Assessing cognitive abilities in disorders of consciousness (DOC) relies on assessments of overt behaviour, such as the ability to follow commands. Neuroimaging has shown that absence of overt behavior does not necessarily indicate absence of covert cognition, raising questions about behaviour-only assessment. Several electroencephalographic (EEG) markers of higher cognitive functions (event-related potentials; ERPs) have shown the potential to differentiate between DOC states, as well as predict awakening and condition upon emergence. However, no one ERP has emerged with sensitivity and specificity high enough to be widely accepted, showing that further investigation is needed. More recently, evidence has emerged for fluctuations of ERP detectability in DOC over the course of several hours, and for prognostic power of changes in ERP presentation between testing sessions. This investigation builds on such findings towards improving evaluation of cognition in DOC. A testing battery combining several well-known auditory ERPs was administered to a comatose patient over a 24-hour period during two recording sessions one week apart, as well as to a sample of healthy young adults. The patient scored 3 and 6 on the Glasgow Coma Scale (GCS) during the first and second session, respectively. The results show that changes in GCS score were accompanied by changes in ERP detectability. The results also suggest detectability fluctuations over the course of 24 hours, which in turn suggests that repeated testing is necessary for complete evaluation. Future work should validate these findings with a larger sample; additionally, establishing population norms for single-subject prevalence, latency, and amplitude of ERPs would improve confidence in interpreting patient results. With the current understanding of both healthy and DOC ERPs, detecting ERP presence may contribute to a positive DOC prognosis with a degree of confidence, but caution must be exercised in making negative prognoses or high-stakes care decisions based on ERP absence. / Thesis / Master of Science (MSc) / Assessing cognitive abilities in disorders of consciousness such as coma currently relies on assessments of overt behaviour, such as the ability to follow commands or react to a stimulus. Neuroimaging has shown that absence of overt behavior does not necessarily indicate absence of covert cognition, raising questions about behaviour-only assessment. This study describes a neuroimaging testing battery aimed at evaluating a hierarchy of cognitive functions without the need for a behavioural response by measuring brain activity driven by auditory stimulation. This battery was administered to a comatose patient over a 24-hour period during two recording sessions one week apart, as well as to a sample of healthy young adults. The results show that changes in the patient’s condition between testing sessions was accompanied by detectable and quantifiable change in their stimulus-driven brain activity. The results also suggest fluctuations in the patient’s ability to produce detectable responses over the course of 24 hours, which in turn suggests that repeated testing is necessary for a complete evaluation. Overall, neuroimaging provides a promising avenue for non-behavioral assessment of cognition, which will greatly benefit a population whose physical faculties may be compromised.

Humans must process fleeting auditory information in real time, such as speech and music. The amplitude modulation of the acoustic waveforms of speech and music is rhythmically organized in time, following, for example, the beats of music or the syllables of speech, and this property enables temporal prediction and proactive perceptual optimization. At the neural level, external rhythmic sensory input entrains internal neural oscillatory activities, including low-frequency (e.g., delta, 1-4 Hz) phase, high-frequency (e.g., beta, 15-25 Hz) power, and their phase-amplitude coupling. These neural entrainment activities represent internal temporal prediction and proactive perceptual optimization. The present thesis investigated two critical but previously unsolved questions. First, do these multiple entrainment mechanisms for tracking auditory rhythm have distinct but coordinated perceptual functions? Second, does regularity in the temporal (when) domain associate with prediction and perception in the orthogonal spectral (what) domain of audition? This thesis addressed these topics by combining electroencephalography (EEG), psychophysics, and statistical modeling approaches. Chapter II shows that beta power entrainment reflects both rhythmic temporal prediction (when events are expected) and violation of spectral information prediction (what events are expected). Chapter III further demonstrates that degree of beta power entrainment prior to a pitch change reflects how well an upcoming pitch change will be predicted. Chapter IV reveals that rhythmic organization of sensory input proactively facilitates pitch perception. Trial-by-trial behavioural-neural associations suggested that delta phase entrainment reflects temporal expectation, beta power entrainment reflects temporal attention, and their phase-amplitude coupling reflects the alignment of these two perceptual mechanisms and is associated with auditory-motor communication. Together, this thesis advanced our understanding of how neural entrainment mechanisms relate to perceptual functions for tracking auditory events in time, which are essential for perceiving speech and music. / Thesis / Doctor of Science (PhD) / Perceiving speech and musical sounds in real time is challenging, because they occur in rapid succession and each sound masks the previous one. Rhythmic timing regularities (e.g., musical beats, speech syllable onsets) may greatly aid in overcoming this challenge, because timing regularity enables the brain to make temporal predictions and, thereby, anticipatorily prepare for perceiving upcoming sounds. This thesis investigated the perceptual and neural mechanisms for tracking auditory rhythm and enhancing perception. Perceptually, rhythmic regularity in streams of tones facilitates pitch perception. Neurally, multiple neural oscillatory activities (high-frequency power, low-frequency phase, and their coupling) track auditory inputs, and they are associated with distinct perceptual mechanisms (enhancing sensitivity or decreasing reaction time), and these mechanisms are coordinated to proactively track rhythmic regularity and enhance audition. The findings start the discussion of answering how the human brain is able to process and understand the information in rapid speech and musical streams.

