Thesis (Ph.D.)--Boston University / PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you. / Normal hearing is typically defined by threshold audibility, or the loudness of sounds that an individual is able to hear. This convention exists despite the fact that everyday communication relies on extracting and interpreting features of supra-threshold sound. Many normal-hearing listeners struggle to perform certain supra-threshold auditory tasks, and debate persists as to whether such difficulties originate from deficits in cognitive processing or in peripheral, sensory encoding. In this work, we show that there are large individual differences among normal-hearing adults (18 to 55 years), who were asked to report a stream of digits located directly ahead in a simulated rectangular room. Simultaneous, competing masker digit streams were simulated at locations 15° left and right of center, and the level of reverberation was adjusted to vary task difficulty. Performance was best in the anechoic condition and worst in the high-reverberation condition, but listeners nearly always reported a digit from one of the three competing streams, showing that reverberation did not render the digits unintelligible. Most importantly, inter-subject differences were extremely large. These differences were not significantly correlated with age, memory span, or hearing status. They were, however, correlated with behavioral differences in the ability to detect small frequency modulations in pure tones and with the strength of the frequency following response (FFR), a physiological measure of spectro-temporal detail encoding in supra-threshold sounds early in the auditory pathway. The decomposition of the FFR into envelope and carrier components shows that envelope frequency following is the preferred cue for completing the spatial attention task, but it degrades with early aging. As a result, older listeners depend more on carrier phase locking cues than younger people. These results suggest that differences in peripheral encoding help explain individual differences in the ability to communicate in challenging settings, but that aging also has a separate, dissociable effect on early encoding in the auditory system. Tests like these may help tease apart contributions of peripheral and central deficits to communication impairments, ultimately leading to new approaches for helping listeners cope with complex listening environments. / 2031-01-02

La caractérisation du ressenti global du bruit intérieur d’habitacle passe par la définition des conditions conduisant à l’audibilité de ces composantes fréquentielles, émergeant du bruit de fond. Mon travail de thèse s’est attaché à décomposer les situations de masquage pouvant apparaître au sein d’automobile ou de train, en complexifiant progressivement les stimuli au cours des mesures de masquage, en laboratoire. Un certain nombre de choix méthodologiques ont dû être effectués, limitant l’étude aux sons stationnaires, sans modulation d’amplitude, sans déphasage entre les oreilles.Nous nous sommes confrontés tout d’abord à la question du mode de reproduction. Nous avons souligné les difficultés rencontrées lors de la mesure de l’étalonnage des casques d’écoute. Nous avons validé l’écoute au casque étalonné au tympan, en comparant les mesures de seuils masqués de sons purs dans un bruit large bande, à une écoute en chambre sourde, face à une enceinte monophonique.Ensuite, nous avons complexifié le contenu spectral du masque en présentant des bruits comportant des tonalités marquées. Plusieurs modèles perceptifs ont été testés de façon à prédire l’élévation des seuils mesurés.Enfin, nous avons étudié l’amélioration à la détection d’un signal multifréquentiel et développé un modèle, issu de la théorie de la détection du signal, applicable aux signaux présentant des différences en niveau entre les composantes. L’influence du bruit masquant a également été révélé par la mesure de seuils de signaux multifréquentiels dans un bruit d’habitacle automobile. Un unique modèle de détection de signaux émergents, applicable aux signaux stationnaires, a été proposé. Ces travaux ouvrent de nombreuses perspectives, comme la poursuite du travail sur les émergences multifréquentielles, la prise en compte de la relation de phase entre les oreilles, l'étude des sons non stationnaires ou les phénomènes attentionels. / Emergences like tonal components take part in automobile and railroad acoustic comfort. These signals are totally or partially masked by the background noise, of automobile or train coaches. Determining the audibility of spectrally complex signals in a complex broadband noise masker, with tonalities or not, is yet an unanswered question and an industry expectation to characterize the overall sound quality of train/car cabins. The purpose of my PhD thesis was to measure detection thresholds for tones or complex tones, masked by a broadband noise, with pronounced tonal components or not. Several choices must have been performed, restricting study to stationary sounds, without modulation of amplitude, without inter-aural phase differences.First, different methods of sound reproduction are compared measuring detection thresholds. We underlined difficulties met during the measure of the calibration of headphones We validated the eardrum calibration, by comparing detection thresholds of pure sounds in a broad band noise, in a anechoic room, in front of a monophonic loudspeaker.Then, the masking thresholds of pure tones in the presence of maskers with pronounced tonal components are measured. Several perceptual models were tested in order to predict the elevation of the measured thresholds.Finally, we studied the improvement in detection of a multitone complex and developed a model to predict masking thresholds, based on the statistical summation model, applicable to multicomponent signals with differences in level between components. The influence of tonalities have been revealed with the car cabin noise.A threshold model, applicable to the stationary sounds, is proposed. Several perspectives are discussed, from time-variant signals to inter-aural differences or attention phenomena for example.

