Cochlear implant (CI) devices afford many profoundly deaf individuals worldwide partially restored hearing ability. Although CI users achieve remarkable speech perception with contemporary multichannel CI devices, their music perception ability is generally unsatisfactory. Improved CI-mediated music perception ability requires that the underlying constraints hindering processing of music-relevant information need to be identified and understood. This study puts forward a systematic approach, informed by the neurocognitive mechanisms underlying music perception in normal hearing (NH), for investigating implant-mediated music perception. Psychoacoustical experiments were used to explore the extent to which music-relevant information delivered to the central auditory system following peripheral electrical stimulation supports music perception. Task-specific stimuli and test procedures were developed to assess perception of pitch, rhythm and loudness information, both as separate and in combined form, in sound-field listening conditions. CI users’ unsuccessful judgement of the musical character of short, novel single-voice melodies suggests that insufficient information reaches the central auditory processing system to effect a unified musical percept. This is despite sound field frequency discrimination behaviour being better than had been expected and rhythm perception ability with regard to short tone sequences of varying pitch and rhythmic complexity being comparable to that of NH listeners. CI listeners also performed similarly to NH listeners during pitch-dependent loudness perception tasks. Within the framework of a hierarchical, modular processing system underlying music perception, it appears that early pitch processing deficits propagate throughout the music processing system to exert an overriding inhibitory perceptual effect. The outcomes of this study not only underline the importance of delivering sufficient pitch information to the electrically stimulated auditory system but also show that music perception in CI-mediated hearing should be investigated and understood as the outcome of an integrated perceptual system. / Thesis (PhD)--University of Pretoria, 2011. / Electrical, Electronic and Computer Engineering / Unrestricted

Cross modality matching is a magnitude matching procedure, developed to study the relationships between sensory modalities. Auditory and visual sensory integration can be examined through cross modality matching of brightness and loudness. Brightness and loudness are natural correlates of one another as they both represent the parameter of intensity for their respective sensory modalities. Past studies have demonstrated that typical individuals tend to match brighter lights with louder sounds and dimmer lights with softer sounds. The current study utilized a modified cross modality matching procedure, combined with electroencephalography (EEG) data, to examine the cortical response to sensory integration. It was hypothesized that the response latency and cortical distribution of the EEG data would show differences between matched and unmatched conditions of light and sound stimuli. Light and sound stimuli were presented to 10 participants (five males and five females between the ages of 18 and 28 years) in a forced choice paradigm. The behavioral responses, reaction times, and EEG data were recorded for each patient. Results demonstrated that there were significant differences in behavioral reaction time among the stimulus conditions. However, reaction times were only significantly faster for the loudest sound paired with the brightest light. No other pairs of matched stimuli resulted in faster reaction times. Event related potentials (ERPs) were identified for matched and unmatched stimulus conditions. No differences were identified in latency of the ERPs among conditions. Additionally, source localization revealed that dipole locations for each stimulus condition remained relatively constant in the prefrontal cortex. As the prefrontal cortex has been found to be associated with decision-making and sensory integration, it can be concluded that sensory integration did occur. However, the processing of sensory information did not change for matched or unmatched conditions of light and sound.

The conversion of audio from the digital to analog domain has the potential to result in distortion due to converter overload. This occurs because some peaks in the signal cannot be defined digitally and only become problematic during the conversion into the analog domain, exceeding the level that can be represented by the converter, causing it to overload. Although True Peak limiting and metering can prevent and monitor this issue, some professional mastering engineers choose not to do so. The study tested claims made against overload prevention, including the adequacy of headroom in modern D/A converters and the inaudibility of the distortion caused by overload. Preference was also added to the audibility claim. Measurements show that there is not enough headroom in modern D/A converters to avoid overload, but the distortion created by overload is generally inaudible in an uncompressed WAVE format hard rock song. Additionally, there is no clear preference. The measurements found that overload only occurs when the device's volume is raised to its maximum output.

No description available.

