Modulation Masking Research Articles

Effects of linguistic experience on the ability to benefit from temporal and spectral masker modulation

Masked speech perception can often be improved by modulating the masker temporally and/or spectrally. These effects tend to be larger in normal-hearing listeners than hearing-impaired listeners, and effects of temporal modulation are larger in adults than young children [Hall et al. (2012). Ear Hear. 33, 340-348]. Initial reports indicate non-native adult speakers of the target language also have a reduced ability to benefit from temporal masker modulation [Stuart et al. (2010). J. Am. Acad. Aud. 21, 239-248]. The present study further investigated the effect of masker modulation on English speech recognition in normal-hearing adults who are non-native speakers of English. Sentence recognition was assessed in a steady-state baseline masker condition and in three modulated masker conditions, characterized by spectral, temporal, or spectro-temporal modulation. Thresholds for non-natives were poorer than those of native English speakers in all conditions, particularly in the presence of a modulated masker. The group differences were consistent across maskers when assessed in percent correct, suggesting that a single factor may limit the performance of non-native listeners similarly in all conditions.

Effects of linguistic experience on the ability to benefit from temporal and spectral masker modulation

Effects of linguistic experience on the ability to benefit from temporal and spectral masker modulation

Audio watermarking based on amplitude modulation masking and its use of knowledge of the auditory system

Audio watermarking based on amplitude modulation masking and its use of knowledge of the auditory system

Phase effects in masking by harmonic complexes: Speech recognition

Harmonic complexes that generate highly modulated temporal envelopes on the basilar membrane (BM) mask a tone less effectively than complexes that generate relatively flat temporal envelopes, because the non-linear active gain of the BM selectively amplifies a low-level tone in the dips of a modulated masker envelope. The present study examines a similar effect in speech recognition. Speech reception thresholds (SRTs) were measured for a voice masked by harmonic complexes with partials in sine phase (SP) or in random phase (RP). The masker's fundamental frequency (F0) was 50, 100 or 200 Hz. SRTs were considerably lower for SP than for RP maskers at 50-Hz F0, but the two converged at 100-Hz F0, while at 200-Hz F0, SRTs were a little higher for SP than RP maskers. The results were similar whether the target voice was male or female and whether the masker's spectral profile was flat or speech-shaped. Although listening in the masker dips has been shown to play a large role for artificial stimuli such as Schroeder-phase complexes at high levels, it contributes weakly to speech recognition in the presence of harmonic maskers with different crest factors at more moderate sound levels (65 dB SPL).

Objective measures of binaural masking level differences and comodulation masking release based on late auditory evoked potentials

The audibility of important sounds is often hampered due to the presence of other masking sounds. The present study investigates if a correlate of the audibility of a tone masked by noise is found in late auditory evoked potentials measured from human listeners. The audibility of the target sound at a fixed physical intensity is varied by introducing auditory cues of (i) interaural target signal phase disparity and (ii) coherent masker level fluctuations in different frequency regions. In agreement with previous studies, psychoacoustical experiments showed that both stimulus manipulations result in a masking release (i: binaural masking level difference; ii: comodulation masking release) compared to a condition where those cues are not present. Late auditory evoked potentials (N1, P2) were recorded for the stimuli at a constant masker level, but different signal levels within the same set of listeners who participated in the psychoacoustical experiment. The data indicate differences in N1 and P2 between stimuli with and without interaural phase disparities. However, differences for stimuli with and without coherent masker modulation were only found for P2, i.e., only P2 is sensitive to the increase in audibility, irrespective of the cue that caused the masking release. The amplitude of P2 is consistent with the psychoacoustical finding of an addition of the masking releases when both cues are present. Even though it cannot be concluded where along the auditory pathway the audibility is represented, the P2 component of auditory evoked potentials is a candidate for an objective measure of audibility in the human auditory system.

