Apports du réhaussement à l'étude du rôle de l'enveloppe temporelle dans l'identification de la parole (application à la compensation des troubles d'intelligibilité d'origine neurosensorielle)

Le but de cette recherche consiste à étudier le rôle de l'enveloppe temporelle (les fluctuations lentes d'amplitude, <500 Hz) dans la perception de la parole. Cinq études psychoacoustiques examinent les effets d'un rehaussement (ou expansion) d'enveloppe temporelle sur l'identification de la parole chez les sujets normo-entendants et malentendants. Les capacités d'identification sont mesurées dans le silence et en présence d'un bruit stationnaire ou fluctuant, à l'aide de stimuli de type CV, VCV ou de phrases. Dans les deux premières études, les stimuli de parole sont dégradés spectralement alors que dans les trois études suivantes, les stimuli sont préservés dans le domaine spectral. Deux algorithmes d'expansion sont utilisés afin d'augmenter le contraste de l'inveloppe des stimuli....The goal of the present research was to investigate the role of temporal-envelope cues (the slow amplitude fluctuations, <500 Hz) in speech perception. To address this issue, five psychoacoustic studies examined the effects of temporal-envelope expansion on speech identification in bath normal-hearing and hearing-impaired listeners. Speech identification was measured in quiet and in the presence of a stationary or fluctuating noise, using CV, VCV or sentence stimuli....PARIS5-BU Saints-Pères (751062109) / SudocSudocFranceF

Relative contribution of off- and on-frequency spectral components of background noise to the masking of unprocessed and vocoded speech

The present study examined the relative influence of the off- and on-frequency spectral components of modulated and unmodulated maskers on consonant recognition. Stimuli were divided into 30 contiguous equivalent rectangular bandwidths. The temporal fine structure (TFS) in each “target” band was either left intact or replaced with tones using vocoder processing. Recognition scores for 10, 15 and 20 target bands randomly located in frequency were obtained in quiet and in the presence of all 30 masker bands, only the off-frequency masker bands, or only the on-frequency masker bands. The amount of masking produced by the on-frequency bands was generally comparable to that produced by the broadband masker. However, the difference between these two conditions was often significant, indicating an influence of the off-frequency masker bands, likely through modulation interference or spectral restoration. Although vocoder processing systematically lead to poorer consonant recognition scores, the deficit observed in noise could often be attributed to that observed in quiet. These data indicate that (i) speech recognition is affected by the off-frequency components of the background and (ii) the nature of the target TFS does not systematically affect speech recognition in noise, especially when energetic masking and∕or the number of target bands is limited

The Noise Susceptibility of Various Speech Bands

The degrading influence of noise on various critical bands of speech was assessed. A modified version of the compound method [Apoux and Healy (2012) J. Acoust. Soc. Am. 132, 1078–1087] was employed to establish this noise susceptibility for each speech band. Noise was added to the target speech band at various signal-to-noise ratios to determine the amount of noise required to reduce the contribution of that band by 50%. It was found that noise susceptibility is not equal across the speech spectrum, as is commonly assumed and incorporated into modern indexes. Instead, the signal-to-noise ratio required to equivalently impact various speech bands differed by as much as 13 dB. This noise susceptibility formed an irregular pattern across frequency, despite the use of multi-talker speech materials designed to reduce the potential influence of a particular talker\u27s voice. But basic trends in the pattern of noise susceptibility across the spectrum emerged. Further, no systematic relationship was observed between noise susceptibility and speech band importance. It is argued here that susceptibility to noise and band importance are different phenomena, and that this distinction may be underappreciated in previous works

Speech-Material and Talker Effects in Speech Band Importance

Band-importance functions created using the compound method [Apoux and Healy (2012). J. Acoust. Soc. Am. 132, 1078–1087] provide more detail than those generated using the ANSI technique, necessitating and allowing a re-examination of the influences of speech material and talker on the shape of the band-importance function. More specifically, the detailed functions may reflect, to a larger extent, acoustic idiosyncrasies of the individual talker\u27s voice. Twenty-one band functions were created using standard speech materials and recordings by different talkers. The band-importance functions representing the same speech-material type produced by different talkers were found to be more similar to one another than functions representing the same talker producing different speech-material types. Thus, the primary finding was the relative strength of a speech-material effect and weakness of a talker effect. This speech-material effect extended to other materials in the same broad class (different sentence corpora) despite considerable differences in the specific materials. Characteristics of individual talkers\u27 voices were not readily apparent in the functions, and the talker effect was restricted to more global aspects of talker (i.e., gender). Finally, the use of multiple talkers diminished any residual effect of the talker

On the mechanisms involved in the recovery of envelope information from temporal fine structure

Three experiments were designed to provide psychophysical evidence for the existence of envelope information in the temporal fine structure (TFS) of stimuli that were originally amplitude modulated (AM). The original stimuli typically consisted of the sum of a sinusoidally AM tone and two unmodulated tones so that the envelope and TFS could be determined a priori. Experiment 1 showed that normal-hearing listeners not only perceive AM when presented with the Hilbert fine structure alone but AM detection thresholds are lower than those observed when presenting the original stimuli. Based on our analysis, envelope recovery resulted from the failure of the decomposition process to remove the spectral components related to the original envelope from the TFS and the introduction of spectral components related to the original envelope, suggesting that frequency- to amplitude-modulation conversion is not necessary to recover envelope information from TFS. Experiment 2 suggested that these spectral components interact in such a way that envelope fluctuations are minimized in the broadband TFS. Experiment 3 demonstrated that the modulation depth at the original carrier frequency is only slightly reduced compared to the depth of the original modulator. It also indicated that envelope recovery is not specific to the Hilbert decomposition