pO2 QUALITY OF AUDITORY PERCEPTIONS. 



the perception for high tones. Abnormal power of hearing low tones is present 

 also in cases of rheumatic facial paralysis, that for hearing high tones in cases of 

 absence of the tympanic membrane, the malleus and the incus. The stapedius 

 is said to possess the power of making the highest high tones (even up to 80,000 

 vibrations) perceptible at the expense of the low ones. Pathologically, an 

 increased perception for high tones is found in conjunction with any condition 

 producing increased tension of the sound-conducting apparatus. 



If the eye be compared with the ear, it is evident that the ear greatly exceeds 

 the eye in its range of perception. As the red of the spectrum makes about 456 

 billions of vibrations in the second, and the visible violet only 667 billions, the eye 

 can take cognizance only of vibrations of the other that are less than i octave 

 from each other (double number of vibrations). 



How many vibrations must follow successively for the ear to receive 

 the impression of a tone ? Two are sufficient in the case of low tones up 

 to 3168 vibrations, 5 for a tone of 6000, 10 for one of 7040 per second, 

 20 for all tones. When tones follow one another in rapid succession, 

 they are heard as separate tones if there is an interval of at least o.i 

 second between them; if the interval is less, tones become fused, al- 

 though for many musical tones a shorter interval is sufficient. 



A person is said to have an "accurate ear' 7 who is able to distinguish a 

 difference in the pitcji of two tones of nearly the same number of vibra- 

 tions. This power^an be greatly increased by practice, so that musi- 

 cians can distinguish tones that have only a difference of pitch of -^-g- 

 or even T^IRT f their number of vibrations. It is easier to determine 

 differences in pitch' from the purity of musical intervals than when 

 tones are almost in unison. 



With reference to the time-sense of the ear, it should be remarked 

 that time is appreciated with greater precision by the ear than by any 

 other sense-organ. 



Pathological. Many normal persons are said to hear the same tone higher 

 with one ear than with the other; v. Wittich found that, during an attack of in- 

 flammation of the ear; he heard a tone a half-note higher with one ear than with 

 the other, Spalding even a minor third higher. In a case seen by Moos, the deep 

 tones were heard one-third of a tone too high, the high ones too low. Perhaps the 

 cause of the unilateral heightening of tone-perception associated with this condition, 

 which has been designated binaural diplacusis, consists in an abnormal change 

 in those portions of the labyrinth that are set in sympathetic vibration. The 

 condition designated monaural diplacusis, in which a note sounded in one ear 

 is perceived as two notes, is rare. It is due to the irritation of the elements 

 producing the second tone in addition to those producing the first tone. In 

 rare cases, sudden loss of the perception of certain tones has been observed, for 

 example bass-deafness; in a case described by Magnus, the tones from d 1 to h 1 

 were not heard. 



Perception of Intensity. With respect to the intensity of the tone it has 

 been established that it is dependent upon the amplitude of the vibrations of 

 the sounding body. The intensity of the tone is proportional to the square of 

 the amplitude of the vibrations; consequently, with an amplitude multiplied 

 2, 3, 01-4 times, the intensity of the tone is 4, 9, 1 6 times as great. As the sound- 

 vibrations are transmitted to the ear by the wave-movements of the air, it is evi- 

 dent that, just as the waves in water become progressively smaller and smaller 

 with the distance from their point of origin, until they finally disappear, so also 

 the intensity of the sound diminishes with the distance of the sounding body 

 from the ear, and finally it must become zero. The sound-intensities, however, 

 are not exactly as the inverse ratios of the squares of the distances from the ear 

 to the source of the sound, but the intensity diminishes slowly near the source 

 of the sound, and more rapidly as the distance increases. The ear is little sen- 

 sitive to differences in intensity; differences can be distinguished, if the intensities 

 are in the proportion of 72 MOO. 



For the determination of the sound-intensity that is necessary to stimulate 

 the ear the following methods may be pursued: (i) A feeble source of sound, 



