<p> Animal studies have shown that the tonotopic organization of the auditory cortex is not statically fixed, but can be remodeled by experience. The purpose of this study was to investigate whether or not frequency discrimination training can induce changes in the cortical representation of a selected frequency in humans. Six human subjects were trained for approximately 3 weeks to detect a change in pitch between two tones (40Hz amplitude modulated) using a standard frequency of 2040 Hz. Each subject was tested on his/her discriminative ability before and after training using three different standards (2040Hz, 1840Hz, and 2240Hz). EEG data were recorded both before and after training and changes in transient and steady-state responses were investigated. Behaviourally, every subject improved at the discrimination task using the trained frequency. However, only three subjects demonstrated transfer to both untrained frequencies. In the EEG data, the P2-Nl amplitude increased in five of the six subjects and the Nllatency decreased in all six for the 2040Hz set. These two findings were statistically significant (p<0.05) for the group. There were no statistically significant findings for the side frequencies. The change in the 40 Hz steady-state response was also not significant, increasing in three subjects and decreasing in the other three. These findings indicate that changes are expressed in the secondary auditory cortex. These findings may also be applicable to the treatment of tinnitus. </p> / Thesis / Master of Science (MSc)

No description available.

The increasing use of auditory graphs and sonifications in technology is leading to a wider variety of system users, which, in turn, suggests a need for research in how differences between individual listeners affect sound interpretation. As a first step in this arena, the current study investigates the question of whether or not cognitive abilities and musical experience predict frequency and tempo discrimination in individuals. Participants in the study were 30 undergraduate students from Georgia Institute of Technology and 20 adults from the Atlanta, Georgia community. In the cognitive ability session, participants completed the Operation Span (Ospan) task as a measure of working memory capacity and the Ravens Progressive Matrices task as a measure of spatial reasoning. In the auditory discrimination session, participants performed a tempo and a frequency discrimination task. Demographics on age, gender, handedness, years of playing a musical instrument, and years of formal musical training were also collected. A correlational analysis of all variables was performed. Paired-samples t-tests on the Weber fractions of the six threshold means were also performed to determine if there were any significant differences between the frequency thresholds and the tempo thresholds. Lastly, multiple hierarchical regressions were performed on each of the six dependent variables to identify significant predictors of frequency and tempo discrimination. The paired samples t-tests show a significant difference between 250 Hz and 840 Hz and between 250 Hz and 1600 Hz, a violation of Webers Law. However, this violation of Webers Law may be explained by the small sample size used in the study. The t-tests also show a significant difference between the means of 150 ms and 250 ms and between the means of 250 ms and 350 ms. The results of the regression analyses show that good performance on Ravens seems to predict lower thresholds at 1600 Hz. The results also show that good scores on Ospan appear to predict lower thresholds at 350 ms ICI. In addition to these significant predictors from the regression analyses, there are many significant correlations that provide further support that cognitive abilities are related to frequency and tempo discrimination.

