A Re-examination of the Effect of Masker Phase Curvature on Non-simultaneous Masking

Abstract

Forward masking of a sinusoidal signal is determined not only by the masker’s power spectrum but also by its phase spectrum. Specifically, when the phase spectrum is such that the output of an auditory filter centred on the signal has a highly modulated (“peaked”) envelope, there is less masking than when that envelope is flat. This finding has been attributed to non-linearities, such as compression, reducing the average neural response to maskers that produce more peaked auditory filter outputs (Carlyon and Datta, J Acoust Soc Am 101:3636–3647, 1997). Here we evaluate an alternative explanation proposed by Wotcjzak and Oxenham (Wojtczak and Oxenham, J Assoc Res Otolaryngol 10:595–607, 2009). They reported a masker phase effect for 6-kHz signals when the masker components were at least an octave below the signal frequency. Wotcjzak and Oxenham argued that this effect was inconsistent with cochlear compression, and, because it did not occur at lower signal frequencies, was also inconsistent with more central compression. It was instead attributed to activation of the efferent system reducing the response to the subsequent probe. Here, experiment 1 replicated their main findings. Experiment 2 showed that the phase effect on off-frequency forward masking is similar at signal frequencies of 2 and 6 kHz, provided that one equates the number of components likely to interact within an auditory filter centred on the signal, thereby roughly equating the effect of masker phase on the peakiness of that filter output. Experiment 3 showed that for some subjects, masker phase also had a strong influence on off-frequency backward masking of the signal, and that the size of this effect correlated across subjects with that observed in forward masking. We conclude that the masker phase effect is mediated mainly by cochlear non-linearities, with a possible additional effect of more central compression. The data are not consistent with a role for the efferent system.

Neural processing and perception of Schroeder‐phase harmonic tone complexes in the gerbil: Relating single‐unit neurophysiology to behavior

“…SCHR+ and SCHR− complexes with equal duty cycles have equal long‐term magnitude spectra and similar acoustical envelopes (ENVs). To date, the perception of SCHR complexes has been evaluated primarily in birds (Dooling et al, 2002) and humans (Carlyon et al, 2017; Drennan et al, 2008; Kohlrausch & Sander, 1995; Oxenham & Dau, 2001, 2004), whereas neural studies have focused on small mammals (e.g., Cedolin & Delgutte, 2010; Recio, 2001). The present study in the Mongolian gerbil for the first time relates behavior and single‐unit responses to SCHR complexes at different levels of the auditory pathway in the same species in order to investigate the physiological basis of perception.…”

“…Interesting perceptual differences between SCHR stimuli challenge some of the basic premises of hearing science, such as the role of the magnitude and phase spectra of complex sounds. Consequently, SCHR complexes have played a key role in psychophysical investigations of cochlear function and neural coding, including the phase response of auditory filters (e.g., Carlyon et al, 2017; Kohlrausch & Sander, 1995; Oxenham & Dau, 2001, 2004), the effect of the phase spectrum on masking (e.g., Carlyon & Datta, 1997; Smith et al, 1986), and sensitivity to temporal fine structure (TFS; e.g., Dooling et al, 2002; Drennan et al, 2008).…”