On the detection of extremely small changes in sound intensity.

A number of investigators 1-19 have recently reported that certain kinds of hearing loss are apparently accompanied by unusually keen differential sensitivity to intensity. Their studies indicated that, in hearing loss due to cochlear lesion, the patient was able to discriminate smaller intensity changes than a listener with normal hearing. Furthermore, many of these investigators made the assumption that the apparent reduction of the intensity difference limen was due to the presence of loudness recruitment in the affected ear. On the basis of this assumed causal relationship, it was proposed that the measurement of the intensity difference limen afforded an indirect test for the presence of loudness recruitment. A normal-sized difference limen was thought to imply the absence of recruitment, while an abnormally small difference limen was interpreted to indicate the presence of recruitment. Some investigators have failed to confirm these observations. Studies by Liden and Nilsson 20 and Lund-Iversen

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