Neurological evidence indicates that instrumental musicians experience changes in the auditory system following skill acquisition and sensory training; yet, little is known about auditory neural plasticity in formally trained vocal musicians. Furthermore, auditory pitch discrimination and laryngeal control are recognized as essential skills for vocal musicians; however, the relationship between physiological variables, perceptual abilities, and vocal production is unclear. Electrophysiologic and psychoacoustic measures were used to examine pitch production accuracy as well as pre-attentive and active pitch discrimination between nonmusicians and two classes of musicians. Participants included 40 formally trained musicians (19 vocalists/21 instrumentalists) and 21 nonmusician controls. All were right-handed young adult females with normal hearing. Stimuli were harmonic tone complexes approximating the physical characteristics of piano tones and represented the mid-frequency range of the untrained female vocal register extending from C4 to G4 (F0 = 261.63-392 Hz). Vocal pitch recordings were spectrally analyzed to determine pitch production accuracy. Difference limens for frequency (DLFs) were obtained by an adaptive psychophysical paradigm. Pre-attentive auditory discrimination was assessed by auditory evoked potentials (AEPs), including the mismatch negativity (MMN). A standard tone (G4 = 392 Hz) and three deviants differing in frequency (1.5%, 3%, and 6% below) were presented in a multi-deviant paradigm. All musicians demonstrated superior pitch perception and vocal production compared to nonmusicians. Pitch perception and production accuracy did not significantly differ between vocalists and instrumentalists; however, pitch production accuracy was most consistent within the vocalist group. Music training appears to facilitate both auditory perception and vocal production regardless of music specialty. Pitch perception and production were correlated skills only for instrumental musicians. Vocalists demonstrated minimal variability for both skills so that perception and production were not correlated. These two skills may be independent abilities between which a relationship develops with training. AEP analysis revealed an influence of musical expertise on neural responses as early as 50 ms after onset of musically relevant stimuli. MMN responses indicate that vocal musicians as well as instrumental musicians have superior sensory memory representations for acoustic parameters of harmonic stimuli and imply that auditory neural sensitivity is developed by intense music training.

For cochlear implant (CI) listeners, poorer than normal speech recognition abilities are typically attributed to degraded spectral acuity. However, estimates of spectral acuity have most often been obtained using simple (tonal) stimuli, presented directly to the implanted electrodes, rather than through the speech processor as occurs in everyday listening. Further, little is known about spectral acuity for dynamic stimuli, as compared to static stimuli, even though the perception of dynamic spectral cues is important for speech perception. The primary goal of the current study was to examine spectral acuity in CI listeners, and a comparison group of normal hearing (NH) listeners, for both static and dynamic stimuli presented through the speech processor. In addition to measuring static and dynamic spectral acuity for simple stimuli (pure tones) in Experiment 1, spectral acuity was measured for complex stimuli (synthetic vowels) in Experiment 2, because measures obtained with speech-like stimuli are more likely to reflect listeners’ ability to make use of spectral cues in naturally-produced speech. Sixteen postlingually-deaf, adult CI users and sixteen NH listeners served as subjects in both experiments. In Experiment 1, frequency discrimination limens (FDLs) were obtained for 1.5 kHz reference tones, and frequency glide discrimination limens (FGDLs) were obtained for pure-tone frequency glides centered on 1.5 kHz. Glide direction identification thresholds (GDITs) were also measured, in order to determine the amount of frequency change required to identify glide direction. All three measures were obtained for stimuli having both longer (150 ms) and shorter (50 ms) durations. Spectral acuity for dynamic stimuli (FGDLs, GDITs) was poorer than spectral acuity for static stimuli (FDLs) for both listener groups at both stimulus durations. Stimulus duration had a significant effect on thresholds in NH listeners, for all three measures, but had no significant effect on thresholds in CI listeners for any measure. Regression analyses revealed no systematic relationship between FDLs and FGDLs in NH listeners at either stimulus duration. For CI listeners, the relationship between FDLs and FGDLs was significant at both stimulus durations, suggesting that, for tonal signals, the factors that determine spectral acuity for static stimuli also largely determine spectral acuity for dynamic stimuli. In Experiment 2, estimates of static and dynamic spectral acuity were obtained using three-formant synthetic vowels, modeled after the vowel /^/. Formant discrimination thresholds (FDTs) were measured for changes in static F2 frequency, whereas formant transition discrimination thresholds (FTDTs) were measured for stimuli that varied in the extent of F2 frequency change. FDTs were measured with 150-ms stimuli, and FTDTs were measured with both 150-ms and 50-ms stimuli. For both listener groups, FTDTs were similar for the longer and shorter stimulus durations, and FTDTs were larger than FDTs at the common duration of 150 ms. Measures from Experiment 2 were compared to analogous measures from Experiment 1 in order to examine the effect of stimulus context (simple versus complex) on estimates of spectral acuity. For NH listeners, measures obtained with complex stimuli (FDTs, FTDTs) were consistently larger than the corresponding measures obtained with simple stimuli (FDLs, FGDLs). For CI listeners, the relationship between simple and complex measures differed across two subgroups of subjects. For one subgroup, thresholds obtained with complex stimuli were smaller than those obtained with simple stimuli; for another subgroup the pattern was reversed. On the basis of these findings, it was concluded that estimates of spectral acuity obtained with simple stimuli cannot accurately predict estimates of spectral acuity obtained with complex (speech-like) stimuli in CI listeners. However, a significant relationship was observed between FDTs and FTDTs. Thus, similar to the measures obtained with pure-tone stimuli in Experiment 1 (FDLs and FGDLs), estimates of static spectral acuity (FDTs) appear to predict estimates of dynamic spectral acuity (FTDTs) when both measures are obtained with stimuli of similar complexity in CI listeners. Taken together, findings from Experiments 1 and 2 support the following conclusions: (1) Dynamic spectral acuity is poorer than static spectral acuity for both simple and complex stimuli. This outcome was true for both NH and CI listeners, despite the fact that absolute thresholds were substantially larger, on average, for the CI group. (2) For stimuli having the same level of complexity (i.e., tonal or speech-like), dynamic spectral acuity in CI listeners appears to be determined by the same factors that determine spectral acuity for static stimuli. (3) For CI listeners, no systematic relationship was observed between analogous measures of spectral acuity obtained with simple, as compared to complex, stimuli. (4) It is expected that measures of spectral acuity based on complex stimuli would provide a better indication of CI users’ ability to make use of spectral cues in speech; therefore, it may be advisable for studies attempting to examine the relationship between spectral acuity and speech perception in this population to measure spectral acuity using complex, rather than simple, stimuli. (5) Findings from the current study are consistent with recent vowel identification studies suggesting that some poorer-performing CI users have little or no access to dynamic spectral cues, while access to such cues may be relatively good in some better-performing CI users. However, additional research is needed to examine relationship between estimates of spectral acuity obtained here for speech-like stimuli (FDTs, FTDTs) and individual CI users’ perception of static and dynamic spectral cues in naturally-produced speech.

