UMD Theses and Dissertations
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Item THE IMPACT OF MILD TRAUMATIC BRAIN INJURY ON TIME-FREQUENCY ERP MEASURES AND NEUROPSYCHOLOGICAL FUNCTIONING: A LONGITUDINAL STUDY OF ACUTELY INJURED SERVICE MEMBERS(2020) Watts, Adreanna Massey; Bernat, Edward; Psychology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Traumatic Brain Injury (TBI) is the most common injury in recent military conflicts, with nearly 500,000 service members sustaining a TBI since 2000. Mild TBI (mTBI), or concussion, is by far the most common type of TBI and has been associated with long-term cognitive complaints and functional impairment. While clinical assessment of mTBI (i.e., MRI and performance-based cognitive testing) occasionally captures subtle abnormalities in the acute period following mTBI, these measurements lack the sensitivity to assess the time course of cognitive recovery from mTBI. The current study assessed cognitive changes from the acute to chronic period following mTBI using advanced time-frequency event-related potential (ERP) analysis, which isolates rapid regional brain activity and measures the functional communication within and between brain networks in response to varying task stimuli. The validity of these ERP biomarkers was evaluated with correlations between abnormal ERP findings and widely used clinical measures of cognitive functioning (i.e., neuropsychological tests and self-reported cognitive symptoms). Differences between mTBI caused by blast explosion versus impact to the head were also evaluated. A sample of 173 service members, comprising an mTBI group, an orthopedically-injured control group, and a healthy control group, completed ERP, neuropsychological, and self-report assessments within weeks following injury and again six months later. Results suggested that mTBI leads to cognitive changes that persist in the acute to post-acute period following injury (i.e., up to 12 weeks). These cognitive changes were reflected by alterations in ERP time-frequency amplitude and functional connectivity measures, and they remained apparent even when controlling for psychiatric symptoms. ERP differences were also evident between blast-related and impact-related mTBI. Conversely, neuropsychological test performance was not sensitive to mTBI. Abnormal ERP time-frequency measures were related to self-reported cognitive symptoms, suggesting these ERP measures are valid biomarkers of cognitive difficulties following mTBI. Critically, cognitive functioning as assessed by ERP measures returned to a level indistinguishable from controls 7-9 months following mTBI, even though more than a third of mTBI patients continued to report cognitive symptoms. These persistent cognitive complaints were more related to post-injury psychiatric symptoms than to the direct effects of brain injury.Item THE COMPARISON OF L1 AND L2 CASE PROCESSING: ERP EVIDENCE FROM TURKISH(2019) KARATAS, NUR BASAK; Gor, Kira; Second Language Acquisition and Application; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation investigates the morphological and morphosyntactic processing of case-marking by native and nonnative speakers of Turkish, through behavioral and electrophysiological responses. The study explores the locus of case processing costs during first (L1) and second language (L2) word recognition both in isolation and in sentences. It identifies the factors leading to persistent problems that late L2 learners face in attaining native-like processing of case assignment. To this end, the first experiment (a visual lexical decision task) examines whether different case forms generate differential processing costs, based on four main comparisons that reflect case properties and its status in the inflectional paradigm: 1) structural (genitive, accusative) vs. lexical (dative) case; 2) argument (accusative, dative) vs. non-argument (genitive); 3) higher (genitive) vs. lower type frequency (accusative, dative), and 4) citation form (nominative) vs. oblique cases (genitive, accusative, dative). The behavioral findings show significantly larger processing costs (i.e., longer reaction times and lower accuracy rates) for the genitive than the nominative case (citation form) across both subject groups, and than other oblique cases in L2 group only. ERP findings show significantly larger processing costs for the genitive than the accusative, and for the dative than the accusative only in L2 group. When the same case-inflected nouns were placed in a sentence context, larger N400 effects were found for the genitive, compared to the nominative and accusative in L1 group only. Together, these results suggest that different case forms generate differential processing costs in both subject groups, and L2 learners’ difficulty with the non-argument genitive and lexical dative oblique cases are at the level of form rather than sentence structure. The second (sentence) experiment also examined the processing of case errors (i.e., substitution of the accusative for the dative or vice versa on the object). ERP findings show