Independent Component Analysis of Event-Related Electroencephalography During Speech and Non-Speech Discrimination: : Implications for the Sensorimotor ∆∞ Rhythm in Speech Processing

Background: The functional significance of sensorimotor integration in acoustic speech processing is unclear despite more than three decades of neuroimaging research. Constructivist theories have long speculated that listeners make predictions about articulatory goals functioning to weight sensory analysis toward expected acoustic features (e.g. analysis-by-synthesis; internal models). Direct-realist accounts posit that sensorimotor integration is achieved via a direct match between incoming acoustic cues and articulatory gestures. A method capable of favoring one account over the other requires an ongoing, high-temporal resolution measure of sensorimotor cortical activity prior to and following acoustic input. Although scalp-recorded electroencephalography (EEG) provides a measure of cortical activity on a millisecond time scale, it has low-spatial resolution due to the blurring or mixing of cortical signals on the scalp surface. Recently proposed solutions to the low-spatial resolution of EEG known as blind source separation algorithms (BSS) have made the identification of distinct cortical signals possible. The µ rhythm of the EEG is known to briefly suppress (i.e., decrease in spectral power) over the sensorimotor cortex during the performance, imagination, and observation of biological movements, suggesting that it may provide a sensitive index of sensorimotor integration during speech processing. Neuroimaging studies have traditionally investigated speech perception in two-forced choice designs in which participants discriminate between pairs of speech and nonspeech control stimuli. As such, this classical design was employed in the current dissertation work to address the following specific aims to: 1) isolate independent components with traditional EEG signatures within the dorsal sensorimotor stream network; 2) identify components with features of the sensorimotor µ rhythm and; 3) investigate changes in timefrequency activation of the µ rhythm relative to stimulus type, onset, and discriminability (i.e., perceptual performance). In light of constructivist predictions, it was hypothesized that the µ rhythm would show significant suppression for syllable stimuli prior to and following stimulus onset, with significant differences between correct discrimination trials and those discriminated at chance levels. Methods: The current study employed millisecond temporal resolution EEG to measure ongoing decreases and increases in spectral power (event-related spectral perturbations; ERSPs) prior to, during, and after the onset of acoustic speech and tone-sweep stimuli embedded in white-noise. Sixteen participants were asked to passively listen to or actively identify speech and tone signals in a two-force choice same/different discrimination task. To investigate the role of ERSPs in perceptual identification performance, high signal-to-noise ratios (SNRs) in which speech and tone identification was significantly better than chance (+4dB) and low SNRs in which performance was below chance (-6dB and -18dB) were compared to a baseline of passive noise. Independent component analysis (ICA) of the EEG was used to reduce artifact and source mixing due to volume conduction. Independent components were clustered using measure product methods and cortical source modeling, including spectra, scalp distribution, equivalent current dipole estimation (ECD), and standardized low-resolution tomography (sLORETA). Results: Data analysis revealed six component clusters consistent with a bilateral dorsal-stream sensorimotor network, including component clusters localized to the precentral and postcentral gyrus, cingulate cortex, supplemental motor area, and posterior temporal regions. Timefrequency analysis of the left and right lateralized µ component clusters revealed significant (pFDR\u3c.05) suppression in the traditional beta frequency range (13-30Hz) prior to, during, and following stimulus onset. No significant differences from baseline were found for passive listening conditions. Tone discrimination was different from passive noise in the time period following stimulus onset only. No significant differences were found for correct relative to chance tone stimuli. For both left and right lateralized clusters, early suppression (i.e., prior to stimulus onset) compared to the passive noise baseline was found for the syllable discrimination task only. Significant differences between correct trials and trials identified at chance level were found for the time period following stimulus offset for the syllable discrimination task in left lateralized cluster. Conclusions: As this is the first study to employ BSS methods to isolate components of the EEG during acoustic speech and non-speech discrimination, findings have important implications for the functional role of sensorimotor integration in speech processing. Consistent with expectations, the current study revealed component clusters associated with source models within the sensorimotor dorsal stream network. Beta suppression of the µ component clusters in both the left and right hemispheres is consistent with activity in the precentral gyrus prior to and following acoustic input. As early suppression of the µ was found prior the syllable discrimination task, the present findings favor internal model concepts of speech processing over mechanisms proposed by direct-realists. Significant differences between correct and chance syllable discrimination trials are also consistent with internal model concepts suggesting that sensorimotor integration is related to perceptual performance at the point in time when initial articulatory hypotheses are compared with acoustic input. The relatively inexpensive, noninvasive EEG methodology used in this study may have translational value in the future as a brain computer interface (BCI) approach. As deficits in sensorimotor integration are thought to underlie cognitive-communication impairments in a number of communication disorders, the development of neuromodulatory feedback approaches may provide a novel avenue for augmenting current therapeutic protocols

When is evolutionary branching in predator-prey systems possible with an explicit carrying capacity?