Especially important in developing improved cochlear implants is to develop a deeper understanding of the processing of sound in the central auditory nervous system, for both acoustic and electrical stimulation of the auditory system. This thesis contributes to this objective through cochlear implant psychoacoustic research and modelling of auditory system sound processing. The primary hypothesis of the thesis was that the same underlying mechanisms are responsible for sound perception in both electric and acoustic hearing. Thus, if appropriate models are created for normal acoustic hearing, they should be able to predict psychoacoustic data from electric hearing when the model input is changed from acoustic to electrical stimulation. A second hypothesis was that electrode interaction could be measured by gap detection and that predictions of current spread in the cochlea could be obtained from gap detection data. Measured gap detection thresholds in three cochlear implant users were a function of the physical separation of electrode pairs used for the two stimuli that bound the gap, resulting in a U-shaped "tuning curve" for this across-channel condition. Models of gap detection in acoustic and electric hearing were created to explain these U-shaped curves. A technique was developed to obtain estimates of cochlear current spread from gap detection data. Predictions of electrode discrimination were obtained from the current spread estimates, and these were compared to data measured in cochlear implant users. The model for acoustic hearing could predict the U -shaped curves found in acoustic hearing, and when the input spike train statistics were adapted appropriately, the same model could also predict gap detection data for electric hearing. Predictions of current spread exhibited current peaks close to the electrodes and had length constants between 0.5 mm and 3 mm, similar to measured data quoted in literature. Predictions of electrode discrimination correlated well with measured data in one subject, but not in two others. The primary conclusion from the modelling results is that if the mechanisms of central auditory nervous system signal processing of acoustic stimulation are understood, these same mechanisms may be applied to understand the signal processing in auditory electrical stimulation and to predict psychoacoustic data for electrical stimulation. A second conclusion is that spatial mechanisms, as opposed to temporal mechanisms, may determine gap detection thresholds in the across-channel condition. This is important in cochlear electrical stimulation, where spike trains are strongly phase-locked to the stimulus and temporal mechanisms cannot predict gap detection thresholds. A third conclusion is that gap detection can be used to measure channel interaction and to predict current distributions in the cochlea, although there is still uncertainty about the accuracy of these predictions. However, the gap detection data and predictions for current distributions indicate that electrodes are not discriminable when they are closer than 1.5 mm. The implication of these last two conclusions taken together is that research should focus on obtaining better spatial resolution in cochlear implants. / Thesis (PhD)--University of Pretoria, 2001. / Electrical, Electronic and Computer Engineering / Unrestricted

