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PubMed1996

Treatment of severe exacerbation of chronic obstructive pulmonary disease with mask-applied continuous positive airway pressure.

The efficacy of mask-applied continuous positive airway pressure (CPAP) in the treatment of patients with acute severe exacerbations of chronic obstructive pulmonary disease (COPD) was examined. Ten patients with severe exacerbation of COPD who had deteriorated during conventional therapy were treated with face-mask delivered CPAP (+5 cmH2O; Downs Vital signs Inc., New Jersey, USA) instead of tracheal intubation and mechanical ventilation. The patients that were selected required mental alertness, intact upper airway reflexes, the clinical signs of dynamic hyperinflation and a positive end-expiratory pressure auto-(PEEP) manifested as expiratory wheeze and grunting. Nine out of 10 patients responded promptly to mask-CPAP with less distress, better oxygenation, lower respiratory and pulse rates. There was no significant change in arterial carbon dioxide tension with mask-CPAP treatment. One patient deteriorated on mask-CPAP and required intubation and mechanical ventilation. Three patients died (none of these patients died during the acute period of exacerbation). It was concluded that Mask-CPAP may be an alternative to mechanical ventilation in the treatment of selected patients with severe hypercapnic exacerbations of COPD.

Aged↗

PubMed2001

Informational and energetic masking effects in the perception of two simultaneous talkers.

Although most recent multitalker research has emphasized the importance of binaural cues, monaural cues can play an equally important role in the perception of multiple simultaneous speech signals. In this experiment, the intelligibility of a target phrase masked by a single competing masker phrase was measured as a function of signal-to-noise ratio (SNR) with same-talker, same-sex, and different-sex target and masker voices. The results indicate that informational masking, rather than energetic masking, dominated performance in this experiment. The amount of masking was highly dependent on the similarity of the target and masker voices: performance was best when different-sex talkers were used and worst when the same talker was used for target and masker. Performance did not, however, improve monotonically with increasing SNR. Intelligibility generally plateaued at SNRs below 0 dB and, in some cases, intensity differences between the target and masking voices produced substantial improvements in performance with decreasing SNR. The results indicate that informational and energetic masking play substantially different roles in the perception of competing speech messages.

Adult↗

PubMed2001

Forward- and simultaneous-masked thresholds in bandlimited maskers in subjects with normal hearing and cochlear hearing loss.

Forward- and simultaneous-masked thresholds were measured at 0.5 and 2.0 kHz in bandpass maskers as a function of masker bandwidth and in a broadband masker with the goal of estimating psychophysical suppression. Suppression was operationally defined in two ways: (1) as a change in forward-masked threshold as a function of masker bandwidth, and (2) as a change in effective masker level with increased masker bandwidth, taking into account the nonlinear growth of forward masking. Subjects were younger adults with normal hearing and older adults with cochlear hearing loss. Thresholds decreased as a function of masker bandwidth in forward masking, which was attributed to effects of suppression; thresholds remained constant or increased slightly with increasing masker bandwidth in simultaneous masking. For subjects with normal hearing, slightly larger estimates of suppression were obtained at 2.0 kHz rather than at 0.5 kHz. For hearing-impaired subjects, suppression was reduced in regions of hearing loss. The magnitude of suppression was strongly correlated with the absolute threshold at the signal frequency, but did not vary with thresholds at frequencies remote from the signal. The results suggest that measuring forward-masked thresholds in bandlimited and broadband maskers may be an efficient psychophysical method for estimating suppression.

Adult↗

PubMed2001

Consonant identification under maskers with sinusoidal modulation: masking release or modulation interference?

The present study investigated the effect of envelope modulations in a background masker on consonant recognition by normal hearing listeners. It is well known that listeners understand speech better under a temporally modulated masker than under a steady masker at the same level, due to masking release. The possibility of an opposite phenomenon, modulation interference, whereby speech recognition could be degraded by a modulated masker due to interference with auditory processing of the speech envelope, was hypothesized and tested under various speech and masker conditions. It was of interest whether modulation interference for speech perception, if it were observed, could be predicted by modulation masking, as found in psychoacoustic studies using nonspeech stimuli. Results revealed that masking release measurably occurred under a variety of conditions, especially when the speech signal maintained a high degree of redundancy across several frequency bands. Modulation interference was also clearly observed under several circumstances when the speech signal did not contain a high redundancy. However, the effect of modulation interference did not follow the expected pattern from psychoacoustic modulation masking results. In conclusion, (1) both factors, modulation interference and masking release, should be accounted for whenever a background masker contains temporal fluctuations, and (2) caution needs to be taken when psychoacoustic theory on modulation masking is applied to speech recognition.