No description available.

Listeners with severe-sloping losses often don’t perceive high-frequency sound cues. Conventional amplification fails to provide these cues due to loudness discomfort experienced by the listener, and/or acoustic feedback. Alternative signal-processing solutions include shifting higher frequencies down to lower frequencies, or providing electrical stimulation via a speech processor. Three experiments were carried out on adult hearing-impaired listeners to determine the best way of providing high-frequency information: conventional amplification, frequency compression or cochlear implantation.

Objective: This study examined the influence of prescription on hearing aid (HA) fitting characteristics and 5-year developmental outcomes of children. Design: A randomised controlled trial implemented as part of a population-based study on Longitudinal Outcomes of Children with Hearing Impairment (LOCHI). Study sample: Two-hundred and thirty-two children that were fit according to either the National Acoustic Laboratories (NAL) or Desired Sensation Level (DSL) prescription. Results: Deviation from targets and root-mean-square error in HA fitting revealed no significant difference between fitting prescriptions. Aided audibility quantified by using the Speech Intelligibility Index (SII) model showed that DSL provided higher audibility than NAL at low and medium input levels but not at high input level. After allowing for hearing loss desensitisation, differences in audibility between prescription groups were significant only at low input level. The randomised trial of prescription that was implemented for 163 children revealed no significant between-group differences in speech production, perception, and language; but parent-rated functional performance was higher for the DSL than for the NAL group. Conclusions: Proximity to prescriptive targets was similar between fitting prescriptions. The randomised trial revealed differences in aided audibility at low input level between prescription groups, but no significant differences in speech and language abilities.

This review presents a brief history of the evolution of speech audiometry from the 1800s to present day. The two-component aspect of hearing loss (audibility and distortion), which was formalized into a framework in past literature, is presented in the context of speech recognition. The differences between speech recognition in quiet and in background noise are discussed as they relate to listeners with normal hearing and listeners with hearing loss. A discussion of the use of sentence materials versus word materials for clinical use is included as is a discussion of the effects of presentation level on recognition performance in quiet and noise. Finally, the effects of age and hearing loss on speech recognition are considered.

