Pitch representations in the auditory nerve : two concurrent complex tones

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2008.Includes bibliographical references (p. 39-43).Pitch differences between concurrent sounds are important cues used in auditory scene analysis and also play a major role in music perception. To investigate the neural codes underlying these perceptual abilities, we recorded from single fibers in the cat auditory nerve in response to two concurrent harmonic complex tones with missing fundamentals and equal-amplitude harmonics. We investigated the efficacy of rate-place and interspike-interval codes to represent both pitches of the two tones, which had fundamental frequency (FO) ratios of 15/14 or 11/9. We relied on the principle of scaling invariance in cochlear mechanics to infer the spatiotemporal response patterns to a given stimulus from a series of measurements made in a single fiber as a function of FO. Templates created by a peripheral auditory model were used to estimate the FOs of double complex tones from the inferred distribution of firing rate along the tonotopic axis. This rate-place representation was accurate for FOs above about 900 Hz. Surprisingly, rate-based FO estimates were accurate even when the two-tone mixture contained no resolved harmonics, so long as some harmonics were resolved prior to mixing. We also extended methods used previously for single complex tones to estimate the FOs of concurrent complex tones from interspike-interval distributions pooled over the tonotopic axis. The interval-based representation was accurate for FOs below about 900 Hz, where the two-tone mixture contained no resolved harmonics. Together, the rate-place and interval-based representations allow accurate pitch perception for concurrent sounds over the entire range of human voice and cat vocalizations.by Erik Larsen.S.M

Importance of spike timing in touch: an analogy with hearing?

Touch is often conceived as a spatial sense akin to vision. However, touch also involves the transduction and processing of signals that vary rapidly over time, inviting comparisons with hearing. In both sensory systems, first order afferents produce spiking responses that are temporally precise and the timing of their responses carries stimulus information. The precision and informativeness of spike timing in the two systems invites the possibility that both implement similar mechanisms to extract behaviorally relevant information from these precisely timed responses. Here, we explore the putative roles of spike timing in touch and hearing and discuss common mechanisms that may be involved in processing temporal spiking patterns

Neural representations of pitch : role of peripheral frequency selectivity

Thesis (Ph. D.)--Harvard-MIT Division of Health Sciences and Technology, 2006.Includes bibliographical references (p. 129-140).Investigating the neural mechanisms underlying the perception of the pitch of harmonic complex tones is of great importance for many reasons. Changes in pitch convey melody in music, and the superposition of different pitches is the basis for harmony. Pitch has an important role in speech, where it carries prosodic features and information about speaker identity. Pitch plays a major role in auditory scene analysis: differences in pitch are a major cue for sound source segregation, while frequency components that share a common fundamental frequency (FO) tend to be grouped into a single auditory object. In psychophysics, a positive correlation is commonly observed between the estimated "resolvability" of individual harmonics of complex tones, assumed to depend primarily on the frequency selectivity of the cochlea, and the strength of the corresponding pitch percepts. In this study, possible neural codes for the pitch of harmonic complex tones were investigated in the auditory nerve of anesthetized cats, with particular focus on their dependence on cochlear frequency selectivity, which was measured directly using both complex tones and band-reject noise. A "rate-place" representation of pitch, based on cues to peripherally-resolved harmonics in profiles of average discharge rate along tonotopically-arranged neurons, was compared to a "temporal" representation, based on periodicity cues in the distributions of interspike intervals of the entire auditory nerve.(cont.) Although both representations were viable in the range of FOs of cat vocalizations, neither was entirely satisfactory in accounting for psychophysical data. The rate-place representation degraded rapidly with increasing stimulus level and could not account for the upper limit of the perception of the pitch of missing-F0 in humans, while the interspike-interval representation could not predict the correlation between psychophysical pitch salience and peripheral harmonic resolvability. Therefore, we tested an alternative, "spatio-temporal" representation of pitch, where cues to the resolved harmonics arise from the spatial pattern in the phase of the basilar membrane motion. The spatio-temporal representation was relatively stable with level and was consistent with an upper limit for the pitch of missing-F0, thus becoming the strongest candidate to explain several major human pitch perception phenomena.by Leonardo Cedolin.Ph.D

Disordered Eating Behaviors and Sexual Harassment in Italian Male and Female University Students

The aim of this study is to describe sexual harassment among Italian university students and analyze the relationship between harassment and disordered eating behaviors. An observational survey was conducted among university students at Trieste University (Italy) in spring 2014. Students answered an anonymous self-administered questionnaire about sexual harassment, including three domains\u2014sexual harassment, unwanted comments on physical appearance, cyber-harassment\u2014and disordered eating behaviors. The global sexual harassment index was computed with three levels: Level 0, no harassment; Level 1, harassment in at least one of the three domains; and Level 2, harassment in two or three domains. Disordered eating behaviors were classified by at least one of the following: (a) eating without being able to stop or vomiting at least once or twice a month, (b) using laxatives or diuretics at least once or twice a week, (c) monitoring weight every day, and (d) dieting at least very often. The sample included 759 students (347 men and 412 women; 18-29 years old). Experiencing sexual harassment was related to eating disorder symptoms for both genders with a regular gradient: the higher the harassment score, the more frequent the disordered eating behavior symptoms, even after adjusting for age and previous sexual violence. The association was stronger for males than females. Sexual harassment and disordered eating behaviors have long been considered mainly a female problem. Men are not exempt from these problems and in some cases may be more affected than women. The topics should be assessed in men and women

