensity dis- 

 crimination of pure tones. This type of 

 research is fundamental to our understand- 

 ing the particular signal under investigation, 

 as well as to our understanding the basic 

 operation of the ear. Other experiments 

 were concerned solely with the specific means 

 of producing the signal, and can be 

 considered applied research or tests. Such 

 experiments, on the other hand, contribute 

 little to our understanding of the basic 

 phenomena of hearing, and the experiments 



SIGNAL -TO-NOISe RATiO IN 08 



Fig. 2. The effect of signal-to-noise ratio on the 

 discrimination between the A and N signals of a 

 radio range with and without a narrow band-pass 

 filter. (After Flynn e< aZ., 5) 



would in fact be quite unnecessary if we 

 knew enough about how the ear works. 



On submarines, simple signals like the 

 radio range could be used to provide lateral 

 directional information for positioning guns 

 or radar equipments. Continuous and auto- 

 matically transmitted information could in- 

 crease both speed and precision of gun 

 positioning, for example, and would certainly 

 make manpower shortages less critical. 



Flyhar 



The word Flyhar is an abbreviation of 

 "flying by auditory reference" and has been 

 applied to attempts to provide auditory sig- 

 nals for use in flight. In 1936 de Florez (1) 

 demonstrated that pilots can fly by means 

 of auditory signals presented in earphones, 

 even though his method did not involve 



