Temporal Envelope Fluctuations Research Articles

The role of carrier spectral composition in the perception of musical pitch.

Temporal envelope fluctuations of natural sounds convey critical information to speech and music processing. In particular, musical pitch perception is assumed to be primarily underlined by temporal envelope encoding. While increasing evidence demonstrates the importance of carrier fine structure to complex pitch perception, how carrier spectral information affects musical pitch perception is less clear. Here, transposed tones designed to convey identical envelope information across different carriers were used to assess the effects of carrier spectral composition to pitch discrimination and musical-interval and melody identifications. Results showed that pitch discrimination thresholds became lower (better) with increasing carrier frequencies from 1k to 10k Hz, with performance comparable to that of pure sinusoids. Musical interval and melody defined by the periodicity of sine- or harmonic complex envelopes across carriers were identified with greater than 85% accuracy even on a 10k-Hz carrier. Moreover, enhanced interval and melody identification performance was observed with increasing carrier frequency up to 6k Hz. Findings suggest a perceptual enhancement of temporal envelope information with increasing carrier spectral region in musical pitch processing, at least for frequencies up to 6k Hz. For carriers in the extended high-frequency region (8-20k Hz), the use of temporal envelope information to music pitch processing may vary depending on task requirement. Collectively, these results implicate the fidelity of temporal envelope information to musical pitch perception is more pronounced than previously considered, with ecological implications.

Predicting Perceived Vocal Roughness Using a Bio-Inspired Computational Model of Auditory Temporal Envelope Processing.

Vocal roughness is often present in many voice disorders but the assessment of roughness mainly depends on the subjective auditory-perceptual evaluation and lacks acoustic correlates. This study aimed to apply the concept of roughness in general sound quality perception to vocal roughness assessment and to characterize the relationship between vocal roughness and temporal envelop fluctuation measures obtained from an auditory model. Ten /ɑ/ recordings with a wide range of roughness were selected from an existing database. Ten listeners rated the roughness of the recordings in a single-variable matching task. Temporal envelope fluctuations of the recordings were analyzed with an auditory processing model of amplitude modulation that utilizes a modulation filterbank of different modulation frequencies. Pitch strength and the smoothed cepstral peak prominence were also obtained for comparison. Individual simple regression models yielded envelope standard deviation from a modulation filter with a low center frequency (64.3 Hz) as a statistically significant predictor of vocal roughness with a strong coefficient of determination (r 2 = .80). Pitch strength and CPPS were not significant predictors of roughness. This result supports the possible utility of envelope fluctuation measures from an auditory model as objective correlates of vocal roughness.

Prediction of vocal roughness using measures of temporal envelope fluctuation obtained from an auditory model

Vocal roughness often is present in many voice disorders, but the assessment of roughness mainly depends on the subjective auditory-perceptual evaluation and lacks unique acoustic correlates. This study aimed to apply the concept of roughness in general sound quality perception to vocal roughness assessment and to characterize the relationship between vocal roughness and temporal envelope fluctuation measures obtained from a biologically inspired auditory processing model. Ten /ɑ/ recordings with a wide range of roughness were selected from an existing database. Ten listeners evaluated perceived roughness using a single-variable matching task. Temporal envelope fluctuations of the recordings were analyzed with an auditory processing model of amplitude modulation based on a modulation filterbank tuned to different modulation frequencies. Pitch strength and the smoothed cepstral peak prominence (CPPS) also were computed for comparison. Individual simple regression models yielded envelope standard deviation from a modulation filter with a low center frequency (64.3 Hz) as a statistically significant predictor of vocal roughness with a strong coefficient of determination (R2 = 0.81). Pitch strength and CPPS were not significant predictors of roughness. These results support the utility of envelope fluctuation measures from an auditory model as objective correlates of vocal roughness. [Work supported by NIH R01DC009029.]

Masking of short tones in noise: Evidence for envelope-based, rather than energy-based detection.