Adult↗

PubMed2003

Asymmetry of masking between complex tones and noise: partial loudness.

This experiment examined the partial masking of periodic complex tones by a background of noise, and vice versa. The tones had a fundamental frequency (F0) of 62.5 or 250 Hz, and components were added in either cosine phase (CPH) or random phase (RPH). The tones and the noise were bandpass filtered into the same frequency region, from the tenth harmonic up to 5 kHz. The target alone was alternated with the target and the background; for the mixture, the background and target were either gated together, or the background was turned on 400 ms before, and off 200 ms after, the target. Subjects had to adjust the level of either the target alone or the target in the background so as to match the loudness of the target in the two intervals. The overall level of the background was 50 dB SPL, and loudness matches were obtained for several fixed levels of the target alone or in the background. The resulting loudness-matching functions showed clear asymmetry of partial masking. For a given target-to-background ratio, the partial loudness of a complex tone in a noise background was lower than the partial loudness of a noise in a complex tone background. Expressed as the target-to-background ratio required to achieve a given loudness, the asymmetry typically amounted to 12-16 dB. When the F0 of the complex tone was 62.5 Hz, the asymmetry of partial masking was greater for CPH than for RPH. When the F0 was 250 Hz, the asymmetry was greater for RPH than for CPH. Masked thresholds showed the same pattern as for partial masking for both F0's. Onset asynchrony had some effect on the loudness matching data when the target was just above its masked threshold, but did not significantly affect the level at which the target in the background reached its unmasked loudness. The results are interpreted in terms of the temporal structure of the stimuli.

Adult↗

PubMed2003

Informational masking and musical training.

The relationship between musical training and informational masking was studied for 24 young adult listeners with normal hearing. The listeners were divided into two groups based on musical training. In one group, the listeners had little or no musical training; the other group was comprised of highly trained, currently active musicians. The hypothesis was that musicians may be less susceptible to informational masking, which is thought to reflect central, rather than peripheral, limitations on the processing of sound. Masked thresholds were measured in two conditions, similar to those used by Kidd et al. [J. Acoust. Soc. Am. 95, 3475-3480 (1994)]. In both conditions the signal was comprised of a series of repeated tone bursts at 1 kHz. The masker was comprised of a series of multitone bursts, gated with the signal. In one condition the frequencies of the masker were selected randomly for each burst; in the other condition the masker frequencies were selected randomly for the first burst of each interval and then remained constant throughout the interval. The difference in thresholds between the two conditions was taken as a measure of informational masking. Frequency selectivity, using the notched-noise method, was also estimated in the two groups. The results showed no difference in frequency selectivity between the two groups, but showed a large and significant difference in the amount of informational masking between musically trained and untrained listeners. This informational masking task, which requires no knowledge specific to musical training (such as note or interval names) and is generally not susceptible to systematic short- or medium-term training effects, may provide a basis for further studies of analytic listening abilities in different populations.

Adult↗

PubMed2003

Psychometric functions for informational masking.

The term informational masking has traditionally been used to refer to elevations in signal threshold resulting from masker uncertainty. In the present study, the method of constant stimuli was used to obtain complete psychometric functions (PFs) from 44 normal-hearing listeners in conditions known to produce varying amounts of informational masking. The listener's task was to detect a pure-tone signal in the presence of a broadband noise masker (low masker uncertainty) and in the presence of multitone maskers with frequencies and amplitudes that varied at random from one presentation to the next (high masker uncertainty). Relative to the broadband noise condition, significant reductions were observed in both the slope and the upper asymptote of the PF for multitone maskers producing large amounts of informational masking. Slope was affected more for some listeners and conditions while asymptote was affected more for others; consequently, neither parameter alone was highly predictive of individual thresholds or the amount of informational masking. Mean slopes and asymptotes varied nonmonotonically with the number of masker components in a manner similar to mean thresholds, particularly when the estimated effect of energetic masking on thresholds was subtracted out. As in past studies, the threshold data were well described by a model in which trial-by-trial judgments are based on a weighted sum of levels in dB at the output of independent auditory filters. The psychometric data, however, complicated the model's interpretation in two ways: First, they suggested that, depending on the listener and condition, the weights can either reflect a fixed influence of masker components on each trial or the effect of occasionally mistaking a masker component for the signal from trial to trial. Second, they indicated that in either case the variance of the underlying decision variable as estimated from PF slope is not by itself great enough to account for the observed changes in informational masking.

