Keywords: speech production; model; fMRI; Broca’s area; premotor cortex; motor cortex; speech acquisition; sensorimotor learning; neural transmission delays This paper describes a neural model of speech acquisition and production that accounts for a wide range of acoustic, kinematic, and neuroimaging data concerning the control of speech movements. The model is a neural network whose components correspond to regions of the cerebral cortex and cerebellum, including premotor, motor, auditory, and somatosensory cortical areas. Computer simulations of the model verify its ability to account for compensation to lip and jaw perturbations during speech. Specific anatomical locations of the model’s components are estimated, and these estimates are used to simulate fMRI experiments of simple syllable production. 1 1

The influence of a native language on learning new speech sounds in adulthood is addressed using a network model in which speech categories are attractors implemented through interactive activation and Hebbian learning. The network has a representation layer that receives topographic projections from an input layer and has reciprocal excitatory connections with deeper layers. When applied to an experiment in which Japanese adults were trained to distinguish the English /r/–/l / contrast (McCandliss, Fiez, Protopapas, Conway, & McClelland, 2002), the model can account for many aspects of the experimental results, such as the time course and outcome of the learning, how it varies as a function of feedback, the relative efficacy of adaptive and initially easy training stimuli versus nonadaptive and difficult stimuli, and the development of a discrimination peak at the acquired category boundary. The model is also able to capture some aspects of the individual differences in learning.

Linguistic experience alters an individual’s perception of speech. We here provide evidence of the effects of language experience at the neural level from two magnetoencephalography (MEG) studies that compare adult American and Japanese listeners ’ phonetic processing. The experimental stimuli were American English /ra / and /la / syllables, phonemic in English but not in Japanese. In Experiment 1, the control stimuli were /ba / and /wa / syllables, phonemic in both languages; in Experiment 2, they were non-speech replicas of /ra / and /la/. The behavioral and neuromagnetic results showed that Japanese listeners were less sensitive to the phonemic /r–l / difference than American listeners. Furthermore, processing non-native speech sounds recruited significantly greater brain resources in both hemispheres and required a significantly longer period of brain activation in two regions, the superior temporal area and the inferior parietal area. The control stimuli showed no significant differences except that the duration effect in the superior temporal cortex also applied to the non-speech replicas. We argue that early exposure to a particular language produces a bneural commitmentQ to the acoustic properties of that language and that this neural commitment interferes with foreign language processing, making it less efficient.

Abstract not found

This dissertation investigates the phenomenon of language-specificity in the auditory perception of Chinese tones. Chinese and American English (AE) listeners participated in a series of perception experiments, which involved short ISIs (300ms in Experiment 1 and 100ms elsewhere) and an AX discrimination (limited set in Experiments 2 and 3, speeded response in Experiments BJ, RG and YT) or AX degreeof-difference rating (Experiment 4) task. All experiments used natural speech monosyllabic tone stimuli, except Experiment 2, which used sinewave simulations of Putonghua (Beijing Mandarin) tones. AE listeners showed psychoacoustic listening in all experiments, paying much attention to onset and offset pitch. Chinese listeners showed language-specific patterns in all experiments to various degrees. The most robust language-specific effects of Putonghua were found in Experiments 1, 3 and 4, where the T214 (as well as T35) neutralization rule shortened the perceptual distance between T35 and T214 (or that between T55 and T35) for Chinese listeners. Cross-dialectal as well as age differences were observed among Chinese listeners in Experiments BJ, RG and YT