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Abstract
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.
Highlights
Human communication relies heavily on the functional integrity of the auditory system
Pertaining to Hypothesis 1 Temporal α Cluster Characteristics In line with the hypothesis that independent component analysis (ICA) would identify bilateral α components localized to posterior superior temporal gyri (pSTG), 15/29 participants generated components with less than 20% residual variance (RV) contributing to both the left and right temporal α clusters
event related spectral perturbation (ERSP) Analysis in Production (SylP, WorP) The second hypothesis was that ERSP analysis of auditory α clusters would reveal α event related synchronization (ERS) in time periods coinciding with overt production
Summary
Human communication relies heavily on the functional integrity of the auditory system. Auditory cortical regions reside bilaterally in the temporal lobes, extending posteriorly along the superior temporal gyri (STG) to include primary and association regions These regions allow humans to sense sounds and are tuned to speech, providing spectro-temporal analysis of complex acoustic speech signals (Specht, 2014). During continuous error-free unperturbed speech production, internally based predictions match the reafferent feedback, minimizing the need for corrective feedback This accurate matching is thought to have a subtractive (i.e., canceling) effect, producing a net attenuation of activity in auditory regions, which is paramount to distinguishing our own speech from that of others (Blakemore et al, 2000; Wolpert and Flanagan, 2001). This proposal is supported by evidence of lowered auditory thresholds to self-produced vs. externally produced sound (Reznik et al, 2014)
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