In adult populations, it is generally accepted there is an overall male advantage on spatial tasks and an overall female advantage on verbal tasks. These differences are inconsistent in children. The present study examined relations among age, sex, EEG hemispheric activation, and performance on spatial and verbal tasks. Thirty-two eight-year-olds (16 boys) and 32 college students (16 men) had EEG recorded at baseline and while performing a computerized 2-dimensional Gingerbread Man mental rotation task, a computerized 2-dimensional Alphanumeric mental rotation task, a computerized 3-dimensional Basketball Player mental rotation task, and a computerized Lexical Decision-Making task. Additionally, participants completed a paper-and-pencil Water Level task and an oral Verbal Fluency task. On the 2-dimensional Alphanumeric and 3-dimensional Basketball Player mental rotation tasks men performed better than boys, but the performance of women and girls did not differ. On the Lexical Decision-Making and Water level tasks, men performed better than women, while there was no difference between boys and girls. No sex differences were found on the 2-dimensional Gingerbread Man mental rotation task or Verbal Fluency task. Analyses of task-related data also indicate that computer familiarization or computer related task demands might contribute to sex differences on computerized tasks. EEG analyses indicated that, on the 2-dimensional Alphanumeric mental rotation task, men exhibited more left posterior temporal activation than women, while there were no differences between boys and girls. Additionally, there was evidence that simple, or 2-dimensional, mental rotation tasks are associated with left posterior brain activation, while 3-dimensional mental rotation tasks are associated with right posterior brain activation. On the 2-dimensional Gingerbread Man mental rotation task, males exhibited more activation of the left parietal area than females, while on the 2-dimensional Alphanumeric mental rotation task, men exhibited more activation of the left posterior temporal area than women. On the 3-dimensional Basketball player mental rotation task, all participants exhibited greater activation of the right parietal area than the left parietal area. / Ph. D.

One of the most intriguing and enduring issues in contemporary developmental cognitive neuroscience centers on the development of the ability to remember past experiences and the neural systems which support this capacity. Over the past 25 years, through methodological advancements and direct challenges to established assumptions, the focus of this developmental question has shifted to highlight the second half of the first year of life as the time when true explicit memory functionally emerges and begins to rapidly develop. The purpose of the following study was to test specific hypotheses regarding the biobehavioral development of explicit memory during infancy and present a new approach to studying the behavioral and physiological expression of this system. This study, which was guided by hypothesized neural substrates of this memory system, is the first direct investigation of continuous brain electrical activity during both the encoding and retrieval phases of explicit memory processing in infants. Memory-related differences in behavior and task-related brain activity in individual cortical areas were of particular interest. The results of this study provided some support for the hypothesis that baseline-to-task changes in EEG power can distinguish between successful and unsuccessful ordered-recall memory. Specifically, decreases in brain-electrical activity relative to a baseline period were found at both frontal and temporal locations during stimulus encoding and retrieval for infants who failed the recall tests. However, either no change, or increases in EEG power at frontal and temporal sites was related to successful performance on this task. In addition, different patterns of brain-electrical activity were present for correct and incorrect responses from the same child. This study contributes to our understanding of the biobehavioral expression of infant explicit memory in three main ways. First, changes in both frontal and temporal lobe activity are directly involved in explicit memory processing both during event encoding as well as retrieval. Second, this work provides evidence of a developmentally appropriate and valid pattern of electrophysiology specific to explicit memory processing. Finally, this study bridges the gap between a classic behavioral task of infant memory (which has been conceptually linked to neuropsychological data) and current developmental cognitive neuroscience. / Ph. D.