Infants' detection and discrimination of sounds in modulated maskers

Adults and 7-month-old infants were compared in detection and discrimination of sounds in modulated maskers. In two experiments, the level of a target sound was varied to equate listeners' performance in unmodulated noise, and performance was assessed at that level in a noise modulated with the envelope of single-talker speech. While adults' vowel discrimination and tone detection were better in the modulated than in the unmodulated masker, infants' vowel discrimination was poorer in the modulated than in the unmodulated masker. Infants' tone detection was the same in the two maskers. In two additional experiments, each age group was tested at one level with order of testing in modulated and unmodulated maskers counterbalanced across subjects. Both infants and adults discriminated between vowels better in single-talker modulated and sinusoidally amplitude modulated (SAM) maskers than in an unmodulated masker, but infants' modulated-unmodulated difference was smaller than than that of adults. Increasing the modulation depth of the SAM masker did not affect the size of infants' modulated-unmodulated difference. However, infants' asymptotic performance in a modulated masker limits the extent to which their performance could improve. Infants can make use of information in masker dips, but masker modulation may also interfere with their ability to process the target.

The role of high-frequency envelope fluctuations for speech masking release

The speech-based envelope power spectrum model (sEPSM; Jo/rgensen and Dau, 2011; Jo/rgensen et al., 2013) was shown to successfully predict speech intelligibility in conditions with stationary and fluctuating interferers, reverberation, and spectral subtraction. The key element in the model was the multi-resolution estimation of the signal-to-noise ratio in the envelope domain (SNRenv) at the output of a modulation filterbank. The simulations suggested that mainly modulation filters centered in the range from 1-8 Hz contribute to speech intelligibility in the case of stationary maskers whereas modulation filters tuned to frequencies above 16 Hz might be important in the case of fluctuating maskers. In the present study, the role of high-frequency envelope fluctuations for speech masking release was further investigated in conditions of speech-on-speech Simulations were compared to various measured data from normal-hearing listeners (Festen and Plomp, 1990; Christiansen et al., 2013). The results support the hypothesis that high-frequency envelope fluctuations (>30 Hz) are essential for speech intelligibility in conditions with speech interferers. While the sEPSM reflects effects of energetic and modulation masking in speech intelligibility, the remaining unexplored effect in some conditions may be attributed to, and defined as, informational masking.

Understanding Excessive SNR Loss in Hearing-Impaired Listeners

Traditional audiometric measures, such as pure-tone thresholds or unaided word-recognition in quiet, appear to be of marginal use in predicting speech understanding by hearing-impaired (HI) individuals in background noise with or without amplification. Suprathreshold measures of auditory function (tolerance of noise, temporal and frequency resolution) appear to contribute more to success with amplification and may describe more effectively the distortion component of hearing. However, these measures are not typically measured clinically. When combined with measures of audibility, suprathreshold measures of auditory distortion may provide a much more complete understanding of speech deficits in noise by HI individuals. The primary goal of this study was to investigate the relationship among measures of speech recognition in noise, frequency selectivity, temporal acuity, modulation masking release, and informational masking in adult and elderly patients with sensorineural hearing loss to determine whether peripheral distortion for suprathreshold sounds contributes to the varied outcomes experienced by patients with sensorineural hearing loss listening to speech in noise. A correlational study. Twenty-seven patients with sensorineural hearing loss and four adults with normal hearing were enrolled in the study. The data were collected in a sound attenuated test booth. For speech testing, subjects' verbal responses were scored by the experimenter and entered into a custom computer program. For frequency selectivity and temporal acuity measures, subject responses were recorded via a touch screen. Simple correlation, step-wise multiple linear regression analyses and a repeated analysis of variance were performed. Results showed that the signal-to-noise ratio (SNR) loss could only be partially predicted by a listener's thresholds or audibility measures such as the Speech Intelligibility Index (SII). Correlations between SII and SNR loss were higher using the Hearing-in-Noise Test (HINT) than the Quick Speech-in-Noise test (QSIN) with the SII accounting for 71% of the variance in SNR loss for the HINT but only 49% for the QSIN. However, listener age and the addition of suprathreshold measures improved the prediction of SNR loss using the QSIN, accounting for nearly 71% of the variance. Two standard clinical speech-in-noise tests, QSIN and HINT, were used in this study to obtain a measure of SNR loss. When administered clinically, the QSIN appears to be less redundant with hearing thresholds than the HINT and is a better indicator of a patient's suprathreshold deficit and its impact on understanding speech in noise. Additional factors related to aging, spectral resolution, and, to a lesser extent, temporal resolution improved the ability to predict SNR loss measured with the QSIN. For the HINT, a listener's audibility and age were the only two significant factors. For both QSIN and HINT, roughly 25-30% of the variance in individual differences in SNR loss (i.e., the dB difference in SNR between an individual HI listener and a control group of NH listeners at a specified performance level, usually 50% word or sentence recognition) remained unexplained, suggesting the need for additional measures of suprathreshold acuity (e.g., sensitivity to temporal fine structure) or cognitive function (e.g., memory and attention) to further improve the ability to understand individual variability in SNR loss.

