Modulation Detection Interference Research Articles

Modulation masking produced by a low-frequency pure tone

An intense low-frequency tone can affect the perception of amplitude modulation (AM) applied to a high-frequency carrier. Here, thresholds for detecting AM of a 3000-Hz carrier were measured in the presence of a 50-Hz pure tone at 91 dB SPL. When the carrier was presented at 20 dB sensation level (SL), the thresholds were higher than in the absence of the 50-Hz tone, increased when the AM frequency was increased from 20 to 100 Hz, and did not show a maximum near 50 Hz, as would be expected if the effect of the 50-Hz tone resulted from modulation detection interference. When the AM frequency was fixed at 50 Hz, the AM detection thresholds showed a minimum when the phase of the AM was 90° ahead of the phase of the 50-Hz tone (denoted Δφ = 90°) and a maximum for Δφ = 270°. To assess the role of the outer hair cells (OHCs), AM detection thresholds were measured as a function of Δφ using SLs of 20 and 50 dB for normal-hearing participants and 20 dB for hearing-impaired participants. It was assumed that the latter would have impaired OHC function. The pattern of the results was similar across SLs and groups: AM detection thresholds were 8–10 dB lower for Δφ = 90° than for Δφ = 270° in all cases. This suggests that the OHCs do not play a large role in these effects and supports the idea that the low-frequency tone biases the responses of inner hair cells tuned to high frequencies.

Differences in Auditory Perception Between Young and Older Adults When Controlling for Differences in Hearing Loss and Cognition.

This study was designed to examine age effects on various auditory perceptual skills using a large group of listeners (155 adults, 121 aged 60–88 years and 34 aged 18–30 years), while controlling for the factors of hearing loss and working memory (WM). All subjects completed 3 measures of WM, 7 psychoacoustic tasks (24 conditions) and a hearing assessment. Psychophysical measures were selected to tap phenomena thought to be mediated by higher-level auditory function and included modulation detection, modulation detection interference, informational masking (IM), masking level difference (MLD), anisochrony detection, harmonic mistuning, and stream segregation. Principal-components analysis (PCA) was applied to each psychoacoustic test. For 6 of the 7 tasks, a single component represented performance across the multiple stimulus conditions well, whereas the modulation-detection interference (MDI) task required two components to do so. The effect of age was analyzed using a general linear model applied to each psychoacoustic component. Once hearing loss and WM were accounted for as covariates in the analyses, estimated marginal mean thresholds were lower for older adults on tasks based on temporal processing. When evaluated separately, hearing loss led to poorer performance on roughly 1/2 the tasks and declines in WM accounted for poorer performance on 6 of the 8 psychoacoustic components. These results make clear the need to interpret age-group differences in performance on psychoacoustic tasks in light of cognitive declines commonly associated with aging, and point to hearing loss and cognitive declines as negatively influencing auditory perceptual skills.

Detection of modulated rippled noise

Bill Yost's study of modulation detection interference (MDI) was in part motivated by his earlier work with temporally modulated rippled noise (RN) which indicated difficulty monitoring a single auditory channel in the presence of cross-channel modulation. The present work further evaluated parameters in the processing of dynamic spectral profiles. In the first experiment, gain in RN generation was sinusoidally modulated. If the gain sign remained unchanged during modulation, modulation resulted in a roughly constant increment in ripple-detection thresholds across change in modulation rate from 2 to 128 Hz. However, cross-sign gain modulation led to a lowpass result with thresholds increasing with modulation rate. A similar lowpass result was obtained in the second ripple-detection experiment in which delay in RN generation was modulated. The third experiment measured thresholds for detecting delay modulation. Thresholds, in terms of Weber ratios, rose with increasing modulation rate from 2 to 8 Hz. Across experiments, the lowpass results contrast with MDI in which interference decreases with increasing modulation rate. With dynamic spectral profiles, there is significant envelope modulation of individual auditory channels due to stimulus frequency excursions. Results suggest a limitation imposed by cross-channel envelope incoherence in utilizing this envelope modulation.

