Sinusoidal Maskers Research Articles

Masking additivity in an excitation‐pattern model.

An excitation‐pattern model [Moore and Glasberg, Hear. Res. 28, 209–225 (1987)] was used to predict the masking additivity of two simultaneous sinusoidal maskers. The prediction relies on the assumption that masked threshold is reached when the addition of the signal to the masker produces a critical difference in the masker excitation pattern (EP) at any center frequency (the critical EP difference is termed criterion EPD). For equally effective maskers, masking additivity was assumed be equal to the difference between two signal levels: The level that produces the criterion EPD with the combination of maskers minus the level that produces the criterion EPD with the individual maskers. Excitation‐pattern predictions of masking additivity were obtained for signal frequencies of 500, 1000, and 5000 Hz, each masked by two sinusoidal maskers symmetrically placed about the signal frequencies; maskers frequencies within and outside the signal ERB were considered. The masking additivity predicted by the EP model is compared to that predicted by the modified power law model [Humes et al., J. Acoust. Soc. Am. 83, 188–202 (1988)], and to masking‐additivity data [Lutfi, J. Acoust. Soc. Am. 73, 262–267 (1983)].

Mechanisms underlying nonmonotonic Weber functions in forward‐masked intensity discrimination

Nonmonotonic growth in threshold for intensity discrimination has been noted for pure tones preceded by intense sinusoidal maskers; thresholds are highest for 40–60 dB SPL standards, producing what has often been described as a ‘‘midlevel hump.’’ Both physiologic and cognitive factors have ben suggested as mechanisms underlying this phenomenon. Three subjects received four conditions designed to examine this issue. A 2IFC paradigm assessed intensity discrimination of 1000‐Hz, 100‐ms sinusoids. A no‐masker condition provided a baseline. Three forward‐masked conditions were implemented: An ipsilateral condition that typically produces a mid‐level hump; a contralateral condition in which the hump is typically absent or greatly reduced; and a binaural condition presenting these two maskers simultaneously (contralateral stimulation was 13 dB greater than ipsilateral stimulation; listeners perceived only the contralateral masker). It was argued that if this condition produced a hump despite a perceptually absen...

Overshoot as a function of sinusoidal masker frequencies in vibrotactile sensation

Overshoot as a function of sinusoidal masker frequencies in vibrotactile sensation

Vibrotactile thresholds for detection of sinusoidal vibration as a function of stimulus duration measured in the presence of vibratory background noise

Thresholds for the detection of sinusoidal vibration were measured for stimuli ranging in duration from 15 to 1000 ms. The test stimuli were 250‐Hz bursts of vibration with 10‐ms rise‐fall times applied through either a 3.0 or 0.01 cm2 contactor to the thenar eminence of the right hand. Thresholds were measured in the presence of and in the absence of narrow‐band noise with frequencies centered around that of the test stimuli. Temporal summation, as indicated by a decrease in thresholds as stimulus duration increases, was observed at all intensities of the noise masker. This was true whether the stimulus was delivered through a large contactor designed to stimulate the Pacinian channel or through the small contactor designed to stimulate non‐Pacinian systems. On the other hand, when stimuli were detected in the presence of sinusoidal maskers, the amount of temporal summation depended on the intensity of the masker in a way predictable from the hypothesis that temporal summation can occur in the Pacinian, but not in one of the non‐Pacinian channels.

Phase effects in masking of one modulation frequency by another

Masking of one modulation frequency by another was measured in a 3IFC task. The carrier was broadband noise at a spectrum level of 30 dB SPL. This was amplitude modulated by a sinusoidal masker or a sinusoidal signal plus a sinusoidal masker. Masker modulation depth was fixed at 25% or 50%, and masker frequencies ranged from 2–800 Hz. Threshold signal modulation depth was measured for signals of 4, 16, 100, and 400 Hz. The masking functions showed broad tuning for modulation frequency consistent with that seen by Bacon and Grantham [J. Acoust. Soc. Am. 85, 2575–2580 (1989)]. For example, for a signal modulation frequency of 100 Hz, the amount of masking only varied over 5 dB for masker modulation frequencies from 40 to 140 Hz. Thresholds were phase dependent for masker frequencies of half, equal to, or twice the signal frequency. For equal signal and masker frequency, thresholds were consistent with detection of differences in envelope power, independent of signal/masker phase. Results are discussed in te...