The monaural temporal window based on masking period pattern data in school-aged children and adults

Several lines of evidence indicate that auditory temporal resolution improves over childhood, whereas other data implicate the development of processing efficiency. The present study used the masking period pattern paradigm to examine the maturation of temporal processing in normal-hearing children (4.8 to 10.7 yrs) compared to adults. Thresholds for a brief tone were measured at 6 temporal positions relative to the period of a 5-Hz quasi-square-wave masker envelope, with a 20-dB modulation depth, as well as in 2 steady maskers. The signal was a pure tone at either 1000 or 6500 Hz, and the masker was a band of noise, either spectrally wide or narrow (21.3 and 1.4 equivalent rectangular bandwidths, respectively). Masker modulation improved thresholds more for wide than narrow bandwidths, and adults tended to receive more benefit from modulation than young children. Fits to data for the wide maskers indicated a change in window symmetry with development, reflecting relatively greater backward masking for the youngest listeners. Data for children >6.5 yrs of age appeared more adult-like for the 6500- than the 1000-Hz signal. Differences in temporal window asymmetry with listener age cannot be entirely explained as a consequence of a higher criterion for detection in children, a form of inefficiency.

Cross-Modal Modulation Masking: A Psychophysical and EEG Investigation of Simultaneous Acoustic and Vibrotactile Amplitude Modulation.

Event Abstract Back to Event Cross-Modal Modulation Masking: A Psychophysical and EEG Investigation of Simultaneous Acoustic and Vibrotactile Amplitude Modulation. Justin R. Timora1* and Timothy W. Budd1 1 University of Newcastle, Australia Aims: Modulation masking refers to a disruption in the ability to detect amplitude modulation (AM) in sound in the presence of an auditory masker with a similar temporal pattern. Previously, we have shown that multisensory presentations of acoustic and vibrotactile AM stimuli increase auditory and vibrotactile AM detection thresholds, suggesting a cross-modal modulation masking effect. Prior psychoacoustic research suggests that this masking effect is dependent on the phase of the AM masker. This study aimed to determine whether cross-modal phase differences for simultaneously presented acoustic and vibrotactile AM stimuli increase AM detection thresholds and whether this is reflected in the steady-state response (SSR) elicited by the same multisensory stimulus combinations. Method: A 2I-3AFC psychophysical procedure was used to estimate AM detection thresholds for auditory and vibrotactile stimuli at two AM rates (27 and 40 Hz) and three cross-modal phase conditions: None (AM stimulation in the target modality only); Same (AM in both modalities /no cross-modal phase difference); Different (AM stimulation in both modalities/180˚ phase difference). In a separate EEG session SSR activity was measured to the same stimulus combinations. Results: Vibrotactile AM thresholds significantly varied according to Phase F(2,28)= 4.81,p = .02. Thresholds for the Same condition were higher relative to None F(1,14) = 8.06, p =.01. Differences between None and Different were non-significant. The influence of Phase on auditory 27 and 40 Hz SSR activity significantly varied according to AM rate F(2,16) = 8.65, p =.003, F(2,16) = 6.43, p=.01, with greater increases in activity at the EEG frequency corresponding to the AM rate. Conclusions: The increased sensitivity to vibrotactile AM stimuli resulting from a cross-modal phase difference suggests a release from masking and provides further evidence of cross-modal modulation masking. Cross-modal AM stimulation increases auditory SSR activity at the frequency of stimulation but has no effect on vibrotactile SSR activity which suggests a dissociation between SSR activity and AM detection. Keywords: amplitude modulation, auditory steady-state responses (ASSRs), vibrotactile steady-state responses, cross-modal modulation masking, temporal processing Conference: ASP2013 - 23rd Annual meeting of the Australasian Society for Psychophysiology, Wollongong, Australia, 20 Nov - 22 Nov, 2013. Presentation Type: Poster Presentation Topic: Perception Citation: Timora JR and Budd TW (2013). Cross-Modal Modulation Masking: A Psychophysical and EEG Investigation of Simultaneous Acoustic and Vibrotactile Amplitude Modulation.. Conference Abstract: ASP2013 - 23rd Annual meeting of the Australasian Society for Psychophysiology. doi: 10.3389/conf.fnhum.2013.213.00006 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 31 Oct 2013; Published Online: 05 Nov 2013. * Correspondence: Mr. Justin R Timora, University of Newcastle, Newcastle, Australia, justin.timora@uon.edu.au Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Justin R Timora Timothy W Budd Google Justin R Timora Timothy W Budd Google Scholar Justin R Timora Timothy W Budd PubMed Justin R Timora Timothy W Budd Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Effects of Reverberation on Speech Recognition in Stationary and Modulated Noise by School-Aged Children and Young Adults

