Early/middle evoked potentials to tone bursts in quiet, white noise and notched noise

Early/middle auditory-evoked potentials were recorded on 10 normal-hearing adults using 500-, 1 000, and 2 000-Hz tone bursts having 4-ms rise-fall and 1-ms plateau times. The stimuli were presented in quiet, white noise and notched noise at 50, 40, 30, 20 and 10 dB nHL. The noises were selected to improve frequency specificity by masking those regions of the cochlea that do not correspond to the test stimulus. The recording-amplifier system had a bandpass of 55-1 500 Hz; electric activity was measured during the 25-ms post-stimulus interval. The three waves observed during this time interval (P10, N15, and P20) were labeled to reflect polarity and latency. The results revealed no differences among stimulus conditions (quiet, white noise, notched noise) in the number of identifiable responses for any wave at any intensity. Moreover, no P10, N15 or P20 latency differences were observed among conditions at 40 dB nHL and below. When 500-Hz tone bursts were presented at 50 dB nHL, however, significantly shorter response latencies were observed in quiet than when the tone bursts were mixed with white noise or notched noise. It was concluded that frequency specificity can be improved when tone bursts are mixed with notched noise or white noise. White noise is preferred, however, because it can be implemented with less complex instrumentation and calibration than notched noise.