A speech envelope landmark for syllable encoding in human superior temporal gyrus.

The most salient acoustic features in speech are the modulations in its intensity, captured by the amplitude envelope. Perceptually, the envelope is necessary for speech comprehension. Yet, the neural computations that represent the envelope and their linguistic implications are heavily debated. We used high-density intracranial recordings, while participants listened to speech, to determine how the envelope is represented in human speech cortical areas on the superior temporal gyrus (STG). We found that a well-defined zone in middle STG detects acoustic onset edges (local maxima in the envelope rate of change). Acoustic analyses demonstrated that timing of acoustic onset edges cues syllabic nucleus onsets, while their slope cues syllabic stress. Synthesized amplitude-modulated tone stimuli showed that steeper slopes elicited greater responses, confirming cortical encoding of amplitude change, not absolute amplitude. Overall, STG encoding of the timing and magnitude of acoustic onset edges underlies the perception of speech temporal structure

Behavioral, computational, and neuroimaging studies of acquired apraxia of speech

A critical examination of speech motor control depends on an in-depth understanding of network connectivity associated with Brodmann areas 44 and 45 and surrounding cortices. Damage to these areas has been associated with two conditions-the speech motor programming disorder apraxia of speech (AOS) and the linguistic/grammatical disorder of Broca's aphasia. Here we focus on AOS, which is most commonly associated with damage to posterior Broca's area (BA) and adjacent cortex. We provide an overview of our own studies into the nature of AOS, including behavioral and neuroimaging methods, to explore components of the speech motor network that are associated with normal and disordered speech motor programming in AOS. Behavioral, neuroimaging, and computational modeling studies are indicating that AOS is associated with impairment in learning feedforward models and/or implementing feedback mechanisms and with the functional contribution of BA6. While functional connectivity methods are not yet routinely applied to the study of AOS, we highlight the need for focusing on the functional impact of localized lesions throughout the speech network, as well as larger scale comparative studies to distinguish the unique behavioral and neurological signature of AOS. By coupling these methods with neural network models, we have a powerful set of tools to improve our understanding of the neural mechanisms that underlie AOS, and speech production generally

Some acoustic and articulatory correlates of phrasal stress in Spanish

All spoken languages show rhythmic patterns. Recent work with a number of different languages (English, Japanese, Mandarin Chinese, and French) suggests that metrically (hierarchically) assigned stress levels of the utterance show strong correlations with the amount of jaw displacement, and corresponding F1 values. This paper examines some articulatory and acoustic correlates of Spanish rhythm; specifically, we ask if there is a correlation between phrasal stress values metrically assigned to each syllable and acoustic/articulatory values. We used video recordings of three Salvadoran Spanish speakers to measure maximum jaw displacement, mean F0, mean intensity, mean duration, and mid-vowel F1 for each vowel in two Spanish sentences. The results show strong correlations between stress and duration, and between stress and F1, but weak correlations between stress and both mean vowel intensity and maximum jaw displacement. We also found weak correlations between jaw displacement and both mean vowel intensity and F1

Measuring perceptual centers using the phase correction response

The perceptual center (P-center) is fundamental to the timing of heterogeneous event sequences, including music and speech. Unfortunately, there is currently no comprehensive and reliable model of P-centers in acoustic events, so P-centers must instead be measured empirically. This study reviews existing measurement methods and evaluates two methods in detail—the rhythm adjustment method and a new method based on the phase correction response (PCR) in a synchronous tapping task. The two methods yielded consistent P-center estimates and showed no evidence of P-center context dependence. The PCR method appears promising because it is accurate and efficient and does not require explicit perceptual judgments. As a secondary result, the magnitude of the PCR is shown to vary systematically with the onset complexity of speech sounds,which presumably reflects the perceived clarity of a sound’s P-center

Hearing the Moment: Measures and Models of the Perceptual Centre

The perceptual centre (P-centre) is the hypothetical specific moment at which a brief event is perceived to occur. Several P-centre models are described in the literature and the first collective implementation and rigorous evaluation of these models using a common corpus is described in this thesis, thus addressing a significant open question: which model should one use? The results indicate that none of the models reliably handles all sound types. Possibly this is because the data for model development are too sparse, because inconsistent measurement methods have been used, or because the assumptions underlying the measurement methods are untested. To address this, measurement methods are reviewed and two of them, rhythm adjustment and tap asynchrony, are evaluated alongside a new method based on the phase correction response (PCR) in a synchronized tapping task. Rhythm adjustment and the PCR method yielded consistent P-centre estimates and showed no evidence of P-centre context dependence. Moreover, the PCR method appears most time efficient for generating accurate P-centre estimates. Additionally, the magnitude of the PCR is shown to vary systematically with the onset complexity of speech sounds, which presumably reflects the perceived clarity of a sound’s P-centre. The ideal outcome of any P-centre measurement technique is to detect the true moment of perceived event occurrence. To this end a novel P-centre measurement method, based on auditory evoked potentials, is explored as a possible objective alternative to the conventional approaches examined earlier. The results are encouraging and suggest that a neuroelectric correlate of the P-centre does exist, thus opening up a new avenue of P-centre research. Finally, an up to date and comprehensive review of the P-centre is included, integrating recent findings and reappraising previous research. The main open questions are identified, particularly those most relevant to P-centre modelling

An analysis of speech rate strategies in ageing

Effects of age and speech rate on movement cycle duration were assessed using electromagnetic articulography. In a repetitive task syllables were articulated at eight rates, obtained by metronome and self-pacing. Results indicate that increased speech rate is associated with increasing movement cycle duration stability, while decreased rate leads to a decrease in uniformity of cycle duration, supporting the view that alterations in speech rate are associated with different motor control strategies involving durational manipulations. The relative contribution of closing movement durations increases with decreasing speech rate, and is a more dominant strategy for elderly speakers

