The human auditory perception system is much more noise-robust than any state-of theart automatic speech recognition (ASR) system. It is expected that the noise-robustness of speech feature vectors may be improved by employing more human auditory functions in the feature extraction procedure. Forward masking is a phenomenon of human auditory perception, that a weaker sound is masked by the preceding stronger masker. In this work, two human auditory mechanisms, synaptic adaptation and temporal integration are implemented by filter functions and incorporated to model forward masking into MFCC feature extraction. A filter optimization algorithm is proposed to optimize the filter parameters. The performance of the proposed method is evaluated on Aurora 3 corpus, and the procedure of training/testing follows the standard setting provided by the Aurora 3 task. The synaptic adaptation filter achieves relative improvements of 16.6% over the baseline. The temporal integration and modified temporal integration filter achieve relative improvements of 21.6% and 22.5% respectively. The combination of synaptic adaptation with each of temporal integration filters results in further improvements of 26.3% and 25.5%. Applying the filter optimization improves the synaptic adaptation filter and two temporal integration filters, results in the 18.4%, 25.2%, 22.6% improvements respectively. The performance of the combined-filters models are also improved, the relative improvement are 26.9% and 26.3%.

Estudos sobre a orientação da atenção que utilizam o procedimento de Posner têm demonstrado dois efeitos: uma facilitação inicial no processamento do estímulo que aparece no lugar para onde dirigiu-se a atenção e subsequentemente um prejuízo no processamento deste estímulo, neste local. Em um trabalho anterior não evidenciamos o efeito facilitador da orientação da atenção em uma tarefa de tempo de reação simples. Levantamos algumas hipóteses para explicar este efeito oposto. Para testarmos tais hipóteses realizamos 6 experimentos. Nos dois primeiros, examinamos em que medida a presença de tentativas de pegada influenciava a expressão do efeito negativo do estímulo precedente. No terceiro examinamos a possibilidade do estímulo precedente ser capaz de reduzir a responsividade. No quarto equalizamos a intensidade efetiva do estímulo alvo nas duas posições em que ele podia ser apresentado (mesma e oposta). No quinto e no sexto avaliamos a evolução temporal do efeito negativo do estímulo precedente, na tentativa de determinar até que ponto ela teria alguma relação com a evolução temporal esperada para um mascaramento anterógrado. O sexto experimento poderia adicionalmente fornecer alguma pista de uma contribuição de uma inibição de retorno, neste caso precoce, para o efeito negativo encontrado. Em todos esses casos a influência atencional do estímulo precedente presumivelmente continuaria a ocorrer, mas seria suplantada pela influência contrária coexistente. Em conjunto, nossos resultados sugerem que o efeito negativo do estímulo precedente em uma tarefa de tempo de reação simples, se deve a uma interferência com o processamento do estímulo alvo, caracterizando uma inibição de natureza sensorial. / Studies about attention orienting that use Posner?s procedure have demonstrated two effects: an initial facilitation of responsivit when the target stimulus appears in the same location as the prime stimulus and a subsequent inhibition of this responsvity. In a previous work we could not find the early facilitatory effect of attention orienting in a simple reaction time task. The hypotheses that we raised to explain this unexpected finding were tested in six experiments. In the first two ones, we examined whether the presence of catch trials influenced the expression of the negative effect of the prime stimulus. In the third experiment we examined the possibility that the prime stimulus reduced responsivity. In the fourth experiment we equalized the intensity of the target stimulus in the two locations where it could be presented (same and opposite). In the fifth and in sixth experiments we evaluated the time course of the negative effect of the prime stimulus, as an attempt to verify whether it would be compatible with a forward masking process. The sixth experiment could additionally give some clue about a contribution of inhibition of return, in this case precocious, to the found negative effect. In all these cases the attentional influence of the prime stimulus would presumably continue to occur, but would be supplanted by the contrary negative of this stimulus influence. Overall, our results suggest that the negative effect of the prime stimulus in a simple reaction time task is due to an interference with the processing of the target stimulus, characterizing a kind of sensory inhibition.