Episodic memory is a critical component of human cognition. Episodic memory involves recollection of the contextual details surrounding an event, the capacity for mental time travel of past and future events, and is characterized by the subjective awareness that an event has been personally experienced. It is fundamental to our understanding of this complex memory system to examine how episodic memory emerges during the course of development. The present investigation explored the developmental improvement in episodic memory processing assessing recollection of factual information and the source of this information (i.e., source memory) between early to middle childhood. The electrophysiological (EEG) correlates of fact and source memory processing and measures of executive function were also examined as potential sources of variation in episodic memory. The focus of Study 1 was to examine source memory development in early childhood in a sample of 4- and 6-year-olds. Results revealed that older children were better able to recall both fact and source information. Source memory measures were correlated to early executive ability, namely measures of working memory, inhibitory control and set-shifting. Frontal EEG accounted for unique variation in fact recall but not source recall, whereas temporal EEG did not predict fact or source recall performance. The focus of Study 2 was to examine source memory development in middle childhood in a sample of 6- and 8-year-olds. Older children were better on fact recall, but both ages were comparable on source recall. Frontal EEG uniquely predicted fact recall performance beyond the contribution of age and language. Both frontal and parietal EEG and executive function predicted variation in source recall performance. In contrast, temporal EEG did not uniquely predict fact or source recall performance. Lastly, Study 3 was a longitudinal investigation of source memory between early and middle childhood. Although age-related increases in performance were evident, Time 1 and Time 2 source memory measures were not correlated. This investigation contributes to our understanding of the developmental changes in source memory processing between early and middle childhood, and identifies that patterns of frontal and parietal brain activity and executive function skills contribute to early episodic memory formation. / Ph. D.

Episodic memory refers to context based explicit memory and shows vast improvements during middle childhood. In this study, episodic encoding was manipulated using stimuli that were hypothesized to require active or passive processing. Nine to eleven-year-old children were presented with a recall task using lower resolution (active processing) and clear (passive processing) images. It was hypothesized that children would recall more low resolution images than clear images. Executive function ability was also assessed to investigate possible contributions to performance. Furthermore, this study investigated whether frontal and temporal brain electrophysiology predicted unique variance in recall performance. Results suggested that overall there were no performance differences between low resolution and clear images; however, differences may exist within task blocks. Electrophysiology at temporal scalp locations and executive functions predicted unique variance in memory task performance. Specifically, set-shifting and working memory predicted a unique amount of variance in memory task performance. The results suggest that explicit memory may require certain executive processes more than others, and that active and passive processing may enhance this effect. / Master of Science

Brain-Computer Interfaces (BCIs) that rely on motor imagery currently allow subjects to control quad-copters, robotic arms, and computer cursors. Recent advancements have been made possible because of breakthroughs in fields such as electrical engineering, computer science, and neuroscience. Currently, most real-time BCIs use hand-crafted feature extractors, feature selectors, and classification algorithms. In this work, we explore the different classification algorithms currently used in electroencephalographic (EEG) signal classification and assess their performance on intracranial EEG (iEEG) data. We first discuss the motor imagery task employed using iEEG signals and find features that clearly distinguish between different classes. Second, we compare the different state-of-the-art classifiers used in EEG BCIs in terms of their error rate, computational requirements, and feature interpret-ability. Next, we show the effectiveness of these classifiers in iEEG BCIs and last, show that our new classification algorithm that is designed to use spatial, spectral, and temporal information reaches performance comparable to other state-of-the-art classifiers while also allowing increased feature interpret-ability. / Master of Science / Brain-Computer Interfaces (BCIs) as the name suggests allows individuals to interact with computers using electrical activity captured from different regions of the brain. These devices have been shown to allows subjects to control a number of devices such as quad-copters, robotic arms, and computer cursors. Applications such as these obtain electrical signals from the brain using electrodes either placed non-invasively on the scalp (also known as an electroencephalographic signal, EEG) or invasively on the surface of the brain (Electrocorticographic signal, ECoG). Before a participant can effectively communicate with the computer, the computer is calibrated to recognize different signals by collecting data from the subject and learning to distinguish them using a classification algorithm. In this work, we were interested in analyzing the effectiveness of using signals obtained from deep brain structures by using electrodes place invasively (also known as intracranial EEG, iEEG). We collected iEEG data during a two hand movement task and manually analyzed the data to find regions of the brain that are most effective in allowing us to distinguish signals during movements. We later showed that this task could be automated by using classification algorithms that are borrowed from electroencephalographic (EEG) signal experiments.

