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. / Responses of coincidence-detecting neurons are a direct function of the temporal structure of their input patterns. Quantitative studies of coincidence-detection provide insight into how neural processing of temporal information contributes to psychophysical performance. This study explored in detail the response properties of model coincidence-detection cells that receive inputs from auditory-nerve (AN) fibers. It also focused on the role of these model cells in coding of complex sounds related to psychophysical tasks for which temporal cues are believed to be important. Performance of model cells was evaluated quantitatively for different model parameters, including the width of the coincidence window, the number of input AN fibers, the characteristic frequencies (CFs) of the input AN fibers, and mixed strengths of the inputs. Results suggest that model cells with low CFs are very sensitive to the phase relationship of the input AN responses. The response properties of the model cells were also compared with results of physiological studies, and the coincidence-detection model predicts several response properties that were previously believed to be difficult to explain. Models for psychophysical detection and discrimination were designed based on population responses of model coincidence cells. Quantitative predictions of masked detection suggest that the most sensitive model cells for detection are the cells whose input AN responses are out of phase when a tone is added to the noise. The temporal structure in AN responses changes with signal-to-noise ratio and does not change as the overall level changes; thus, this model predicts psychophysical performance better than energy-based models under conditions in which the overall level of the stimulus varies randomly from trial to trial. The comparison of the coincidence-detection model and models based on other cues (e.g. envelope detector and channel theory) and implications for the theory of complex sound processing are also discussed. / 2031-01-01

The application of the label music to complex sound requires structure. Musical or rhythmic structure can be thought of as being due to the interaction of two theoretically distinct structures of phrase and metre. Perception of both metrical and phrase structure is dependent not only on the physical structure of the acoustic presentation but also upon cognitive structure being imposed on the auditory sensations. Early work in the psychology of music focused on establishing the perceptual cues that determine the parsing of music in time. These perceptual determinants can be categorized on the basis of the theoretical components of music: melody, harmony, rhythm, and timbre. With the exception of accent strength based on stability judgments of tones or chords (i.e., structural accenting), phenomenal accents have been assumed by some theorists to be equally-salient, additive, and categorical. The assumption of equal accent strength not only has been applied to different phenomenal accents within a theoretical component category but also between categories. Three series of experiments were conducted to test the assumption of equal weight and additivity of rhythmic cues. In the first series, a harmonic and a temporal accent were pitted against each other in such a way as to form different rhythm patterns. As well, two harmonic conditions which varied in the frequency of chord presentations (i.e., the compositerhythm) but not the frequency of chord changes (i.e., the harmonic-rhythm) were presented. Musicians and nonmusicians were requested to report perceived rhythm patterns in an attempt to determine the relative salience of the harmonic and temporal accents. In addition, a behavioural measure of the perceived metre was taken. Results indicated that the location of chord changes was the main determinant of subjects' rhythmic perceptions and the perceived onset of a measure. As well, although subjects primarily inferred different metres based on the composite-rhythm, an interaction of metrical and rhythmic choices was found indicating that perception of rhythm patterns and inference of metrical structure may not always be independent. In the second series of experiments, the contribution of harmonic-temporal and harmonic-structural features to the perception of rhythm patterns was investigated by pitting a harmonic and a temporal accent against each other in such a way as to form 5 possible rhythm patterns. Across the experiments, the chord progressions employed were varied, as was the timing of chord onsets (i.e., the composite-rhythm) and changes (i.e., the harmonic-rhythm). In all experiments, musicians and nonmusicians were requested to report perceived rhythm patterns in an attempt to determine the relative salience of the various accents. Results indicated that changes in the composite-and harmonic-rhythm led to a predictable change in an inferred metrical structure, and that all diatonic chord progressions lead to similar patterns of responses in which coincidences of harmonic, temporal, and inferred metrical accents were perceptually salient events. When a nondiatonic chord progression was employed however, there was neither evidence of an inferred metre, nor of responses on the basis of accent coincidence. Overall, musicians were found to primarily report rhythm patterns defined by the location of harmonic accents, while nonmusicians reported rhythm patterns defined by an inferred metrical structure. In the third series of experiments, the relative contribution of cues for metre inference was determined. In many theories of metre inference, the cues which serve as markers for major metrical accent locations are the basis from which one infers or determines a metre. However, phrase and metrical structure often support one another with phrase boundaries coinciding with metrically important locations. Thus, it becomes difficult to determine which cues, if any, are used exclusively, or predominantly as the basis for metre inference. Three experiments were conducted in which different time-spans defined by harmonic, melodic, and temporal accents, and their coincidences were systematically pitted against one another. Musicians and nonmusicians were requested to identify the metre of the stimuli as belonging to a category of either a triple (e.g., 6/8 or 3/4 time), or a duple metre (e.g., 2/4 or 4/4 time). It was found that musicians use harmonic information much more often and reliably than do nonmusicians who also use the temporal accent to define a metrical structure. Nevertheless, across the experiments, when a harmonic accent was present, subjects used that accent to define the metre. Furthermore, the coincidence of melodic accents was used more often than a temporal accent to determine a metrical structure. Together the three series of experiments highlight the significant role of harmonic accents in the perception of rhythm patterns in music. / Thesis / Doctor of Philosophy (PhD)

No description available.

