Learning to recognize and produce foreign speech sounds can be challenging, particularly when only subtle differences distinguish these new sounds from phonemes in the native language. Functional neuroimaging evidence shows that the motor cortex is involved in speech production and in perceptual phonemic processing. This highlights the embodied nature of speech perception, predicting the potential benefits of sensorimotor-based training approaches to enhance the acquisition of foreign speech sounds. Hence, here we first review current findings on the motor contribution to not only native but also non-native phoneme perception. Available evidence has established that motor cortical activity especially shows up under non-optimal perceptual conditions, such as when native phonemes are degraded by noise or when listeners perceive non-native speech sounds. Drawing upon this evidence, we then review training paradigms that have been developed for learning foreign phonemes, with a special emphasis on those embedding manual gestures as cues to represent phonetic features of the to-be-learned speech sounds. By pointing to both strengths and caveats of available studies, this review allows us to delineate a clear framework and opens perspectives to optimize foreign phoneme learning, and ultimately support perception and production.

The present study aims to provide an outline of lexical networks between sounds and meanings in Taiwan Mandarin. Both the phonological and semantic relations are explored by a free word association task. Previous research has demonstrated a significant influence of phonology on Indo-European networks and suggested the influence of semantics on languages with lexicography such as Mandarin. With a new methodology in which word frequency, syllable type, syllable structure, tone structure, imageability, and parts of speech are carefully considered for the experimental stimuli, a total of 248 responses were collected from six Taiwan Mandarin native speakers. The results of lexical associations suggest that: 1) semantic relations show a stronger connection than phonological ones in Taiwan Mandarin networks; 2) rhymes present a stronger influence on associations than initial segments. The understanding of lexical organization in the human brain may contribute to further research on functions of associations and networks between human and artificial intelligence.

Embodied theories of cognition consider language as grounded in the sensorimotor system. Converging evidence shows that speech perception induces activations of sensorimotor brain areas that are involved in speech production. Notably, motor activity is elicited during both native and non-native phoneme perception, and it is somatotopically organized depending on the place of articulation of native phonemes. Specific motor activity is elicited depending on distinct articulatory features: listening to bilabial and dental consonants activates the cortical motor representations of the lips and the tongue, respectively. However, some studies have not replicated this precise somatotopic mapping within the motor cortex for native speech perception, while others have shown premotor recruitment only when speech sounds are degraded yet identifiable. Thus, the necessity and role of motor activation in processing both native and non-native, as well as clear and degraded, speech sounds remain uncertain. When speech in the native language is distorted by noise, or when sounds come from a foreign language, motor regions seem to support speech perception by retrieving articulatory features that are grounded in the speech production system. Given this motor contribution, the question arises of whether training that engages motor regions might enhance the learning and processing of non-native phonemes.
This thesis aims to explore sensorimotor processing in speech perception through an experimental study using functional magnetic resonance imaging (fMRI) and a review of foreign language learning paradigms with sensorimotor training. In the experimental study, we combined behavioral and fMRI measures and conducted Multivariate Pattern Analyses (MVPA) to investigate how sensorimotor regions are activated as a function of, and encode the phonetic features of native and foreign phonemes under optimal and degraded perceptual conditions. We show that neural activity for lip and tongue articulatory movements in the precentral gyrus predicts neural activation for bilabial and dental degraded native consonants, thus highlighting somatotopic coding of articulatory features in the motor cortex. Moreover, sensorimotor neural patterns associated with the perception of native and non-native phonemes reflect the phonetic similarity between speech sounds both within and between the two language repertoires. In the review article, we first outline current findings on speech processing in the context of embodied cognition, highlighting the functional contribution of the motor cortex to speech perception. We discuss the contribution of sensorimotor activity to foreign language learning, especially for phonemes, through gestural training that strengthens the embodiment of foreign articulatory features. Finally, we propose potential developments in training paradigms and directions for future neuroimaging studies to address existing gaps in the literature.
This thesis therefore contributes to ongoing discussions on motor resonance in native speech perception, especially under challenging conditions, as well as addresses gaps in understanding the motor contribution to non-native phoneme perception. Our fMRI study provides solid empirical evidence that the motor system, in conjunction with the auditory system, is fundamental to speech perception. We corroborate the sensorimotor nature of speech processing, both for native and non-native languages, thus opening pathways for advancements in foreign language learning. By offering an overview of sensorimotor training paradigms, together with neuroimaging evidence for central sensorimotor processes in speech perception, our research lays a foundation for future investigations exploiting the embodied nature of language processing.

Current theories and models of lexical organization assume that the stimulation of an association results in an activation spreading to the related concepts within mental networks. Several factors have also been suggested to affect those connections to meet different purposes of lexical access such as frequency, imageability, lexical effect, lexical categories, and phonological similarity. Word association tasks have been widely implemented to psychological research of mental lexicon and memory; through the relations between stimuli and responses, different levels of processing are able to be traced. However, most research related to Mandarin lexicon investigated the associated responses without concerning linguistic features in Mandarin as the basis. The present study therefore aims to provide an outline of the lexical organization in Taiwan Mandarin by free word associations. Topics to be explored involve 1) the tendency of lexical organization, and 2) the influences of linguistic features in Taiwan Mandarin lexicon.
With the new methodology conducted, in which the 21 possible onsets for disyllabic words and linguistic influences in Taiwan Mandarin are considered, total of 406 responses are collected from ten Taiwan Mandarin native speakers (age mean= 23.8 years old; SD= 1.9; 5 males and 5 females). The results of free word associations in the present study suggest the following: 1) a semantic tendency of lexical organization in Taiwan Mandarin; 2) the tendency of paradigmatic relation, semantic instead of phonological relation, rhyming relation, and the consistency of syntactic categories in nouns are presented during associations in Taiwan Mandarin lexicon. However, regarding limited literature and the small scale of the present study, further research on phonological organization in mental lexicon across languages is suggested. The understanding of lexical organization in human brains may contribute to the further research on the functions of associations and networks between human and artificial intelligence.