In this study we use the theory of adaptive dynamics firstly to explore the differences in evolutionary behaviour of a generalist predator (or more specifically an omnivorous or intraguild predator) in a predator-prey model, with a Holling Type II functional response, when two distinct forms for the carrying capacity are used. The first of these involves the carrying capacity as an emergent property, whilst in the second it appears explicitly in the dynamics. The resultant effect this has on the intraspecific competition in each case is compared. Taking an identical trade-off in each case, we find that only with an emergent carrying capacity is evolutionary branching possible. Our study then concentrates solely on the case where the carrying capacity appears explicitly. Using the same model as above, but choosing alternate trade-offs, we find branching can occur with an explicit carrying capacity. Our investigation finishes by taking a more general functional response in an attempt to derive a condition for when branching can or cannot occur. For a predator-prey model, branching cannot occur if the functional response can be separated into two components, one a function of the population densities, X and Z, and the other a function of the evolving parameter z (traded off against the intrinsic growth rate), i.e. if F(z, X, Z) = F1(z)F2(X, Z). This search for evolutionary branching is motivated by its possible role in speciation

Can possible evolutionary outcomes be determined directly from the population dynamics?

Traditionally, to determine the possible evolutionary behaviour of an ecological system using adaptive dynamics, it is necessary to calculate the fitness and its derivatives at a singular point. We investigate the claim that the possible evolutionary behaviour can be predicted directly from the population dynamics, without the need for calculation, by applying three criteria - one based on the form of the density dependent rates and two on the role played by the evolving parameters. Taking a general continuous time model, with broad ecological range, we show that the claim is true. Initially, we assume that individuals enter in class 1 and move through population classes sequentially; later we relax these assumptions and find that the criteria still apply. However, when we consider models where the evolving parameters appear non-linearly in the dynamics, we find some aspects of the criteria fail; useful but weaker results on possible evolutionary behaviour now apply

Eye-to-face Gaze in Stuttered Versus Fluent Speech

The present study investigated the effects of viewing audio-visual presentations of stuttered relative to fluent speech samples on the ocular reactions of participants. Ten adults, 5 males and 5 females, aged 18-55 who had a negative history of any speech, language and hearing disorders participated in the study. Participants were shown three 30 second audio-visual recordings of stuttered speech, and three 30 second audio-visual recordings of fluent speech, with a three second break (black screen) between the presentation of each video. All three individuals who stutter were rated as ‘severe’ (SSI-3, Riley, 1994), exhibiting high levels of struggle filled with overt stuttering behaviors such as repetitions, prolongations and silent postural fixations on speech sounds, in addition to tension-filled secondary behaviors such as head jerks, lip protrusion, and facial grimaces. During stuttered and fluent conditions, ocular behaviors of the viewers including pupillary movement, fixation time, eye-blink, and relative changes in pupil diameter were recorded using the Arrington ViewPoint Eye-Tracker infrared camera and the system’s data analysis software (e.g., Wong & Cronin-Colomb & Neargarder, 2005) via a 2.8GHz Dell Optiplex GX270 computer. For all ocular measures except fixation time, there were significant (p\u3c.05) differences for stuttered relative to fluent speech. There was an increase in the number of pupillary movements, blinks, and relative change in pupil diameter and a decrease in time fixated when viewing stuttered relative to fluent speech samples. While not significant, participants fixated or directed their attention for less time during stuttered than fluent conditions, indicating decreased attention overall during stuttered speech samples. Increases in eye-blink data and pupil-dilation data were also significant. Because both eye-blink, as a measure of the startle reflex, and pupil-dilation are resistant to voluntary control or are completely under the control of the autonomic nervous system, significant increases in both for stuttered relative to fluent speech indicate a visceral reaction to stuttering

