242 AUDITORY PERCEPTIONS. [BOOK in. 



impressive cries without experiencing " recurrent " auditory sen- 

 sations. 



854. In one important respect the parallel between hearing 

 and sight fails. When we see an object, the rays of light coming 

 from the object excite a particular part of the retinal expansion ; 

 and our appreciation of the position which that object holds in 

 space is based on our power of " localizing " retinal changes. The 

 terminal expansion of the auditory nerve however has no such 

 definite relations to the positions in space of objects from whence 

 sounds are proceeding ; we have 110 evidence that any particular 

 part either of the organ of Corti or of the maculae is alone or 

 specially affected by sounds coming from a particular quarter; 

 and the evidence that sounds affect the three cristae differently 

 according to the direction of the sound is at least.doubtful. Hence 

 we possess no " auditory field " which can be directly compared with 

 the " visual field ; " and our conclusions as to the direction in which 

 the sounds which reach our ears have travelled, our judgments as 

 to the position in space of bodies exciting auditory sensations are 

 formed in an indirect manner. 



The vast majority of the sounds which we hear reach the 

 auditory epithelium by way of the tympanic membrane and chain 

 of ossicles ; even the sounds which are conducted to the ear through 

 the bones and hard parts of the head pass to a large extent by this 

 way ( 818); in normal hearing the auditory sensations which are 

 generated by vibrations transmitted directly through the bony 

 walls of the labyrinth to the perilymph are probably insignificant. 

 Now it is only in relation to these latter that the disposition in 

 space of the three semicircular canals can possibly have any 

 meaning ; the vibrations reaching the perilymph by way of the 

 tympanic membrane, whatever their original direction, have all 

 the same direction when they enter at the fenestra ovalis, and 

 fall in the same way upon the three semicircular canals. We may 

 therefore conclude that the position in space of the three canals 

 in question has nothing to do with our ordinary judgments as to 

 the direction of sounds. In forming those judgments we are 

 assisted mainly by two things. 



In the first place a peculiar character of the outwardness which 

 we attribute to our usual auditory sensations, that by which we 

 judge the sound to arise not only outside the internal ear but 

 outside our whole body, seems, in some way, largely dependent 

 on the vibrations which cause the sensation having travelled along 

 the external auditory passage. If the two passages be filled 

 with fluid the hearer refers the sounds which he hears, in spite 

 of their starting at some distance off, not to the external world 

 outside himself, but to the inside of his own head ; the sounds 

 appear to him to come, not it may be remarked from the internal 

 ear or any part of it, but from the roof of the mouth, or the top of 

 the skull or the back of the head. So also if the ear-pieces of a 