Dans un environnement naturel, le champ acoustique est complexe (plusieurs sources, différentes positions spatiales, acoustique du lieu,...) et l'écoute est binaurale. Le filtrage acoustique opéré par la tête, le buste et les pavillons de l'auditeur (dépendant de la direction) induit donc systématiquement des différences interaurales de temps, de niveau et de spectre. Des modèles de sonie existent et permettent de prédire la sonie des sons stationnaires dans des situations d'écoute simples (ISO-532B (1975), DIN-45631 (1990), ANSI-S3.4 (2007)). L'écoute doit être monaurale (une seule oreille) ou diotique (même son aux deux oreilles), correspondant à une source en incidence frontale en champ libre, ou en champ diffus. En revanche, ces modèles échouent pour prédire la sonie lorsque des différences interaurales importantes interviennent. La thèse s’est ainsi intéressée à la sonie des champs acoustiques stationnaires, impliquant une ou plusieurs sources, soit artificielles et spatialisées en champ libre, soit réelles dans une acoustique naturelle. De nouveaux éléments ont été apportés dans la compréhension dont l'information contenue dans les signaux reçus aux oreilles de l’auditeur est combinée pour former un unique percept de sonie binaurale dans les situations d’écoute dichotiques (gain de sommation binaural, cas de plusieurs sources, effet de la corrélation interaurale,…). D’une part, une hypothèse pour essayer d’expliquer les différences interindividuelles observées dans les stratégies de sommation binaurales a pu être testée ; la robustesse et la stabilité au cours du temps de ces stratégies individuelles a été mise en avant. D’autre part, trois principaux modèles psychophysiques de sonie binaurale (ANSI-S3.4 (2007), Moore et Glasberg (2007), Sivonen et Ellermeier (2008)) ont été testés sur l’ensemble des données expérimentales (impliquant différents niveaux de réalisme), permettant de préciser la performance et les domaines de validité respectifs de chacun de ces modèles dans des situations d’écoute fortement dichotiques. / Listening in a natural environment implies to consider complex sound fields (several sound sources, different spatial positions, reflections…) and a binaural listening configuration. As a consequence, differences in time, level and spectrum between the two at-ear signals are systematically induced by the direction-dependant physical filtering from the human head, torso and pinnae. Existing loudness models provide accurate predictions under simplified listening situations (ISO-532B (1975), DIN-45631 (1990), ANSI-S3.4 (2007)). These models have been designed to use monaural (only one ear) or diotic (same signal at the two ears) signals, equivalent to one sound source with a frontal incidence, in a free or diffuse field. However, the models fail to predict loudness when the interaural differences are large. The present document focuses on the loudness of stationary sound fields, made up of one or several, artificial or real sound sources, in a free field or in a real environment. New elements have been brought to light regarding how, in a dichotic listening situation, information is combined from the two ears to produce one unique binaural loudness percept (binaural gain, case of several sound sources, effect of interaural correlation,...). On the one hand, one hypothesis have been tested in order to try to explain the interindividual differences observed in binaural loudness summation ; the robustness and stability over time of these individual strategies have been highlighted. On the other hand, predictions from the three main psychophysical models of binaural loudness (ANSI-S3.4 (2007), Moore et Glasberg (2007), Sivonen et Ellermeier (2008)) have been compared with all of the subjective data (involving different levels of realism), which allowed us to define more accurately the domain of validity and performance of these models in highly dichotic listening situations.

Auditory filters were derived in 20 normal-hearing human listeners at center frequencies (CFs) of 913, 1095, 3651, and 4382 Hz using the roex (p,r) method. Comparisons were made between slopes of the filters' skirts at the neighboring CFs with filter output levels of 45 and 70 dB. The same comparisons were made with regard to filter equivalent rectangular bandwidth (ERB). In the 1000-Hz region, the low-frequency slopes (Pl) of filters centered at 913 and 1095 Hz were significantly correlated at both stimulus levels, while the high-frequency slopes (Pu) were similar only at the high test level. In the 4000-Hz region, for sinusoids of 3651 and 4382 Hz, the level effect was clearer as both Pu and Pl values diverged at the low level but were related at high levels. The ERBs centered at the same CFs displayed a similar level dependence. At the stimulus level most likely to be affected by an active feedback mechanism, auditory filters centered at nearly the same frequency displayed quite distinct frequency selectivity, and this trend was stronger in the 4000-Hz region than the 1000-Hz region. The findings suggest that a saturating, active cochlear mechanism may not be distributed evenly, or contribute to peripheral tuning with equal effectiveness throughout the length of the partition.

Background: An important goal of providing amplification to children with hearing loss is to ensure that hearing aids are adjusted to match targets of prescriptive procedures as closely as possible. The Desired Sensation Level (DSL) v5 and the National Acoustic Laboratories’ prescription for nonlinear hearing aids, version 1 (NAL-NL1) procedures are widely used in fitting hearing aids to children. Little is known about hearing aid fitting outcomes for children with severe or profound hearing loss. Purpose: The purpose of this study was to investigate the prescribed and measured gain of hearing aids fit according to the NAL-NL1 and the DSL v5 procedure for children with moderately severe to profound hearing loss; and to examine the impact of choice of prescription on predicted speech intelligibility and loudness. Research Design: Participants were fit with Phonak Naida V SP hearing aids according to the NAL-NL1 and DSL v5 procedures. The Speech Intelligibility Index (SII) and estimated loudness were calculated using published models. Study Sample: The sample consisted of 16 children (30 ears) aged between 7 and 17 yr old. Data Collection and Analysis: The measured hearing aid gains were compared with the prescribed gains at 50 (low), 65 (medium), and 80 dB SPL (high) input levels. The goodness of fit-to-targets was quantified by calculating the average root-mean-square (RMS) error of the measured gain compared with prescriptive gain targets for 0.5, 1, 2, and 4 kHz. The significance of difference between prescriptions for hearing aid gains, SII, and loudness was examined by performing analyses of variance. Correlation analyses were used to examine the relationship between measures. Results: The DSL v5 prescribed significantly higher overall gain than the NAL-NL1 procedure for the same audiograms. For low and medium input levels, the hearing aids of all children fit with NAL-NL1 were within 5 dB RMS of prescribed targets, but 33% (10 ears) deviated from the DSL v5 targets by more than 5 dB RMS on average. For high input level, the hearing aid fittings of 60% and 43% of ears deviated by more than 5 dB RMS from targets of NAL-NL1 and DSL v5, respectively. Greater deviations from targets were associated with more severe hearing loss. On average, the SII was higher for DSL v5 than for NAL-NL1 at low input level. No significant difference in SII was found between prescriptions at medium or high input level, despite greater loudness for DSL v5 than for NAL-NL1. Conclusions: Although targets between 0.25 and 2 kHz were well matched for both prescriptions in commercial hearing aids, gain targets at 4 kHz were matched for NAL-NL1 only. Although the two prescriptions differ markedly in estimated loudness, they resulted in comparable predicted speech intelligibility for medium and high input levels.

