BASIC PSYCHOLOGICAL PROBLEMS 



211 



comparisons between frequency discrimina- 

 tion of glide tones and abruptly changing 

 tones would be valuable. 



Simultaneous Frequency and Intensity Dis- 

 crimination 



Another kind of experiment which is par- 

 ticularly pertinent to auditory signaling 

 problems is the complex discrimination type 

 of experiment. What happens to frequency 

 discrimination when both tones are not of 

 the same intensity, or when both frequency 

 and intensity change simultaneously? Does 

 discrimination deteriorate seriously when an 

 observer must report changes in either in- 

 tensity or frequency, or both simultaneously? 

 Can an observer alternate intensity discrim- 

 ination with frequency discrimination with- 

 out one or the other breaking down? These 

 questions and many similar ones cannot be 

 answered without further research. 



Pattern Discrimination 



Still another area of research which would 

 be most valuable for the problems of audi- 

 tory signalling is that of auditory patterns 

 and pattern discrimination. What little 

 work has been done in this area has been 

 concerned with time patterns, usually with 

 respect to learning telegraphic code. Taylor 

 (34) has summarized this research, al- 

 though very little of it is directly useful for 

 the design of auditory signals. Other types 

 of problems concern intensity and frequency 

 patterns. Can one frequency pattern of a 

 series of tones be discriminated from an- 

 other? Can enough easily discriminable 

 patterns be devised to provide for all the 

 alternative kinds of information in one sig- 

 naling system? It is quite possible than an 

 auditory pattern composed of alternating 

 frequencies would provide a very positive 

 kind of signaling system. 



Stimulus Interactions 



In a complex auditory signaling system, 

 it will be necessary to change more than one 



physical parameter, and the observer wiU 

 have to make judgments about more than 

 one physical parameter. But judgments are 

 made about psychological parameters, and 

 frequently changing one physical variable 

 changes more than one psychological var- 

 iable. It is necessary, then, to know about 

 such effects so they can be avoided when 

 necessary. 



It has long been known that the loudness 

 of a tone depends on its frequency (4) and 

 that the pitch of a tone depends on its in- 

 tensity (29). 



We know that the loudness of a tone 

 changes with duration. Fig. 4 illustrates 



■ 5 10 20 50 100 200 



TONE DURATION IN MILLISECONDS 



Fig. 4. The effect of tone duration on loudness 

 The ordinate values are the equivalent loudness 

 levels of tones of various durations. The intensity 

 and frequency of the steady tone are indicated. 

 (After Munson, 25) 



how great this change may be, and is adapted 

 from a report by Munson (25). Notice that 

 the equivalent intensity of a tone may vary 

 by as much as 30 db when the duration of 

 the tone is changed from 5 to 200 milli- 

 seconds. Hughes (20), Garner and Miller 

 (15), and Garner (11) have shown that the 

 threshold of a tone varies inversely with its 

 duration over a wide range. 



Garner (12) has recently shown that the 

 loudness of a series of tones increases with 

 an increase in repetition rate, as illustrated 

 in Fig. 5. In an earlier paper (10), he had 

 also demonstrated that the threshold of a 

 tone changes with a change in repetition rate. 