A psychophysical evaluation of a model for suppression and excitation in remote masking

In the classical literature both the masking and the suppression of one tone by a second tone of lower frequency have been shown to be nonlinear functions of overall level. Here, the relation between these two tasks is further constrained by measuring both remote masking and suppression with the same subjects. The remote masking experiment measures the effect of a 602‐Hz sinusoidal masker on the detectability of a simultaneous 1500‐Hz sinusoidal signal, while the suppression experiment measures the effect of a 602‐Hz sinusoidal suppressor on the forward masking produced by a 1500‐Hz sinusoid. The data agree with earlier studies and are interpreted in the context of the multiple band pass nonlinearity model [J. L. Goldstein, “Updating cochlear driven models of auditory perception: A model for nonlinear auditory frequency analyzing filters,” in Working Models of Human Perception, edited by B. Elsendoorn and H. Bouma (Academic, New York, 1989), pp. 19–57], which suggests that both excitatory and suppressive mechanisms influence remote masking. [Work supported by NSF and AFOSR.]

Transition from simultaneous to forward masking III: Phase effects

The relative phase of a sinusoidal masker and signal necessarily has a large effect upon the signal power required for a simultaneous‐masked threshold but has no effect on the forward‐masked threshold. Threshold for a 20‐ms (20‐ms raised cosine ramps with no steady state produced a signal 20 ms long measured at the half‐voltage points on the envelope), 1‐kHz sinusoid, masked by a 300‐ms (no ramps), 1‐kHz sinusoid, was measured as a function of the signal's temporal position to examine how the phase effect disappeared in the transition from simultaneous to forward‐masking conditions. Although listeners differ, the phase effect remains unchanged at least until 10% of the signal energy is subject to forward masking and is substantially reduced, if not eliminated, when 50% of the signal is subject to forward masking. These results are interpreted to indicate that forward masking tends to be the more sensitive detection process when a signal is subject to both simultaneous and forward masking.

Vibrotactile masking: effects of stimulus onset asynchrony and stimulus frequency.

Vibrotactile thresholds for the detection of a 50-ms vibratory stimulus on the thenar eminence of the hand were measured in the presence of and in the absence of a 700-ms suprathreshold vibratory masking stimulus. When thresholds were measured in the presence of the masking stimulus, stimulus onset asynchrony (SOA) was varied so that backward, simultaneous, and forward masking could be measured. The amount of masking, expressed as threshold shift, was greatest when the test stimulus was presented near the onset or offset of the masking stimulus. For both backward and forward masking, the amount of masking decreased as a function of increasing stimulus onset asynchrony. Comparisons were made of the amounts of masking measured when the test and masking stimuli were both sinusoids, and when the test stimulus was a sinusoid and the masking stimulus was noise. In all conditions, the masked threshold decreased approximately 4.0 dB when SOA was increased from 100 to 650 ms with reference to the onset of the 700-ms masking stimulus. More simultaneous masking was observed when sinusoidal test stimuli were detected in the presence of noise than when they were detected in the presence of sinusoidal maskers of the same frequency. The functions were essentially identical for detection of a low-frequency (20 Hz) test stimulus mediated by a non-Pacinian channel and detection of a high-frequency (250 Hz) test stimulus mediated by the Pacinian channel.

Failure to obtain comodulation masking release with frequency-modulated maskers.

