820 AUDITORY AFTER-SENSATIONS AND COLOUR ASSOCIATIONS. 



Amongst subjective auditory sensations arc the after -vibrations, especially of intense and 

 continued musical tones : the tinnitus aurium (p. 606), which often accompanies abnormal 

 movements of the blood in the ear, may be due to a mechanical stimulation of the auditory 

 fibres, perhaps bv the blood-stream (Brenner). ' 



[Drugs. Cannabis indica seems to act on the hearing centre, giving rise to subjective sounds ; 

 the hearing is rendered more acute by strychnin ; while quinine and sodic salicylate in large 

 doses cause ringing in the ears (Brunton).] 



Entotical perceptions, which are due to causes within the ear itself, are such as hearing the 

 puh- -beats in the surrounding arteries, and the rushing sound of the blood, which is especially 

 strong when there is increased resonance of the ear (as when the meatus or tympanum is closed, 

 or when fluid accumulates in the latter), during increased cardiac action, or in hyperesthesia 

 of the auditory nerve {Brenner). Sometimes there is a cracking noise in the maxillary 

 articulation, the noise produced by traction of the muscles on the Eustachian tube ( 411), and 

 when air is forced into the latter, or when the membrana tympani is forced outwards or 

 inwards (j 350). 



Fatigue. The ear after a time becomes fatigued, either for one tone or for a series of tones 

 which have acted on it, while the perceptive activity is not affected for other tones. Complete 

 recovery, however, takes place in a few seconds (UrbaiUschitsch). 



Auditory After-Sensations. (1) Those that correspond to positive after-sensations, where the 

 after-sensation is so closely connected with the original tone that both appear to be continuous. 

 (2) There are some after-sensations, where a pause intervenes between the end of the objective 

 and the beginning of the subjective tone (UrbaiUschitsch). (3) There seems also to be a form 

 corresponding to negative after-images. 



In miue persons, tin- perception of a tone is accompanied by the occurrence of subjective colours, 

 or the sensation of light, e.g., the sound of a trumpet, accompanied by the sensation of yellow. 

 More seldom visual sensations of this kind are observed when the nerves of taste, smell, or 

 touch are excited (Xussbaumer, Lchmann and Blender). It is more common to find that an 

 intense sharp sound is accompanied by an associated sensation of the sensory nerves. Thus 

 many people experience a cold shudder when a slate pencil is drawn in a peculiar manner 

 serosa a slate. 



[Colour Associations. Colour is in some persons instantaneously associated with sound, and 

 Galtou remarks that it is rather common in children, although in an ill-developed degree, and 

 tin tendency seems to be very hereditary. Sometimes a particular colour is associated with a 

 particular letter, vowel sounds particularly evoking colours. Galton has given coloured 

 i |u mutations of these colour associations, and he points out their relation to what he calls 

 number-forms, or the association of certain forms with certain numbers.] 



An auditory impulse communicated to one ear at the same time often causes an increase in 

 the auditory function of the other ear, in consequence of the stimulation of the auditory centres 

 of both sides (Urbantschitsch, Eitelberu). 



Other Stimuli. The auditory apparatus, besides being excited by sound-waves, is also 

 affected by heterologous stimuli. It is stimulated meclmnieally by a sudden blow on the ear. 

 The effects of electricity and pathological conditions are referred to in 350. 



419. COMPARATIVE -HISTORICAL. The lowest fishes, the cyclostomata (Petromyzon), 

 have a saccule provided with auditory hairs containing otoliths, and communicating with two 

 semicircular canals, while the myxinoids have only one semicircular canal. Most of the other 

 fishes, however, have a utricle communicating with three semicircular canals. In the carp, 

 prolongations of the labyrinth communicate with the swimming-bladder. In amphibia, the 

 structure of the labyrinth is somewhat like that in fishes, but the cochlea is not typically 

 develojwd. Most amphibia, except the frog, arc devoid of a membrana tympani. Only the 

 fenestra ovalis (not the rotunda) exists, and it is connected in the frog by three ossicles with 

 the freely-exposed membrana tympani. Amongst reptiles the appendix to the saccule, corre- 

 sponding to the cochlea, begins to be prominent. In the tortoise it is saccular, but in the 

 crocodile it is longer, and somewhat curved and dilated at the end. In all reptiles the 

 fenestra rotunda is developed, whereby the cochlea is connected with the labyrinth. In 

 crocodiles and birds, the cochlea is divided into a scala vestibuli and S. tympani. Snakes are 

 devoid of a tympanic cavity. In birds both saccules (fig. 591, IV, U S') are united (Basse), 

 the canal of the cochlea (U C), which is connected by means of a fine tube (C) with the 

 8accuI ls larger, and shows indications of a spiral arrangement, and has a flask -like blind 

 end, the lagena (L). The auditory ossicles in reptiles and birds are reduced to one column-like 

 rod, corresponding to the stapes, and called the columella. The lowest mammals (Echidna) 

 have structures very like those of birds, while the higher mammals have the same type as in 

 man (fig. 591, III). The Eustachian tube is always open in the whale. 



Amongst invertebrate, the auditory organ is very simple in medusie and mollusca. It is 

 merely a bladder filled with fluid, with the auditory nerves provided with the ganglia in its 

 walls. Hair-cells occur in the interior, provided with one or more otoliths. Hensen observed 

 that in aome of the annulosa, when sound was conducted into the water, some of the auditory 



