Abstract
Melnick [J. Acoust. Soc. Amer. 46, 1585–1586(L) (1969)], in a study of auditory sensitization using a threshold-tracking procedure, reported a negative threshold shift of 2 dB for a 1000-Hz signal following 3 min of quiet as well as following 3 min of exposure to 1000 Hz at 40 dB SL. This could not be due to an assumed sensitizing effect of a previous sound. A series of experiments was conducted to isolate factors contributing to this negative shift. Prolonged threshold tracking at 500 Hz (10 min) following 3 min of quiet revealed a negative shift which did not return to thresholds measured prior to the quiet period. When three tracking periods (3 min) were interspersed by 2 periods (3 min) of quiet or 40 dB SL of 500 Hz, negative threshold shift persisted following both the tone exposure and the quiet periods. In another experiment, six repetitions of a tracking task did not eliminate negative threshold shift following quiet. Test-tone mode (pulsed or continuous) and direction of approach to the initial tracking period (ascending or descending) did not matter. Negative threshold shift seems to be a minute but hardy phenomenon.
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