Temporal Effects on Negative Threshold Shift

Abstract

A small but significant negative threshold shift (decrease in hearing threshold) has been reported following particular sound exposures and has been called sensitization. Similar negative threshold shifts of 2 to 3 dB have been observed in experiments of similar design but with a period of quiet substituted for the sound exposure. This negative shift following what amounts to an interruption in threshold tracking was the dependent variable in this series of three experiments concerned with temporal independent variables. The test tone was a continuous tone of 500 Hz. Threshold was tracked using a recording attenuator. As the interrupting quiet period was lengthened from 1 to 4 min the magnitude of the negative shift increased from 2 to 4 dB. In a 14-min tracking session during which seven tracking periods were interrupted by 1-min quiet intervals, the negative shift was maximum at the outset but still was increasing at the end of the session. Finally, 1 h of isolation in a sound-treated room prior to experimental tracking reduced but did not eliminate the negative-threshold shift.