Timbre and Loudness on the Localisation of Sounds. 283 



This view of the illusory function of tactual sensations in sound localisa- 

 tion receives support from other data afforded by my subjects. Many of 

 them, at their early stages of practice, seemed compelled to objectify the 

 sound in tactual visual terms. Thus to one subject a sound at 90° v. 

 " appears to come from a central point," while one at 180° "appears to come 

 from different sides as if entering the ear by various rays instead of by a 

 central one." Another subject said " I can't attend to the sensation as such ; 

 I have to fancy a motor cycle behind me," or " I fancy myself in a wood 

 with the sound (given at 180°) low down at the end of the path before me." 

 A third subject observed " I give each sound a body, and each is generally 

 circular — a ball." A fourth subject, who had described the variator sounds 

 as generally coming down and hitting her, observed that the buzzer sounds 

 " seemed in many cases to remain in their place and to throw out a sort of 

 pseudopod, like a wriggling worm pulling its tail through." In view of these 

 descriptions, need we hesitate to ascribe localisations of tactual sensation, 

 when they occur, to an inevitable tendency to treat localised sounds as if 

 they were external objects describable in visual and tactual language, and as 

 if they hit the ear, face, vertex, or occiput according to their localisation 

 determined on the basis of timbre and loudness ? 



IV. Conclusions. 



1. The "laterality" of a sound {i.e. its estimated position in relation to 

 the median " sagittal " plane) is determined by binaural differences or 

 equality of intensity of the sensation.* Experimental changes in the timbre 

 or loudness of a sound make no difference in its laterality. 



As soon as an infant begins to take notice of sounds, their laterality is at 

 once appreciated. There are no trial movements of the head, this way or 

 that, for sounds placed to one side of the median sagittal plane. The 

 reception by one ear of a stimulus stronger than that reaching the other ear 

 at once determines in the infant a movement of the head and eyes to bring 

 the latter towards the source of the sound. 



2. On the other hand, even in adult life, the grossest errors are made in 

 determining the incidence of a sound (i.e. its estimated position in relation to 

 the horizontal " interaural " line), unless the subject has been practised in 

 the changes in timbre and loudness produced by such changes of incidence, 

 or unless he is allowed to make movements of the head, the effect of which 

 is to vary the timbre and loudness of the sound while it is being heard. 



* And, according to Lord Rayleigh, by binaural differences or identity of phase of the 

 sound waves (see, however, footnote to p. 267). 



VOL. LXXXVIII. — B. Y 