The "temporal effect" in simultaneous masking may be characterized by better probe detection thresholds for a short, tonal probe presented at the temporal center of a masker compared to at the onset of a masker. Energy-based models of masking have been used to interpret the temporal effect as evidence that the gain of the auditory system decreases during acoustic stimulation. This study shows that masking from temporal-envelope fluctuations of a precursor or from a temporal gap between stimuli violates the assumptions of energy-based models and complicates the interpretation of temporal effects in terms of a reduction in gain. Detection thresholds were measured for a 6-ms, 4000-Hz probe preceded by a narrowband precursor and presented 2-, 197-, or 392-ms after the onset of a narrowband masker. The delay between the precursor offset and masker onset ranged from -2 to 250 ms. Probe thresholds were elevated in the presence of precursors with fluctuating compared to flattened temporal envelopes and when a temporal gap was inserted between the precursor and masker. The results suggest that the interpretation and design of temporal-effect studies should consider the masking effects of temporal-envelope fluctuations. These findings are consistent with speech-perception experiments that show masking from temporal-envelope fluctuations.

Effects of Masker Envelope Fluctuations on the Temporal Effect.

Under certain conditions, detection thresholds in simultaneous masking improve when the onset of a short sinusoidal probe is delayed from the onset of a long masker. This improvement, known as the temporal effect, is largest for broadband maskers and is smaller or absent for narrowband maskers centered on the probe frequency. This study tests the hypothesis that small or absent temporal effects for narrowband maskers are due to the inherent temporal envelope fluctuations of Gaussian noise. Temporal effects were measured for narrowband noise maskers with fluctuating ("fluctuating maskers") and flattened ("flattened maskers") temporal envelopes as a function of masker level (Exp. I) and in the presence of fluctuating and flattened precursors (Exp. II). The temporal effect was absent for fluctuating narrowband maskers and as large as ~ 7dB for flattened narrowband maskers. The AC-coupled power of the temporal envelopes of precursors and maskers accounted for 94% of the variance in probe detection thresholds measured with fluctuating and flattened precursors and maskers. These results suggest that masker temporal envelope fluctuations contribute to the temporal effect and should be considered in future modeling efforts.

Don't speak too fast! Processing of fast rate speech in children with specific language impairment.

BackgroundPerception of speech rhythm requires the auditory system to track temporal envelope fluctuations, which carry syllabic and stress information. Reduced sensitivity to rhythmic acoustic cues has been evidenced in children with Specific Language Impairment (SLI), impeding syllabic parsing and speech decoding. Our study investigated whether these children experience specific difficulties processing fast rate speech as compared with typically developing (TD) children.MethodSixteen French children with SLI (8–13 years old) with mainly expressive phonological disorders and with preserved comprehension and 16 age-matched TD children performed a judgment task on sentences produced 1) at normal rate, 2) at fast rate or 3) time-compressed. Sensitivity index (d′) to semantically incongruent sentence-final words was measured.ResultsOverall children with SLI perform significantly worse than TD children. Importantly, as revealed by the significant Group × Speech Rate interaction, children with SLI find it more challenging than TD children to process both naturally or artificially accelerated speech. The two groups do not significantly differ in normal rate speech processing.ConclusionIn agreement with rhythm-processing deficits in atypical language development, our results suggest that children with SLI face difficulties adjusting to rapid speech rate. These findings are interpreted in light of temporal sampling and prosodic phrasing frameworks and of oscillatory mechanisms underlying speech perception.

Binaural Pitch Fusion: Effects of Amplitude Modulation.

Hearing-impaired adults, including both cochlear implant and bilateral hearing aid (HA) users, often exhibit broad binaural pitch fusion, meaning that they fuse dichotically presented tones with large pitch differences between ears. The current study was designed to investigate how binaural pitch fusion can be influenced by amplitude modulation (AM) of the stimuli and whether effects differ with hearing loss. Fusion ranges, the frequency ranges over which binaural pitch fusion occurs, were measured in both normal-hearing (NH) listeners and HA users with various coherent AM rates (2, 4, and 8 Hz); AM depths (20%, 40%, 60%, 80%, and 100%); and interaural AM phase and AM rate differences. The averaged results show that coherent AM increased binaural pitch fusion ranges to about 2 to 4 times wider than those in the unmodulated condition in both NH and bilateral HA subjects. Even shallow temporal envelope fluctuations (20% AM depth) significantly increased fusion ranges in all three coherent AM rate conditions. Incoherent AM introduced through interaural differences in AM phase or AM rate led to smaller increases in binaural pitch fusion range compared with those observed with coherent AM. Significant differences between groups were observed only in the coherent AM conditions. The influence of AM cues on binaural pitch fusion shows that binaural fusion is mediated in part by central processes involved in auditory grouping.

