Auditory filter shapes derived in simultaneous and forward masking

The frequency selectivity of an auditory filter system is often conceptualized as a bank of bandpass auditory filters. Over the past 30 years, many simultaneous masking experiments using notched-noise maskers have been done to define the shape of the auditory filters (e.g., Glasberg and Moore 1990; Patterson and Nimmo-Smith 1980; Rosen and Baker, 1994). The studies of Glasberg and Moore (2000) and Baker and Rosen (2006) are notable inasmuch as they measured the human auditory filter shape over most of the range of frequencies and levels encountered in everyday hearing. The advantage of using notched-noise masking is that one can avoid off-frequency listening and investigate filter asymmetry. However, the derived filter shapes are also affected by the effects of suppression. The tunings of auditory filters derived from data collected in forward masking experiments were apparently sharper than those derived from simultaneous masking experiments, especially when the signal levels are low. The tuning of a filter is commonly believed to be affected by cochlear nonlinearity such as the effect of suppression. In past studies, the tunings of auditory filters derived from simultaneous masking data were wider than those of filters derived from nonsimultaneous (forward) masking data (Moore and Glasberg 1978; Glasberg and Moore 1982; Oxenham and Shera 2003). Heinz et al. (2002) showed that a tuning is generally sharpest when stimuli are at low levels and that suppression may affect tuning estimates more at high characteristic frequencies (CFs) than at low CFs. If the suggestion of Heinz et al. (2002) holds, i.e., if suppression affects frequency changes, comparing the filter bandwidths derived from simultaneous and forward masking experiments would indicate this. In this study we attempt to estimate filter tunings using both simultaneous and forward masking experiments with a notched-noise masker to investigate how the effects of suppression affect estimates of frequency selectivity across signal frequencies, signal levels, notch conditions (symmetric and asymmetric), and signal delays. This study extends the study of Unoki and Tan (2005).

The shape of the auditory filter was estimated at center frequencies of 4, 12, 14, and 16 kHz for normally hearing subjects, using the notched-noise method. A specially designed sound delivery system was used to generate a high-frequency masking noise with a flat spectrum. For all test frequencies, the auditory filter shapes were estimated at a noise spectrum level (N0) of 40 dB. The mean equivalent rectangular bandwidths (ERBs) of the auditory filter at 4, 12, and 14 kHz were close to the extrapolated values given by Glasberg and Moore [Hear. Res. 47, 103-108 (1990)]. At 16 kHz, the mean ERB was close to the extrapolated value given by Moore and Glasberg [J. Acoust. Soc. Am. 74, 750-753 (1983)]. At 12 and 14 kHz, the auditory filter shapes were also estimated at a noise spectrum level of 50 dB. The mean ERBs of the auditory filter were wider for the higher spectrum level, consistent with previous results obtained at lower center frequencies.

The threshold of a pulsed sinusoid centered in a notched-noise masker was measured as a function of the bandwidth of the notch. Assuming that the amount of masking reflects the amount of noise passing through an auditory filter centered on the signal frequency, the derivative of a curve fitted to the data is an estimate of the auditory filter shape [R. D. Patterson, “Auditory filter shape,” J. Acoust. Soc. Am. 55, 802–809 (1974)]. Estimated of the bandwidth of the auditory filter, defined as the half-power bandwidth, were found for three frequencies (1000, 2000, and 4000 Hz) and five noise spectrum levels (10, 20, 30, 40, and 50 dB). The bandwidth of the auditory filter increases with masker intensity above 30-dB noise spectrum level. At these higher intensities, an interaction with signal frequency is also observed, the bandwidth being relatively greater at higher frequencies. [This research was supported by the NIH.]

