Timbre and Loudness on the Localisation of Sounds. 281 



accordingly ascribed to a single position, median or lateral, instead of to two 

 lateral positions. 



Further, when the tones are of different pitch, it is impossible to see how 

 tactual sensibility can be the basis of their separate localisation. For suppose 

 that one pinna, meatus or drum receives a series of tactual stimuli from the 

 one tone, and that the opposite pinna, meatus or drum receives another series 

 from the other, it is inconceivable how the subject can refer these two series 

 of tactual stimuli to their respective tones; how can he decide which tone to 

 allot to which ear merely on the basis of his tactual sensations ? Again, 

 suppose that a subject has become absolutely deaf in both ears ; why on the 

 hypothesis of tactual localisation should he not still be able on request to 

 localise successfully a sound stimulus though unable to hear it as sound ? Yet 

 this is inconceivable save in the case of the very lowest tones, the stimuli of 

 which evoke tactual as well as (indeed ultimately in place of) auditory 

 sensations. Moreover, the unimportance of the tympanic membrane in sound 

 localisation is shown by the preservation of localisation in cases where the 

 membrane has been removed through disease, and in cases of tinnitus aurium 

 where the sensations although localised arise subjectively, within the inner ear. 



That tactual stimuli received by the pinna play a part in the localisation 

 of sounds in the median sagittal plane is rendered highly improbable by 

 a priori considerations. The following experiment, moreover, appears 

 decisive. After preliminary practice, I acquired correct localisation of sounds 

 in this plane ; whereupon I placed a short piece of narrow rubber tubing in 

 each ear, the result of which was to make an obvious change in the loudness 

 and timbre of the sounds heard. Now if the pinna had been responsible for 

 the previously correct localisation, no change should have resulted from the 

 insertion of the rubber tubes into the two meatus. But in point of fact, I was 

 quite unable to localise the sounds correctly, and had to start afresh re-learn- 

 ing them. There was no doubt in my mind that I had based my previously 

 correct localisations on changes in the relative loudness and timbre of the 

 sounds dependent on their position in regard to the ears. The results of this 

 experiment confirm those already described in this paper showing the definite 

 changes in localisation produced by definite changes in the loudness and 

 timbre of the sounds. 



Nevertheless, the belief that auditory localisation is, at bottom, of tactual 

 origin dies hard. Started by "Weber* and perpetuated by Wundtf and others, 

 the tactual hypothesis has been recently invoked by Hocart and McDougallt 



* 'Ber. d. KgL Sachs. Ges. d. Wiss.,' 1848, p. 237 ; 1851, p. 29. 



t ' Grundziige der Physiologischen Psychologies 5th ed., voL 4, p. 487. 



$ ' Brit. Journ. Psychol.,' vol. 2, pp. 386-405 (1908). 