These experiments were intended to determine whether comodulation masking release (CMR) occurs for maskers that are modulated in frequency rather than in amplitude. In experiment I, thresholds for a sinusoidal signal were measured in the presence of two continuous sinusoidal maskers: one was centered at the signal frequency (1.0 kHz), and the other was positioned at flanking frequencies ranging from 0.5 to 2.0 kHz. The two maskers were frequency modulated (FM) by the same low-pass-noise modulator (correlated condition) or by independent noise modulators (uncorrelated condition). Thresholds were the same for the correlated and uncorrelated maskers, i.e., no CMR occurred. This was also true when the flanking band was presented in the ear opposite to that containing the signal and the on-frequency masking band. In experiment II, 25-Hz-wide noise maskers were used. The on-frequency band was sinusoidally frequency modulated, while the off-frequency band either had the same FM or no FM. Thresholds were similar for the two conditions, again indicating that no CMR occurred. The results suggest that, unlike amplitude modulation, correlated FM of the masker in different frequency bands does not give rise to a release from masking.

Channel interactions measured by forward‐masked “place” tuning curves with multichannel electrical stimulation

Simultaneous stimulation of multichannel intracochlear electrodes can give rise to peripheral and central channel interactions. The ability to eliminate or predict and control the interactions produced by a given electrode geometry is a processing goal for optimizing performance with a multichannel cochlear implant. Previous studies have used loudness summation and forward‐masking pattern techniques to estimate interactions between channels of electrical stimulation. In this study, interactions between bipolar channels of analog electrical stimulation were estimated using a forward‐masking paradigm with a fixed‐level, fixed‐location probe. By varying the electrode location of a 200‐Hz, 300‐ms sinusoidal masker and determining the level of the masker at each location necessary to just mask a 200‐Hz, 10‐ms probe, a “place” tuning curve was derived. The level of masker required at a given location to mask the probe depends on the amount of excitation produced by the probe and reflects, in part, the degree to which there is overlap of neural populations responding to each stimulus. These “place” tuning curves, which display interactions as a function of masker location were determined for several probe levels and probe locations. Results and implications for speech processing strategies will be discussed.

Masking of short tone bursts of frequency sweeps

Masked thresholds for a short probe tone are greater for sweep‐frequency tonal maskers than for stationary sinusoidal maskers at equal SPL, and greatest for sweep rates of 20–30 oct/s [G. F. Smoorenburg and F. Coninx, Hearing Res. 3, 301–316 (1980)]. The present study examined possible explanations for this surprising phenomenon and concentrated on the effects of masker level on probe threshold. Masked thresholds were obtained for a 10‐ms, 1‐kHz tone temporally centered in the 100‐ms masker. The maskers were swept in frequency at rates of 0–80 oct/s and passed through 1 kHz at 50 ms. At the lower masker levels, maximum masking occurred at sweep rates of 15–25 oct/s. At higher levels, little influence of sweep rate on masked thresholds was seen. Although there were substantial individual differences in slopes, the growth‐of‐masking functions had slopes less than one with minimum slopes at 20–25 oct/s. The shallow slopes are a distinguishing feature of sweep‐frequency masking and may provide a basis for understanding this important phenomenon. [Supported by NINCDS grant NS12125 and SSHRC‐Canada.]

Factors affecting thresholds for sinusoidal signals in narrow-band maskers with fluctuating envelopes.