a qualitative difference between L1 and L2 morphosyntactic patterns: P600 was missing while early negativities (N400 and left anterior negativity, LAN) were present in L2 group. These results suggest that advanced L2 learners evaluate the verb argument structure (LAN) and semantic fit (N400), but do not attempt to reparse the sentence (P600), unlike native speakers.Item Electrophysiology of Social Reward Processing in Schizophrenia(2018) Catalano, Lauren; Blanchard, Jack J; Psychology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Poor social outcomes have been long observed in schizophrenia. Most studies have identified social cognition as an important contributor to social functioning. Recent research suggests that some people with schizophrenia do not appropriately respond to social rewards, including facial expression of positive affect. The aim of the current study was (1) to use electroencephalogram (EEG) and the event related potential (ERP) technique to examine how people with schizophrenia (SZ) and healthy control (HC) participants anticipate and respond to social (smiles) and nonsocial (money) types of feedback; (2) to examine how deficits in social reward processing are associated with motivation and pleasure deficits and social functioning; and (3) to examine differential contributions of social cognition and social reward processing in understanding functioning. Social and monetary incentive delay tasks were used to characterize reward processing. The stimulus preceding negativity (SPN) was evaluated as an index of reward anticipation, and the reward positivity (RewP) was evaluated as an index of reward sensitivity. Results indicated that HC participants (n = 22) showed significantly more anticipation of reward feedback than neutral feedback, as indexed by the SPN. SZ participants (n = 25) showed similar anticipation regardless of whether there was a potential to win a reward. SZ participants were more sensitive to social rewards than HC participants, as indexed by a larger RewP. We were unable to measure the RewP on the money task; however, exploratory analyses on a P2 component suggested there were no group differences in nonsocial reward sensitivity. Within the SZ group, reduced social reward anticipation was related to greater motivation and pleasure deficits but not social functioning. Social cognition was not significantly related to social functioning or social reward processing in the SZ sample. This is the first study to measure the electrophysiological correlates of social and nonsocial reward processing in schizophrenia. Findings provide preliminary evidence of a generalized anticipatory deficit in schizophrenia that is related to impairments in motivation and pleasure. Reward sensitivity to social rewards appears to be intact. Future experimental design considerations are discussed.Item SECOND LANGUAGE LEXICAL REPRESENTATION AND PROCESSING OF MANDARIN CHINESE TONES(2018) Pelzl, Eric; DeKeyser, Robert; Second Language Acquisition and Application; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation investigates second language (L2) speech learning challenges by testing advanced L2 Mandarin Chinese learners’ tone and word knowledge. We consider L2 speech learning under the scope of three general hypotheses. (1) The Tone Perception Hypothesis: Tones may be difficult for L2 listeners to perceive auditorily. (2) The Tone Representation Hypothesis: Tones may be difficult for L2 listeners to represent effectively. (3) The Tone Processing Hypothesis: Tones may be difficult for L2 listeners to process efficiently. Experiments 1 and 2 test tone perception and representation using tone identification tasks with monosyllabic and disyllabic stimuli with L1 and advanced L2 Mandarin listeners. Results suggest that both groups are highly accurate in identification of tones on isolated monosyllables; however, L2 learners have some difficulty in disyllabic contexts. This suggests that low-level auditory perception of tones presents L2 learners with persistent long-term challenges. Results also shed light on tone representations, showing that both L1 and L2 listeners are able to form abstract representations of third tone allotones. Experiments 3 and 4 test tone representation and processing through the use of online (behavioral and ERP) and offline measures of tone word recognition. Offline results suggest weaknesses in L2 learners’ long-term memory of tones for specific vocabulary. However, even when we consider only trials for which learners had correct and confident explicit knowledge of tones and words, we still see significant differences in accuracy for rejection of tone compared to vowel nonwords in lexical recognition tasks. Using a lexical decision task, ERP measures in Experiment 3 reveal consistent L1 sensitivity to tones and vowels in isolated word recognition, and individual differences among L2 listeners. While some are sensitive to both tone and vowel mismatches, others are only sensitive to vowels or not at all. Experiment 4 utilized picture cues to test neural responses tied directly to