Audrey Bürki

What affects the presence versus absence of schwa and its duration: a corpus analysis of French connected speech.

This study presents an analysis of over 4000 tokens of words produced as variants with and without schwa in a French corpus of radio-broadcasted speech. In order to determine which of the many variables mentioned in the literature influence variant choice, 17 predictors were tested in the same analysis. Only five of these variables appeared to condition variant choice. The question of the processing stage, or locus, of this alternation process is also addressed in a comparison of the variables that predict variant choice with the variables that predict the acoustic duration of schwa in variants with schwa. Only two variables predicting variant choice also predict schwa duration. The limited overlap between the predictors for variant choice and for schwa duration, combined with the nature of these variables, suggest that the variants without schwa do not result from a phonetic process of reduction; that is, they are not the endpoint of gradient schwa shortening. Rather, these variants are generated early in the production process, either during phonological encoding or word-form retrieval. These results, based on naturally produced speech, provide a useful complement to on-line production experiments using artificial speech tasks.

ERP correlates of word production predictors in picture naming: a trial by trial multiple regression analysis from stimulus onset to response

A major effort in cognitive neuroscience of language is to define the temporal and spatial characteristics of the core cognitive processes involved in word production. One approach consists in studying the effects of linguistic and pre-linguistic variables in picture naming tasks. So far, studies have analyzed event-related potentials (ERPs) during word production by examining one or two variables with factorial designs. Here we extended this approach by investigating simultaneously the effects of multiple theoretical relevant predictors in a picture naming task. High density EEG was recorded on 31 participants during overt naming of 100 pictures. ERPs were extracted on a trial by trial basis from picture onset to 100 ms before the onset of articulation. Mixed-effects regression models were conducted to examine which variables affected production latencies and the duration of periods of stable electrophysiological patterns (topographic maps). Results revealed an effect of a pre-linguistic variable, visual complexity, on an early period of stable electric field at scalp, from 140 to 180 ms after picture presentation, a result consistent with the proposal that this time period is associated with visual object recognition processes. Three other variables, word Age of Acquisition, Name Agreement, and Image Agreement influenced response latencies and modulated ERPs from ~380 ms to the end of the analyzed period. These results demonstrate that a topographic analysis fitted into the single trial ERPs and covering the entire processing period allows one to associate the cost generated by psycholinguistic variables to the duration of specific stable electrophysiological processes and to pinpoint the precise time-course of multiple word production predictors at once.

Phonetic reduction versus phonological deletion of French schwa: Some methodological issues

Abstract A categorical phonological process of deletion is traditionally assumed to account for the alternation of schwa with zero in French. This process is assumed to result in two discrete outputs: forms with schwa (i.e., schwa variants) and forms without schwa (i.e., non-schwa variants). However, the two studies we present here suggest a more complex picture. In the first study, we investigate the phonetic variability of schwa in a large number of occurrences of schwa variants and find that schwa, like other segments in French, undergoes phonetic reduction. As a consequence, some tokens without schwa in connected speech may be the result of a process of gradual phonetic reduction rather than the result of a categorical process of alternation. In the second study, we examine the perception of schwa word tokens extracted from connected speech. We show that deciding whether a token was produced with or without the schwa is not always possible. Furthermore, listeners rely on other types of cues than acoustic ones in order to make their judgements (i.e., speech rate, word length and segmental context). These findings have important theoretical and methodological implications that must be taken into account in the empirical study of French schwa alternation.

Do speakers have access to a mental syllabary? ERP comparison of high frequency and novel syllable production.

The transformation of an abstract phonological code into articulation has been hypothesized to involve the retrieval of stored syllable-sized motor plans. Accordingly, gestural scores for frequently used syllables are retrieved from memory whereas gestural scores for novel and possibly low frequency syllables are assembled on-line. The present study was designed to test this hypothesis. Participants produced disyllabic pseudowords with high frequency, low frequency and non-existent (novel) initial syllables. Behavioral results revealed slower production latencies for novel than for high frequency syllables. Event-related potentials diverged in waveform amplitudes and global topographic patterns between high frequency and low frequency/novel syllables around 170 ms before the onset of articulation. These differences indicate the recruitment of different brain networks during the production of frequent and infrequent/novel syllables, in line with the hypothesis that speakers store syllabic-sized motor programs for frequent syllables and assemble these motor plans on-line for low frequency and novel syllables.

Lexical Representation of Schwa Words: Two Mackerels, but Only One Salami.

The present study investigated the lexical representations underlying the production of English schwa words. Two types of schwa words were compared: words with a schwa in poststress position (e.g., mackerel), whose schwa and reduced variants differ in a categorical way, and words with a schwa in prestress position (e.g., salami), whose variants differ in a noncategorical way. Participants named pseudohomophones and matched pseudowords corresponding to schwa and reduced variants of these words. Results revealed an advantage for pseudohomophones over matched pseudowords for both variants of poststress schwa words but only for schwa variants of prestress schwa words. As the pseudohomophone advantage is assumed to reflect the activation of a phonologically matching stored phonological representation, these results suggest that both variants of poststress schwa words are lexically represented while only schwa variants of prestress schwa words are. This result extends the proposal that words with two categorically distinct variants are stored in the production lexicon with 2 representations to another language and demonstrates that this 2-lexeme account does not generalize to pronunciation variants differing from one another in a noncategorical fashion. This finding challenges one of the widely shared assumption of generative models of word production: that content words have only 1 phonological representation. On the other hand, it provides further evidence in favor of another fundamental assumption of these models: that lexical representations are abstract sets of segments rather than fully detailed exemplars.

