Timbre and Loudness on the Localisation of Sounds. 277 



(i) " tactual " sensations. Of course in the positions used in the horizontal 

 plane (ii) laterality could afford no clue as to the fore or aft localisation of 

 the sound. The remaining factor (hi), differences in timbre, loudness, and 

 nearness, proved the most important criterion in learning to localise the 

 sounds correctly. One of the subjects complained of special difficulty in 

 distinguishing sounds at 90° h. and at 45° h. ; another of special difficulty 

 in distinguishing sounds at 90° h. and at 135° h. At 135° h. the sound 

 seemed to two subjects " more remote and weaker," " less clear and less 

 distinct," than at 45° h. or 90° h. ; the third subject, however, observed that 

 at 135° h. it was " nearer and more rounded," " not so veiled," as at 45° h. 



3. Experimental Variations in the Timbre and Loudness of the Sounds — 



(a) For Sounds in the Median Vertical Sagittal Plane. — In the case of two 

 subjects, after being thoroughly practised in the correct localisation of sounds 

 given at 0°, 90° v., and 180°, instructive results were obtained by experi- 

 mentally varying (i) the timbre and (ii) the loudness of the variator sounds. 

 In both subjects variations in timbre (produced by varying the position of 

 the slides) yielded less striking errors of localisation than variations in 

 loudness (produced by varying the position of the horn). Thus in one 

 subject, who had just given 17 of 18 answers correctly for the normal or 

 B position of the slides and horn, variations in the position of the slides 

 produced one doubtful and one ambiguous* answer in 11, while variations in 

 the position of the horn gave one wrong and four doubtful or ambiguous 

 answers in nine. On another occasion the same subject, after giving two 

 doubtful or ambiguous answers in 18 for the normal position of the slides 

 and horn, gave 10 wrong answers and one doubtful answer in 18 when the 

 position of the horn was varied. The disturbing uncertainty thus produced 

 was in some degree carried over to the subsequent experiments immediately 

 carried out with variations in the position of the slides, when three wrong 

 and two doubtful or ambiguous answers in 13 were returned. 



The second subject, who was examined only for the positions 0° and 90° v., 

 gave five wrong and two doubtful or ambiguous answers in 27 for the normal 

 or B position of the slides and horn, followed by three wrong and two 

 doubtful or ambiguous answers in 18 when the position of the slides was 

 varied. On another occasion, when the same subject had just given 12 con- 

 secutive right answers for the normal or B position of the slides and horn, 

 six wrong answers in 21 were obtained by varying the position of the horn. 

 In both subjects it was found that, whereas the sounds at 0° suffered least, 



* An answer is " doubtful " when the subject is obviously uncertain ; it is " ambiguous " 

 when the subject ascribes to the sound alternative positions, of which one is correct. 



