Spectral and Temporal Parameters of Contralateral Signals Altering Temporary Threshold Shift

The test ear of each of nine normal-hearing subjects was exposed for three minutes to a 1000-Hz tone at 110 dB SPL. Either a 4000-Hz tone at 105 dB SPL or a broad-band noise at 100 dB SPL was presented to the contralateral ear during exposure. Four different temporal patterns were used for each contralateral signal: (1) continuous, (2) 18 seconds on/18 seconds off, (3) 1.8 seconds on/1.8 seconds off, and (4) 0.18 seconds on/0.18 seconds off. A control condition, consisting of the absence of contralateral stimulation, also was used. Pre- and postexposure thresholds for the test ear were tracked at a signal one-half octave above the exposure frequency. Resultant data indicated that reduction in temporary threshold shift was greatest for conditions involving rapidly pulsed (1.8 and 0.18 seconds on-off) contralateral signals. We hypothesized that these data were reflective of the dynamic properties of the acoustic reflex. Specifically, we posited that the acoustic reflex manifests less adaptation in response to rapid signal-repetition rates and relatively more adaptation to sustained or slowly pulsed signals.