Une perte auditive neurosensorielle est généralement associée à uneréduction de l’intelligibilité de la parole, et ce tout particulièrement dans le bruit.Les contributions respectives d’une réduction de l'audibilité et de déficitssupraliminaires sont encore débattues.L'objectif principal de cette thèse était d'évaluer l'effet spécifique desdéficits supraliminaires sur l’intelligibilité de la parole. L'effet de l'audibilité étaitcontrôlé en mesurant l’intelligibilité de signaux de parole sans signification filtrésdans les régions basses et moyennes fréquences au sein desquelles la détection desons purs était normale chez des auditeurs malentendants présentant par ailleursune perte auditive en hautes fréquences. Dans ces régions fréquentielles oùl’audibilité est supposée normale, des déficits d'intelligibilité de la parole légers àsévères ont été observés dans le silence comme dans le bruit chez les auditeursmalentendants. Les déficits étaient similaires dans les bruits masquantstationnaires et fluctuants. Ces résultats démontrent l’influence des déficitsauditifs supraliminaires sur l’intelligibilité de la parole.Le second objectif de cette thèse était d'étudier l'origine de ces déficitssupraliminaires. Les résultats indiquent qu’une réduction de la sélectivitéfréquentielle cochléaire ne peut pas expliquer entièrement les déficitsd’intelligibilité de la parole des auditeurs malentendants. L'influence de lasensibilité à la structure temporelle fine reste incertaine / Speech intelligibility is reduced for listeners with sensorineural hearingloss, especially for speech in noise. The extent to which this reduction is due toreduced audibility or to supra-threshold deficits is still debated.The main goal of this PhD work was to investigate the specific influenceof supra-threshold deficits on speech intelligibility. The effect of audibility wascontrolled for by measuring speech intelligibility for hearing-impaired listenersusing nonsense speech signals filtered in low- and mid-frequency regions wherepure-tone sensitivity was normal. Hearing-impaired listeners with hearing loss inhigh-frequency regions showed mild to severe intelligibility deficits for speechboth in quiet and in noise in these frequency regions of normal audibility. Similardeficits were obtained for speech in steady and fluctuating masking noises. Thisprovides additional evidence that speech intelligibility may be strongly influencedby supra-threshold auditory deficits.The second aim of this PhD work was to investigate the origin of thesesupra-threshold deficits. Results showed that reduced frequency selectivity cannotentirely explain the speech intelligibility deficits of the hearing-impaired listeners.The influence of temporal fine structure sensitivity remained unclear

Creating the optimal balance between dialogue level and ambient sound is extremely important in media productions. This process is however inherently difficult due to that people’s requirements and preferences are not uniform. Speech intelligibility is affected by a multitude of factors, such as hearing impairments, audio quality and listening equipment. Recent EU directives on accessibility calls for improved audio clarity features for broadcast content. To accommodate these requirements, the broadcast industry needs to develop functionality for enhanced dialogue clarity and, optimally, put listeners in control of these features. Many speech enhancement techniques exist, this paper uses Sveriges Radio as a case study to evaluate several of these methods. A study on enhancing speech intelligibility through the use of dynamic range control and blind source separation is presented and results show that both methods can have a positive impact. Dynamic range control proves efficient in increasing intelligibility by reducing dynamic variations. It is also well suited to implement in an existing two-channel infrastructure, common in the radio industry, due to being included in novel audio codecs. Blind source separation is found to best be used in moderation due to the risk of audio quality degradation, and is primarily suited for prerecorded material on account of the processing time needed. / Att skapa en optimal balans mellan dialognivå och bakgrundsljud är oerhört viktigt i medieproduktioner. Detta är dock i sig komplicerat på grund av människors olika förutsättningar och preferenser. Taluppfattbarheten påverkas av en mängd faktorer, såsom hörselnedsättningar, ljudkvalitet och lyssningsutrustning. Nya EU-direktiv om tillgänglighet ställer krav på förbättrade funktioner för ljudtydlighet i etermedia. För att tillgodose dessa krav behöver branschen utveckla funktionalitet för ökad dialogtydlighet och företrädesvis också stöd för att lyssnarna själva ska kunna styra dessa funktioner. Det finns många tekniker för att öka taluppfattbarheten, denna artikel använder Sveriges Radio som fallstudie för att utvärdera flera av dessa metoder. En studie om möjligheten till förbättrad taluppfattbarhet genom kontroll av ljudets dynamik (dynamic range control) och blindkallseparation (blind source separation) presenteras, och resultaten visar att båda metoderna kan ha en positiv inverkan. Dynamisk kontroll visar sig vara effektiv för att öka taluppfattbarheten genom att jämna ut dynamiskt innehåll. Tekniken lämpar sig också bra för implementering i en befintlig tvåkanals-infrastruktur, vilket är vanligt inom radioindustrin, på grund av att den inkluderas i nya ljud-kodekar. Blindkallseparation används bäst med måtta på grund av risk for ljudkvalitetsförsämring och är i första hand lämpad för förinspelat material på grund av den processeringstid som behövs.