Effects of Expanding Envelope Fluctuations on Consonant Perception in Hearing-Impaired Listeners.

This study examined the perceptual consequences of three speech enhancement schemes based on multiband nonlinear expansion of temporal envelope fluctuations between 10 and 20 Hz: (a) “idealized” envelope expansion of the speech before the addition of stationary background noise, (b) envelope expansion of the noisy speech, and (c) envelope expansion of only those time-frequency segments of the noisy speech that exhibited signal-to-noise ratios (SNRs) above −10 dB. Linear processing was considered as a reference condition. The performance was evaluated by measuring consonant recognition and consonant confusions in normal-hearing and hearing-impaired listeners using consonant-vowel nonsense syllables presented in background noise. Envelope expansion of the noisy speech showed no significant effect on the overall consonant recognition performance relative to linear processing. In contrast, SNR-based envelope expansion of the noisy speech improved the overall consonant recognition performance equivalent to a 1- to 2-dB improvement in SNR, mainly by improving the recognition of some of the stop consonants. The effect of the SNR-based envelope expansion was similar to the effect of envelope-expanding the clean speech before the addition of noise.

Speech Masking in Normal and Impaired Hearing: Interactions Between Frequency Selectivity and Inherent Temporal Fluctuations in Noise.

Recent studies in normal-hearing listeners have used envelope-vocoded stimuli to show that the masking of speech by noise is dominated by the temporal-envelope fluctuations inherent in noise, rather than just overall power. Because these studies were based on vocoding, it was expected that cochlear-implant (CI) users would demonstrate a similar sensitivity to inherent fluctuations. In contrast, it was found that CI users showed no difference in speech intelligibility between maskers with and without inherent envelope fluctuations. Here, these initial findings in CI users were extended to listeners with cochlear hearing loss and the results were compared with those from normal-hearing listeners at either equal sensation level or equal sound pressure level. The results from hearing-impaired listeners (and in normal-hearing listeners at high sound levels) are consistent with a relative reduction in low-frequency inherent noise fluctuations due to broader cochlear filtering. The reduced effect of inherent temporal fluctuations in noise, due to either current spread (in CI users) or broader cochlear filters (in hearing-impaired listeners), provides a new way to explain the loss of masking release experienced in CI users and hearing-impaired listeners when additional amplitude fluctuations are introduced in noise maskers.

Pitch perception and representations of frequency in the peripheral auditory system: What’s missing in cochlear implants?

Pitch is a crucial feature of auditory perception. It conveys information about melody and harmony in music, and conveys prosodic and (in tone languages) lexical information in speech. Although pitch has been studied formally for many decades, there still remains considerable uncertainty regarding how frequency and pitch information is coded and represented in the auditory periphery. This uncertainty means it is unclear whether and how pitch information can best be conveyed via cochlear implants. Cochlear-implant users have been shown to be sensitive to changes in the place of stimulation within the cochlea (“place” pitch) and to changes in the pulse rate presented to the electrode (“rate” pitch), at least up to rates of around 300 Hz. Place pitch in cochlear implants is probably best compared to “brightness” and rate pitch has most in common with the relatively weak pitch produced by temporal-envelope fluctuations in normal-hearing listeners. Neither type of pitch seems to provide the salient and accurate pitch sensations associated with normal hearing. Studies in both normal-hearing listeners and cochlear-implant users will be reviewed to shed light on the mechanisms of pitch perception and on the challenges involved in restoring pitch to cochlear-implant users. [Work supported by NIH grant R01DC005216.]

Speech perception in tones and noise via cochlear implants reveals influence of spectral resolution on temporal processing.

Under normal conditions, human speech is remarkably robust to degradation by noise and other distortions. However, people with hearing loss, including those with cochlear implants, often experience great difficulty in understanding speech in noisy environments. Recent work with normal-hearing listeners has shown that the amplitude fluctuations inherent in noise contribute strongly to the masking of speech. In contrast, this study shows that speech perception via a cochlear implant is unaffected by the inherent temporal fluctuations of noise. This qualitative difference between acoustic and electric auditory perception does not seem to be due to differences in underlying temporal acuity but can instead be explained by the poorer spectral resolution of cochlear implants, relative to the normally functioning ear, which leads to an effective smoothing of the inherent temporal-envelope fluctuations of noise. The outcome suggests an unexpected trade-off between the detrimental effects of poorer spectral resolution and the beneficial effects of a smoother noise temporal envelope. This trade-off provides an explanation for the long-standing puzzle of why strong correlations between speech understanding and spectral resolution have remained elusive. The results also provide a potential explanation for why cochlear-implant users and hearing-impaired listeners exhibit reduced or absent masking release when large and relatively slow temporal fluctuations are introduced in noise maskers. The multitone maskers used here may provide an effective new diagnostic tool for assessing functional hearing loss and reduced spectral resolution.

