Many people exposed to sinewave analogues of speech first report hearing them as electronic glissando and, later, when they switch into a dspeech modeT, hearing them as syllables. This perceptual switch modifies their discrimination abilities, enhancing perception of differences that cross phonemic boundaries while diminishing perception of differences within phonemic categories. Using high-density evoked potentials and fMRI in a discrimination paradigm, we studied the changes in brain activity that are related to this change in perception. With ERPs, we observed that phonemic coding is faster than acoustic coding: The electrophysiological mismatch response (MMR) occurred earlier for a phonemic change than for an equivalent acoustic change. The MMR topography was also more asymmetric for a phonemic change than for an acoustic change. In fMRI, activations were also significantly asymmetric, favoring the left hemisphere in both perception modes. Furthermore, switching to the speech mode significantly enhanced activation in the posterior parts of the left superior gyrus and sulcus relative to the non-speech mode. When responses to a change of stimulus were studied, a cluster of voxels in the supramarginal gyrus was activated significantly more by a phonemic change than by an acoustic change. These results demonstrate that phoneme perception in adults relies on a specific and highly efficient left-hemispheric network, which can be activated in top-down fashion when processing ambiguous speech/non-speech stimuli.

Newly born infants are able to finely discriminate almost all human speech contrasts and their phonemic category boundaries are initially identical, even for phonemes outside their target language. A connectionist model is described which accounts for this ability. The approach taken has been to develop a model of innately guided learning in which an artificial neural network (ANN) is stored in a "genome" which encodes its architecture and learning rules. The space of possible ANNs is searched with a genetic algorithm for networks that can learn to discriminate human speech sounds. These networks perform equally well having been trained on speech spectra from any human language so far tested (English, Cantonese, Swahili, Farsi, Czech, Hindi, Hungarian, Korean, Polish, Russian, Slovak, Spanish, Ukranian and Urdu). Training the feature detectors requires exposure to just one minute of speech in any of these languages. Categorisation of speech sounds based on the network representations showed the hallmarks of categorical perception, as found in human infants and adults.

& Investigating the degree of similarity between infants ’ and adults ’ representation of speech is critical to our understanding of infants ’ ability to acquire language. Phoneme perception plays a crucial role in language processing, and numerous behavioral studies have demonstrated similar capacities in infants and adults, but are these subserved by the same neural substrates or networks? In this article, we review event-related potential (ERP) results obtained in infants during phoneme discrimination tasks and compare them to results from the adult literature. The striking similarities observed both in behavior and ERPs between initial and mature stages suggest a continuity in processing and neural structure. We argue that infants have access at the beginning of life to phonemic representations, which are modified without training or implicit instruction, but

Mapping from acoustic signals to lexical representations is a complex process mediated by a number of different levels of representation. This paper reviews properties of the phonetic and phonological levels, and hypotheses about how category structure is represented at each of these levels, and evaluates these in light of relevant electrophysiological studies of phonetics and phonology. The paper examines evidence for two alternative views of how infant phonetic representations develop into adult representations, a structure-changing view and a structure-adding view, and suggests that each may be better suited to different kinds of phonetic categories. Electrophysiological results are beginning to provide information about phonological representations, but less is known about how the more abstract representations at this level could be coded in the brain.

One of the central findings of speech perception is that identical acoustic signals can be perceived as different speech sounds depending on adjacent speech context. Although these phonetic context effects are ubiquitous in speech perception, their neural mechanisms remain largely unknown. The present work presents a review of recent data suggesting that spectral content of speech mediates phonetic contex effects and argues that these effects are likely to be governed by general auditory processes. A descriptive framework known as spectral contrast is presented as a means of interpreting these findings. Finally, and most centrally, four behavioral exavioral2 that begin to delineate the level of the auditory system at which interactions among stimulus components occur are described. Two of theseexe2II-5P2 investigate the influence of diotic versus dichotic presentation upon two phoneticcontex effects. Results indicate thatcontex effects remain even whencontex is presented to the ear contralateral to that of the target syllable. The other two exC4)CW2EexC4) the time course of phoneticcontex effects by manipulating the silent interval between contex and target syllables. These studies reveal that phonetic context effects persist for hundreds of milliseconds. Results are interpreted in terms of auditory mechanism with particular attention to the putative link between auditory enhancement and phonetic context effects.