Acoustic Stimulation↗

PubMed2004

Informational masking in hearing-impaired and normal-hearing listeners: sensation level and decision weights.

Informational masking (IM) refers to elevations in signal threshold caused by masker uncertainty. The purpose of this study was to investigate two factors expected to influence IM in hearing-impaired listeners. Masked thresholds for a 2000-Hz signal in the presence of simultaneous multitone maskers were measured in 16 normal-hearing (NH) and 9 hearing-impaired (HI) listeners. The maskers were 70 dB SPL average total power and were comprised of fixed-frequency components between 522 and 8346 Hz that were separated from each other by at least 1/3 oct and from the signal by at least 2/3 octs. Masker uncertainty was manipulated by randomly presenting each masker component with probability p = 0.1,0.2,...,0.9, or 1.0 across different trial blocks. Energetic masking was estimated as the amount of masking for p = 1.0, where masker uncertainty was minimum. IM was estimated as the amount of masking in excess of energetic masking. Decision weights were estimated by a regression of the listener's yes/no responses against the presence or absence of the signal and masker components. The decision weights and sensation levels (SLs) of the stimulus components were incorporated as factors in a model that predicts individual differences in IM based on the level variance (in dB) at the output of independent auditory filters [Lutfi, J. Acoust. Soc. Am. 94, 748-758 (1993)]. The results showed much individual variability in IM for the NH listeners (over 40 dB), but little IM for most HI listeners. When masker components were presented to a group of NH listeners at SLs similar to the HI listeners, IM was also similar to the HI listeners. IM was also similar for both groups when the level per masker component was 10 dB SL. These results suggest that reduced masker SLs for HI listeners decrease IM by effectively reducing masker variance. Weighting efficiencies, computed by comparing each listener's pattern of weights to that of an ideal analytic listener, were a good predictor of individual differences in IM among the NH listeners. For the HI listeners weighting efficiency and IM were unrelated because of the large variation in masker SLs among individual listeners, the small variance in IM, and perhaps because broadened auditory filters in some listeners increased the covariance in auditory filter outputs.

Adult↗

PubMed2005

Release from informational masking by time reversal of native and non-native interfering speech.

In many studies, the influence of intelligibility of the interfering speech is avoided by reversing it in time. Usually, intelligibility with time-reversed interfering speech indeed is higher compared to that with normal interfering speech. However, due to the nature of speech, reversed speech also gives rise to increased forward masking. The latter will result in a decrease in intelligibility. Thus, differences in intelligibility as a consequence of reversing speech in time are due to two opposite effects. This paper describes a speech reception threshold (SRT) test with intelligible and unintelligible interfering speech played normally and time-reversed. With Dutch listeners, Swedish reversed interfering speech gave a rise in SRT of 2.3 dB compared with the Swedish interfering speech (played normally). The difference can be attributed to differences in forward masking. Dutch time-reversed interfering speech gave a decrease in SRT of 4.3 dB compared to (intelligible) Dutch interfering speech. The latter is the result of both a release from informational masking and an increase in forward masking. Therefore, the amount of informational masking is larger than 4.3 dB and, if one assumes similar differences in forward masking for Dutch and Swedish speech, may amount to 6.6 dB.

Acoustic Stimulation↗

PubMed2005

Forward masking of amplitude modulation: basic characteristics.

In this study we demonstrate an effect for amplitude modulation (AM) that is analogous to forward making of audio frequencies, i.e., the modulation threshold for detection of AM (signal) is raised by preceding AM (masker). In the study we focused on the basic characteristics of the forward-masking effect. Functions representing recovery from AM forward masking measured with a 150- ms 40- Hz masker AM and a 50- ms signal AM of the same rate imposed on the same broadband-noise carrier, showed an exponential decay of forward masking with increasing delay from masker offset. Thresholds remained elevated by more than 2 dB over an interval of at least 150 ms following the masker. Masked-threshold patterns, measured with a fixed signal rate (20, 40, and 80 Hz) and a variable masker rate, showed tuning of the AM forward-masking effect. The tuning was approximately constant across signal modulation rates used and consistent with the idea of modulation-rate selective channels. Combining two equally effective forward maskers of different frequencies did not lead to an increase in forward masking relative to that produced by either component alone. Overall, the results are consistent with modulation-rate selective neural channels that adapt and recover from the adaptation relatively quickly.