The width of the auditory filter in children

Auditory filter shapes derived from forward and simultaneous masking at low frequencies: Implications for human cochlear tuning

Measures of frequency selectivity from forward masking indicate sharper tuning than those from simultaneous masking (Houtgast, 1974; Moore, 1978). We show that a simple relation between forward and simultaneous masking predicts this result. Consider the masking of a 10-ms, sinusoidal signal of frequency fs = 2.0 kHz by a 200-ms, 50-Hz-wide narrow-band noise masker with center frequency fm. Let Df = fm − fs be the frequency interval between the signal and the masker, and let Dt = ts − tm be the time interval between their offsets. We may define the following three masking conditions: (1) on-frequency forward, Dt = 15 ms, Df = 0 Hz, (2) off-frequency simultaneous, Dt = 0 ms, Df = 200 Hz, and (3) off-frequency forward, Dt = 15 ms, Df = 200 Hz. Masking functions (signal intensity at masked threshold versus masker intensity) were obtained in each of these conditions. Our preliminary data indicate that the off-frequency forward masking function (F) is predicted reasonably well by the composite relation F = G(kH), where G is the on-frequency forward masking function, H is the off-frequency simultaneous masking function, and k is a constant. Predictions were equally as good for other values of Df, yielding the expected difference in tuning between simultaneous and forward measures.

Forward masking occurs when noise is presented before the target signal, making the latter difficult to be perceived. It is related to temporal auditory processing and consequently to speech recognition in noisy environments, which may decline with age. Interest in forward masking has grown in the last years. Studies investigate psychoacoustic and electrophysiological recordings in different age- groups. The purpose of the study was to investigate the effect of forward masking on frequency following response (FFR) as a function of age. Cross-sectional analytical observational study. We assessed 69 normal-hearing participants of both genders assigned to three groups: 40 young individuals (aged 18-25 years, mean age = 22 years 8 months), 21 middle-age individuals (aged 25-55 years, mean age = 37 years 2 months), and 8 seniors (aged <55 years, mean age = 65 years 3 months). FFRs were recorded using the /da/ syllable with and without noise. The /da/ syllable and speech-shaped noise were monaurally presented to the participants' right ears through ER-3a insert earphones. Electrodes were placed in M1 and M2 (-), Fz (+), and Fpz (ground). Acquisition occurred under two conditions: (1) the/da/ syllable presented without the noise and (2) the /da/ syllable presented 4 msec after the noise. Data show that (1) considering the mean values of all participants, there was a significant latency delay of all waves (PV, A, PW, PX, PY, PZ, and O) when the /da/ syllable was presented 4 msec after the masking noise as compared with the condition without noise, that is, forward masking occurred in all components of the FFR responses, and (2) for the youngest group and the middle-age group, forward masking was seen for all waves, except PX in the latter one; for the senior group, an irregular pattern was observed (presence of forward masking in PA, PY, PZ, and O). This pattern may be due to an aging effect on FFR responses even without noise presence, which makes it more difficult to identify forward masking effect in this population. Although it is well documented in the literature that forward masking increases with age, this is less evident on FFR recordings in the senior population. An aging effect was identified in FFR responses. Forward masking was identified in FFR responses of all groups but less evident in senior population.

In a previous experiment [R. H. Margolis and A. M. Small, J. Speech Hearing Res. 18, 571–587 (1975)] the characteristics of the auditory filter were investigated by measuring the detectability (d′) of a long duration (250 msec) tonal signal as a function of the cutoff frequency of a continuous, low-pass, computer-synthesized, noise masker. In the present research, two experiments were conducted to explore the effects of certain procedural variables on the characteristics of the auditory filter inferred from low-pass masking data. In experiment I auditory filter characteristics were found to be critically dependent upon the range over which d′ is allowed to vary. Baseline detectability and the procedure for computing d′ from P(C) were found to be critical variables. In experiment II the effect of a pulsed versus continuous masker was explored. The signal was a 500-msec tone with a rise-fall time of 25 msec. The masker was gated identically to the tone or left on continuously. Tonal signals were slightly more detectable in the pulsed masker condition. The results of these experiments have led to the design of a notch-noise, pulsed-masking experiment for the investigation of auditory filter characteristics in normal and pathological ears. [Work supported by NIH and the Deafness Research Foundation.]