Alteration of the dynamic modulation of auditory beta-band oscillations by voice power during speech-in-noise

Event Abstract Back to Event Alteration of the dynamic modulation of auditory beta-band oscillations by voice power during speech-in-noise Marc Vander Ghinst1*, Mathieu Bourguignon1, Vincent Wens1, Brice Marty1, Marc Op De Beeck1, Patrick Van Bogaert1, Serge Goldman1 and Xavier De Tiège1 1 Université Libre de Bruxelles, Belgium Introduction During continuous speech listening, listener’s low β-band (LBB, 13–20 Hz) oscillations in bilateral superior temporal gyri (STG) are dynamically modulated (in a speech-sensitive manner) by the speaker’s voice power, LBB power being reduced when the voice power increases and vice-versa (Bourguignon et al. in preparation). These amplitude modulations are paced by speech temporal envelope at a ~0.5 Hz. Here, we investigate the impact of a fluctuating background noise on the dynamic modulation of listener’s LBB oscillations. Methods Neuromagnetic activity of twenty right-handed and native French speaking adults (10 females, mean age 30 y) was recorded using whole-scalp MEG (Elekta) while they listened to five different recorded texts read in French by different native French-speaking readers. Recordings were mixed with a “cocktail party” type noise at different signal to noise ratios (SNR; No noise, +5dB, 0dB, -5dB, -10dB). Coherence between LBB power modulations and speech temporal envelope fluctuations at ~0.5 Hz was computed for each subject and condition. Coherent sources were reconstructed using minimum norm estimates. Statistical assessment of coherence levels was performed using surrogate data analyses. The influence of the SNR on coherence levels was assessed using one-way ANOVA. Results Without noise, significant coupling between LBB and speech power occurred in 18 subjects at bilateral STG (group-level source coherence, right STG: 0.025, left STG: 0.028). When speech merged into noise, this coupling significantly vanished (p<10-6, ANOVA), with only, 4 subjects showing significant coupling at +5 dB, 2 subjects at 0 dB and 2 subjects at -5 dB. Discussion This study demonstrates that a cocktail party background drastically reduces the coupling at 0.5 Hz between LBB and voice power fluctuations at the STG. These data are congruent with recent studies that showed reduced β-band suppression during speech-in-noise (Schepers et al., 2013). References Schepers, I. M., Schneide T.R., Hipp, J.F., Engel, A.K., Senkowski D. (2013). Noise alters beta-band activity in superior temporal cortex during audiovisual speech processing. Neuroimage. 70, 101-112. Keywords: Speech in noise, Magnetoencephalography, Speech Perception, Auditory Perception, Auditory Cortex Conference: Belgian Brain Council 2014 MODULATING THE BRAIN: FACTS, FICTION, FUTURE, Ghent, Belgium, 4 Oct - 4 Oct, 2014. Presentation Type: Poster Presentation Topic: Basic Neuroscience Citation: Vander Ghinst M, Bourguignon M, Wens V, Marty B, Op De Beeck M, Van Bogaert P, Goldman S and De Tiège X (2014). Alteration of the dynamic modulation of auditory beta-band oscillations by voice power during speech-in-noise. Conference Abstract: Belgian Brain Council 2014 MODULATING THE BRAIN: FACTS, FICTION, FUTURE. doi: 10.3389/conf.fnhum.2014.214.00030 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: 27 Jun 2014; Published Online: 30 Jun 2014. * Correspondence: Dr. Marc Vander Ghinst, Université Libre de Bruxelles, Brussels, 1070, Belgium, marcvdg@gmail.com 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 Marc Vander Ghinst Mathieu Bourguignon Vincent Wens Brice Marty Marc Op De Beeck Patrick Van Bogaert Serge Goldman Xavier De Tiège Google Marc Vander Ghinst Mathieu Bourguignon Vincent Wens Brice Marty Marc Op De Beeck Patrick Van Bogaert Serge Goldman Xavier De Tiège Google Scholar Marc Vander Ghinst Mathieu Bourguignon Vincent Wens Brice Marty Marc Op De Beeck Patrick Van Bogaert Serge Goldman Xavier De Tiège PubMed Marc Vander Ghinst Mathieu Bourguignon Vincent Wens Brice Marty Marc Op De Beeck Patrick Van Bogaert Serge Goldman Xavier De Tiège 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.

