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The Influence of Timbre and Loudness on the Localisation of 



Sounds. 

 By Charles S. Myers. 



(Communicated by Prof. C. S. Sherrington, F.R.S. Received June 3, — Read 



June 25, 1914.) 



I. Introductory. 



In analysing the factors determining our localisation of sounds, it will be 

 found convenient to distinguish " laterality : ' from " incidence." By the 

 laterality of a sound I mean its apparent position in relation to the median 

 vertical front-to-back, or "sagittal," plane; thus, a sound may give the 

 impression of rightward or leftward laterality, or it may appear to have zero 

 laterality — that is to say, its position may seem to be in the median plane. 

 By the incidence of a sound I means its apparent position in relation to the 

 horizontal " interaural " or " coronal " line, thus, a sound may give the 

 impression of more or less upward, downward, forward, or backward 

 incidence, or it may appear to be directly sideward, neither above nor below, 

 neither in front of nor behind, the interaural line — when the incidence is of 

 zero value. 



I consider it important to distinguish at the outset these two elements in 

 localisation, since they are dependent on very different factors. In normal 

 subjects, that is to say, in persons who have normal binaural hearing, the 

 one certain and obvious determinant of laterality consists in binaural 

 differences of intensity. A sound is localised on the side of that ear which 

 receives the stronger stimulus; it is localised in the middle line, midway 

 between the two ears, when they are equally stimulated by the sound.* 



But such binaural differences of intensity must clearly fail as a basis of our 

 determination of incidence. Whether a median sound lies immediately in 

 front of or behind us, or whether it is placed immediately above or below our 



* Another determinant of laterality, binaural differences of wave phase, was suggested 

 in 1907 by Lord Bayleigh (' Phil. Mag.,' vol. 13, pp. 214-231, 316-319) ; but, taking into 

 consideration the physiological fact that, owing to the bone conduction of sound across 

 the skull, it is impossible to stimulate one ear without stimulating the other, I have 

 indicated, in collaboration with H. A. Wilson ['Roy. Soc.'Proc.,' A, vol. 80, pp. 260-266 ; 

 'Brit. Journ. Psychol.,' vol. 2, pp. 363-385 (1908)], how the effects of binaural phase 

 differences are ultimately explicable in terms of the differences in binaural intensity to 

 which they may be supposed to give rise. Lord Eayleigh has since [' Roy. Soc. Proc.,' A, 

 vol. 83, pp. 61-64 (1909)], allowed that " for the moment the choice between the competing 

 views [as to the manner in which phase differences at the two ears produce their effect] is 

 likely to depend upon preconceptions as to the maimer in which the nerves act." 



