Spectral and level effects in auditory signal enhancement

Auditory enhancement refers generally to the increased perceptual salience of a spectral region when that region is preceded by its spectral complement, e.g., reinserting a missing component in a harmonic complex makes that component "pop out." One manifestation of enhancement is the increased detectability of a signal in certain spectro-temporal configurations. In the present experiments, detection thresholds were measured for a 2-kHz signal that was masked by an inharmonic complex with a spectral notch centered at 2-kHz. When the masker was preceded by a precursor/adaptor with a spectral gap identical to that of the masker, detection thresholds were lowest when the gap width was 0.6 octave. The amount of signal enhancement, the difference in thresholds between the no-precursor and precursor conditions, decreased for smaller and larger gap widths. In addition, this general result was robust for precursors such as band-reject noise and harmonic complexes that were different in perceptual quality from the masker. This suggests that grouping/segregation processes do not mediate enhancement as assessed here. Similarly, significant enhancement was observed with precursor-masker level differences over a 40-dB range. Overall, these results further indicate that frequency resolution is a dynamic process that depends on spectro-temporal context. They also are consistent with a mechanism involving adaptation of inhibition that likely occurs at low levels in the auditory system.