The auditory system is able to recognize auditory objects and is thought to form predictive models of them even though the acoustic information arriving at our ears is often imperfect, intermixed, or distorted. We investigated implicit regularity extraction for acoustically intact versus disrupted six-tone sound patterns via event-related potentials (ERPs). In an exact-repetition condition, identical patterns were repeated; in two distorted-repetition conditions, one randomly chosen segment in each sound pattern was replaced either by white noise or by a wrong pitch. In a roving-standard paradigm, sound patterns were repeated 1–12 times (standards) in a row before a new pattern (deviant) occurred. The participants were not informed about the roving rule and had to detect rarely occurring loudness changes. Behavioral detectability of pattern changes was assessed in a subsequent behavioral task. Pattern changes (standard vs. deviant) elicited mismatch negativity (MMN) and P3a, and were behaviorally detected above the chance level in all conditions, suggesting that the auditory system extracts regularities despite distortions in the acoustic input. However, MMN and P3a amplitude were decreased by distortions. At the level of MMN, both types of distortions caused similar impairments, suggesting that auditory regularity extraction is largely determined by the stimulus statistics of matching information. At the level of P3a, wrong-pitch distortions caused larger decreases than white-noise distortions. Wrong-pitch distortions likely prevented the engagement of restoration mechanisms and the segregation of disrupted from true pattern segments, causing stronger informational interference with the relevant pattern information

L’objectif de cette thèse a été de développer des outils d’exploration des modifications perceptuelles lors de l’écoute de sons complexes dans la schizophrénie et de confronter les résultats de ces outils à des données neurophysiologiques. Le premier résultat de notre thèse est d’avoir confirmé dans la modalité auditive des modifications de l’organisation perceptuelle lors de l’écoute de sons complexes. En effet, nous avons montré, chez les patients souffrant de schizophrénie comparativement aux témoins, d’une part une difficulté de catégorisation des sons environnementaux de type son d’impact, et d’autre part, une modification de la perception de la familiarité et de la bizarrerie pour des sons environnementaux et abstraits, indiquant une modification d’organisation des données de l’audition dans une forme univoque et consensuelle.Le deuxième résultat de notre thèse est d’avoir confirmé, par une méthode d’induction perceptuelle consistant à présenter des stimuli plus ou moins envahissants, la présence d’un sentiment d’envahissement perceptuel plus important chez les patients souffrants de schizophrénie comparativement aux témoins. Cet envahissement perceptuel était corrélé significativement avec une mesure neurophysiologique du filtrage sensoriel par potentiels évoqués dans le paradigme des doubles clics audio (diminution d’amplitude de la composante P50 au deuxième stimulus comparativement au premier stimulus). Nous avons également traduit et validé en langue française un auto-questionnaire appelé Sensory Gating Inventory (SGI) permettant de compléter l’évaluation psychophysiologique des modifications perceptuelles reliées aux anomalies du filtrage sensoriel. / The aim of this PhD was to develop tools for analyzing perceptual modifications induced by complex sounds in schizophrenia and to relate these changes to neurophysiological data. The first result of our work enabled to confirm that complex sounds modify the auditory perceptual organization. Indeed, we first showed a deficit of categorization of environmental sounds (impact sounds) in patients with schizophrenia compared with controls, and secondly a difference in the perception of familiarity and strangeness for environmental and abstract sounds, indicating a modification of data organization of hearing in a unique and consensual form.The second result of our work revealed, by a perceptual induction method, the presence of a larger perceptual sense of inundation in patients suffering from schizophrenia compared with controls when submitted to more or less invasive stimuli. This perceptual inundation was significantly correlated with a neurophysiological measurement of sensory gating with evoked responses in the paradigm of double audio clicks (decrease in amplitude of the P50 component after the second stimulus as compared to the first stimulus). We have also translated a self-administered questionnaire called “Sensory Gating Inventory” (SGI) to French and validated it in order to complete the psychophysiological assessment of perceptual changes related to abnormal sensory gating.