Neuromagnetic Evidence for Early Auditory Restoration of Fundamental Pitch

Background: Understanding the time course of how listeners reconstruct a missing fundamental component in an auditory stimulus remains elusive. We report MEG evidence that the missing fundamental component of a complex auditory stimulus is recovered in auditory cortex within 100 ms post stimulus onset. Methodology: Two outside tones of four-tone complex stimuli were held constant (1200 Hz and 2400 Hz), while two inside tones were systematically modulated (between 1300 Hz and 2300 Hz), such that the restored fundamental (also knows as ‘‘virtual pitch’’) changed from 100 Hz to 600 Hz. Constructing the auditory stimuli in this manner controls for a number of spectral properties known to modulate the neuromagnetic signal. The tone complex stimuli only diverged on the value of the missing fundamental component. Principal Findings: We compared the M100 latencies of these tone complexes to the M100 latencies elicited by their respective pure tone (spectral pitch) counterparts. The M100 latencies for the tone complexes matched their pure sinusoid counterparts, while also replicating the M100 temporal latency response curve found in previous studies. Conclusions: Our findings suggest that listeners are reconstructing the inferred pitch by roughly 100 ms after stimulus onset and are consistent with previous electrophysiological research suggesting that the inferential pitch is perceived i

Across-Channel Timing Differences as a Potential Code for the Frequency of Pure Tones

When a pure tone or low-numbered harmonic is presented to a listener, the resulting travelling wave in the cochlea slows down at the portion of the basilar membrane (BM) tuned to the input frequency due to the filtering properties of the BM. This slowing is reflected in the phase of the response of neurons across the auditory nerve (AN) array. It has been suggested that the auditory system exploits these across-channel timing differences to encode the pitch of both pure tones and resolved harmonics in complex tones. Here, we report a quantitative analysis of previously published data on the response of guinea pig AN fibres, of a range of characteristic frequencies, to pure tones of different frequencies and levels. We conclude that although the use of across-channel timing cues provides an a priori attractive and plausible means of encoding pitch, many of the most obvious metrics for using that cue produce pitch estimates that are strongly influenced by the overall level and therefore are unlikely to provide a straightforward means for encoding the pitch of pure tones

Analisi dell'efficacia di un'attivita terapeutica specifica in contrazione eccentrica del quadricipite femorale. Recupero funzionale in pazienti artrosici in seguito ad intervento di protesi totale di ginocchio(PTG)

Presupposti: L'intervento di artroprotesi totale di ginocchio (PTG) è considerato la soluzione elettiva nei pazienti artosici. Dalla letteratura, tuttavia, emerge come la permanente debolezza del Quadricipite femorale (QF) in seguito ad intervento di PTG precluda il completo recupero funzionale di tali pazienti. Obiettivi: Questo studio sperimentale ha voluto verificare i cambiamenti in termini di performance funzionale tra due gruppi di pazienti (sperimentale e di controllo) sottoposti ad intervento di PTG. In seguito a quest’ultimo, al gruppo di controllo (GC) è stato somministrato un protocollo di trattamento standard, mentre al gruppo sperimentale (GS) è stata somministrata in aggiunta al protocollo standard una singola attività terapeutica specifica in contrazione eccentrica per il QF. Disegno dello studio: È stato condotto uno studio longitudinale randomizzato controllato a singolo cieco. Luogo e durata: Lo studio è stato condotto dal 01 Marzo 2016 al 30 Luglio 2016 presso l'Unità Operativa MFR dell’Ospedale Civile di Vittorio Veneto. Pazienti: Trentasette pazienti hanno preso parte allo studio: 19 hanno costituito il gruppo sperimentale (GS) e 18 il gruppo di controllo (GC). Intervento: I pazienti sono stati assegnati casualmente al GS o al GC. Ai pazienti di entrambi i gruppi è stato somministrato il protocollo di trattamento standard utilizzato nella struttura ospitante; al gruppo sperimentale è stata somministrata in aggiunta un’attività terapeutica specifica in contrazione eccentrica del QF. Misurazioni: Gli outcome primari erano funzionali e sono stati ottenuti attraverso Timed Up and Go (TUG), Stair Climb Test (SCT) e 40m Fast-paced Walk Test (40m), scelti in base alle indicazioni dell’OARSI. Gli outcome secondari sono stati il Range of Motion (ROM) in flessione ed estensione del ginocchio. La raccolta dati è avvenuta in due momenti: al momento della dimissione (T0) e a 30 giorni dalla dimissione (T1). L’outcome terziario è stato individuato nell’utilizzo di bastoni canadesi durante il cammino al momento T1. Gli outcome sono stati valutati da un esaminatore cieco. Risultati: Per l’outcome primario al tempo T0 non si sono avuti miglioramenti statisticamente significativi nelle tre prove funzionali. Al tempo T1, tuttavia, il t-test mostra un p-value statisticamente significativo, rispettivamente per TUG p-value<0.001, per 40m p-value<0.001 e per SCT p-value=0.002. Per l’outcome secondario al tempo T1 risulta un miglioramento significativo per il ROM in flessione con un p-value=0.02 secondo il test esatto di Fisher, mentre il ROM in estensione non mostra risultati statisticamente significativi. Per l’outcome terziario nel GS risulta 3 una diminuzione dell'utilizzo di entrambi i bastoni al tempo T1 rispetto al GC; infatti, per quanto riguarda il GS, il 47% utilizza un solo bastone, il 37% due bastoni e il 16% nessun bastone, mentre nel GC, l'83% utilizza due bastoni e il 17% un solo bastone. Conclusioni: I pazienti che hanno aggiunto al trattamento standard un’attività specifica per il QF in contrazione eccentrica hanno avuto migliori risultati funzionali e hanno inoltre riportato un maggiore recupero del ROM in flessione. Malgrado i limiti dello studio condotto, i risultati si dimostrano di notevole interesse per la pratica clinica riabilitativa