Age-related differences in modulation detection interference and interference release

Age-related declines have been observed in auditory tasks related to temporal processing, but less work has been conducted in middle-aged listeners and in auditory sound segregation tasks. This experiment addresses these issues by evaluating modulation detection interference (MDI) and release from MDI using streaming in young, middle-aged and older listeners. Using a standard MDI paradigm, we measured amplitude modulation detection thresholds of a high-frequency tone in different conditions: in quiet, in the presence of a low-impact unmodulated interferer, and in the presence of a high-impact modulated interferer. Then, we measured streaming-based release from MDI using four modulated precursors designed to perceptually capture the interferer and therefore reduce the amount of interference. Preliminary data suggest that middle-aged normal-hearing listeners experience similar MDI to young listeners and also receive a large release from interference when precursors are present. Additional data will be presented from older listeners, who experience slightly greater MDI than younger listeners.

Modulation detection interference in cochlear implant listeners under forward masking conditions.

Little is known about cochlear implant (CI) users' ability to process amplitude modulation (AM) under conditions of forward masking (forward-modulation detection/discrimination interference, or F-MDI). In this study, F-MDI was investigated in adult CI listeners using direct electrical stimulation via research interface. The target was sinusoidally amplitude modulated at 50 Hz, and presented to a fixed electrode in the middle of the array. The forward masker was either amplitude modulated at the same rate (AM) or unmodulated and presented at the peak amplitude of its AM counterpart (steady-state peak, SSP). Results showed that the AM masker produced higher modulation thresholds in the target than the SSP masker. The difference (F-MDI) was estimated to be 4.6 dB on average, and did not change with masker-target delays up to 100 ms or with masker-target spatial electrode distances up to eight electrodes. Results with a coherent remote cue presented with the masker showed that confusion effects did not play a role in the observed F-MDI. Traditional recovery from forward masking using the same maskers and a 20-ms probe, measured in four of the subjects, confirmed the expected result: higher thresholds with the SSP masker than the AM masker. Collectively, the results indicate that significant F-MDI occurs in CI users.

Modulation masking attributes of narrowband and low-noise noise forward maskers in normal-hearing and hearing-impaired listeners

Savel and Bacon (2003) measured detection thresholds for a 4000 Hz pure-tone signal in the presence of a narrowband noise (NBN) or a low-noise noise (LNN) simultaneous masker. The authors asserted that fluctuations in the envelope of the NBN were likely responsible for its increased masking effectiveness. Because modulation detection interference (MDI) is larger for hearing-impaired (HI) than normal-hearing (NH) listeners using modulated simultaneous maskers (e.g., Lorenzi et al., 1997) and forward maskers (e.g., Koopman et al., 2008), we measured detection thresholds for NH and HI listeners for pure tones in the presence of either NBN or LNN forward maskers that were either 1-ERB wide or 1/3-ERB wide. Based on previous MDI findings (Koopman et al., 2008), we predicted larger differences in masked thresholds for the NBN and LNN conditions for HI than NH listeners. These results for detection thresholds for pure-tone signals have implications for interpreting differences in modulated forward masking for NH and HI listeners. [Work supported by grants from NIH/NIDCD.]

Encoding of amplitude modulation upon interference in remote frequency regions

The modulation detection threshold for a sinusoidally amplitude modulated target tone was measured in the presence of another amplitude modulated interference tone. The interferer had a carrier frequency of 700 Hz and a modulation rate of 40 Hz. The target carrier frequency was 1300 Hz, and its modulation rate was 23, 33, 43, 63, and 80 Hz in separate conditions. During the psychophysical experiment, the auditory frequency following response (FFR) phase-locked to the 700-Hz carrier and the auditory steady-state response (ASSR) phase locked to the 40-Hz modulator were recorded. It was hypothesized that when greater interference occurs (when the interferer and target had closer modulation rates), the neural representation to the interferer might be enhanced or suppressed to a lesser degree. Neither the FFR nor ASSR demonstrated dependency on the target modulation rate, and no significant correlation was found between the behavioral and these two types of physiological measures. Results suggest the possibility that the modulation detection interference might originate from a location that is more central to the neural structures that give rise to FFR and the 40-Hz ASSR.

