On- and Off-Frequency Forward Masking by Schroeder-Phase Complexes

Abstract

Forward masking by harmonic tone complexes was measured for on-and off-frequency maskers as a function of masker phase curvature for two masker durations (30 and 200 ms). For the lowest signal frequency (1 kHz), the results matched predictions based on the expected interactions between the phase curvature and amplitude compression of peripheral auditory filtering. For the higher signal frequencies (2 and 6 kHz), the data increasingly departed from predictions in two respects. First, the effects of the masker phase curvature became stronger with increasing masker duration, inconsistent with the expected effects of the fast-acting compression and time-invariant phase response of basilar membrane filtering. Second, significant effects of masker phase curvature were observed for the off-frequency masker using a 6-kHz signal, inconsistent with predictions based on linear processing of stimuli well below the signal frequency. New predictions were generated assuming an additional effect with a longer time constant, consistent with the influence of medial olivocochlear efferent activation on otoacoustic emissions in humans. Reasonable agreement between the predicted and the measured effects suggests that efferent activation is a potential candidate mechanism to explain certain spectro-temporal masking effects in human hearing.

Additivity of nonsimultaneous masking for short Gaussian-shaped sinusoids

“…The MOCR has an onset delay of about 25 ms (Backus and Guinan, 2006). Wojtczak and Oxenham (2009) reported that the differences they found in forward masking between long and short maskers can be explained by a model incorporating MOCR-controlled gain reduction. Jennings et al (2009) found some indications that the presence of a precursor stimulus preceding a 20-ms forward masker reduces the cochlear gain.…”

“…Assuming that the BM is more compressive without activation of the MOCR, it can be hypothesized that excess masking is stronger for a Gaussian masker than for longer maskers. Indeed, the results of some recent nonsimultaneous masking experiments suggest the importance of the masker duration by means of the effect of the MOCR on cochlear compression (Jennings et al, 2009;Wojtczak and Oxenham, 2009;Plack and Arifianto, 2010). One goal of the present study was to measure masking additivity for very short Gaussian maskers to rule out the influence of the MOCR and to compare the results with those from the literature for different maskers which might have involved MOCR effects.…”

Phase effects in masking by harmonic complexes: Speech recognition

“…A recent study (Wojtczak and Oxenham, 2009) showed that the combination of compression and negative curvature was in some cases insufficient to explain phase effects observed in forward masking conditions. They suggested a more complex picture in which the medial olivo-cochlear reflex could modulate the non-linearity of the BM depending on the spectral region and the masker duration.…”

Illusory Auditory Continuity Despite Neural Evidence to the Contrary

“…Our second finding shows that the occluder had similar effects on the continuity illusion and forward masking. Based on the notion that forward masking depends primarily on the long-term internal excitation evoked by the masker (Carlyon and Datta 1997b ; Wojtczak and Oxenham 2009), this suggests that the illusion depends on a neural representation of the average excitation evoked by the occluder—possibly related to the specific loudness of the occluder, i.e., its loudness within the critical band centered on the frequency of the target sound (Mauermann and Hohmann 2007). …”