Slide Slam G1
Motor planning of speech and of uncommonly produced non-speech gestures
Monica Lancheros1, Marina Laganaro1; 1Faculty of Psychology and Educational Science, University of Geneva
The relationship between speech and other types of oromotor behaviors is a matter of debate in the literature. Some authors propose a specialized motor control system for speech (Ziegler et al., 2003) whereas some others suggest a general motor system shared for speech and other related motor tasks (Ballard et al., 2003). In a previous study, we investigated whether the motor planning of high and low frequency syllables activated the same neurophysiological networks involved in planning the motor codes of commonly produced non-speech sequences (Lancheros et al., 2020). Results indicated recruitment of the same neural networks but they were differently involved, especially in the motor planning of high frequency speech items relative to commonly produced non-speech gestures; infrequent syllables were found to be somehow intermediate between those two types of stimuli. In the present study, we aim to investigate the neural correlates of rarely produced non-speech gestures by means of high density electroencephalographic (EEG) evoked response potentials (ERPs). Uncommon non-speech gestures are issued from a pilot study in which participants were asked to rate at what frequency they have heard/produced a bunch of sounded orofacial movements presented in short video clips. The less common non-speech gestures were chosen (n=18) and they were carefully matched, in terms of acoustic and somatosensory targets, to high and low frequency syllables. The three types of stimuli were presented to participants in a delayed production task, where speakers prepare an utterance, but produce it overtly after a short delay. This type of task allows targeting the “latest” production stages, where the linguistic message is transformed into the corresponding articulated speech. Preliminary results on 10 participants show significantly longer reaction times for uncommon non-speech gestures as compared to high frequency syllables, whereas no differences are found between the production of uncommon non-speech gestures and low frequency syllables. As concerning the ERP results, they reveal the same global electrophysiological patterns across conditions on the stimulus locked ERPs. Regarding the latest stages before articulation in response-locked ERPs, significant differences in the distribution of the same microstates are found between uncommon non-speech gestures and both high and low frequency syllables in a time-window extending from -50 to -275 ms relative to the vocal onset. Those results are consistent with previous findings, suggesting that motor planning of uncommonly produced non-speech gestures recruit the same brain networks of high and low frequency syllables, but those networks are differently involved. What remains surprising though is that the mentioned differences in response-locked ERPs are present in a standard delayed production task, in which neither behavioral nor neural differences are expected during pre-articulatory processes. In fact, since participants are given the time to retrieve/prepare the motor codes of each stimuli during the delay, they are expected to launch the previously retrieved/prepared speech and non-speech motor plans in a similar way once the response cue is presented. Those results need to be compared to a delayed production task combined with an articulatory suppression task, for which we are currently collecting the data.