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.

Level-Dependent Changes in Perception of Speech Envelope Cues

Level-dependent changes in temporal envelope fluctuations in speech and related changes in speech recognition may reveal effects of basilar-membrane nonlinearities. As a result of compression in the basilar-membrane response, the "effective" magnitude of envelope fluctuations may be reduced as speech level increases from lower level (more linear) to mid-level (more compressive) regions. With further increases to a more linear region, speech envelope fluctuations may become more pronounced. To assess these effects, recognition of consonants and key words in sentences was measured as a function of speech level for younger adults with normal hearing. Consonant-vowel syllables and sentences were spectrally degraded using "noise vocoder" processing to maximize perceptual effects of changes to the speech envelope. Broadband noise at a fixed signal-to-noise ratio maintained constant audibility as speech level increased. Results revealed significant increases in scores and envelope-dependent feature transmission from 45 to 60 dB SPL and decreasing scores and feature transmission from 60 to 85 dB SPL. This quadratic pattern, with speech recognition maximized at mid levels and poorer at lower and higher levels, is consistent with a role of cochlear nonlinearities in perception of speech envelope cues.

A physiologically based model for temporal envelope encoding in human primary auditory cortex

Communication sounds exhibit temporal envelope fluctuations in the low frequency range (<70 Hz) and human speech has prominent 2–16 Hz modulations with a maximum at 3–4 Hz. Here, we propose a new phenomenological model of the human auditory pathway (from cochlea to primary auditory cortex) to simulate responses to amplitude-modulated white noise. To validate the model, performance was estimated by quantifying temporal modulation transfer functions (TMTFs). Previous models considered either the lower stages of the auditory system (up to the inferior colliculus) or only the thalamocortical loop. The present model, divided in two stages, is based on anatomical and physiological findings and includes the entire auditory pathway. The first stage, from the outer ear to the colliculus, incorporates inhibitory interneurons in the cochlear nucleus to increase performance at high stimuli levels. The second stage takes into account the anatomical connections of the thalamocortical system and includes the fast and slow excitatory and inhibitory currents. After optimizing the parameters of the model to reproduce the diversity of TMTFs obtained from human subjects, a patient-specific model was derived and the parameters were optimized to effectively reproduce both spontaneous activity and the oscillatory part of the evoked response.

Level-dependent changes in perception of temporal envelope cues.

Level-dependent changes in speech recognition may reveal effects of basilar-membrane nonlinearities on temporal envelope fluctuations. It is hypothesized that, as a result of the compressive effects of the active cochlear mechanism, the “effective” magnitude of speech envelope fluctuations will be reduced as speech level increases from lower (more linear) to conversational (more compressive) regions. With further increases from conversational levels (to a more linear region), temporal envelope fluctuations will become more pronounced. Accordingly, speech recognition will be maximized at conversational levels due to the optimal “flattened” envelope and then decline at lower or higher levels. To test these assumptions, speech recognition scores were measured as a function of level for adults with normal hearing. Speech stimuli were spectrally degraded using “noise vocoder” processing so that perceptual effects of modifications to the speech temporal envelope can be revealed. As vocoded speech level increased, background noise level also increased, maintaining a fixed signal-to-noise ratio to minimize sensation-level effects on speech recognition scores. Discussion will focus on level-dependent effects for different speech stimuli and the role of nonlinearities on perception of temporal envelope cues. [Work supported by NIH/NIDCD]