The purpose of this study was to determine how combinations of reverberation and noise, typical of environments in many elementary school classrooms, affect normal-hearing school-aged children's speech recognition in stationary and amplitude-modulated noise, and to compare their performance with that of normal-hearing young adults. In addition, the magnitude of release from masking in the modulated noise relative to that in stationary noise was compared across age groups in nonreverberant and reverberant listening conditions. Last, for all noise and reverberation combinations the degree of change in predicted performance at 70% correct was obtained for all age groups using a best-fit cubic polynomial. Bamford-Kowal-Bench sentences and noise were convolved with binaural room impulse responses representing nonreverberant and reverberant environments to create test materials representative of both audiology clinics and school classroom environments. Speech recognition of 48 school-aged children and 12 adults was measured in speech-shaped and amplitude-modulated speech-shaped noise, in the following three virtual listening environments: nonreverberant, reverberant at 2 m, and reverberant at 6 m. Speech recognition decreased in the reverberant conditions and with decreasing age. Release from masking in modulated noise relative to stationary noise decreased with age and was reduced by reverberation. In the nonreverberant condition, participants showed similar amounts of masking release across ages. The slopes of performance-intensity functions increased with age, with the exception of the nonreverberant modulated masker condition. The slopes were steeper in the stationary masker conditions, where they also decreased with reverberation and distance. In the presence of a modulated masker, the slopes did not differ between the two reverberant conditions. The results of this study reveal systematic developmental changes in speech recognition in noisy and reverberant environments for elementary-school-aged children. The overall pattern suggests that younger children require better acoustic conditions to achieve sentence recognition equivalent to their older peers and adults. In addition, this is the first study to report a reduction of masking release in children as a result of reverberation. Results support the importance of minimizing noise and reverberation in classrooms, and highlight the need to incorporate noise and reverberation into audiological speech-recognition testing to improve predictions of performance in the real world.

Effects of masker envelope irregularities on tone detection in narrowband and broadband noise maskers

Introducing coherent masker envelope modulation to frequency regions neighboring the signal frequency can reduce detection thresholds for a pure-tone signal. Verhey and Ernst (2009) reported that irregular masker modulation conferred greater benefit than regular modulation when the masker was broadband, but that there was no difference when the masker was narrowband. The present study evaluated two possible explanations for this result: one based on modulation adaptation and the other based on the introduction of relatively long-duration modulation minima in the irregular masker modulation condition. The first experiment replicated the results of Verhey and Ernst (2009), but also included conditions in which a 12.5-ms signal was presented in a 12.5-ms modulation minimum, which was exempted from envelope jitter. The second experiment used a continuous masker and suspended jitter during epochs associated with either a 12.5- or 87.5-ms signal. No benefit of masker envelope irregularity before or after the signal was observed in either experiment. These findings are inconsistent with an explanation based on modulation adaptation, implicating instead the introduction of relatively long-duration modulation minima in the large masking release obtained for a long-duration signal in an irregularly modulated masker.

Dip listening or modulation masking? Call recognition by green treefrogs (Hyla cinerea) in temporally fluctuating noise

Despite the importance of perceptually separating signals from background noise, we still know little about how nonhuman animals solve this problem. Dip listening, an ability to catch meaningful 'acoustic glimpses' of a target signal when fluctuating background noise levels momentarily drop, constitutes one possible solution. Amplitude-modulated noises, however, can sometimes impair signal recognition through a process known as modulation masking. We asked whether fluctuating noise simulating a breeding chorus affects the ability of female green treefrogs (Hyla cinerea) to recognize male advertisement calls. Our analysis of recordings of the sounds of green treefrog choruses reveal that their levels fluctuate primarily at rates below 10Hz. In laboratory phonotaxis tests, we found no evidence for dip listening or modulation masking. Mean signal recognition thresholds in the presence of fluctuating chorus-like noises were never statistically different from those in the presence of a non-fluctuating control. An analysis of statistical effects sizes indicates that masker fluctuation rates, and the presence versus absence of fluctuations, had negligible effects on subject behavior. Together, our results suggest that females listening in natural settings should receive no benefits, nor experience any additional constraints, as a result of level fluctuations in the soundscape of green treefrog choruses.

