Timbre and Loudness on the Localisation of Sounds. 275 



as I have already mentioned, the position of the auricle is adapted for 

 " catching " sounds coming from in front (and in consequence of which our 

 auditory acuity is keener for forward than for rearward sounds). But 

 turning the head alters, too, the timhre of the sounds ; a forward sound 

 appears to the ear not only louder than, but also of a different timbre from, 

 the sound placed to the rear.* 



It is noteworthy, however, that, whereas change in the position of the head 

 while the sound was being heard was remarkably effective in correcting errors 

 of localisation, change in the position of the sound while the head was at rest 

 proved of little or no advantage for such correction. It generally resulted in 

 an interpretation of increased or diminished loudness, or of increased or 

 diminished distance of the sound ; less frequently, a movement of the sound 

 was detected, but the direction of the movement was not always correctly 

 given, and the initial error in localisation failed to be corrected by the 

 detected movement of the sound. This difference in effect between what 

 may be conveniently termed " active " and " passive " change in the position 

 of the sound is of considerable interest in relation to the associated function 

 of the semicircular canals and (in animals) of the movements of the auricle. 



Two other factors which are conceivably of importance in determining the 

 incidence of sounds, but which were almost wholly eliminated in these 

 experiments, may be briefly mentioned. Of these the influence of expecta- 

 tion has been already alluded to on p. 273, and was almost always success- 

 fully ruled out by the noiseless movement of the perimeter. On several 

 occasions I expressly asked the subjects if they had any notion of where the 

 sound was coming from, and they generally replied that they had no idea. 

 In everyday life, however, and, perhaps, in many of the experiments other- 

 wise conducted, various cues may determine a favourable attitude of 

 expectation in the subject. The remaining factor, the effect of sound 

 reflections from the ceiling, walls, and floor, was prevented by the peculiar 

 construction of the sound-proof room (pp. 268-270). But in everyday life 

 and after brief practice in experiments, conducted under ordinary conditions, 

 there are indications that such reflections are taken into account and thus 

 assist in determining the incidence of the sound.f 



* It is practically impossible to increase the loudness of a sound {i.e. the intensity of 

 the fundamental and its overtones) without altering its timbre (the relative intensity of 

 the fundamental and its overtones). Even if this could be physically realised, the 

 varying position of the peculiarly formed auricle relatively to the sound may be expected 

 to influence the ease with which it takes up the different overtones contained in the 

 sound. 



t Since writing this, I have examined two subjects, first in an ordinary room, and 

 later (after a rest) in the sound-proof room, using the perimeter with an attached 