Estudos sobre a orientação da atenção que utilizam o procedimento de Posner têm demonstrado dois efeitos: uma facilitação inicial no processamento do estímulo que aparece no lugar para onde dirigiu-se a atenção e subsequentemente um prejuízo no processamento deste estímulo, neste local. Em um trabalho anterior não evidenciamos o efeito facilitador da orientação da atenção em uma tarefa de tempo de reação simples. Levantamos algumas hipóteses para explicar este efeito oposto. Para testarmos tais hipóteses realizamos 6 experimentos. Nos dois primeiros, examinamos em que medida a presença de tentativas de pegada influenciava a expressão do efeito negativo do estímulo precedente. No terceiro examinamos a possibilidade do estímulo precedente ser capaz de reduzir a responsividade. No quarto equalizamos a intensidade efetiva do estímulo alvo nas duas posições em que ele podia ser apresentado (mesma e oposta). No quinto e no sexto avaliamos a evolução temporal do efeito negativo do estímulo precedente, na tentativa de determinar até que ponto ela teria alguma relação com a evolução temporal esperada para um mascaramento anterógrado. O sexto experimento poderia adicionalmente fornecer alguma pista de uma contribuição de uma inibição de retorno, neste caso precoce, para o efeito negativo encontrado. Em todos esses casos a influência atencional do estímulo precedente presumivelmente continuaria a ocorrer, mas seria suplantada pela influência contrária coexistente. Em conjunto, nossos resultados sugerem que o efeito negativo do estímulo precedente em uma tarefa de tempo de reação simples, se deve a uma interferência com o processamento do estímulo alvo, caracterizando uma inibição de natureza sensorial. / Studies about attention orienting that use Posner?s procedure have demonstrated two effects: an initial facilitation of responsivit when the target stimulus appears in the same location as the prime stimulus and a subsequent inhibition of this responsvity. In a previous work we could not find the early facilitatory effect of attention orienting in a simple reaction time task. The hypotheses that we raised to explain this unexpected finding were tested in six experiments. In the first two ones, we examined whether the presence of catch trials influenced the expression of the negative effect of the prime stimulus. In the third experiment we examined the possibility that the prime stimulus reduced responsivity. In the fourth experiment we equalized the intensity of the target stimulus in the two locations where it could be presented (same and opposite). In the fifth and in sixth experiments we evaluated the time course of the negative effect of the prime stimulus, as an attempt to verify whether it would be compatible with a forward masking process. The sixth experiment could additionally give some clue about a contribution of inhibition of return, in this case precocious, to the found negative effect. In all these cases the attentional influence of the prime stimulus would presumably continue to occur, but would be supplanted by the contrary negative of this stimulus influence. Overall, our results suggest that the negative effect of the prime stimulus in a simple reaction time task is due to an interference with the processing of the target stimulus, characterizing a kind of sensory inhibition.

<p>Humans are able to hear and detect small changes in sound across a wide dynamic range despite limited dynamic ranges of individual auditory nerve fibers. One mechanism that may adjust the dynamic range is the medial olivocochlear reflex (MOCR), a bilateral sound-activated system which decreases amplification of sound by the outer hair cells in the cochlea. Much of the previous physiological MOCR research has used long broadband noise elicitors. In behavioral measures of gain reduction, a fairly short elicitor has been found to be maximally effective for an on-frequency, tonal elicitor. However, the effect of the duration of broadband noise elicitors on behavioral tasks is unknown. Additionally, MOCR effects measured using otoacoustic emissions (OAEs), have not consistently shown a positive correlation with behavioral gain reduction tasks. This finding seems counterintuitive if both measurements share a common generation mechanism. The current study measured the effects of ipsilateral broadband noise elicitor duration on psychoacoustic gain reduction (Chapter 2) and transient-evoked OAEs (TEOAEs) (Chapter 3) estimated from a forward-masking paradigm. Changes in the TEOAE were measured in terms of magnitude and phase. When phase was accounted for in the TEOAEs, the time constants were approximately equal to the psychoacoustic time constants, and were relatively short (~80 ms). When only changes in TEOAE magnitude were measured, and phase was omitted, the average time constants were longer (~172-ms). Overall, the psychoacoustic and physiological data were consistent with the timecourse of gain reduction by the MOCR. However, when the magnitudes from these data were directly compared in a linear mixed-effects model (Chapter 4), no positive predictive relationship was found, and in some cases there was a significant negative association between the physiological and psychoacoustic measures of gain reduction as a function of elicitor duration. The multitude of factors involved in this relationship are discussed, as are the implications of dynamic range adjustment in everyday listening conditions (noisy backgrounds) in both normal and hearing impaired listeners (Chapter 5).</p>