tone and vowel mismatches. Results suggest strong L1 sensitivity to vowel mismatches. No other significant results were found. The final chapter considers how the three hypotheses shed light on the results as a whole, and how they relate to the broader context of L2 speech learning.Item EFFECTS OF REWARD CONTEXT ON FEEDBACK PROCESSING AS INDEXED BY TIME-FREQUENCY ANALYSIS(2016) Massey, Adreanna; Bernat, Edward; Psychology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The role of reward context has been investigated as an important factor in feedback processing. Previous work has demonstrated that the amplitude of the feedback negativity (FN) depends on the value of the outcome relative to the range of possible outcomes in a given context, not the objective value of the outcome. However, some research has shown that the FN does not scale with loss magnitude in loss-only contexts, suggesting that some contexts do not show a pattern of context-dependence. Time-frequency decomposition techniques have proven useful for isolating important activity, and have shown that time-domain ERPs can be better represented as separable processes in delta (0-3 Hz) and theta (3-7 Hz). Thus, the current study seeks to assess whether the role of context in feedback processing is better elucidated using time-frequency analysis. Results revealed that theta was more context-dependent and showed a binary response to best-worst differences in the gain and even contexts. Delta was more context-independent: the best outcomes scaled linearly with reward magnitude and best-worst differences scaled with context valence. Our findings reveal that theta and delta are differentially sensitive to context and that context valence may play a critical role in determining how the brain processes good and bad outcomes.Item THE NEUROPHYSIOLOGICAL BASIS FOR EMOTIONAL MAINTENANCE AND REDUCED GOAL-DIRECTED BEHAVIOR IN SCHIZOPHRENIA(2014) Llerena, Katiah; Blanchard, Jack J; Psychology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)The current study investigated the neurophysiological underpinnings of emotional maintenance in schizophrenia (SCZ) and whether aberrant neural responses predicted deficits in affective decision making and real-world motivated behavior. Event-related potentials (ERPs) were recorded from 27 SCZ outpatients and 23 healthy controls (CN) during an emotional maintenance task in which participants were presented an initial image for 3 seconds and then required to maintain a mental representation of the intensity that image over a delay period of varying lengths and determine whether the initial image was more or less intense than the second image. The Late Positive Potential (LPP) was used as a neurophysiological marker of emotional maintenance during the delay period. SCZ showed normal in-the-moment emotion experience to positive stimuli; however, SCZ rated negative and neutral pictures as more intense than CN. SCZ also displayed deficits in emotional maintenance accuracy. Furthermore, ERP data indicated reduced LPP amplitude during picture viewing for SCZ compared to CN, and only CN showed persistence of the LPP for positive stimuli into the offset delay period for approximately 1 second and this was significantly associated with behavioral emotional maintenance performance. Behavioral emotional maintenance performance also significantly predicted clinically rated negative symptoms (motivation and pleasure) and poor functional outcome. Thus, impairments in emotional maintenance may offer a promising new theory as to why people with SCZ fail to pursue goal-directed activities.Item Using a high-dimensional model of semantic space to predict neural activity(2014) Jackson, Alice Freeman; Bolger, Donald J; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation research developed the GOLD model (Graph Of Language Distribution), a graph-structured semantic space model constructed based on co-occurrence in a large corpus of natural language, with the intent that it may be used to explore what information may be present about relationships between words in such a model and the degree to which this information may be used to predict brain responses and behavior in language tasks. The present study employed GOLD to examine genera relatedness as well as two specific types of relationship between words: semantic similarity, which refers to the degree of overlap in meaning between words, and associative relatedness, which refers to the degree to which two words occur in the same schematic context. It was hypothesized that this graph-structured model of language constructed based on co-occurrence should easily capture associative relatedness, because this type of relationship is thought to be present directly in lexical co-occurrence. Additionally, it was hypothesized that semantic similarity may be extracted from the intersection of the set of first-order connections, because two words that are semantically similar may occupy similar thematic or syntactic roles across contexts and thus would co-occur lexically with the same set of nodes. Based