When a short signal tone is presented after a noise or tone masker, the threshold for detecting the signal is raised the smaller the gap duration between the masker and the signal is. This phenomenon is termed forward masking and refers to the fact that a masker affects the signal threshold when both are presented in a non-simultaneous, consecutive manner. With increasing temporal separation, signal threshold usually drops to performance in silence when the gap is in the region of hundreds of milliseconds. As a possible explanation for forward masking, mainly two different mechanisms have been discussed in the literature: (i) continuation or persistence of neural activity (e.g., Plomp 1964; Oxenham and Moore 1994), referring to temporal integration of neural activity at presumably higher stages than the auditory nerve; (ii) neural adaptation (e.g., Duifhuis 1973; Nelson and Swain 1996), assuming adaptation at various levels of the auditory pathway (including high levels). A third possible source for interaction of masker and signal is linked to the ringing of the auditory filters but is generally assumed to be negligible for signal frequencies of 1 kHz or higher (e.g., Vogten 1978). It is still unclear whether temporal integration or adaptation can better account for forward masking in various stimulus configurations (Oxenham 2001), nor have both mechanisms been compared directly in a common modeling framework to investigate their relation. The current study compares two well established models of temporal processing in the auditory system using a unified modeling framework: (i) the temporal-window model (e.g., Oxenham and Moore 1994) representing a temporal-integration mechanism and (ii) the adaptation-loop model (e.g., Dau et al. 1996) as the representative for the adaptation mechanism. The unified modeling framework shares a compressive, non-linear auditory filter stage and a template-based (optimal detector) decision stage. The question is, whether the temporal-window model and the adaptation-loop model can be considered

The effects of masker intensity and masker frequency on the threshold of a 1‐kHz, 20‐ms probe were assessed in forward masking, with a masker‐probe delay of 5 ms. In general, probe threshold is a power function of masker intensity, with an exponent considerably less than unity; the exponent and constant of proportionality depend upon masker frequency. For example, with a 1‐kHz masker, a 10‐dB increase in masker level increases probe threshold by only about 5 dB, over a 60‐dB range of masker intensities. The nonlinear relation between probe threshold and masker intensity is consistent with the increased “selectivity” sometimes observed in forward‐masked tuning curves as compared with those obtained in simultaneous masking. These data then emphasize the importance of nonlinear intensity effects, in addition to possible changes in true frequency selectivity, in determining the form of psychophysical tuning curves obtained in forward masking and their relation to those obtained in simultaneous masking. [Supported by NICHD, NINCDS.]

Thresholds for the detection of gaps in sinusoidal signals were measured as a function of frequency (100-2000 Hz) and level (25-85 dB SPL) in 11 normally hearing subjects. The sinusoids were presented in a background noise intended to mask spectral splatter associated with the gap. In a separate experiment, auditory filter shapes and detection efficiency were estimated for the same 11 subjects using the notched-noise method, at center frequencies of 100, 200, 400, and 800 Hz. Gap thresholds varied only slightly with frequency over the range 400-2000 Hz, but increased markedly at 200 and 100 Hz. At all center frequencies, gap thresholds were almost invariant with level for levels above 55 dB SPL. Gap thresholds increased at low levels, reaching values about 50% greater than their asymptotic values at a sensation level of about 20 dB. The decrease in auditory filter bandwidth with decreasing center frequency does not seem sufficient to account for the increase in gap thresholds. Also, individual gap thresholds at a given center frequency were not significantly correlated with the bandwidth of the auditory filter at that center frequency, as would be expected if the auditory filter played a role in limiting gap detection. Detection efficiency decreased with decreasing center frequency. Individual differences in detection efficiency were significantly correlated with gap thresholds. However, changes in detection efficiency with frequency do not seem to be of the right form to account for the increase in gap thresholds at low frequencies. It seems likely that there is a central sliding temporal integrator which integrates over longer times at lower center frequencies.

From gated tone thresholds measured in the presence of "comb-filtered" (sinusoidal energy spectrum) noise maskers, the shape of the "auditory filter" was estimated in five frequency regions, 0.5, 1, 2, 4, and 8 kHz, at a number of masker levels. The auditory filter shape became wider, asymmetrical, and shifted towards lower frequencies as the level increased, for filters with center frequencies in excess of 1 kHz. The assumptions inherent in the derivation of the filter functions are discussed, and it is concluded that the likely deviation from these assumptions (in particular, as a result of the generation of nonlinear distortion products) leads to only small errors in the shapes of the derived filter functions.

