Consequences of peripheral frequency selectivity for nonsimultaneous 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).

Recent research on forward masking and backward masking has led us to the hypothesis that combined forward and backward masking may involve at least two different types of interaction patterns. The previously documented interaction results in masking are greater than predicted by the simple summation of masking effects obtained with each masker alone (Lynn & Small, 1977; Patterson, 1971; Wilson & Carhart, 1971). Another possible type of interaction is based upon the finding that backward masking, but not forward masking, can be reduced by cues providing timing information (Puleo & Pastore, 1980). A forward masker appears to involve minimum temporal uncertainty (Pastore & Freda, 1980) and, therefore, should be able to act as such a source of timing information to reduce the contribution of a later occurring backward masker. Both types of interaction patterns were found, with the specific forward and backward masker parameters determining which pattern is observed.

A low-pass noise (1500-Hz cutoff) with a sinusoidal variation in its amplitude spectrum (ripple noise) was used to mask a 1000-Hz signal (10 msec) in both a forward and a simultaneous masking procedure. The masked thresholds of the signal were measured as a function of the number of peaks (ripples) in the amplitude spectrum of the noise. The procedure was similar to that used by Houtgast who reported it at the 83rd meeting of the Acoustical Society. Houtgast used a pulsation threshold technique with ripple noise to study frequency selectivity. Pulsation threshold is similar to simultaneous forward and backward masking. The data of the present study indicate that results similar, but not identical, to Houtgast's can be obtained with forward masking alone. The frequency selectivity obtained with the forward masking procedure is sharper than has been previously obtained and might indicate the presence of lateral inhibition.

The joint effect of forward and backward visual masking appears to be more extended in time than that predicted from an algebraic summation of individual forward and backward masking effects. It is suggested that this apparent extension of the temporal range of masking arises from the summation of forward and backward masking effects which in themselves are insufficient to influence observed performance. Such latent masking effects are possible if it is not assumed that when stimulus identification reaches the 100% level the mask has no effect at all on the stimulus.

Exploring facial emotion perception in schizophrenia using transcranial magnetic stimulation and spatial filtering

The differences in the suppression effect observed in forward and backward masking are consistent with an interpretation that suppression in forward masking results from a reduction of the effective level of the masker in the aditory periphery, and that the suppression in backward masking is influenced by these peripheral processes, but is dominated by additional, central processes. This conclusion is supported by experiments that show differences in the effect of ipsilateral versus contralateral presentation of the suppressor, and differences in the amount of the suppression observed as a function of the level, duration, and frequency of the suppressor.

Deficient rapid auditory processing (RAP) has been associated with early language impairment and dyslexia. Using an auditory masking paradigm, children with language disabilities perform selectively worse than controls at detecting a tone in a backward masking (BM) condition (tone followed by white noise) compared to a forward masking (FM) condition (tone preceded by white noise). Tallal's (1980) auditory processing hypothesis posits that abnormal RAP leads to reduced (or impaired) phonological awareness (PA), resulting in reading and language difficulties. Alternative theories suggest that impaired PA may have more of a top-down effect on auditory processing. The current study examines RAP in children tested at two time points, average age 5.6 and average age 8.3, in order to test causal relations between RAP and PA in a path analysis. Additional hierarchical regressions examine how well RAP predicts reading ability when accounting for PA and vocabulary. The path analysis indicates a top-down effect, such that PA has a larger impact on BM over time than the reverse. Regressions indicate no direct impact of RAP on reading ability. The path analysis provides evidence against the auditory processing hypothesis and instead suggests that between the ages of 5 and 8 it is variability in early phonological representations that predicts subsequent lower-level rapid auditory processing.

Backward masking is the phenomenon that an intense masker masks a weak and brief probe that Precedes the masker.Usually it has been attributed to the notion that in the Auditory pathway the neural response to a louder signal propagates faster than the response to a weak signal. Therefore, the response to the masker would overtake the probe response, thereby masking it. As argued before on a largely qualitative basis (Duifhuis 1972a, b), the acute peripheral frequency analysis can already cause temporal overlap of probe and masker, due to transient effects of peripheral filtering (transient masking, Duifhuis 1973). A further quantitative analysis of the peripheral contribution to backward masking appeared desirable. Recently this analysis has been worked out, using a descriptive model of the peripheral auditory system (Duifhuis, 1973). The present state of the modelling art implies that the theory will be a crude, but hopefully a significant first approximation. The main lines of the theory are presented in this paper, together with some tentative supporting neurophysiological data.KeywordsAuditory NerveMasker LevelPeripheral Auditory SystemProbabilistic TransducerBackward MaskingThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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.