Acoustic Stimulation↗

PubMed2006

Release from speech-on-speech masking by adding a delayed masker at a different location.

The amount of masking exerted by one speech sound on another can be reduced by presenting the masker twice, from two different locations in the horizontal plane, with one of the presentations delayed to simulate an acoustical reflection. Three experiments were conducted on various aspects of this phenomenon. Experiment 1 varied the number of masking talkers from one to three and the signal-to-noise (S/N) ratio from -12 to +4 dB. Evidence of masking release was found for every combination of these variables tested. For the most difficult conditions (multiple maskers and negative S/N) the amount of release was approximately 10 dB. Experiment 2 varied the timing of leading and lagging masker presentations over a broad range, to include shorter delay times where room reflections of speech are rarely noticed by listeners and longer delays where reflections can become disruptive. Substantial masking release was found for all of the shorter delay times tested, and negligible release was found at the longer delays. Finally, Experiment 3 used speech-spectrum noise as a masker and searched for possible energetic masking release as a function of the lead-lag time delay. Release of up to 4 dB was found whenever delays were 2 ms or less. No energetic masking release was found at longer delays.

Acoustic Stimulation↗

PubMed2006

Informational masking of speech in children: auditory-visual integration.

The focus of this study was the release from informational masking that could be obtained in a speech task by viewing a video of the target talker. A closed-set speech recognition paradigm was used to measure informational masking in 23 children (ages 6-16 years) and 10 adults. An audio-only condition required attention to a monaural target speech message that was presented to the same ear with a time-synchronized distracter message. In an audiovisual condition, a synchronized video of the target talker was also presented to assess the release from informational masking that could be achieved by speechreading. Children required higher target/distracter ratios than adults to reach comparable performance levels in the audio-only condition, reflecting a greater extent of informational masking in these listeners. There was a monotonic age effect, such that even the children in the oldest age group (12-16.9 years) demonstrated performance somewhat poorer than adults. Older children and adults improved significantly in the audiovisual condition, producing a release from informational masking of 15 dB or more in some adult listeners. Audiovisual presentation produced no informational masking release for the youngest children. Across all ages, the benefit of a synchronized video was strongly associated with speechreading ability.

Adolescent↗

PubMed1978

Temporal factors and suppression effects in backward and forward masking.

We discuss several experiments examining the influence of temporal parameters on suppression effects in backward and forward masking. The signal is always a brief 10-ms 2-kHz sinusoid; the masker a narrow band of noise of 40-dB spectrum level, 200-Hz wide, centered at the signal frequency. In some conditions, the presence of a second band of noise of the same spectral level in the region of 2300--3700 Hz appears to suppress the effects of the masker. Changes in the amount of suppression are examined as functions of the delay and duration of the suppressor (experiments 1 and 2). Adding the suppressor during the 50-ms interval nearest the signal produces changes in the signal threshold that are similar to those produced by reducing the level of the masker during this interval for both backward and forward masking (experiment 4). The similarity of these results suggests the operation of peripheral processes common to both backward and forward masking. However, if one increases the duration of the suppressor beyond this 50-ms interval there is no effect on forward masking, but large additional reductions in backward masking. This difference, in conjunction with other recent experiments, suggests the operation of additional central processes in backward masking. For some observers, these additional processes appear to operate over fairly long periods of time (250-500 ms). Such long durations are inconsistent with the estimates of integration time (less than or equal to 200 ms) obtained for these same observers (experiment 3).

Adult↗

PubMed1980

Contralateral cueing effects in backward masking.

The role of stimulus uncertainty in backward masking was investigated using a Monaural Detection with Contralateral Cueing (MDCC) paradigm. Cues temporally synchronous with and phase locked to the signal (20-ms segment of 500-Hz sinusoid) reduced backward masking, with the amount of reduction being independent of the phase relationship between the cue and the signal. Band-limited noise cues synchronous with the signal also reduced the amount of backward masking, with cue bandwidth having only a small differential effect on the amount of reduction. The important parameter of the cue in reducing backward masking was the temporal synchrony between the cue and the signal; a silent gap in a broadband noise served as an effective cue. These results confirm that, unlike simultaneous masking, backward masking involves a high degree of temporal uncertainty.

Acoustic Stimulation↗

PubMed1982

Inverse frequency dependence of simultaneous tone-on-tone masking patterns at low levels.