Masking Release for Sweeping Masker Components with Correlated Envelopes

To separate sounds from different sound sources, common properties of natural sounds are used by the auditory system, such as coherent temporal envelope fluctuations and correlated changes of frequency in different frequency regions. The present study investigates how the auditory system processes a combination of these cues using a generalized comodulation masking release (CMR) paradigm. CMR is the effect of a better signal detectability in the presence of comodulated maskers than in the presence of maskers with uncorrelated envelope fluctuations across frequencies. Using a flanking-band paradigm, the results of the first experiment of the present study show that CMR is still observed for the masker and the signal coherently sweeping up or down in frequency over time, up to a sweep rate of six octaves per second. Motivated by the successful modeling of CMR using filters sensitive to temporal modulations and recent physiological evidence of spectro-temporal modulation filters, the second experiment investigates whether CMR is also observed for spectro-temporal masker modulations generated using time-shifted versions of the masker envelope for each component. The thresholds increase as soon as the temporally coherent masker modulation is changed to a spectro-temporal masker modulation, indicating that spectro-temporal modulation filters are presumably not required in CMR models.

Phoneme recognition in modulated maskers by normal-hearing and aided hearing-impaired listeners

This study measured the influence of masker fluctuations on phoneme recognition. The first part of the study compared the benefit of masker modulations for consonant and vowel recognition in normal-hearing (NH) listeners. Recognition scores were measured in steady-state and sinusoidally amplitude-modulated noise maskers (100% modulation depth) at several modulation rates and signal-to-noise ratios. Masker modulation rates were 4, 8, 16, and 32 Hz for the consonant recognition task and 2, 4, 12, and 32 Hz for the vowel recognition task. Vowel recognition scores showed more modulation benefit and a more pronounced effect of masker modulation rate than consonant scores. The modulation benefit for word recognition from other studies was found to be more similar to the benefit for vowel recognition than that for consonant recognition. The second part of the study measured the effect of modulation rate on the benefit of masker modulations for vowel recognition in aided hearing-impaired (HI) listeners. HI listeners achieved as much modulation benefit as NH listeners for slower masker modulation rates (2, 4, and 12 Hz), but showed a reduced benefit for the fast masker modulation rate of 32 Hz.

Notionally steady background noise acts primarily as a modulation masker of speech

Stone et al. [J. Acoust. Soc Am. 130, 2874-2881 (2011)], using vocoder processing, showed that the envelope modulations of a notionally steady noise were more effective than the envelope energy as a masker of speech. Here the same effect is demonstrated using non-vocoded signals. Speech was filtered into 28 channels. A masker centered on each channel was added to the channel signal at a target-to-background ratio of -5 or -10 dB. Maskers were sinusoids or noise bands with bandwidth 1/3 or 1 ERB(N) (ERB(N) being the bandwidth of "normal" auditory filters), synthesized with Gaussian (GN) or low-noise (LNN) statistics. To minimize peripheral interactions between maskers, odd-numbered channels were presented to one ear and even to the other. Speech intelligibility was assessed in the presence of each "steady" masker and that masker 100% sinusoidally amplitude modulated (SAM) at 8 Hz. Intelligibility decreased with increasing envelope fluctuation of the maskers. Masking release, the difference in intelligibility between the SAM and its "steady" counterpart, increased with bandwidth from near-zero to around 50 percentage points for the 1-ERB(N) GN. It is concluded that the sinusoidal and GN maskers behaved primarily as energetic and modulation maskers, respectively.