on these hypotheses, a set of relationship metrics were extracted from the GOLD model, and machine learning techniques were used to explore predictive properties of these metrics. GOLD successfully predicted behavioral data as well as neural activity in response to words with varying relationships, and its predictions outperformed those of certain competing models. These results suggest that a single-mechanism account of learning word meaning from context may suffice to account for a variety of relationships between words. Further benefits of graph models of language are discussed, including their transparent record of language experience, easy interpretability, and increased psychologically plausibility over models that perform complex transformations of meaning representation.Item The effect of mental stress on brain dynamics and performance related to attention control during a vigilance task: An electroencephalographic investigation(2013) Russell, Bartlett Anne Healy; Hatfield, Bradley D; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Anxiety can increase distractibility and undermine the quality of psychomotor performance. Models of attention processing postulate that anxiety consumes limited executive resources necessary for maintaining goal-oriented, "top-down" attention control and suppressing stimulus-driven "bottom-up" distraction. Attention Control Theory (ACT) predicts that anxiety adversely affects the efficiency, and particularly inhibitory components of executive, frontally mediated top-down attention control. We used two approaches for examining this model. First, though attention affects synchrony among neural structures, information regarding how human oscillatory patterns (measured with electroencephalography, EEG) change as state anxiety increases is limited. Second, while anxiety affects the balance between top-down and bottom-up mechanisms, to our knowledge no one has yet measured anxiety's effect on attention using a neural measure of top-down control in conjunction with more traditional bottom-up measures of attention capture (e.g., the P3 event related potential, or ERP). Purpose: Study 1 examines the oscillatory patterns (spectral dynamics) of the cortex in order to investigate whether frontal regions exhibit patterns of reduced efficiency and altered networking with posterior regions during threat of shock. In order to assess the relationship between top-down and bottom-up attention dynamics, Study 2 uses the same threat protocol to measure attention-directed top-down modulation of sensory signaling (steady-state visual evoked potential, or ssVEP modulation) and of bottom-up attention capture by discrete targets and distractors (Event Related Potentials, ERPs). Results: The spectral analyses in Study 1 suggest decreased processing efficiency and decreased frontal networking (coherence) with more posterior regions as anxiety increased. Reduced coherence, however, could indicate either increased or decreased top-down focus; Study 2 provides more insight. Neural responses to task-relevant targets (ERPs) diminished as threat increased, while responses to task-irrelevant distractors remained unchanged. Contrary to what ACT would predict, we observed an increase in attention modulation of an ssVEP frequency associated with amplifying the task-relevant signal and no change in an ssVEP associated with inhibiting task-irrelevant stimuli. These findings suggest top-down attention control increased under threat, but was not enough to prevent degraded processing of task-relevant targets coincident with reduced efficiency on task performance. Implications and suggestions for refining ACT are discussed.Item GOVERNANCE STRATEGIES FOR ENTERPRISE APPLICATION SYSTEM IMPLEMENTATIONS(2013) Ghosh, Saumyendu N.; Skibniewski, Miroslaw J; Civil Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Enterprise application system implementations are highly complex implementations that automate several business functions, such as financials, accounting, supply chain, customer services management, human resources management and reporting among others. This study aims at providing an alternative view of organization's enterprise application system (EAS) acceptance. Despite the large body of literature, there are still empirical inquiries to investigate the EAS system implementation from adopters' perspectives and how to identify risks in a multi-stakeholder and dynamic environment. The thesis consists of three essays on various aspects of relationship between enterprise application implementation in a multi-stakeholder environment and project governance. Valid measurement scales for predicting organization's acceptance of enterprise systems are in short supply. The first essay develops and validates new scales for two specific variables, integration and inter-dependency risks. These variables are hypothesized as key determinant for organizational success of enterprise application implementations by mitigating risks involved in a multi-stakeholder environment. A model of organization acceptance of enterprise systems