Auditory and cognitive factors underlying individual differences in aided speech-understanding among older adults

This study was designed to address individual differences in aided speech understanding among a relatively large group of older adults. The group of older adults consisted of 98 adults (50 female and 48 male) ranging in age from 60 to 86 (mean = 69.2). Hearing loss was typical for this age group and about 90% had not worn hearing aids. All subjects completed a battery of tests, including cognitive (6 measures), psychophysical (17 measures), and speech-understanding (9 measures), as well as the Speech, Spatial, and Qualities of Hearing (SSQ) self-report scale. Most of the speech-understanding measures made use of competing speech and the non-speech psychophysical measures were designed to tap phenomena thought to be relevant for the perception of speech in competing speech (e.g., stream segregation, modulation-detection interference). All measures of speech understanding were administered with spectral shaping applied to the speech stimuli to fully restore audibility through at least 4000 Hz. The measures used were demonstrated to be reliable in older adults and, when compared to a reference group of 28 young normal-hearing adults, age-group differences were observed on many of the measures. Principal-components factor analysis was applied successfully to reduce the number of independent and dependent (speech understanding) measures for a multiple-regression analysis. Doing so yielded one global cognitive-processing factor and five non-speech psychoacoustic factors (hearing loss, dichotic signal detection, multi-burst masking, stream segregation, and modulation detection) as potential predictors. To this set of six potential predictor variables were added subject age, Environmental Sound Identification (ESI), and performance on the text-recognition-threshold (TRT) task (a visual analog of interrupted speech recognition). These variables were used to successfully predict one global aided speech-understanding factor, accounting for about 60% of the variance.

Dynamic range compression effects on modulation detection interference.

Some evidence suggests that perceived amplitude modulation (AM) depth may be exaggerated for listeners with cochlear hearing loss (HI) compared to listeners with normal hearing (NH) due to a less compressive auditory system. Consistent with this, several researchers have demonstrated that interfering AM causes more masking of a target AM (modulation detection interference; MDI) in HI than NH listeners. This effect might be due to the exaggerated perceived modulation depth in HI listeners. There is also evidence that the modulation depth of amplitude envelope fluctuations will be reduced by dynamic range compression (often used in hearing aids). MDI should therefore be smaller with a compressed interferer, due to the reduced modulation depth of the interferer. However, Shen and Lentz (2010) showed the opposite result. Specifics of that study included a processor that resulted in some artifacts and somewhat extreme compression parameters. The present study uses a low-distortion compressor with a range of compression parameters to investigate the effect of compression representative of wearable aids on MDI. We will report the influence of input level (re: kneepoint) and attack/release time on MDI in NH and HI listeners.

Effect of fast-acting compression on modulation detection interference for normal hearing and hearing impaired listeners

To determine the effects of hearing loss and fast-acting compression on auditory grouping based on across-frequency modulation, modulation detection interference (MDI) was measured in listeners with normal hearing and hearing loss. MDI, the increase in the amplitude-modulation detection threshold of a target presented with an interferer distant in frequency, was measured using a 500-Hz target and a 2140-Hz interferer, both modulated with narrow-band noises of the same bandwidth. The two modulated tones were presented at equal loudness levels to listeners with normal hearing and hearing loss in the absence (Exp. 1) and in the presence (Exp. 2) of fast-acting compression applied to the interferer. Modulation detection thresholds increased with increasing modulation depth of the interferer by similar amounts for the two groups of listeners, suggesting that across-frequency grouping based on amplitude modulation is not altered by hearing impairment. Compression provided an additional increase in thresholds for both groups, indicating that compression algorithms might alter across-frequency grouping cues. Partial support for an idea that compression's effect of sharpening the onsets after each envelope valley is provided by a third experiment which found somewhat greater interference produced by square-wave modulation than sine-wave modulation at larger interferer modulation depths.

Modulation detection interference in listeners with cochlear hearing loss: Effect of modulation depth and onset delay.