Sentence recognition in noise promoting or suppressing masking release by normal-hearing and cochlear-implant listeners

Normal-hearing (NH) listeners maintain robust speech understanding in modulated noise by "glimpsing" portions of speech from a partially masked waveform--a phenomenon known as masking release (MR). Cochlear implant (CI) users, however, generally lack such resiliency. In previous studies, temporal masking of speech by noise occurred randomly, obscuring to what degree MR is attributable to the temporal overlap of speech and masker. In the present study, masker conditions were constructed to either promote (+MR) or suppress (-MR) masking release by controlling the degree of temporal overlap. Sentence recognition was measured in 14 CI subjects and 22 young-adult NH subjects. Normal-hearing subjects showed large amounts of masking release in the +MR condition and a marked difference between +MR and -MR conditions. In contrast, CI subjects demonstrated less effect of MR overall, and some displayed modulation interference as reflected by poorer performance in modulated maskers. These results suggest that the poor performance of typical CI users in noise might be accounted for by factors that extend beyond peripheral masking, such as reduced segmental boundaries between syllables or words. Encouragingly, the best CI users tested here could take advantage of masker fluctuations to better segregate the speech from the background.

The effect of carrier level on tuning in amplitude-modulation masking

The effect of carrier level on tuning in modulation masking was investigated for noise and tonal carriers. Bandwidths of the modulation filters, estimated from the masked detection thresholds using an envelope power spectrum model, were independent of level for the noise carrier but seemed to decrease with increasing level for the tonal carrier. However, the apparently sharper tuning could be explained by increased modulation sensitivity and modulation dynamic range with increasing level rather than improved modulation-frequency selectivity. Consistent with this interpretation, the addition of a high-pass noise with a level adjusted to maintain the same threshold for the detection of the signal modulation for each carrier level used eliminated the effect of level on tuning. Overall, modulation filters estimated from psychophysical data do not depend on level in contrast to the modulation transfer functions obtained from neural recordings in the inferior colliculus in physiological studies. The results highlight differences between the characteristics of modulation processing obtained from neural data and perception. The discrepancies indicate the need for further investigation into physiological correlates of tuning in modulation processing.

Infants' vowel discrimination in modulated noise

Adult listeners detect and discriminate target sounds better in amplitude modulated noise than in unmodulated noise. This study examined infants' ability to take advantage of masker modulation to improve sensitivity to a target. Listeners were 7–9-month-old infants and 18–30-year-old adults. Vowel discrimination in noise was tested. Listeners learned to respond when a repeated vowel changed from /a/ to /i/ or from /i/ to /a/. An observer-based method was used to assess sensitivity to the vowel change. The maskers were speech-spectrum noise either unmodulated, amplitude modulated with the envelope of single-talker speech or sinusoidally amplitude modulated at 8 Hz with a 75% modulation depth. The overall level of the maskers was 60 dB SPL. The level of the vowels, chosen to yield an average d' of 1 in the unmodulated masker, was 46 dB SPL for adults and 58 dB SPL for infants. Adults' d' was substantially and significantly higher in both modulated maskers than in the unmodulated masker. Infants' d' was also significantly higher in the two modulated maskers than in the unmodulated masker, but the improvement due to modulation was significantly smaller for infants than for adults. [Work supported by NIDCD R01DC00396 and P30DC04661.]

Effects of non‐simultaneous modulated maskers on amplitude‐modulation depth discrimination.

Wojtczak and Viemeister [J. Acoust Soc. Am. 118, 3198–3210 (2005)] demonstrated that detection thresholds for amplitude modulation (AM) can be increased in the presence of an AM forward masker. In the present study, the effects of forward‐masking on AM detection thresholds were extended to AM processing for easily detectable (suprathreshold) AM modulation depths by measuring the effects of nonsimultaneous AM maskers on AM modulation depth discrimination limens (AM DLs). Signal AM DLs were measured for a range of standard modulation depths. In one experiment the temporal delay between the masker and signal was varied. Consistent with the effects of AM forward maskers on AM detection thresholds [Wojtczak and Viemeister (2005)], the effects of the non‐simultaneous AM maskers on AM DLs were greatest for short masker‐signal delays. In another experiment, the masker‐signal delay was fixed, the signal modulation frequency was fixed, and the modulation frequency of the non‐simultaneous masker was varied. AM DLs for the signal were usually greatest when the signal modulation frequency was equal to the masker modulation frequency. The results of these experiments suggest that non‐simultaneous AM maskers can affect suprathreshold AM processing but non‐simultaneous AM maskers become less effective as the modulation depth of the standard increased.