CHANGES IX PROGRAM BAXD WIDTH 7 



the curve was extended step by step up to 15 kc. Finally, the origin was 

 shifted so as to express the liminal curve with respect to 15 kc. instead of 3 

 kc. 



It was mentioned above that a number of tests were introduced without 

 the knowledge of the observ^ers in which the conditions were not changed, 

 the band width remaining constant while the illuminated letters were 

 switched. This produced the most interesting psychological result that 

 observers voted nearly two to one for the letter appearing in the right- 

 hand position in the signal, on each of the six tests of this kind. This raises 

 the question as to whether this effect impaired the results on the other tests. 



In the course of the tests, comparisons between each pair of band widths 

 were presented 10 times, 6 times with music and 4 times with speech. The 

 letters corresponding to the two conditions were assigned more or less at 

 random from the three letters A, B, and C. Taking 11 of these groups of 

 tests in which the narrower band was represented about as often by the 

 right hand as b}' the left hand of the pair of letters chosen, the average vote 

 for the right-hand letter was 51.1*:^ and for the left-hand letter was 48.9%. 

 The difference between these two figures is too small to be significant. It 

 is therefore concluded that when there was a real difference, the observers 

 were not measurably influenced by their slight subconscious predilection for 

 the right-hand letter. It would be interesting to correlate this phenomenon 

 with the right or lef t-handedness of the observers. This point illustrates the 

 extreme care that must be taken in conducting judgment tests of this sort 

 to insure that no irrelevant factors affect the statistical result. 



The curves of Fig. 4 permit drawing the following conclusions: 



1. Increases in band width can be detected up to 15 kc. for both music 

 and speech. The fact that this is true for speech is rather surprising. 

 However, above about 5 kc, changes in band width are twice as readily 

 detectable on music as on speech. 



2. It requires an increase in band width from 8 to 15 kc. to be as readily 

 detected as an increase from 5 to 8 kc, for both speech and music. 



3. The following intervals correspond to one liminal unit and are there- 

 fore just discernible half of the time to the observers: 



Speech: 5 to 8 kc; 8 to 15 kc. 



Music: 5 to 6^ kc; 6^ to 8 kc; 8 to 11 kc; 11 to 15 kc 

 In considering these conclusions, the fundamental assumption and limita- 

 tions of the data should be borne in mind. First, the data were obtained 

 from tests with a certain group of observers and on certain program mate- 

 rial. Curves of somewhat different slope would doubtless be obtained with 

 observers of different average age, experience, musical appreciation, etc. 

 It is likely, however, that this would affect the absolute importance of the 

 different intervals in liminal units rather than the relative values. As noted 