In this paper we describe a method for comparing frequency selectivity in simultaneous and forward masking. The method is designed to eliminate off-frequency listening, which may have had a confounding influence in earlier studies. Thresholds for 1-kHz sinusoidal signals were measured as a function of the width of a spectral notch, centered at 1 kHz, a noise masker. In experiment I thresholds were measured in forward masking for signal durations of 5, 15, and 45 ms, with a noise spectrum level of 40 dB SPL/Hz. Thresholds decreased with increasing notch width for all signal durations. However, the change was more gradual at longer signal durations. This is consistent with a model in which the process of decay of masking follows the auditory filter. For each signal duration, threshold was also measured as a function of the level of a noise without a spectral notch. Each signal threshold for the notch-noise condition was then expressed as the level of a flat-spectrum noise which would give the same masking. When transformed in this way, the data for the three signal durations coincide, and can be interpreted in terms of the same auditory filter. In experiment II the 5-ms signals, whose level was fixed, followed the masker with delays of 5, 15, or 25 ms. The noise spectrum level was varied to find threshold. The change in threshold with notch width was independent of signal delay, confirming that the process of decay of masking follows the auditory filter. Experiment III showed that short-term spectral changes produced by differences in the shapes of the envelopes of signal and masker did not influence the results. In experiment IV thresholds for a 5-ms signal were measured in simultaneous and forward masking, both for a fixed noise level and for a fixed signal level. The derived auditory filters are similar for the two types of measure for each type of masking. However, the auditory filters derived in forward masking have bandwidths 17% smaller and slopes 48% greater than those in simultaneous masking. The differences between simultaneous and forward masking are interpreted in terms of suppression.

The temporal evolution of masking and frequency selectivity was studied in the goldfish using classical respiratory conditioning and a tracking psychophysical procedure. The temporal position of a brief tonal signal within a longer duration, tonal masker has little or no effect on signal detectability when the frequency of the masker is less than or equal to that of the signal. For masker frequencies above that of the signal, signal detectability improves as the signal onset is delayed relative to that of the masker. These patterns of tone-on-tone masking are quite similar to those observed for humans. These temporal masking patterns are qualitatively similar in shape to the peristimulus-time histogram profiles of the low-frequency saccular fibers thought to be used in this task. Frequency- and time-dependent changes in signal detectability result in specific changes in the sharpness of psychophysical tuning curves (PTC). In general, PTCs determined for signals occurring at masker onset are the most broadly tuned, and PTCs determined in forward masking are the most sharply tuned. The PTCs for signals temporally centered in the masker are intermediate. These results suggest that temporal tone-on-tone masking patterns and the temporal evolution of psychophysical tuning curves result from the response properties of peripheral auditory-nerve fibers.

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.]

Comparisons between psychophysical tuning curves and masking patterns obtained via forward masking will be presented. Tuning curves were measured for probe frequencies from 250 to 3000 Hz at 10 dB S.L. and 20 dB S.L. In general it was observed that sharpness of tuning as reflected by Q10 dB increased with increasing probe frequency. Masking patterns from the same subjects were obtained at corresponding masker frequencies and at sensation levels from 10–90 dB. Again, increasing selectivity was evident for higher frequency maskers. In all experiments the nonlinearity of the underlying forward masking function, for both similar and dissimilar probe-masker frequency sets, was apparent. Discussion will center on the implications of these findings for the use of forward masking to estimate the spectral resolution of the auditory system, as well as for the mechanism(s) of very short term auditory fatigue. [This work supported by a grant from NIH.]

The perceptual phenomena of temporal and spectral masking (critical band masking) [B. C. J. Moore, Frequency Selectivity in Hearing (Academic, New York, 1986)] are related to the ear’s limited temporal and spectral resolution. This resolution is known from psychoacoustic experiments but is not typically incorporated in the time-frequency representations used in audio signal processing. A joint time-frequency distribution, modeling both critical band masking and nonsimultaneous (forward and backward) masking, is described here. Applications for such a distribution include audio compression and the modeling of room acoustics. The distribution is developed within the framework of Cohen’s class of generalized time-frequency distributions [L. Cohen, ‘‘Time-frequency distributions—A review,’’ Proc. IEEE 77, 941–981 (1989)] and is a development from the constant Q modal distribution [W. J. Pielemier and G. H. Wakefield, ‘‘A high resolution time-frequency representation for musical instrument analysis,’’ J. Acoust. Soc. Am. 98, 2382–2396 (1996)]. The design and implementation of this auditory model is detailed.

Temporal masking of auditory evoked brainstem responses in human newborns and adults.