Auditory-Motor Learning during Speech Production in 9-11-Year-Old Children

BACKGROUND: Hearing ability is essential for normal speech development, however the precise mechanisms linking auditory input and the improvement of speaking ability remain poorly understood. Auditory feedback during speech production is believed to play a critical role by providing the nervous system with information about speech outcomes that is used to learn and subsequently fine-tune speech motor output. Surprisingly, few studies have directly investigated such auditory-motor learning in the speech production of typically developing children. METHODOLOGY/PRINCIPAL FINDINGS: In the present study, we manipulated auditory feedback during speech production in a group of 9-11-year old children, as well as in adults. Following a period of speech practice under conditions of altered auditory feedback, compensatory changes in speech production and perception were examined. Consistent with prior studies, the adults exhibited compensatory changes in both their speech motor output and their perceptual representations of speech sound categories. The children exhibited compensatory changes in the motor domain, with a change in speech output that was similar in magnitude to that of the adults, however the children showed no reliable compensatory effect on their perceptual representations. CONCLUSIONS: The results indicate that 9-11-year-old children, whose speech motor and perceptual abilities are still not fully developed, are nonetheless capable of auditory-feedback-based sensorimotor adaptation, supporting a role for such learning processes in speech motor development. Auditory feedback may play a more limited role, however, in the fine-tuning of children's perceptual representations of speech sound categories

Analogy making and the structure of implied volatility skew

An analogy based option pricing model is put forward. If option prices are determined in accordance with the analogy model, and the Black Scholes model is used to back-out implied volatility, then the implied volatility skew arises, which flattens as time to expiry increases. The analogy based stochastic volatility and the analogy based jump diffusion models are also put forward. The analogy based stochastic volatility model generates the skew even when there is no correlation between the stock price and volatility processes, whereas, the analogy based jump diffusion model does not require asymmetric jumps for generating the skew

Understanding speech motor control in the context of orofacial biomechanics

A series of experiments are described which explore the relationship between biomechanical properties and the control of jaw movement in speech. This relationship is documented using kinematic analyses in conjunction with a mathematical model of jaw motion and direct measures of jaw stiffness.In the first experiment, empirical and modeling studies were carried out to examine whether the nervous system compensates for naturally occurring forces acting on the jaw during speech. As subjects walk or run, loads to the jaw vary with the direction and magnitude of head acceleration. While these loads are large enough to produce a measurable effect on jaw kinematics, variation in jaw position during locomotion is shown to be substantially reduced when locomotion is combined with speech. This reduction in jaw motion is consistent with the idea that in speech, the control of jaw movement is adjusted to offset the effects of head acceleration. Results of simulation studies using a physiologically realistic model of the jaw provide further evidence that subjects compensate for the effects of self-generated loads by adjusting neural control signals.A second experiment explores the idea that a principle mechanical property of the jaw---its spring-like behavior, or stiffness---might influence patterns of kinematic variation in speech movements. A robotic device was used to deliver mechanical perturbations to the jaw in order to quantify stiffness in the mid-sagittal plane. The observed stiffness patterns were non-uniform, with higher stiffness in the protrusion-retraction direction. Consistent with the idea that kinematic patterns reflect directional asymmetries in stiffness, a detailed relationship between jaw kinematic variability and stiffness was observed---kinematic variability was consistently higher under conditions in which jaw stiffness was low. Modeling studies suggested that the pattern of jaw stiffness is significantly determined by jaw geometrical properties and muscle force generating abilities.A third experiment examines the extent to which subjects are able to alter the three-dimensional pattern of jaw stiffness in a task-dependent manner. Destabilizing loads were applied to the jaw in order to disrupt the ability of subjects to maintain a static jaw posture. Subjects adapted by increasing jaw stiffness in a manner that depended on the magnitude and, to a more limited extent, direction of the destabilizing load. The results support the idea that stiffness properties can be controlled in the jaw, and thus may play a role in regulating mechanical interactions in the orofacial system

Compensation for the gravitational force on the jaw during speech

External loads, such as those due to the orientation of body segments relative to gravity, affect the extent to which control signals result in the achievement of desired goals. The degree to which subjects adjust control signals to compensate for loads provides a measure of what the nervous system knows about forces affecting motion and gives an indication of the complexity of control signals needed for voluntary movement. In the present study, we have explored the hypothesis that subjects take no account of the orientation of the head relative to gravity when making jaw movements during speech. We used a simulation model of the jaw to predict the kinematic effect of using a single set of motor commands (which take no account of the relative direction of the gravitational force) to produce speech-like movements while the body was in three different orientations: upright, prone and supine. The simulations predict a systematic change in jaw pitch angle and horizontal translation resulting from the change in body orientation. Empirical results for five subjects tested under the same conditions as those explored in the simulations are for the most part consistent with the pattern predicted by the model. This suggests that in the case of jaw movements during speech, control signals are not adjusted to account for changes in head and body orientation relative to gravity

Feel what you say: an auditory effect on somatosensory perception.

In the present study, we demonstrate an audiotactile effect in which amplitude modulation of auditory feedback during voiced speech induces a throbbing sensation over the lip and laryngeal regions. Control tasks coupled with the examination of speech acoustic parameters allow us to rule out the possibility that the effect may have been due to cognitive factors or motor compensatory effects. We interpret the effect as reflecting the tight interplay between auditory and tactile modalities during vocal production