Ashley W. Harkrider

Temporal dynamics of sensorimotor integration in speech perception and production: independent component analysis of EEG data

Activity in anterior sensorimotor regions is found in speech production and some perception tasks. Yet, how sensorimotor integration supports these functions is unclear due to a lack of data examining the timing of activity from these regions. Beta (~20 Hz) and alpha (~10 Hz) spectral power within the EEG μ rhythm are considered indices of motor and somatosensory activity, respectively. In the current study, perception conditions required discrimination (same/different) of syllables pairs (/ba/ and /da/) in quiet and noisy conditions. Production conditions required covert and overt syllable productions and overt word production. Independent component analysis was performed on EEG data obtained during these conditions to (1) identify clusters of μ components common to all conditions and (2) examine real-time event-related spectral perturbations (ERSP) within alpha and beta bands. 17 and 15 out of 20 participants produced left and right μ-components, respectively, localized to precentral gyri. Discrimination conditions were characterized by significant (pFDR < 0.05) early alpha event-related synchronization (ERS) prior to and during stimulus presentation and later alpha event-related desynchronization (ERD) following stimulus offset. Beta ERD began early and gained strength across time. Differences were found between quiet and noisy discrimination conditions. Both overt syllable and word productions yielded similar alpha/beta ERD that began prior to production and was strongest during muscle activity. Findings during covert production were weaker than during overt production. One explanation for these findings is that μ-beta ERD indexes early predictive coding (e.g., internal modeling) and/or overt and covert attentional/motor processes. μ-alpha ERS may index inhibitory input to the premotor cortex from sensory regions prior to and during discrimination, while μ-alpha ERD may index sensory feedback during speech rehearsal and production.

Dynamic modulation of shared sensory and motor cortical rhythms mediates speech and non-speech discrimination performance

Oscillatory models of speech processing have proposed that rhythmic cortical oscillations in sensory and motor regions modulate speech sound processing from the bottom-up via phase reset at low frequencies (3–10 Hz) and from the top-down via the disinhibition of alpha/beta rhythms (8–30 Hz). To investigate how the proposed rhythms mediate perceptual performance, electroencephalographic (EEG) was recorded while participants passively listened to or actively identified speech and tone-sweeps in a two-force choice in noise discrimination task presented at high and low signal-to-noise ratios. EEG data were decomposed using independent component analysis and clustered across participants using principle component methods in EEGLAB. Left and right hemisphere sensorimotor and posterior temporal lobe clusters were identified. Alpha and beta suppression was associated with active tasks only in sensorimotor and temporal clusters. In posterior temporal clusters, increases in phase reset at low frequencies were driven by the quality of bottom-up acoustic information for speech and non-speech stimuli, whereas phase reset in sensorimotor clusters was associated with top-down active task demands. A comparison of correct discrimination trials to those identified at chance showed an earlier performance related effect for the left sensorimotor cluster relative to the left-temporal lobe cluster during the syllable discrimination task only. The right sensorimotor cluster was associated with performance related differences for tone–sweep stimuli only. Findings are consistent with internal model accounts suggesting that early efferent sensorimotor models transmitted along alpha and beta channels reflect a release from inhibition related to active attention to auditory discrimination. Results are discussed in the broader context of dynamic, oscillatory models of cognition proposing that top-down internally generated states interact with bottom-up sensory processing to enhance task performance.

Auditory cortical deactivation during speech production and following speech perception: an EEG investigation of the temporal dynamics of the auditory alpha rhythm

Sensorimotor integration (SMI) across the dorsal stream enables online monitoring of speech. Jenson et al. (2014) used independent component analysis (ICA) and event related spectral perturbation (ERSP) analysis of electroencephalography (EEG) data to describe anterior sensorimotor (e.g., premotor cortex, PMC) activity during speech perception and production. The purpose of the current study was to identify and temporally map neural activity from posterior (i.e., auditory) regions of the dorsal stream in the same tasks. Perception tasks required “active” discrimination of syllable pairs (/ba/ and /da/) in quiet and noisy conditions. Production conditions required overt production of syllable pairs and nouns. ICA performed on concatenated raw 68 channel EEG data from all tasks identified bilateral “auditory” alpha (α) components in 15 of 29 participants localized to pSTG (left) and pMTG (right). ERSP analyses were performed to reveal fluctuations in the spectral power of the α rhythm clusters across time. Production conditions were characterized by significant α event related synchronization (ERS; pFDR < 0.05) concurrent with EMG activity from speech production, consistent with speech-induced auditory inhibition. Discrimination conditions were also characterized by α ERS following stimulus offset. Auditory α ERS in all conditions temporally aligned with PMC activity reported in Jenson et al. (2014). These findings are indicative of speech-induced suppression of auditory regions, possibly via efference copy. The presence of the same pattern following stimulus offset in discrimination conditions suggests that sensorimotor contributions following speech perception reflect covert replay, and that covert replay provides one source of the motor activity previously observed in some speech perception tasks. To our knowledge, this is the first time that inhibition of auditory regions by speech has been observed in real-time with the ICA/ERSP technique.