Modulation detection interference (MDI) was measured for listeners with normal hearing (NH) and cochlear hearing loss (HI). The signal was 1 kHz, and the interferer was 2 kHz. The stimuli level was 50 or 22 dB SL. The interferer was modulated with 8 Hz at various modulation depths (25, 50, 75, or 100%). The onset of signal was delayed by 0, 125, 250, 375, 500 or 625 ms relative to onset of the interferer. For NH subjects, MDI increased systematically with increasing modulation depth of the interferer. MDI almost disappeared with 375 or 500 ms onset delay except a condition with the interferer of 25% modulation depth where there was no MDI at all across different onset delay conditions. In contrast, for HI subjects, there was quite an amount of MDI even with the interferer of 25% modulation depth, and MDI was greater than NH for all modulation depths at 0 and 125 ms onset delays, suggesting that the perceived modulation depth of the interferer might be exaggerated for HI than for NH.

Modulation Detection Interference for Asynchronous Presentation of Masker and Target in Listeners With Normal and Impaired Hearing

The sensitivity to sinusoidal amplitude modulations (SAMs) is reduced when other modulated maskers are presented simultaneously at a distant frequency (also referred to as modulation detection interference [MDI]). This article describes the results of onset differences between masker and target as a parameter. Carrier frequencies were 1 kHz (target: 625 ms, 8 Hz SAM) and 2 kHz (masker: 625 ms, 8 Hz SAM; modulation depth = 1) presented at 25 dB SL for listeners with impaired hearing (n = 8) and at 25 dB SL and 50 dB SL for listeners with normal hearing (n = 6). Masker was delayed by 0, 125, 250, 500, 625, or 750 ms relative to the target. Sensitivity to SAMs was reduced in both groups by a modulated masker simultaneous presentation. Reducing the temporal overlap (i.e., increasing the onset delay between masker and target) increased the sensitivity to SAMs in the presence of modulated maskers. The gradual reduction in MDI with increasing asynchrony between masker and target suggests that MDI is not solely related to perceptual grouping. Reduced sensitivity to SAMs due to prior stimulation with SAM stimuli (forward masking), and deficits in across-channel integration, are other factors that may play a role.

Sequential amplitude‐modulation interference across auditory channels and across ears

Forward masking has been demonstrated in the amplitude‐modulation (AM) domain [M. Wojtczak and N. F. Viemeister, J. Acoust. Soc. Am. 118, 3198 (2005)] for masker and signal imposed on the same carrier. This study explores an effect of AM on detection of AM imposed sequentially on a different carrier. Data show that a 40−Hz AM (interferer) imposed on a 2−kHz carrier affects detection of a 40−Hz AM (signal) imposed on a 5.5−kHz carrier after the offset of the interferer AM. The effect is analogous (and similar in size for the shortest interferer−signal delays) to modulation detection interference for simultaneous interferer AM. In another condition, two independent noise samples were presented to opposite ears. In one ear, a 40−Hz masker AM was imposed on the carrier. In the opposite ear, a 40−Hz signal was imposed on the carrier after the offset of the masker modulation. A forward−masking effect similar to but smaller in size than that in monaural presentation was observed. The data from both experiments suggest that the forward−masking effect in the modulation domain occurs at central stages of processing, where information is combined across peripheral channels and where binaural interactions occur. [Work supported by NIH Grants DC00683 and DC006804.]

Listening in the valleys with cochlear implants: Speech perception versus psychophysics

Unlike listeners with normal hearing who can benefit from masking release with modulated noise, cochlear implant users show little release from masking when identifying words in sentences. Little is known about basic mechanisms underlying masking release in speech perception. In the present study, phoneme recognition was evaluated in implant users with tense vowels (/a, i, u, e, o/) and plosives (/p, t, k, b, d, g/) in quiet, steady-state noise and modulated noise at different signal-to-noise ratios (SNRs). In parallel psychophysical experiments, both modulation sensitivity and electrode discrimination were measured in the presence of on- and off-channel maskers, with different fluctuating envelopes. Results from three implant users indicated that unlike the previous findings with sentence materials, these individuals showed some masking release in phoneme recognition. All three participants exhibited masking release with the tense vowels at some SNRs, but only one showed release with the plosives. Modulation detection interference (MDI) was observed in these participants to varying degrees. Whereas MDI was observed in the two participants exhibiting little release with the plosives, no MDI was observed in the participant exhibiting release with the plosives. The relationship between implant users’ phoneme recognition and psychophysical performance will be discussed. [Work supported by NIDCD-R01DC04786.]

