Why Psychiatric Patients Are Intolerant to Noise: a Theoretical View

Sir, Apropos the proposed explanation for the intolerance of noise in the psychiatric patients by Andrade(2000). I wish to supplement following relevant information in this context and offer an alternative hypothesis. 1. Middle ear does not play any role in the modification of the loudness of sound. In human beings the acoustic reflex i.e. reflex contraction of the stapedius muscle in response to loud sound is only a protective reflex and it has a reflex threshold value around 80 dB sound pressure level (SPL)above the subjects absolute threshold in the frequency range 250 Hz to 4 kHz. Further the contraction of tensor tympani muscle also does not occur in response to external sound in the human subjects though it contracts on other sensory stimuli viz. stimulation of cornea by puffs of air on, closing of eyes etc. (Pickles, 1997). 2.Very loud sound it self leads to physical discomfort and aural pain. Although there is wide range of individual variability in this respect of loudness level especially in case of sounds of high frequency range, in normal ears the threshold for pain is in the region of 110 to 130 dB SPL and sound above 80 dB SPL is reported to cause physical discomfort. In abnormal ears this threshold is lowered (WHO, 1980). 3. Perception of the characteristics of the sound ( pitch, loudness, timbre) is the function of inner ear. It is at the level of cochlea & auditory nerve where the basic frequency analysis mechanism for sound perception is stated to established. Information about stimulus frequency, intensity is determined by the distribution and temporal summation of the pattern of neural firing across nerve fibers (Moore, 1997). 4.Damage to inner ear leads to impairment in the frequency analysis mechanism. This leads to failure in the ability to detect and discriminate signals in noise. It also leads to abnormal increase in the loudness perception a phenomenon called loudness recruitment and lowering the threshold for aural discomfort and pain another phenomenon called syscusis. This has been proven by both neurophysiological as well as psychophysiological experiments (Moore, 1997; WHO, 1980). I agree with the statement made in the article that a substantial proportion of patients with psychiatric disorder complain of intolerance of noise. According to my assumptions such cases may be those who are harbouring co-morbid ear diseases and thus leading to loudness recruitment. Due to this phenomenon sound may appear disproportionately loud to them. The handicap due to ear disease might be subtle enough to be identified as felt need by the patients or lying undetected as being shadowed by the psychiatric symptomatology. A very high prevalence of ear disease (up to 66%) has been reported among insane and relation between deafness, ear disease and psychiatric disease in notunknown(Robinson, 1927).