Time-frequency analysis of the EEG mu rhythm as a measure of sensorimotor integration in the later stages of swallowing

OBJECTIVEnElectroencephalography (EEG) was used to map the temporal dynamics of sensorimotor integration relative to the strength and timing of muscular activity during swallowing.nnnMETHODSn64-channel EEG data and surface electromyographic (sEMG) data were recorded from 25 neurologically-healthy adults during swallowing and tongue-tapping. Events were demarcated so that sensorimotor activity primarily from the pharyngeal and esophageal phases of swallowing could be compared to activity resulting from tongue tapping.nnnRESULTSnIndependent component analysis identified bilateral clusters of sensorimotor mu components localized to the premotor and primary motor cortices as well as an infrahyoid myogenic cluster. Subsequent event-related spectral perturbations (ERSP) analyses showed event-related desynchronization (ERD) in the spectral power in the alpha (8-13Hz) and beta (15-25Hz) frequency bands of the mu clusters in both tasks. Mu ERD was stronger during swallowing when compared to tongue tapping (pFDR<.05) and the differences in sensorimotor processing between conditions was greater in the right hemisphere than the left, suggesting stronger right hemisphere lateralization for swallowing than tongue-tapping.nnnCONCLUSIONnMu activity was interpreted as representing a normal feed forward and feedback driven sensorimotor loop during the later stages of swallowing.nnnSIGNIFICANCEnResults support further use of this novel neuroimaging technique to concurrently map neural and muscle activity during swallowing in clinical populations using EEG.

EEG Mu (µ) rhythm spectra and oscillatory activity differentiate stuttering from non-stuttering adults

Abstract Stuttering is linked to sensorimotor deficits related to internal modeling mechanisms. This study compared spectral power and oscillatory activity of EEG mu (&mgr;) rhythms between persons who stutter (PWS) and controls in listening and auditory discrimination tasks. EEG data were analyzed from passive listening in noise and accurate (same/different) discrimination of tones or syllables in quiet and noisy backgrounds. Independent component analysis identified left and/or right &mgr; rhythms with characteristic alpha (&agr;) and beta (&bgr;) peaks localized to premotor/motor regions in 23 of 27 people who stutter (PWS) and 24 of 27 controls. PWS produced &mgr; spectra with reduced &bgr; amplitudes across conditions, suggesting reduced forward modeling capacity. Group time‐frequency differences were associated with noisy conditions only. PWS showed increased &mgr;‐&bgr; desynchronization when listening to noise and early in discrimination events, suggesting evidence of heightened motor activity that might be related to forward modeling deficits. PWS also showed reduced &mgr;‐&agr; synchronization in discrimination conditions, indicating reduced sensory gating. Together these findings indicate spectral and oscillatory analyses of &mgr; rhythms are sensitive to stuttering. More specifically, they can reveal stuttering‐related sensorimotor processing differences in listening and auditory discrimination that also may be influenced by basal ganglia deficits. HighlightsMu (&mgr;) rhythms identified in stuttering and matched control groups in auditory discrimination.Mu (&mgr;) rhythm spectra show reduced forward modeling capacity in stuttering group.Time‐frequency analyses show group differences in predictive coding strategies.

Speech perception, production, and the sensorimotor mu rhythm

The EEG mu (μ) rhythm is considered a measure of sensorimotor integration. This rhythm is commonly identified by co-occuring peaks at ~10Hz(alpha) and ~20 Hz (beta) across the sensorimotor cortex. Suppression of the power within peaks are thought to reflect somatosensory and motor aspects of processing respectively. Suppression of μ power (especially in the beta peak) has been found when performing, imagining or perceiving relevant action (e.g., while watching hand movements and oro-facial movements). μ suppression has also been found to visual speech perception, listening to speech in noise, and when mentally segmenting speech for auditory discrimination, suggesting that it is a sensitive measure of audio-motor integration in speech. The two main goals in this study are to bolster understanding of the timing and function of dorsal stream activity in speech perception by examining ERS/ERD patterns in quiet and noisy discrimination conditions and to provide initial evidence that, via the application of ICA / ERSP, the use of EEG can be extended effectively into speech production. 17 of 20 participants provided left and right p components that were common to perception and production tasks. The most probably source of these components was the premotor cortex (BA 6) with primary motor cortex (BA 4) and primary somatosensory (BA 2/3) cortex providing additional possible sources. Fewer (8 and 7 of 20) participants provided components with average equivalent dipoles emanating from BA 22 and BA 7, respectively, with alpha activity suggesting entrainment within the dorsal stream.