Modulation detection interference with periodic complex modulators

Past studies of modulation detection interference (MDI) have considered the possibility that the effect may in part relate to auditory grouping of the probe and masker. Alternatively as a cross-channel effect, MDI may be representative of informational masking. The present experiments varied modulator waveshape in attempts to distinguish the effects of auditory grouping and informational masking on MDI. In the first experiment, both the slope and duty cycle of the masker modulator varied across conditions with the task to detect either 4- or 10-Hz sinusoidal probe modulation. The effect of masker-modulator waveshape on the detection of 4-Hz probe modulation was generally consistent with change in the perceptual prominence of the masker. The 10-Hz results showed little effect of these manipulations. The second experiment utilized interrupted modulation patterns to allow for either concurrent or sequential envelope fluctuation of the probe and masker. Results showed no effect of modulation concurrency. In both experiments, significant departures from energetic masking in the modulation domain were obtained. Collectively, these results were taken to support an interpretation of the interference in terms of informational masking rather than grouping based on common modulation. [Work supported by NIDCD.]

Detection, direction discrimination, and off-frequency interference of center-frequency modulations and glides for vowel formants

Vowels are mainly classified by the positions of peaks in their frequency spectra, the formants. For normal-hearing subjects, change detection and direction discrimination were measured for linear glides in the center frequency (CF) of formantlike sounds. A CF rove was used to prevent subjects from using either the start or end points of the glides as cues. In addition, change detection and starting-phase (start-direction) discrimination were measured for similar stimuli with a sinusoidal 5-Hz formant-frequency modulation. The stimuli consisted of single formants generated using a number of different stimulus parameters including fundamental frequency, spectral slope, frequency region, and position of the formant relative to the harmonic spectrum. The change detection thresholds were in good agreement with the predictions of a model which analyzed and combined the effects of place-of-excitation and temporal cues. For most stimuli, thresholds were approximately equal for change detection and start-direction discrimination. Exceptions were found for stimuli that consisted of only one or two harmonics. In a separate experiment, it was shown that change detection and start-direction discrimination of linear and sinusoidal formant-frequency modulations were impaired by off-frequency frequency-modulated interferers. This frequency modulation detection interference was larger for formants with shallow than for those with steep spectral slopes.

Factors affecting psychophysical tuning curves for normally hearing subjects

These experiments were conducted to clarify the influence of beats and combination products on psychophysical tuning curves (PTCs) for normally hearing subjects. PTCs for 1- and 4-kHz sinusoidal signals were determined using as maskers a sinusoidal tone and 80-, 160-, and 320-Hz wide bands of noise. PTCs obtained using the sinusoidal masker showed distinct irregularities, particularly for masker frequencies close to the signal frequency. The PTCs determined for the noise maskers were more regular. The broader the masker, the more regular were the shapes of the PTCs. To reduce the detectability of beats produced by the interaction of the signal and masker, a pair of low-frequency tones, called “Modulation detection interference (MDI) tones”, was used to introduce beats at the same rate. The MDI tones reduced the threshold level of the sinusoidal masker by up to 20 dB for frequencies within 300 Hz of the signal frequency; a similar but smaller effect was found when an 80-Hz wide masker was used. Adding a lowpass filtered (LF) noise to the sinusoidal or narrowband noise masker did not affect the low-frequency sides of the PTCs, suggesting no influence of combination products. The LF noise did affect the high-frequency sides of the PTCs, but this can be attributed to it reducing off-frequency listening. To achieve a PTC whose shape around the tip is minimally affected by beats, we propose using a noise masker with a bandwidth approximately equal to the bandwidth of the auditory filter for which the PTC is measured.