Force Amplitude Modulation of Tongue and Hand Movements

Rapid, precise movements of the hand and tongue are necessary to complete a wide range of tasks in everyday life. However, the understanding of normal neural control of force production is limited, particularly for the tongue. Functional neuroimaging studies of incremental hand pressure production in healthy adults revealed scaled activations in the basal ganglia, but no imaging studies of tongue force regulation have been reported. The purposes of this study were (1) to identify the neural substrates controlling tongue force for speech and nonspeech tasks, (2) to determine which activations scaled to the magnitude of force produced, and (3) to assess whether positional modifications influenced maximum pressures and accuracy of pressure target matching for hand and tongue movements. Healthy older adults compressed small plastic bulbs in the oral cavity (for speech and nonspeech tasks) and in the hand at specified fractions of maximum voluntary contraction while magnetic resonance images were acquired. Volume of interest analysis at individual and group levels outlined a network of neural substrates controlling tongue speech and nonspeech movements. Repeated measures analysis revealed differences in percentage signal change and activation volume across task and effort level in some brain regions. Actual pressures and the accuracy of pressure matching were influenced by effort level in all tasks and body position in the hand squeeze task. The current results can serve as a basis of comparison for tongue movement control in individuals with neurological disease. Group differences in motor control mechanisms may help explain differential response of limb and tongue movements to medical interventions (as occurs in Parkinson disease) and ultimately may lead to more focused intervention for dysarthria in several conditions such as PD

After-effects of 10 Hz tACS over the prefrontal cortex on phonological word decisions

Introduction Previous work in the language domain has shown that 10 Hz rTMS of the left or right posterior inferior frontal gyrus (pIFG) in the prefrontal cortex impaired phonological decision-making, arguing for a causal contribution of the bilateral pIFG to phonological processing. However, the neurophysiological correlates of these effects are unclear. The present study addressed the question whether neural activity in the prefrontal cortex could be modulated by 10 Hz tACS and how this would affect phonological decisions. Methods In three sessions, 24 healthy participants received tACS at 10 Hz or 16.18 Hz (control frequency) or sham stimulation over the bilateral prefrontal cortex before task processing. Resting state EEG was recorded before and after tACS. We also recorded EEG during task processing. Results Relative to sham stimulation, 10 Hz tACS significantly facilitated phonological response speed. This effect was task-specific as tACS did not affect a simple control task. Moreover, 10 Hz tACS significantly increased theta power during phonological decisions. The individual increase in theta power was positively correlated with the behavioral facilitation after 10 Hz tACS. Conclusion Our results show a facilitation of phonological decisions after 10 Hz tACS over the bilateral prefrontal cortex. This might indicate that 10 Hz tACS increased task-related activity in the stimulated area to a level that was optimal for phonological performance. The significant correlation with the individual increase in theta power suggests that the behavioral facilitation might be related to increased theta power during language processing

ERP mismatch response to phonological and temporal regularities in speech

Predictions of our sensory environment facilitate perception across domains. During speech perception, formal and temporal predictions may be made for phonotactic probability and syllable stress patterns, respectively, contributing to the efficient processing of speech input. The current experiment employed a passive EEG oddball paradigm to probe the neurophysiological processes underlying temporal and formal predictions simultaneously. The component of interest, the mismatch negativity (MMN), is considered a marker for experience-dependent change detection, where its timing and amplitude are indicative of the perceptual system's sensitivity to presented stimuli. We hypothesized that more predictable stimuli (i.e. high phonotactic probability and first syllable stress) would facilitate change detection, indexed by shorter peak latencies or greater peak amplitudes of the MMN. This hypothesis was confirmed for phonotactic probability: high phonotactic probability deviants elicited an earlier MMN than low phonotactic probability deviants. We do not observe a significant modulation of the MMN to variations in syllable stress. Our findings confirm that speech perception is shaped by formal and temporal predictability. This paradigm may be useful to investigate the contribution of implicit processing of statistical regularities during (a)typical language development.Maastricht University (Grant to BMJ to support women in higher academic positions) and Netherlands Organization for Scientific Research (NWO) 452-16-004info:eu-repo/semantics/publishedVersio

Weak Responses to Auditory Feedback Perturbation during Articulation in Persons Who Stutter: Evidence for Abnormal Auditory-Motor Transformation

Previous empirical observations have led researchers to propose that auditory feedback (the auditory perception of self-produced sounds when speaking) functions abnormally in the speech motor systems of persons who stutter (PWS). Researchers have theorized that an important neural basis of stuttering is the aberrant integration of auditory information into incipient speech motor commands. Because of the circumstantial support for these hypotheses and the differences and contradictions between them, there is a need for carefully designed experiments that directly examine auditory-motor integration during speech production in PWS. In the current study, we used real-time manipulation of auditory feedback to directly investigate whether the speech motor system of PWS utilizes auditory feedback abnormally during articulation and to characterize potential deficits of this auditory-motor integration. Twenty-one PWS and 18 fluent control participants were recruited. Using a short-latency formant-perturbation system, we examined participants’ compensatory responses to unanticipated perturbation of auditory feedback of the first formant frequency during the production of the monophthong [ε]. The PWS showed compensatory responses that were qualitatively similar to the controls’ and had close-to-normal latencies (~150 ms), but the magnitudes of their responses were substantially and significantly smaller than those of the control participants (by 47% on average, p<0.05). Measurements of auditory acuity indicate that the weaker-than-normal compensatory responses in PWS were not attributable to a deficit in low-level auditory processing. These findings are consistent with the hypothesis that stuttering is associated with functional defects in the inverse models responsible for the transformation from the domain of auditory targets and auditory error information into the domain of speech motor commands