Objective: To examine the impact of prescription on predicted speech intelligibility and loudness for children. Design: A between-group comparison of speech intelligibility index (SII) and loudness, based on hearing aids fitted according to NAL-NL1, DSL v4.1, or DSL m[i/o] prescriptions. A within-group comparison of gains prescribed by DSL m[i/o] and NAL-NL2 for children in terms of SII and loudness. Study sample: Participants were 200 children, who were randomly assigned to first hearing-aid fitting with either NAL-NL1, DSL v4.1, or DSL m[i/o]. Audiometric data and hearing-aid data at 3 years of age were used. Results: On average, SII calculated on the basis of hearing-aid gains were higher for DSL than for NAL-NL1 at low input level, equivalent at medium input level, and higher for NAL-NL1 than DSL at high input level. Greater loudness was associated with DSL than with NAL-NL1, across a range of input levels. Comparing NAL-NL2 and DSL m[i/o] target gains revealed higher SII for the latter at low input level. SII was higher for NAL-NL2 than for DSL m[i/o] at medium- and high-input levels despite greater loudness for gains prescribed by DSL m[i/o] than by NAL-NL2. Conclusion: The choice of prescription has minimal effects on speech intelligibility predictions but marked effects on loudness predictions.

No description available.

Background: Prescriptive methods have been at the core of modern hearing aid fittings for the past several decades. Every decade or so, there have been revisions to existing methods and/or the emergence of new methods that become widely used. In 2001 Byrne et al provided a comparison of insertion gain for generic prescriptive methods available at that time. Purpose: The purpose of this article was to compare National Acoustic Laboratories—Non-linear 1 (NAL-NL1), National Acoustic Laboratories—Non-linear 2 (NAL-NL2), Desired Sensation Level Multistage Input/Output (DSL m[i/o]), and Cambridge Method for Loudness Equalization 2—High-Frequency (CAMEQ2-HF) prescriptive methods for adults on the amplification characteristics of prescribed insertion gain and compression ratio. Following the differences observed in prescribed insertion gain among the four prescriptive methods, analyses of predicted specific loudness, overall loudness, and bandwidth of cochlear excitation and effective audibility as well as speech intelligibility of the international long-term average speech spectrum (ILTASS) at an average conversational input level were completed. These analyses allow for the discussion of similarities and differences among the present-day prescriptive methods. Research Design: The impact of insertion gain differences among the methods is examined for seven hypothetical hearing loss configurations using models of loudness perception and speech intelligibility. Study Sample: Hearing loss configurations for adults of various types and degrees were selected, five of which represent sensorineural impairment and were used by Byrne et al; the other two hearing losses provide an example of mixed and conductive impairment. Data Collection and Analysis: Prescribed insertion gain data were calculated in 1/3-octave frequency bands for each of the seven hearing losses from the software application of each prescriptive method over multiple input levels. The insertion gain data along with a diffuse field-to-eardrum transfer function were used to calculate output levels at the eardrums of the hypothetical listeners. Levels of hearing loss and output were then used in the Moore and Glasberg loudness model and the ANSI S3.5-1997 Speech Intelligibility Index model. Results: NAL-NL2 and DSL m[i/o] provided comparable overall loudness of approximately 8 sones for the five sensorineural hearing losses for a 65 dB SPL ILTASS input. This loudness was notably less than that perceived by a normal-hearing person for the same input signal, 18.6 sones. NAL-NL2 and DSL m[i/o] also provided comparable predicted speech intelligibility in quiet and noise. CAMEQ2-HF provided a greater average loudness, similar to NAL-NL1, with more high-frequency bandwidth but no significant improvement to predicted speech intelligibility. Conclusions: Definite variation in prescribed insertion gain was present among the prescriptive methods. These differences when averaged across the hearing losses were, by and large, negligible with regard to predicted speech intelligibility at normal conversational speech levels. With regard to loudness, DSL m[i/o] and NAL-NL2 provided the least overall loudness, followed by CAMEQ2-HF and NAL-NL1 providing the most loudness. CAMEQ2-HF provided the most audibility at high frequencies; even so, the audibility became less effective for improving speech intelligibility as hearing loss severity increased.