The recovery from prior stimulation of the compound action potential (CAP) was measured using a forward masking stimulus paradigm in four normal-hearing, human subjects. The CAP was recorded using a wick electrode placed on the tympanic membrane. The effects of a 4000-Hz, 97-dB SPL conditioning stimulus on CAP amplitude in response to a 4000-Hz probe were measured as a function of conditioner–probe interval for three probe levels. The normalized probe response amplitude was completely recovered to the control values at an average conditioner–probe interval of 1359 ms, similar to that observed in chinchilla (Relkin, E.M., Doucet, J.R., Sterns, A., 1995. Recovery of the compound action potential following prior stimulation: evidence for a slow component that reflects recovery of low spontaneous-rate auditory neurons, Hear. Res. 83, 183–189). The present results are interpreted as a consequence of the slow recovery of low spontaneous-rate (SR), high threshold neurons from prior stimulation (Relkin, E.M., Doucet, J.R., 1991. Recovery from prior stimulation. I: Relationship to spontaneous firing rates of primary auditory neurons. Hear. Res. 55, 215–222) and may provide indirect physiological evidence for the existence of a class of low-SR auditory neurons in humans.

S'ha investigat molt tant els mecanismes neuronals bàsics de l'audició com l'organització psicològica de la percepció de la parla. Tanmateix, en ambdós temes n'hi ha una relativa escassetat en quant a modelització. Aquí describim dos treballs de modelització. Un d'ells proposa un nou mecanisme de millora de selectivitat de freqüències que explica resultats de experiments neurofisiològics investigant manifestacions de forward masking y sobretot auditory streaming en l'escorça auditiva principal (A1). El mecanisme funciona en una xarxa feed-forward amb depressió sináptica entre el tàlem y l'escorça, però mostrem que és robust a l'introducció d'una organització realista del circuit de A1, que per la seva banda explica cantitat de dades neurofisiològics. L'altre treball descriu un mecanisme candidat d'explicar la trobada en estudis psicofísics de diferències en la percepció de paraules entre bilinguës primerencs y simultànis. Simulant tasques de decisió lèxica y discriminació de fonemes, fortifiquem l'hipòtesi de que persones sovint exposades a variacions dialectals de paraules poden guardar aquestes en el seu lèxic, sense alterar representacions fonemàtiques . / Though much experimental research exists on both basic neural mechanisms of hearing and the psychological organization of language perception, there is a relative paucity of modelling work on these subjects. Here we describe two modelling efforts. One proposes a novel mechanism of frequency selectivity improvement that accounts for results of neurophysiological experiments investigating manifestations of forward masking and above all auditory streaming in the primary auditory cortex (A1). The mechanism works in a feed-forward network with depressing thalamocortical synapses, but is further showed to be robust to a realistic organization of the neural circuitry in A1, which accounts for a wealth of neurophysiological data. The other effort describes a candidate mechanism for explaining differences in word/non-word perception between early and simultaneous bilinguals found in psychophysical studies. By simulating lexical decision and phoneme discrimination tasks in an attractor neural network model, we strengthen the hypothesis that people often exposed to dialectal word variations can store these in their lexicons, without altering their phoneme representations. / Se ha investigado mucho tanto los mecanismos neuronales básicos de la audición como la organización psicológica de la percepción del habla. Sin embargo, en ambos temas hay una relativa escasez en cuanto a modelización. Aquí describimos dos trabajos de modelización. Uno propone un nuevo mecanismo de mejora de selectividad de frecuencias que explica resultados de experimentos neurofisiológicos investigando manifestaciones de forward masking y sobre todo auditory streaming en la corteza auditiva principal (A1). El mecanismo funciona en una red feed-forward con depresión sináptica entre el tálamo y la corteza, pero mostramos que es robusto a la introducción de una organización realista del circuito de A1, que a su vez explica cantidad de datos neurofisiológicos. El otro trabajo describe un mecanismo candidato de explicar el hallazgo en estudios psicofísicos de diferencias en la percepción de palabras entre bilinguës tempranos y simultáneos. Simulando tareas de decisión léxica y discriminación de fonemas, fortalecemos la hipótesis de que personas expuestas a menudo a variaciones dialectales de palabras pueden guardar éstas en su léxico, sin alterar representaciones fonémicas.