Effect of modulator asynchrony of sinusoidal and noise modulators on frequency and amplitude modulation detection interference.

The effect on modulation detection interference (MDI) of timing of gating of the modulation of target and interferer, with synchronously gated carriers, was investigated in three experiments. In a two-interval, two-alternative forced choice adaptive procedure, listeners had to detect 15 Hz sinusoidal amplitude modulation (AM) or frequency modulation (FM) imposed for 200 ms in the temporal center of a 600 ms target sinusoidal carrier. In the first experiment, 15 Hz sinusoidal FM was imposed in phase on both target and interferer carriers. Thresholds were lower for nonoverlapping than for synchronous modulation of target and interferer, but MDI still occurred for the former. Thresholds were significantly higher when the modulators were gated synchronously than when the interferer modulator was gated on before and off after that of the target. This contrasts with the findings of Oxenham and Dau [J. Acoust. Soc. Am. 110, 402-408 (2001)], who reported no effect of modulation asynchrony on AM detection thresholds, using a narrowband noise modulator. Using FM, experiment 2 showed that for temporally overlapping modulation of target and interferer, modulator asynchrony had no significant effect when the interferer was modulated by a narrowband noise. Experiment 3 showed that, for AM, synchronous gating of modulation of the target and interferer produced lower thresholds than asynchronous gating, especially for sinusoidal modulation of the interferer. Results are discussed in terms of specific cues available for periodic modulation, and differences between perceptual grouping on the basis of common AM and FM.

Temporal interference in amplitude modulation perception

We observed that, especially for hearing-impaired subjects, the perceived modulation strength of a signal is systematically reduced by the presence of a preceding modulated signal. This suggested that modulation detection interference (MDI) might not only apply in case of simultaneous signals, but also for nonsimultaneous signals. To further investigate this we performed an experiment with normal-hearing and hearing-impaired subjects, in which modulation detection was measured for a target signal (1 kHz carrier, 625 ms duration, 8 Hz amplitude modulation), preceded by an interfering signal (2 kHz carrier, 625 ms, 100% 8 Hz modulation). The onset difference between interfering signal and target signal was varied over a range of 0–1250 ms, thus from simultaneous (the traditional MDI condition) to clearly nonsimultaneous. Based on pilot experiments we hypothesized that normal-hearing subjects showed a rapid increase of sensitivity from simultaneous to nonsimultaneous presentation (essentially no MDI after effect), whereas for the hearing impaired the interference effect was observed up to long onset differences, including clearly nonsimultaneous presentation. The observed differences in modulation interference between normal-hearing and hearing-impaired subjects might explain the differences shown in speech intelligibility in fluctuating background noise. Results will be used to validate this hypothesis.

Modulation detection interference in listeners with normal and impaired hearing.

Listeners were asked to detect amplitude modulation (AM) of a target (or signal) carrier that was presented in isolation or in the presence of an additional (masker) carrier. The signal was modulated at a rate of 10 Hz, and the masker was unmodulated or was modulated at a rate of 2, 10, or 40 Hz. Nine listeners had normal hearing, 4 had a bilateral hearing loss, and 4 had a unilateral hearing loss; those with a unilateral loss were tested in both ears. The listeners with a hearing loss had normal hearing at 1 kHz and a 30- to 40-dB loss at 4 kHz. The carrier frequencies were 984 and 3952 Hz. In one set of conditions, the lower frequency carrier was the signal and the higher frequency carrier was the masker. In the other set, the reverse was true. For the impaired ears, the carriers were presented at 70 dB SPL. For the normal ears, either the carriers were both presented at 70 dB SPL or the higher frequency carrier was reduced to 40 dB SPL to simulate the lower sensation level experienced by the impaired ears. There was considerable individual variability in the results, and there was no clear effect of hearing loss. These results suggest that a mild, presumably cochlear hearing loss does not affect the ability to process AM in one frequency region in the presence of competing AM from another region.