Frequency selectivity estimated using stimulus-frequency otoacoustic emissions and psychophysical masking

Abstract

Psychophysical studies of frequency selectivity have concluded that the relative bandwidths of auditory filters decrease only slightly with increasing center frequency above 1 kHz. In contrast, estimates based on measurements of stimulus-frequency otoacoustic emissions (SFOAEs) in humans and other mammals suggest that frequency selectivity improves significantly with increasing center frequency. Psychophysical measures have mostly used simultaneous masking, which can be influenced by suppression. Since suppressive effects are stronger at high frequencies, these techniques may systematically overestimate filter bandwidths at high center frequencies. This study investigates whether psychophysical and physiological estimates of filter bandwidth can be reconciled if suppressive effects are eliminated by using forward masking. Filter bandwidths at center frequencies of 1, 2, 4, 6, and 8 kHz were measured using the notch-noise technique in simultaneous and forward masking with the signal level fixed at 10 and 30 dB above threshold in quiet. Relative bandwidths estimated in the same subjects using measurements of SFOAE group delay at 40-dB SPL were consistent with earlier results. The psychophysical and physiological estimates of relative bandwidth are generally consistent, suggesting that the relationship between center frequency and filter bandwidth found in previous psychophysical studies may have been influenced by suppression. [Work supported by NIDCD.]