When a signal is higher in frequency than a narrow-band masker, thresholds are lower when the masker envelope fluctuates than when it is constant. This article investigates the cues used to achieve the lower thresholds, and the factors that influence the amount of threshold reduction. In experiment I the masker was either a sinusoid (constant envelope) or a pair of equal-amplitude sinusoids (fluctuating envelope) centered at the same frequency as the single sinusoid (250, 1000, 3000, or 5275 Hz). The signal frequency was 1.8 times the masker frequency. At all center frequencies, thresholds were lower for the two-tone masker than for the sinusoidal masker, but the effect was smaller at the highest and lowest frequencies. The reduced effect at high frequencies is attributed to the loss of a cue related to phase locking in the auditory nerve. The reduced effect at low frequencies can be partly explained by reduced slopes of the growth-of-masking functions. In experiment II the masker was a sinusoid amplitude modulated at an 8-Hz rate. Masker and signal frequencies were the same as for the first experiment. Randomizing the modulation depth between the two halves of a forced-choice trial had no effect on thresholds, indicating that changes in modulation depth are not used as a cue for signal detection. Thresholds in the modulated masker were higher than would be predicted if they were determined only by the masker level at minima in the envelope, and the threshold reduction produced by modulating the master envelope was less at 250 Hz than at higher frequencies. Experiments III and IV reveal two factors that contribute to the reduced release from masking at low frequencies: The rate of increase of masked threshold with decreasing duration is greater at 250 Hz than at 1000 Hz; the amount of forward masking, relative to simultaneous masking, is greater at 250 Hz than at 1000 Hz. The results are discussed in terms of the relative importance of across-channel cues and within-channel cues.

Transient masking and the temporal course of simultaneous tone-on-tone masking.

Previous studies have shown that threshold for a signal in tone-on-tone simultaneous masking is sometimes lower when the masker is continuous than when it is gated. Threshold may also decline as signal onset is delayed relative to the onset of a longer duration masker, though it may increase again near masker offset. In the present study, the level of a 1250-Hz sinusoidal masker was found which would just mask a 20-ms, 1000-Hz sinusoid presented at 10-dB sensation level (SL). Masker duration was 20 or 400 ms; in the latter case, the signal was presented in one of three temporal positions within the masker. The level of the 1250-Hz masker necessary to mask the signal was reduced, sometimes by as much as 20-25 dB, by a 20-ms, 500-Hz sinusoid (transient masker) presented at the times when the signal might occur, but at a level 30 dB below that at which it would mask the 10-dB SL signal. This suggests that, in the earlier studies, at least some of the elevation in threshold in the presence of a short-duration masker or at the beginning (or end) of a longer duration masker may have been due to the transient responses to the masker affecting detection of the signal, but not necessarily masking the signal in terms of excitation in the signal "channel."

Profile analysis and background noise.

Spectral shape discrimination, or profile analysis, of complex waveforms (21 components) in the presence of broadband noise and special sinusoidal maskers of random amplitude was studied. The first experiment involved the discrimination between a standard flat spectrum and a "rippled" spectrum in broadband noise of different spectrum levels. Thresholds obtained under control conditions, without noise or without a standard, were used to estimate constants of an equation that predict thresholds where standard and noise are both present. The model assumes an external variance, produced by the noise, is added linearly to an internal variance caused by the flat standard. The mean squared error is less than 2 dB. The second experiment involved the detection of an increment on the center component of the 21-component standard. Added to the standard was an additional masking sinusoid of random amplitude. Both the frequency and the range of the random amplitude were varied and both showed a systematic influence on the detectability of the 1000-Hz increment.

Confusion effects with sinusoidal and narrow-band noise forward maskers.

In some forward-masking conditions, signal thresholds may be elevated by the listener's inability to distinguish the signal from the preceding masker. In this study, such "confusion" effects are investigated for both sinusoidal and narrow-band noise forward maskers combined with sinusoidal signals of varying duration. Results for the sinusoidal maskers show effects of off-frequency listening for brief signals and possibly small effects of confusion for longer signals. Results for the narrow-band noise maskers show a marked influence of confusion over a wide range of signal durations. This range is in good agreement with that predicted from previous work with "pulsing" maskers [D. Neff, J. Acoust. Soc. Am. 78, 1966-1976 (1985)]. These results suggest that studies using narrow-band noise forward maskers or studies of psychophysical suppression should include direct tests for confusion effects in key conditions.

Simultaneous masking by gated and continuous sinusoidal maskers

Simultaneous masking of a 20-ms, 1-kHz signal was investigated using 50-ms gated and continuous sinusoidal maskers with frequencies below, at, and above 1 kHz. Gated maskers can produce considerably (5-20 dB) more masking than continuous maskers, and this difference does not appear to result from the spread of energy produced by gating either the masker or the signal. For masker frequencies below the signal frequency, this difference in masking is primarily due to the detection of the cubic difference tone in the continuous condition. For masker frequencies at and above the signal frequency, the difference appears to be an important property of masking. Implications of this frequency-dependent effect for measures of frequency selectivity are discussed.