The Bayesian adaptive procedure proposed by Shen and Richards [J. Acoust. Soc. Am. 134(2), 1134–1145 (2013)] was extended to allow the rapid estimation of auditory filters that were asymmetric about their peak frequencies. The estimation of the auditory-filter shape (five free parameters) was achieved using single Bayesian adaptive tracks of 150–200 trials (approximately 15 min to complete). During the experimental track, listeners detected a tonal signal presented with either simultaneous or forward maskers. Both types of maskers consisted of two bands of noises, one on each side of the signal frequency. The Bayesian adaptive procedure iteratively updated the parameter estimates following each experimental trial and determined the stimulus that would maximize the gain of information on the following trial. The stimuli were adaptively manipulated along three dimensions: the masker level and the spectral location of the upper and lower masker bands. The proposed procedure allowed the reliable estimation of the auditory-filter shape for naïve normal-hearing listeners. The model predictions replicated the known effect of the masker-signal simultaneity on the auditory filter.

Background: Forward masking occurs when noise is presented before the target signal, making thelatter difficult to be perceived. It is related to temporal auditory processing and consequently to speechrecognition in noisy environments, which may decline with age. Interest in forward masking has grown inthe last years. Studies investigate psychoacoustic and electrophysiological recordings in different age groups.&lt;br /&gt;Purpose: The purpose of the study was to investigate the effect of forward masking on frequency followingresponse (FFR) as a function of age.&lt;br /&gt;Research Design: Cross-sectional analytical observational study.&lt;br /&gt;Study Sample: We assessed 69 normal-hearing participants of both genders assigned to three groups: 40young individuals (aged 18–25 years,mean age = 22 years, 8 months), 21 middle-age individuals (aged 25–55years, mean age = 37 years, 2 months), and 8 seniors (aged &lt; 55 years, mean age = 65 years, 3 months).&lt;br /&gt;Intervention: FFRs were recorded using the /da/ syllable with and without noise.&lt;br /&gt;Data Collection and Analysis: The /da/ syllable and speech-shaped noise were monaurally presentedto the participants’ right ears through ER-3a insert earphones. Electrodes were placed in M1 and M2 (-),Fz (+), and Fpz (ground). Acquisition occurred under two conditions: (1) the /da/ syllable presented withoutthe noise and (2) the /da/ syllable presented 4 msec after the noise.&lt;br /&gt;Results: Data show that (1) considering the mean values of all participants, there was a significant latencydelay of all waves (PV, A, PW, PX, PY, PZ, and O) when the /da/ syllable was presented 4 msecafter the masking noise as compared with the condition without noise, that is, forward masking occurredin all components of the FFR responses, and (2) for the youngest group and the middle-age group, forwardmasking was seen for all waves, except PX in the latter one; for the senior group, an irregular patternwas observed (presence of forward masking in PA, PY, PZ, and O). This pattern may be due to an agingeffect on FFR responses even without noise presence, which makes it more difficult to identify forwardmasking effect in this population. Although it is well documented in the literature that forward maskingincreases with age, this is less evident on FFR recordings in the senior population.&lt;br /&gt;Conclusions: An aging effect was identified in FFR responses. Forward masking was identified in FFRresponses of all groups but less evident in senior population.&lt;br /&gt;

In recent derivations of auditory filter shape based on tone-in-noise detection experiments, the noise is represented by its power spectrum; that is, it has been assumed that filter shape is largely independent of masker variance. In an attempt to extend the generality of the filter-shape concept, one of the experiments has been replicated using a tonal maker in hopes of demonstrating that filter shapes derived with noise maskers are applicable when the masker variability is markedly reduced. Although some form of detection mechanism must follow the auditory filter, previous studies have not considered the mechanism explicitly. We will discuss the implications of including an energy detector at the output of the filter for the two-tone and noise-masking experiments, and in so doing, will outline the conditions under which changes in stimulus variability will affect performance and through it, the derived filter shapes.