Marina Laganaro

Speaking while doing something else is a daily situation speakers adapt to spontaneously. Dual-task experiments show such adaptation, but how speech is modified remains unclear. This study investigates how concurrent visuo-cognitive-motor tasks modulate speech, focusing on spectro-temporal vowel reduction, within-word vowel-to-vowel coarticulation, and acoustic variability during repeated production of a fixed sentence. Twenty-seven young adult participants performed a speech task alone at the beginning and end of the experiment and concurrently with two non-verbal tasks varying in attentional demand. Speakers in the multitasking condition produced more spectrally centralized and shorter vowels, increased coarticulation, and reduced variability across repetitions. These effects on speech were not modulated by the attentional demand of the concurrent non-verbal task. A repetition effect was found on vowel centralization, which was higher in the last single condition than in the first, but this did not override the dual-task effect. These findings expand upon traditional views of dual-task interference as inherently detrimental or beneficial and question the contribution of attention to speech motor control.

All speakers experience the Tip-of-the-Tongue (ToT) phenomenon when trying to retrieve specific words. ToTs have been explained by a temporary reduction of lexical-phonological transmission or inhibition of competitors in the mental lexicon. An alternative way to approach ToTs is to consider the state of the lexical-semantic network of the speaker. Here we investigate how the organisation of the lexical-semantic network of the speaker differs between accessible words and ToTs. 40 neurotypical young adults performed a picture-naming task with low frequency items to induce ToT states, followed by a continuous free word association task. Accessible words were characterised by richer lexical-semantic networks with more superordinate associates, whereas ToT states were marked by more heterogeneous networks dominated by coordinate associates. The organisation of the lexical-semantic network differs depending on the ability to access the word at a given time at the individual level, providing further hints to understand ToT states.

The study of speech planning/programming may require analysing Event-Related Potentials (ERPs) during articulation. However, ERPs identified during speech production also contain brain signals associated with auditory feedback. Because these processes are both time-locked to the vocal onset, existing algorithms for signal separation have difficulties distinguishing one from the other. Here, we investigated the use of the multi-channel Wiener filter (MWF) to remove the ERP signal related to auditory processing from the ERP signal related to speech production. In a first step, participants were asked to overtly produce mono- or disyllabic pseudowords. In a second step, they had to listen to the recording of their own productions. We used the ERP signal associated with hearing one’s own production (referred to as listening ERPs) to estimate and filter out the auditory part of the production ERP. We investigated three versions of the ERPs during speech articulation: (1) the original production ERPs, (2) the ERPs filtered through the MWF, and (3) subtraction ERPs obtained by subtracting the listening ERPs from the original ERPs. Firstly, we conducted a microstate analysis comparing all three versions of the ERPs. Secondly, we conducted separate microstate analyses comparing mono- versus disyllabic conditions on each of the three versions. The results indicate that the subtraction method alters topography consistency and may remove relevant signal from the ERPs. The filtered ERP produced similar results to the original production ERP and thus, it may be unnecessary to remove auditory feedback or other overlapping signal if time-locked to the production onset.

Numerous factors interfere with the successful transmission of messages during verbal conversations leading speakers to use different speech modes, i.e. specific prototypes of speech with unique phonatory and articulatory characteristics. Despite their omnipresence in verbal exchanges, no theoretical model in the speech production literature has provided a mechanistical account of the encoding processes underpinning speech in different modes. The present study thus aims at proposing how speech modes are planned/programmed relative to standard speech by using the high temporal resolution provided by electroencephalography (EEG). Participants uttered pseudowords in three different conditions - standard speech, speaking louder than usual and faking an English accent in French - during a delayed production task. Event related potential (ERP) of standard speech was contrasted separately with the two non-standard speech modes. Results indicate that speaking by adopting speech modes varying in articulatory and phonatory properties entails increased neural activity of the brain networks that are already involved in standard speech production. Especially, electrophysiological signatures of loud speech and faking an accent were both associated to differences in ERP responses relative to standard speech in a time period covering the last 200 ms preceding the vocal onset. This observation was coherent across waveform analysis (with more extended differences in time and space for faking an accent), topographical dissimilarity analysis and microstates analysis (mode extended for loud speech). The findings highlight that different speech modes are encoded in the last 200 ms preceding their vocal production, possibly in a mode-specific way which will need further investigation.

Loud speech and whispered speech are two distinct speech modes that are part of daily verbal exchanges, but that involve a different employment of the speech apparatus. However, a clear account of whether and when the motor speech (or phonetic) encoding of these speech modes differs from standard speech has not been provided yet. Here, we addressed this question using Electroencephalography (EEG)/Event related potential (ERP) approaches during a delayed production task to contrast the production of speech sequences (pseudowords) when speaking normally or under a specific speech mode: loud speech in experiment 1 and whispered speech in experiment 2. Behavioral results demonstrated that non-standard speech modes entail a behavioral encoding cost in terms of production latency. Standard speech and speech modes’ ERPs were characterized by the same sequence of microstate maps, suggesting that the same brain processes are involved to produce speech under a specific speech mode. Only loud speech entailed electrophysiological modulations relative to standard speech in terms of waveform amplitudes but also temporal distribution and strength of neural recruitment of the same sequence of microstates during a large time window (from approximatively − 220 ms to − 100 ms) preceding the vocal onset. Alternatively, the electrophysiological activity of whispered speech was similar in nature to standard speech. On the whole, speech modes and standard speech seem to be encoded through the same brain processes but the degree of adjustments required seem to vary subsequently across speech modes.

Purpose: The production of speech-like sequences composed of varying syllables has been reported to achieve higher syllable rates than the production of repeated syllables (commonly designed as sequential motion rate [SMR] and alternating motion rate [AMR] tasks, respectively). The faster rate for SMR relative to AMR sequences is explained by different interpretative hypotheses, which remain empirically unexplored. In the present study, we aimed to investigate whether the high syllable rates of SMR sequences are due to the specific sequences used in most studies that involve front-to-back articulatory movements. Method: Syllable rates of SMR sequences composed of different articulatory trajectories (i.e., labial–alveolar–velar [/pateko/], alveolar–velar–labial [/tekopa/], and velar–labial–alveolar [/kopate/]) were compared with those of the AMR sequences /papapa/, /tetete/, and /kokoko/ in 20 participants. Results: The results show higher syllable rates for each of the three SMR sequences as compared to AMR, suggesting that the trajectory of the articulatory movements in the sequential sequences is not the key to achieving higher syllable rates. Conclusion: The syllable rate advantage for SMR over AMR sequences is not explained by the articulatory trajectories included in the former task, indicating that the front-to-back movements generally included in SMR sequences (i.e., /pataka/) are not decisive in achieving a higher syllable rate.