The Effects of Visual Distracter Complexity on Auditory Evoked P3b in Contact Sports Athletes

“Classic” P3b auditory oddball paradigms are insensitive to subtle deficits. An auditory oddball paradigm paired with visual distracters was used to compare football players with history of concussion, football players without history of concussion, and non-contact sport athletes. As hypothesized, increasing complexity of, and attention to, visual distracters reduced P3b amplitude. P3b amplitudes from non-contact athletes were larger than those from football players; however, players with and without a history of concussion were not significantly different. An auditory oddball paradigm with simple visual distracter improves sensitivity to cognitive deficits. Subconcussive impacts may contribute to brain damage frequently attributed to concussions.

Electrophysiological and behavioral measures of phonological processing of auditory nonsense V–CV–VCV stimuli

An event-related potential, the Phonological Mapping Negativity (PMN), has been reported to reflect recognition of phonological mismatches in speech stimuli. The purpose of the present study was to explore how the PMN response to the auditory nonsense syllable reflects phonological processing in isolation without the letter prime or lexical/semantic context. Sixty-four nonsense syllable stimuli were composed for each of three stimulus conditions: phonological match (PM), phonological mismatch with similar sound (PMMS), and phonological mismatch with different sound (PMMD), making a total of 192 stimuli. The PMN was measured from fourteen normal-hearing listeners. Electroencephalogram (EEG) activity was recorded while subjects were listening to the stimuli and responding behaviorally. Subjects were asked to determine what vowel-consonant-vowel (VCV) (e.g. /apa/) would be formed from the combination of the preceding vowel (V) (e.g. /a/) and consonant-vowel (CV) (e.g. /pa/), and press a correct or incorrect response button as soon as they decided whether the target VCV stimulus matched their expectation. In this way, along with the PMN, behavioral response accuracy and reaction times were obtained. The results were as follows: (1) PMN amplitude was not different by stimulus condition, (2) PMN amplitude was larger over frontal and central than posterior regions, but not different between the left versus right hemisphere, (3) PMN was detected in the absence of N400, and (4) behavioral responses were more accurate and faster in PMMD than PM and PMMS. Results indicate that the PMN can reflect phonological processing of auditory nonsense syllables in isolation. The scalp distribution of PMN is most dominant in the fronto-central regions without lateralization. Lastly, behavioral response accuracy and reaction times appear to be influenced by the extent of the task difficulty or processing demand rather than by the extent of phonological violation.

Sensorimotor activity measured via oscillations of EEG mu rhythms in speech and non-speech discrimination tasks with and without segmentation demands

&NA; Better understanding of the role of sensorimotor processing in speech and non‐speech segmentation can be achieved with more temporally precise measures. Twenty adults made same/different discriminations of speech and non‐speech stimuli pairs, with and without segmentation demands. Independent component analysis of 64‐channel EEG data revealed clear sensorimotor mu components, with characteristic alpha and beta peaks, localized to premotor regions in 70% of participants. Time‐frequency analyses of mu components from accurate trials showed that (1) segmentation tasks elicited greater event‐related synchronization immediately following offset of the first stimulus, suggestive of inhibitory activity; (2) strong late event‐related desynchronization in all conditions, suggesting that working memory/covert replay contributed substantially to sensorimotor activity in all conditions; (3) stronger beta desynchronization in speech versus non‐speech stimuli during stimulus presentation, suggesting stronger auditory‐motor transforms for speech versus non‐speech stimuli. Findings support the continued use of oscillatory approaches for helping understand segmentation and other cognitive tasks.

Trait related sensorimotor deficits in people who stutter: An EEG investigation of μ rhythm dynamics during spontaneous fluency

Stuttering is associated with compromised sensorimotor control (i.e., internal modeling) across the dorsal stream and oscillations of EEG mu (μ) rhythms have been proposed as reliable indices of anterior dorsal stream processing. The purpose of this study was to compare μ rhythm oscillatory activity between (PWS) and matched typically fluent speakers (TFS) during spontaneously fluent overt and covert speech production tasks. Independent component analysis identified bilateral μ components from 24/27 PWS and matched TFS that localized over premotor cortex. Time-frequency analysis of the left hemisphere μ clusters demonstrated significantly reduced μ-α and μ-β ERD (pCLUSTERu202f<u202f0.05) in PWS across the time course of overt and covert speech production, while no group differences were found in the right hemisphere in any condition. Results were interpreted through the framework of State Feedback Control. They suggest that weak forward modeling and evaluation of sensory feedback across the time course of speech production characterizes the trait related sensorimotor impairment in PWS. This weakness is proposed to represent an underlying sensorimotor instability that may predispose the speech of PWS to breakdown.