An experimental investigation of the phenomenon of auditory fatigue

Abstract

Auditory fatigue is now known as Temporary Threshold Shift (subsequently abbreviated to TTS). It has been defined as the temporary elevation in the absolute threshold of hearing for a given test sound resulting from preceding auditory stimulation by a given stimulus sound (see Hirsh, 1952, page 177). Associated with the phenomenon there are six physical variables which sub-divide themselves into stimulus, test and recovery factors. In IMS study each of the latter factors was systematically Investigated using four groups of six undergraduate subjects. Thresholds were measured using the Bek6sy (1947) technique of threshold measurement. Control experiments were carried out to verify that TTS results from the application of the stimulus tone, to study the mechanisms involved in the Bekesy technique of threshold measurement and the effects of this technique on the measurement of TTS, to investigate any additive effects of TTS and to study the possibility of any measurement errors resulting from the physical test environment. The results of the experiments showed that the stimulus test and recovery factors all produced a consistent duality of results. It was concluded that the unitary definition of TTS is inadequate and that there are two TTS mechanisms. These are referred to as fatigue and temporal stimulation deafness. Fatigue is associated with moderately intense stimulus tones of fairly short duration. It increases linearly with logarithm of the stimulus duration; it is maximal at stimulus frequencies of 1000, 2000 and 3000 cps; it does not vary significantly with stimulus intensities of up to 90 db. but thence increases rapidly to a maximum; it is maximal at a test frequency equal to the stimulus frequency and recovery from it is complete within one minute of the cessation of the stimulus. Temporary stimulation deafness is associated with high intensity stimulus tones of fairly long duration. It increases linearly with the logarithm of the stimulus duration; it is maximal with stimulus frequencies of 4000 to 6000 cps; it increases rapidly as the stimulus intensity is increased; it is maximal at a test frequency an octave above the stimulus frequency and recovery from it takes longer than one minute from the cessation of the stimulus tone. It is hypothesized that fatigue is a neural, possibly bio-chemical, adaptation effect and that temporary stimulation deafness results from structural damage to the organ of Corti. Other work supports this differentiation. The phenomena of fatigue support either a "place" or a "volley" theory of hearing. The phenomena of temporary stimulation deafness are partially explicable in terms of the anatomical characteristics of the ear.