Inhibitory control is vital to typical development and matures rapidly throughout early childhood. Inhibitory control deficits are seen in both autism spectrum disorders and attention-deficit/hyperactivity disorder and, along with other executive functions, inhibitory control contributes to school success. The tasks used to measure and stress these skills in children have not been fully explored. Even given the cognitive development levels of young children, the current inhibitory control tasks for preschoolers are not completely comparable to the tasks used with adults. For my thesis study, I added a mixed condition to the day/night inhibitory control task in preschool children using methodological design features from the Dimensional Change Card Sort (DCCS) Task. This addition allowed the day/night task to serve as a better analogue to the Stroop task, which is an inhibitory control task commonly used with adults. In addition, electroencephalogram (EEG) illuminated the neural patterns of the task in children at age four. This study demonstrated that the borders condition of the day/night task is an appropriate executive function task that can be used with preschool aged children. / Master of Science

This study examined individual differences in spatial memory performance in 12-month-old infants using brain electrical activity and walking experience. Greenough's experience-expectant and experience-dependent model of development was used to examine EEG power values among infants with different levels of walking experience (non-walkers, novice, experienced). In accordance with this model, a trend was shown for novice walkers to have higher EEG power values than both non-walkers and experienced walkers only in the central region. Walkers were also found to score higher on an object retrieval (OR) spatial memory task than non-walkers, with amount of walking experience being inconsequential. In addition, infants who scored higher on the OR spatial memory task showed a trend for higher EEG power values in medial frontal, central and parietal areas than infants scoring lower on the OR task. This was not the case for the manual search spatial memory task (AB). There was no interaction among spatial memory performance, walking experience and brain electrical activity. The utility of OR as a spatial memory task that requires the integration of relevant perceptual-motor integration is discussed. / Master of Science

The area of cognitive research that has produced the most consistent sex differences is the area of spatial ability. Particularly, males usually perform better on mental rotation tasks than do females. One argument for these differences is that experience with spatial activity drives these differences, such that traditionally more masculine activities require more practice of spatial abilities. Another argument is biological in nature, such that there is either 1) a critical period of development that leads to differential lateralization of the brain, or 2) differential activation of the brain by circulating hormones. Performance on mental rotation tasks has been associated with right parietal activation levels, both during task performance and prior to performance during baseline recordings. The present study examined the relations among sex, age, EEG hemispheric activation (at the 10.5-13.5Hz. frequency band), and 2-dimensional mental rotation task ability. Nineteen eight-year-olds (10 boys) and 20 college students (10 men), had EEG recorded at baseline and while performing a mental rotation task. Men performed better on the mental rotation task than women, while there were no differences between boys and girls. After covarying for baseline EEG high alpha power values, EEG results during the mental rotation task indicated an interaction, with men exhibiting more activation (lower EEG power values at 10.5-13.5Hz) than women in the parietal and posterior temporal regions, while boys' and girls' power values 10.5-13.5Hz did not differ in the parietal or posterior temporal regions. Furthermore, during the baseline condition, men generally exhibited more activation (lower EEG power values at 10.5-13.5Hz) throughout all regions of the scalp. Results support the hypothesis that hormones, or hormonal influence, may result in a biological change which affects both brain activation and performance on mental rotation tasks. / Master of Science