The Acoustic and Peceptual Effects of Series and Parallel Processing

Temporal envelope (TE) cues provide a great deal of speech information. This paper explores how spectral subtraction and dynamic-range compression gain modifications affect TE fluctuations for parallel and series configurations. In parallel processing, algorithms compute gains based on the same input signal, and the gains in dB are summed. In series processing, output from the first algorithm forms the input to the second algorithm. Acoustic measurements show that the parallel arrangement produces more gain fluctuations, introducing more changes to the TE than the series configurations. Intelligibility tests for normal-hearing (NH) and hearing-impaired (HI) listeners show (1) parallel processing gives significantly poorer speech understanding than an unprocessed (UNP) signal and the series arrangement and (2) series processing and UNP yield similar results. Speech quality tests show that UNP is preferred to both parallel and series arrangements, although spectral subtraction is the most preferred. No significant differences exist in sound quality between the series and parallel arrangements, or between the NH group and the HI group. These results indicate that gain modifications affect intelligibility and sound quality differently. Listeners appear to have a higher tolerance for gain modifications with regard to intelligibility, while judgments for sound quality appear to be more affected by smaller amounts of gain modification.

Auditory stream formation affects comodulation masking release retroactively.

Many sounds in the environment have temporal envelope fluctuations that are correlated in different frequency regions. Comodulation masking release (CMR) illustrates how such coherent fluctuations can improve signal detection. This study assesses how perceptual grouping mechanisms affect CMR. Detection thresholds for a 1-kHz sinusoidal signal were measured in the presence of a narrowband (20-Hz-wide) on-frequency masker with or without four comodulated or independent flanking bands that were spaced apart by either 1/6 (narrow spacing) or 1 octave (wide spacing). As expected, CMR was observed for the narrow and wide comodulated flankers. However, in the wide (but not narrow) condition, this CMR was eliminated by adding a series of gated flanking bands after the signal. Control experiments showed that this effect was not due to long-term adaptation or general distraction. The results are interpreted in terms of the sequence of "postcursor" flanking bands forming a perceptual stream with the original flanking bands, resulting in perceptual segregation of the flanking bands from the masker. The results are consistent with the idea that modulation analysis occurs within, not across, auditory objects, and that across-frequency CMR only occurs if the on-frequency and flanking bands fall within the same auditory object or stream.

The pulse-train auditory aftereffect and the perception of rapid amplitude modulations

Prolonged listening to a pulse train with repetition rates around 100 Hz induces a striking aftereffect, whereby subsequently presented sounds are heard with an unusually "metallic" timbre [Rosenblith et al., Science 106, 333-335 (1947)]. The mechanisms responsible for this auditory aftereffect are currently unknown. Whether the aftereffect is related to an alteration of the perception of temporal envelope fluctuations was evaluated. Detection thresholds for sinusoidal amplitude modulation (AM) imposed onto noise-burst carriers were measured for different AM frequencies (50-500 Hz), following the continuous presentation of a periodic pulse train, a temporally jittered pulse train, or an unmodulated noise. AM detection thresholds for AM frequencies of 100 Hz and above were significantly elevated compared to thresholds in quiet, following the presentation of the pulse-train inducers, and both induced a subjective auditory aftereffect. Unmodulated noise, which produced no audible aftereffect, left AM detection thresholds unchanged. Additional experiments revealed that, like the Rosenblith et al. aftereffect, the effect on AM thresholds does not transfer across ears, is not eliminated by protracted training, and can last several tens of seconds. The results suggest that the Rosenblith et al. aftereffect is related to a temporary alteration in the perception of fast temporal envelope fluctuations in sounds.

Steady-spectrum contexts and perceptual compensation for reverberation in speech identification

Perceptual compensation for reverberation was measured by embedding test words in contexts that were either spoken phrases or processed versions of this speech. The processing gave steady-spectrum contexts with no changes in the shape of the short-term spectral envelope over time, but with fluctuations in the temporal envelope. Test words were from a continuum between "sir" and "stir." When the amount of reverberation in test words was increased, to a level above the amount in the context, they sounded more like "sir." However, when the amount of reverberation in the context was also increased, to the level present in the test word, there was perceptual compensation in some conditions so that test words sounded more like "stir" again. Experiments here found compensation with speech contexts and with some steady-spectrum contexts, indicating that fluctuations in the context's temporal envelope can be sufficient for compensation. Other results suggest that the effectiveness of speech contexts is partly due to the narrow-band "frequency-channels" of the auditory periphery, where temporal-envelope fluctuations can be more pronounced than they are in the sound's broadband temporal envelope. Further results indicate that for compensation to influence speech, the context needs to be in a broad range of frequency channels.