Producing and recognizing words with two pronunciation variants: Evidence from novel schwa words

This study examined the lexical representations and psycholinguistic mechanisms underlying the production and recognition of novel words with two pronunciation variants in French. Participants first learned novel schwa words (e.g., /ʃənyk/), which varied in their alternating status (i.e., whether these words were learned with one or two variants) and, for alternating words, in the frequency of their variants. They were then tested in picture-naming (free or induced) and recognition memory tasks (i.e., deciding whether spoken items were learned during the experiment or not). Results for free naming show an influence of variant frequency on responses, more frequent variants being produced more often. Moreover, our data show an effect of the alternating status of the novel words on naming latencies, with longer latencies for alternating than for nonalternating novel words. These induced naming results suggest that both variants are stored as lexical entries and compete during the lexeme selection process. Results for recognition show an effect of variant frequency on reaction times and no effect of variant type (i.e., schwa versus reduced variant). Taken together, our findings suggest that participants both comprehend and produce novel French schwa words using two lexical representations, one for each variant.

Sequential processing during noun phrase production.

This study examined whether the brain operations involved during the processing of successive words in multi word noun phrase production take place sequentially or simultaneously. German speakers named pictures while ignoring a written distractor superimposed on the picture (picture-word interference paradigm) using the definite determiner and corresponding German noun. The gender congruency and the phonological congruency (i.e., overlap in first phonemes) between target and distractor were manipulated. Naming responses and EEG were recorded. The behavioural performance replicated both the phonology and the gender congruency effects (i.e., shorter naming latencies for gender congruent than incongruent and for phonologically congruent than incongruent trials). The phonological and gender manipulations also influenced the EEG data. Crucially, the two effects occurred in different time windows and over different sets of electrodes. The phonological effect was observed substantially earlier than the gender congruency effect. This finding suggests that the processing of determiners and nouns during determiner noun phrase production occurs at least partly sequentially.

Tracking the time course of multi-word noun phrase production with ERPs or on when (and why) cat is faster than the big cat.

Words are rarely produced in isolation. Yet, our understanding of multi-word production, and especially its time course, is still rather poor. In this research, we use event-related potentials to examine the production of multi-word noun phrases in the context of overt picture naming. We track the processing costs associated with the production of these noun phrases as compared with the production of bare nouns, from picture onset to articulation. Behavioral results revealed longer naming latencies for French noun phrases with determiners and pre-nominal adjectives (D-A-N, the big cat) than for noun phrases with a determiner (D-N, the cat), or bare nouns (N, cat). The spatio-temporal analysis of the ERPs revealed differences in the duration of stable global electrophysiological patterns as a function of utterance format in two time windows, from ~190 to 300 ms after picture onset, and from ~530 ms after picture onset to 100 ms before articulation. These findings can be accommodated in the following model. During grammatical encoding (here from ~190 to 300 ms), the noun and adjective lemmas are accessed in parallel, followed by the selection of the gender-agreeing determiner. Phonological encoding (after ~530 ms) operates sequentially. As a consequence, the phonological encoding process is longer for longer utterances. In addition, when determiners are repeated across trials, their phonological encoding can be anticipated or primed, resulting in a shortened encoding process.

Word onset phonetic properties and motor artifacts in speech production EEG recordings

Electrophysiological research using verbal response paradigms faces the problem of muscle artifacts that occur during speech production or in the period preceding articulation. In this context, this paper has two related aims. The first is to show how the nature of the first phoneme influences the alignment of the ERPs. The second is to further characterize the EEG signal around the onset of articulation, both in temporal and frequency domains. Participants were asked to name aloud pictures of common objects. We applied microstate analyses and time-frequency transformations of ERPs locked to vocal onset to compare the EEG signal between voiced and unvoiced labial plosive word onset consonants. We found a delay of about 40 ms in the set of stable topographic patterns for /b/ relative to /p/ onset words. A similar shift was observed in the power increase of gamma oscillations (30-50 Hz), which had an earlier onset for /p/ trials (∼150 ms before vocal onset). This 40-ms shift is consistent with the length of the voiced proportion of the acoustic signal prior to the release of the closure in the vocal responses. These results demonstrate that phonetic features are an important parameter affecting response-locked ERPs, and hence that the onset of the acoustic energy may not be an optimal trigger for synchronizing the EEG activity to the response in vocal paradigms. The indexes explored in this study provide a step forward in the characterization of muscle-related artifacts in electrophysiological studies of speech and language production.

Differences in processing times for distractors and pictures modulate the influence of distractors in picture–word interference tasks

ABSTRACT In the picture–word interference paradigm, participants name pictures while ignoring a distractor word. When targets and distractors share phonemic and/or graphemic content, naming latencies are shorter than when there is no overlap between the two words. This study examines the hypothesis that the facilitation effect is modulated by differences in the time it takes participants to encode the picture name and process the distractor. Participants named pictures while ignoring distractors that either shared a phonological/orthographical syllable with the target word or were unrelated to that word. Response latencies during the naming of the distractors were collected and used as a measure of distractor processing time. The facilitation effect in picture naming was modulated by differences in response times between the picture and word naming tasks. This finding complements previous studies in showing that picture naming processes in the picture–word interference paradigm are influenced by the time course of distractor processing.