Using the Békésy tracking method, tone-on-tone masking patterns were measured with eight subjects at eight masker frequencies between 250 Hz and 6.03 kHz. Masking patterns were obtained for five masker levels between 20 and 60 dB SPL. Test-tone frequencies were chosen within two critical bands above and below the masker frequency. A level-dependent frequency asymmetry of masking was observed at all masker frequencies except at 250 Hz. At low levels there was a greater spread of masking towards the lower frequencies than toward the higher frequencies, but at high levels there was a greater spread of masking towards the higher frequencies than toward the lower frequencies. Only at masker levels of 40 dB SPL were the masking patterns approximately symmetrical.

Auditory Threshold↗

PubMed1984

Temporal integration of forward masking in listeners having sensorineural hearing loss.

Findings are described from three experiments that were designed to contrast estimates of auditory time and frequency analysis in highly practiced, young adult subjects having sensorineural hearing loss of cochlear origin with subjects having normal hearing. In one experiment, pure-tone detection threshold was measured for two durations of tones. For the hearing-impaired subjects, smaller differences were found between thresholds for the two durations of tones than were found for the normally hearing subjects at test frequencies where the sensitivity loss was greatest. In a subsequent forward masking experiment, masked thresholds were obtained at 3 kHz as a function of masker level at several masker durations. The results indicated that, for the range of values tested, masked probe thresholds changed less as a function of masker duration for the hearing-impaired subjects than for normally hearing subjects. However, forward masking grew as a function of masker level more steeply for the hearing-impaired listeners than for the normally hearing listeners. We believe that this result indicates abnormal temporal processing of sequential sounds. In a third experiment, psychophysical tuning curves were measured in a forward masking procedure for two maskers that differed in duration by approximately an order of magnitude. Again, the hearing-impaired subjects demonstrated less change in forward masking as a function of masker duration than normally hearing subjects. Further, the sharpness of the tuning curves from the hearing-impaired listeners was markedly reduced as compared to normal. It is believed that the results reflect a disruption of the normal temporal and spectral representation of sounds in the hearing-impaired subjects.

Auditory Threshold↗

PubMed1985

Additivity of simultaneous masking, revisited.

Lutfi [J. Acoust. Soc. Am. 73, 262-267 (1983)] compared simultaneous masking functions (signal threshold versus masker level) for individual sinusoidal and narrow-band noise maskers, and for those maskers presented in pairs. Lutfi found that the pairs of maskers produced 10-17 dB "excess" masking over that predicted from the linear sum of their individual masking and explained the results in terms of a model in which the effects of the maskers are summed after undergoing independent compressive transformations. This paper describes experiments similar to those of Lutfi, and presents evidence suggesting that Lutfi's results may have been influenced by two factors: (1) combination-product detection, and (2) the use of different detection cues for single maskers and for pairs of maskers. Experiment I showed that when the stimulus conditions were chosen so as to minimize the likelihood of combination-product detection, "excess" masking was only 3-5 dB. Experiment II supported the idea that for a single narrow-band noise masker, subjects make use of the relatively slow envelope fluctuations to enhance performance. When two independent narrow-band noise maskers are added, the effectiveness of this cue is reduced, and between 3 and 9 dB of "excess" masking occurs. When the two noises are derived from the same source, and have correlated envelope fluctuations, no "excess" masking occurs. The results indicate that Lufti's compressive-nonlinearity model clearly fails in some situations.

Auditory Threshold↗

PubMed1986

Procedure-independent growth-of-masking functions.

The forward-masked threshold for a 10-ms, 1-kHz sinusoidal signal was measured as a function of the level of a narrow-band (60-Hz wide) noise masker at five masker frequencies (0.6, 0.8, 1.0, 1.15, and 1.25 kHz) using both a fixed-masker procedure (determine the threshold level of the signal for a fixed level of the masker) and the converse procedure (determine the masker level necessary to just mask a given signal). A common growth-of-masking function describes the results of both procedures for a given masker frequency; i.e., an identical masker and signal lead to identical performance regardless of which is the dependent variable. The growth-of-masking functions for different masker frequencies show varying degrees of nonlinearity. The nonlinearity of the growth-of-masking functions underlies the discrepancies which arise between masking-pattern and tuning-curve data. These discrepancies do not arise because performance somehow depends upon whether the masker or signal is the dependent variable.

Acoustic Stimulation↗