Cortico-Cerebellar Networks Drive Sensorimotor Learning in Speech

Abstract

The motor cortex and cerebellum are thought to be critical for learning and maintaining motor behaviours. Here we use tDCS to test the role of the motor cortex and cerebellum in sensorimotor learning in speech. During productions of 'head', 'bed', and 'dead', the first formant of the vowel sound was altered in real-time towards the first formant of the vowel sound in 'had', 'bad', and 'dad'. Compensatory changes in first and second formant production were used as a measure of motor adaptation. TDCS to either the motor cortex or the cerebellum improved sensorimotor learning in speech compared to sham stimulation. However, in the case of cerebellar tDCS, production changes were restricted to the source of the acoustical error (i.e. the first formant). Motor cortex tDCS drove production changes that offset errors in the first formant, but, unlike cerebellar tDCS, adaptive changes in the second formant also occurred. The results suggest that motor cortex and cerebellar tDCS have both shared and dissociable effects on motor adaptation. The study provides initial causal evidence in speech production that the motor cortex and the cerebellum support different aspects of sensorimotor learning. We propose that motor cortex tDCS drives sensorimotor learning towards previously learned patterns of movement, while cerebellar tDCS focuses sensorimotor learning on error correction.

Speech adaptation to palatal perturbation: Evidence for sensorimotor reorganization across the workspace

“…The present acoustic and kinematic findings build upon the prior result of Lametti et al [6] in demonstrating that talkers are capable of simultaneously adapting speech sounds across the articulatory workspace to a complex physical, multisensory perturbation.…”

“…The capacity for rapid, sensorydriven speech motor adaptation has been examined in numerous experimental studies involving real-time alterations of auditory feedback during speech production [1][2][3][4][5][6][7]. The vast majority of these studies have examined adaptation in very narrow contexts within any given experiment, e.g., one vowel within a small set of words [1][2][3], or a limited number of acoustically similar sentences [4][5][6]. In striking contrast to this prior work, a recent study has demonstrated that talkers are capable of reorganizing speech motor control across the entire vowel space following auditory feedback perturbations affecting multiple sounds during the production of variable sentences [7].…”

Robust Sensorimotor Learning during Variable Sentence-Level Speech

“…While this paradigm has been highly influential for models of speech motor control [5][6][7], a fundamental limitation of this work lies in its reliance on the alteration of a single speech property (e.g., one vowel or transition) within the repeated production of a handful of isolated words or acoustically similar sentences [21][22][23]. During real-world speech, a single speech property is not privileged over others; dozens of phonemes that span a talker's articulatory workspace are combined into complex, interacting, and overlapping motor and sensory patterns.…”

The perils of learning to move while speaking: One-sided interference between speech and visuomotor adaptation

“…Over several hundred utterances, participants adapt their formant productions to reduce the perceived auditory sensory prediction error (Purcell & Munhall, 2006). This form of sensorimotor adaptation is thought to rely on the same cerebellum-dependent implicit process observed in visuomotor adaptation (Houde & Nagarajan, 2011;Lametti, Smith, Freidin, & Watkins, 2017;Parrell, Agnew, Nagarajan, Houde, & Ivry, 2017). However, the extent to which sensorimotor adaptation in speech involves a more explicit process remains unclear.…”