Level dependence of auditory filters in nonsimultaneous masking as a function of frequency

Abstract

Auditory filter bandwidths were measured using nonsimultaneous masking, as a function of signal level between 10 and 35 dB SL for signal frequencies of 1, 2, 4, and 6 kHz. The brief sinusoidal signal was presented in a temporal gap within a spectrally notched noise. Two groups of normalhearing subjects were tested, one using a fixed masker level and adaptively varying signal level, the other using a fixed signal level and adaptively varying masker level. In both cases, auditory filters were derived by assuming a constant filter shape for a given signal level. The filter parameters derived from the two paradigms were not significantly different. At 1 kHz, the equivalent rectangular bandwidth (ERB) decreased as the signal level increased from 10 to 20 dB SL, after which it remained roughly constant. In contrast, at 6 kHz, the ERB increased consistently with signal levels from 10 to 35 dB SL. The results at 2 and 4 kHz were intermediate, showing no consistent change in ERB with signal level. Overall, the results suggest changes in the level dependence of the auditory filters at frequencies above 1 kHz that are not currently incorporated in models of human auditory filter tuning.

Resolvability of components in complex tones and implications for theories of pitch perception

“…The auditory filters may be sharper than assumed in the procedure of Moore et al (1997). For example, the sharpness of tuning revealed in forward masking is greater than that revealed in simultaneous masking (Houtgast, 1977;Moore, 1978;Moore and Glasberg, 1981;Oxenham and Shera, 2003;Oxenham and Simonson, 2006). Sharper filters would lead to larger ripples in the excitation pattern for higher harmonics.…”

“…However, the presence of unresolved harmonics will not always result in a phase effect. Indeed, Oxenham et al (2009) sometimes failed to find a phase effect when N was in the range where F0DLs were high and it seemed very likely that all harmonics were unresolved. Thus all that can be concluded from these results is that they provide no positive evidence for the use of TFS information derived from groups of unresolved harmonics; they do not rule out the possibility that such TFS information can be used.…”

“…Moore et al argued that these low F0DLs supported the TFS hypothesis, and that F0 discrimination was based on changes in the TFS of unresolved harmonics when N was in the range 8e11. Oxenham et al (2009) suggested that the F0DLs measured by Moore et al (2006a) were affected by combination tones of the type 2f1ef2. Such combination tones have frequencies corresponding to harmonics with lower N than those in the stimuli.…”

“…One possible interpretation is that even the 7th harmonic was not resolved, and previous results showing good performance with N ¼ 7 reflected discrimination based on a combination tone with frequency corresponding to N ¼ 6. Another possibility is that the high level of the broadband background noise used by Oxenham et al (2009) adversely affected the ability to extract TFS information. Consistent with this idea, F0DLs decreased (improved) when the broadband background noise (which covered the frequency region of the complex tones) was replaced by a lowpass filtered noise with a cutoff frequency just below the frequency of the lowest component in the complex tones.…”

Evaluating the effects of olivocochlear feedback on psychophysical measures of frequency selectivity

“…The stimulus characteristics of the signal and masker were the same as for the PTC experiment, except the masker was a notched noise instead of a sinusoid. The spectral parameters of the notched noise were set according to Oxenham and Simonson (2006). Specifically, the notched noise was created by independently generating two bands of noise, one above the signal frequency (high-frequency noise band) and the other below the signal frequency (low-frequency noise band).…”