Evolution of host resistance towards pathogen exclusion: the role of predators

Question: Can increased host resistance drive a pathogen to extinction? Do more complex ecosystems lead to significantly different evolutionary behaviour and new potential extinctions? Mathematical method: Merging host-parasite models with predator-prey models. Analytically studying evolution using adaptive dynamics and trade-off and invasion plots, and carrying out numerical simulations. Key assumptions: Mass action (general mixing). All individuals of a given phenotype are identical. Only prey vulnerable to infection. Mutations are small and rare (however, the assumption on the size of mutation is relaxed later). In simulations, very small (negligible) populations are at risk of extinction. Conclusions: The presence of the predator can significantly change evolutionary outcomes for host resistance to a pathogen and can create branching points where none occurred previously. The pathogen (and sometimes the predator) is protected from exclusion if we take mutations to be arbitrarily small; however, relaxing the assumption on mutation size can lead to its exclusion. Increased resistance can drive the predator and/or pathogen to extinction depending on inter-species dynamics, such as the predator's preference for infected prey. Predator co-evolution can move exclusion boundaries and prevent the predator's own extinction if its rate of mutation is high enough (with respect to that of the prey)

Army Officer Corps Science, Technology, Engineering and Mathematics (STEM) Foundation Gaps Place Countering Weapons of Mass Destruction (CWMD) Operations at Risk – Part 1

This is the first of three articles from the authors describing the risk to Joint Operations incurred by an Army that is vulnerable to the STEM challenges faced in a great power competition involving CWMD operations. In this article, we describe the problem. In articles two and three of the series, we will elaborate on the problem utilizing the Joint Publication 3-0 as our guide and recommend solutions to address this gap

Supporting the Initial Work of Evidence-Based Improvement Cycles Through a Data-Intensive Partnership

Purpose: Currently in the education data use literature there is a lack of research and examples that consider the early steps of filtering, organizing, and visualizing data to inform decision making. The purpose of this study is to describe how school leaders and researchers visualized and jointly made sense of data from a common learning management system (LMS) used by students across multiple schools and grades in a charter management organization operating in the United States. To make sense of LMS data, researchers and practitioners formed a partnership to organize complex data sets, create data visualizations, and engage in joint sensemaking around data visualizations to begin to launch continuous improvement cycles. Design: We analyzed LMS data for n=476 students in Algebra I using hierarchical cluster analysis heatmaps. We also engaged in a qualitative case study that examined the ways in which school leaders made sense of the data visualization to inform improvement efforts. Findings: The outcome of this study is a framework for informing evidence-based improvement cycles using large, complex datasets. Central to moving through the various steps in the proposed framework are collaborations between researchers and practitioners who each bring expertise that is necessary for organizing, filtering, and visualizing data from digital learning environments and administrative data systems. Originality: We propose an integrated cycle of data use in schools that builds on collaborations between researchers and school leaders to inform evidence-based improvement cycles

Broadband quantum-dot frequency-modulated comb laser

Frequency-modulated (FM) laser combs, which offer a periodic quasi-continuous-wave output and a flat-topped optical spectrum, are emerging as a promising solution for wavelength-division multiplexing applications, precision metrology, and ultrafast optical ranging. The generation of FM combs relies on spatial hole burning, group velocity dispersion (GVD), Kerr nonlinearity, and four-wave mixing (FWM). While FM combs have been widely observed in quantum cascade Fabry-Perot (FP) lasers, the requirement for a low-dispersion FP cavity can be a challenge in platforms where the waveguide dispersion is mainly determined by the material. Here we report a 60 GHz quantum-dot (QD) mode-locked laser in which both the amplitude-modulated (AM) and the FM comb can be generated independently. The high FWM efficiency of -5 dB allows the QD laser to generate an FM comb efficiently. We also demonstrate that the Kerr nonlinearity can be practically engineered to improve the FM comb bandwidth without the need for GVD engineering. The maximum 3-dB bandwidth that our QD platform can deliver is as large as 2.2 THz. This study gives novel insights into the improvement of FM combs and paves the way for small-footprint, electrically-pumped, and energy-efficient frequency combs for silicon photonic integrated circuits (PICs)