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

L’implant cochléaire devient une ressource importante pour contrer la surdité alors qu’il a été démontré qu’une privation auditive précoce ou tardive affecte le développement des systèmes auditif et visuel. Le but des études présentées dans cette thèse est d’évaluer l’impact développemental d’une privation auditive sur les systèmes auditif et visuel. En premier lieu, l’étude du développement chez une population entendante a montré que les systèmes auditif et visuel se développent à des rythmes distincts et qu’ils atteignent leur maturité respective à des âges différents. Ces conclusions suggèrent que les mécanismes qui sous-tendent ces deux systèmes sont différents et que leur développement respectif est indépendant. Aussi, tel qu’observé par une mesure comportementale et électrophysiologique, la discrimination fréquentielle auditive chez les personnes porteuses d’un implant cochléaire est altérée et corrélée aux performances de perception de la parole. Ces deux études suggèrent que suite à une privation auditive, le traitement auditif diffère d’une personne malentendante à une autre, et que ces différences touchent les processus de bas-niveaux, tel que suggéré par la disparité présente dans les performances de discrimination fréquentielle. La dernière étude observe qu’une privation auditive affecte aussi le développement de la modalité visuelle, tel qu’indiqué par une diminution des capacités de discrimination visuelle observée chez des malentendants. Cette indication appuie l’hypothèse qu’un développement normal de chacun des sens est requis pour un développement optimal des autres sens. Globalement, les résultats présentés dans cette thèse suggèrent que les systèmes auditif et visuel se développent de façon distincte, mais demeurent toutefois interreliés. En effet, une privation auditive affecte non seulement le développement des habiletés auditives, mais aussi celui des habiletés visuelles, suggérant une interdépendance entre les deux systèmes. / The cochlear implant is an important resource for deaf people, as it is known that an auditory deprivation alters the auditory and the visual systems. We aimed to study the impact of deafness on the development of the auditory and visual systems. First, the study of these systems in a hearing population has shown that both systems develop at different rates and reach adult-like levels at different ages. These conclusions suggest that the mechanisms underlying these treatments are different and that their developments are independent. Moreover, as shown with the behavioral and the electrophysiological study, auditory frequency discrimination in cochlear implant users is altered and correlated with the speech perception performance. These two studies suggest that following deafness, the auditory discrimination is different from one individual to another, and also that these differences affect lower processing, as shown by differences found in auditory discrimination. Finally, a hearing deprivation also modifies the visual system, as shown by a reduction in the visual frequency discrimination. This last study suggests that normal development in one modality is required for the efficient development of the other modalities. Globally, the results shown in this thesis suggest that the auditory and visual systems have a distinct development, but are however linked and suggest the interdependence of the two systems.