This paper is a progress report on our work on speech perception using brain imaging techniques. We review our goals, methods, and two experimental paradigms we have used to study classic categorical perception effects, like the one illustrated in Figure 1. This graph illustrates one subject's identification of stimuli from a synthesized /d/--/t/ continuum.

Human newborns discriminate languages from different rhythmic classes, fail to discriminate languages from the same rhythmic class, and fail to discriminate languages when the utterances are played backwards. Recent evidence showing that cotton-top tamarins discriminate Dutch from Japanese, but not when utterances are played backwards, is compatible with the hypothesis that rhythm discrimination is based on a general perceptual mechanism inherited from a primate ancestor. The present study further explores the rhythm hypothesis for language discrimination by testing languages from the same and different rhythmic class. We find that tamarins discriminate Polish from Japanese (different rhythmic classes), fail to discriminate English and Dutch (same rhythmic class), and fail to discriminate backwards utterances from different and same rhythmic classes. These results provide further evidence that language discrimination in tamarins is facilitated by rhythmic differences between languages, and suggest that, in humans, this mechanism is unlikely to have evolved specifically for language. Processing a spoken language requires perceptual mechanisms that operate on the incoming signal and extract information relevant for understanding the linguistic content of the utterance. Human infants begin the language-learning process with sensitivities to many

Language is the crowning achievement of the human species, and it is something that all normal humans can do. The average man is neither a Shakespeare nor a Caravaggio, but he is capable of fluent speech, even if he cannot paint at all. In fact, the average speaker produces approximately 150 words per minute, each word chosen from somewhere between 20,000 and 40,000 alternatives, at error rates below 0.1%. The average child is already well on her way toward that remarkable level of performance by 5 years of age, with a vocabulary of more than 6000 words and productive control over almost every aspect of sound and grammar in her language. Given the magnitude of this achievement, and the speed with which we attain it, some theorists have

An overwhelming majority of speech perception research has focused entirely on the end product of the perceptual process. Perhaps no other phenomenon in cognitive science is as overstudied with these “endpoint ” techniques as the categorical perception of consonants. Recent advances in eye tracking methodologies have allowed us to now look at the intermediate stages of processing in several domains. In this paper we present two studies examining the time course of categorical perception in adults. We demonstrate that, although categorization seems to be present throughout the time-course of categorical perception, it is not immediately discrete. Accompanying simulations suggest that categorical perception may only be a single temporal facet of a more complex, continuously evolving process. Categorical perception has been pervasive in explaining diverse areas of cognition such as speech perception, color perception, music perception, nonhuman speech perception. Most importantly it has been invoked in explaining infants ’ speech perception abilities. Given the results presented here, it seems appropriate to expand any study of categorical perception beyond simply the temporal endpoints to the entire time course of infant perception. However, the inadequacy of current infant methodologies to provide identification data

Recently, speech researchers have begun to examine the formation of speech sound (phonetic) categories and to analyze the internal structure of the consequent categories. One of the most prominent products of this subfield has been the Perceptual Magnet Effect (PME) and the attendant Native Language Magnet (NLM) theory of Kuhl (1991, 2000). In the present paper, a critical review of the evidence for NLM is offered. Because of concerns about the nature of the stimuli, possible confounds inherent in the empirical procedures and failed replications, it is concluded that there is little positive evidence supporting NLM. However, the goal of uncovering the structures of phonetic categories and mechanisms responsible for those structures remains central to an understanding of language acquisition and speech perception more generally. Data from several empirical paradigms investigating the formation and structure of complex auditory categories are beginning to form a coherent picture of phonetic category acquisition.