Vibrotactile forward masking: psychophysical evidence for a triplex theory of cutaneous mechanoreception.

Threshold shifts for the detection of vibrotactile test stimuli were determined as a function of the intensity of a masker. A 50-ms sinusoidal test stimulus was applied to the thenar eminence of the hand 25 ms after the termination of a 700-ms sinusoidal masker applied to the same site. The frequency of the test stimulus and the frequency of the masker were varied. To eliminate the influence of the Pacinian receptor system, stimuli were delivered through a 0.01-cm2 contactor. The results support the hypothesis that the detection of vibration delivered through a small contactor is determined by two separate populations of non-Pacinian receptors. The study constitutes a psychophysical demonstration of the existence of three receptor systems responsible for the detection of vibration.

Binaural masking-level differences with tonal maskers.

The thresholds for monaural and binaural 250-Hz test tones masked by a 250-Hz sinusoidal masker were measured as a function of the duration of the test tone. The signal and masker were presented either in-phase or in-quadrature. Next, the just-noticeable degree of amplitude modulation (AM) and just-noticeable modulation index for frequency modulation (FM) were measured as a function of the rate of modulation. Both sets of results suggest that monaural and binaural time constants have similar values (near 100 ms) and that the hearing system does not seem particularly 'sluggish' with the paradigms we used. In a second series of experiments, we again measured the masking of a tone by a tone of the same frequency. Long duration signals were used and we manipulated the phases of the masker and the signal. In order to interpret the results we require no more than the individual just-noticeable difference in level (monaurally about 1 dB) and the just-noticeable interaural time delay (about 100 microseconds at our signal frequency).

Transition from simultaneous to forward masking II

A stimulus condition in which the signal presentation partially overlaps the end of the masker presentation is intermediate between a simultaneous masking condition (complete overlap) and a forward‐masking condition (no overlap). In two experiments, we sought to determine what underlies signal detection in such conditions. In the first experiment, the masked threshold for a 20‐ms, 1‐kHz sinusoidal signal (20‐ms cosine‐squared ramps with no steady state) was measured as a function of its temporal position with respect to a 400‐ms, 1‐kHz, 70‐dB SPL sinusoidal masker (quadrature phase, 0‐ms ramps). These “transition curves” are compared to those obtained for the “simultaneous‐” and “forward‐masked’ portions of each signal. These signals were generated with 1‐ms ramps during the final 1 ms of the masker such that the portion of the 20‐ms signal which followed the masker was eliminated for the “simultaneous” signal, and the portion which overlapped the masker was eliminated for the “forward” signal, Comparison of these curves for three masker levels shows good agreement with the results from the second experiment in which transition curves were obtained for on‐ and off‐frequency maskers. Both experiments point to a transition region which occurs when 90% to 10% of the signal energy occurs during the masker presentation.

Forward masking by two sequential sinusoidal maskers

Two temporally distinct maskers of 300 and 30 ms were used to forward mask a 10‐ms signal. The signal was a 1000‐Hz sinusoid. The maskers were either 900‐ or 1000‐Hz sinusoids and all four combinations of the masker frequencies were tested. From growth‐of masking functions for individual maskers, levels were chosen to produce 5, 10, or 15 dB of masking for the first masker and 5, 10, 15, or 20 dB of masking for the second masker. When the two maskers were combined, the amount of additional masking, relative to that produced by the more effective masker, ranged from 0–24 dB across listeners and conditions. The smallest amount of additional masking was observed when both maskers were 1000 Hz. The remaining frequency combinations produced roughly similar amounts of additional masking. The results will be discussed in terms of models of additional masking. [Work supported by NIH.]