The aim of the study was to examine central auditory processes compromised by age, age-related hearing loss, and the presentation of a distracting cafeteria noise using auditory event-related potentials (ERPs). In addition, the relation of ERPs to behavioral measures of discrimination was investigated. Three groups of subjects participated: young normal hearing, elderly subjects with normal hearing for their age, and elderly hearing-impaired subjects. Psychoacoustic frequency discrimination thresholds for a 1000-Hz pure tone were determined in quiet and in the presence of a contralateral cafeteria noise. To elicit ERPs, small frequency contrasts were presented with and without noise under unattended and attended conditions. In the attended condition, behavioral measures of d′ detectability and reaction times were also obtained. Noise affected all measures of behavioral frequency discrimination significantly. Except N1, all ERP components in the standard and difference waveforms decreased significantly in amplitude and increased in latency to the same degree in all three subject groups, arguing against a specific age-related sensitivity to the effects of contralateral background noise. For N1 amplitude, the effect of noise was different in the three subject groups, with a complex interaction of age, hearing loss, and attention. Behavioral frequency discrimination was not affected by age but deteriorated significantly in the elderly subjects with hearing loss. In the electrophysiological test, age-related changes occurred at various levels. The most prominent finding in the response to the standard stimuli was a sustained negativity (N2) following P2 in the young subjects that was absent in the elderly, possibly indicating a deficit in the inhibition of irrelevant information processing. In the attended difference waveform, significantly larger N2b and smaller P3b amplitudes and longer N2b and P3b latencies were observed in the elderly indicating different processing strategies. The pronounced age-related changes in the later cognitive components suggest that the discrimination of difficult contrasts, although behaviorally maintained, becomes more effortful in the elderly.

L’implant cochléaire devient une ressource importante pour contrer la surdité alors qu’il a été démontré qu’une privation auditive précoce ou tardive affecte le développement des systèmes auditif et visuel. Le but des études présentées dans cette thèse est d’évaluer l’impact développemental d’une privation auditive sur les systèmes auditif et visuel. En premier lieu, l’étude du développement chez une population entendante a montré que les systèmes auditif et visuel se développent à des rythmes distincts et qu’ils atteignent leur maturité respective à des âges différents. Ces conclusions suggèrent que les mécanismes qui sous-tendent ces deux systèmes sont différents et que leur développement respectif est indépendant. Aussi, tel qu’observé par une mesure comportementale et électrophysiologique, la discrimination fréquentielle auditive chez les personnes porteuses d’un implant cochléaire est altérée et corrélée aux performances de perception de la parole. Ces deux études suggèrent que suite à une privation auditive, le traitement auditif diffère d’une personne malentendante à une autre, et que ces différences touchent les processus de bas-niveaux, tel que suggéré par la disparité présente dans les performances de discrimination fréquentielle. La dernière étude observe qu’une privation auditive affecte aussi le développement de la modalité visuelle, tel qu’indiqué par une diminution des capacités de discrimination visuelle observée chez des malentendants. Cette indication appuie l’hypothèse qu’un développement normal de chacun des sens est requis pour un développement optimal des autres sens. Globalement, les résultats présentés dans cette thèse suggèrent que les systèmes auditif et visuel se développent de façon distincte, mais demeurent toutefois interreliés. En effet, une privation auditive affecte non seulement le développement des habiletés auditives, mais aussi celui des habiletés visuelles, suggérant une interdépendance entre les deux systèmes. / The cochlear implant is an important resource for deaf people, as it is known that an auditory deprivation alters the auditory and the visual systems. We aimed to study the impact of deafness on the development of the auditory and visual systems. First, the study of these systems in a hearing population has shown that both systems develop at different rates and reach adult-like levels at different ages. These conclusions suggest that the mechanisms underlying these treatments are different and that their developments are independent. Moreover, as shown with the behavioral and the electrophysiological study, auditory frequency discrimination in cochlear implant users is altered and correlated with the speech perception performance. These two studies suggest that following deafness, the auditory discrimination is different from one individual to another, and also that these differences affect lower processing, as shown by differences found in auditory discrimination. Finally, a hearing deprivation also modifies the visual system, as shown by a reduction in the visual frequency discrimination. This last study suggests that normal development in one modality is required for the efficient development of the other modalities. Globally, the results shown in this thesis suggest that the auditory and visual systems have a distinct development, but are however linked and suggest the interdependence of the two systems.