Detection of Partially Filled and Empty Temporal Gaps in Low-pass Noise in Subjects With and Without Spontaneous Otoacoustic Emissions (SOAEs)

Strong SOAEs may be interpreted as sources of internal subthreshold noise. In an earlier study, ears with strong evoked otoacoustic emissions (EOAEs) and SOAEs exhibited higher detection thresholds for empty gaps in low-level wide-band signals than did ears with weak EOAEs and no SOAEs suggesting that internal noise created by the SOAEs masked the gap. The hypothesis of this study was that suppression of internal noise, introduced by filling the gap with a low-level signal, would enhance gap detection in subjects with strong EOAEs. Brief decrements in low-pass (0.1-4 kHz) noise stimuli presented at 10 and 20 dB SL were placed at the stimulus midpoint and their duration was varied adaptively Empty gaps were defined by a period of complete silence. For partially filled gaps, decrement depths of 6 or 10 dB, and 6, 10, or 20 dB were used for the 10-dB and 20-dB SL presentation levels, respectively. Subjects with either strong SOAEs and EOAEs or with no SOAEs and weak EOAEs participated For the empty gaps, the subjects with strong emissions exhibited higher mean gap detection thresholds than did subjects with weak emissions for both presentation levels. Individual data for the empty gaps were compared to those for partially filled gaps with the decrement depth equal to the presentation level. The ears with strong emissions exhibited lower thresholds for the partially filled gaps than for the empty ones; whereas, subjects with weak emissions performed poorer with filled than with empty gaps. The results suggest that strong SOAE activity creates an internal noise that affects the detection of empty gaps in a signal presented near the hearing threshold. When the gap is filled with a low-level signal, SOAEs are suppressed, resulting in improved detection of a brief decrement.

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