was developed using these two scales and then tested for reliability from a total of 365 users and nine application groups. The measures were validated using ten different direct measures with reliabilities between 0.72 and 0.96. Integration risk was significantly related with perceived ease of use, consultant's product knowledge and training provided to the end users. Inter-dependency risk was significantly correlated with perceived usefulness, consultant's industry and product knowledge. Both integration and inter-dependency risks are significantly related with success of the new enterprise application. This study would benefit project executives by offering valuable managerial insights that enable them to appreciate and improve integration and inter-dependency of stakeholders. Implications for theory and practice are discussed for two sub-groups: that less experienced resources treat risks differently than more experienced resources, and business applications compared to technical enterprise applications. Academic community has not addressed governance of enterprise application projects that involve dynamic environments and how to mitigate integration and inter-dependency risks. In the second essay it is argued that acceptance of the system from end users is not enough? Adopters of new enterprise wide information technology solutions get most benefit when the solution continues to be adaptable when business, environment or other organizational priorities change - therefore making an implementation sustainable. The second essay discussed characteristics of sustainability of enterprise application implementation from organizational perspective. A case study was used to validate the characteristics of sustainability. The thesis sought to demonstrate the causal relationship between the organization's preparedness for sustainability and the emergence of implementation problems. The study extracted insight into the criticality of certain factors and the type of problems making decisions under weak governance situation. The third essay develops determinants for project governance success of enterprise application implementations by mitigating risks in a multi-stakeholder environment. This essay develops and validates new scales for five specific variables. Definitions of five variables were used to develop a model that was presented for content validity and then tested for reliability from a total of 117 project executives globally. The measures were validated with reliabilities between 0.73 and 0.94. Relationships between five measures were broken down to meaningful components and a three tier project governance structure was proposed to mitigate integration and inter-dependency risks in a multi-stakeholder environment.Item A PROGRAMMATIC RESEARCH APPROACH TO UNDERSTANDING THE IMPACT OF TEAM ENVIRONMENT ON CEREBRAL CORTICAL DYNAMICS AND ATTENTION(2012) Miller, Matthew Walker; Hatfield, Bradley D; Neuroscience and Cognitive Science; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)This dissertation describes a programmatic research approach to understanding how team environments alter individuals' brain dynamics so as to produce variations in individuals' cognitive-motor performances. This research is of fundamental interest as humans frequently perform in team environments. Specifically, the central purpose of this research was to determine if adaptive team environments are conducive to efficient brain dynamics such that tasks are accomplished with minimal neural costs. The dissertation is comprised of four studies (papers), each of which makes a unique contribution to the dissertation's central objective. The first paper reports a positive directional relationship between cerebral cortical activation as well as networking and task load. The second paper describes a new neurophysiological method for indexing attentional reserve, which is positively related to the efficiency of cerebral cortical activation and networking. The third paper describes the development of a paradigm employed to investigate the impact of team environment on neurocognitive functioning. This study used non-physiological techniques to index neurocognitive functioning while participants performed a cognitive-motor task in various team environments. Results suggest that, relative to neutral environments, maintaining performance in maladaptive team environments comes at a neurocognitive cost, while adaptive team environments enhance performance without such a cost. The final study applied the neurophysiological methods described in the first two studies to the team environment paradigm employed in the third study to provide neurobiological evidence in support of the conclusions reached in the third paper. Additionally, the final paper provides insight into the neurobiological changes underlying the alterations in neurocognitive functioning and task performance reported in the third paper. Specifically, the final paper reports that, relative to neutral environments, maintaining performance in maladaptive team environments comes at the expense of the efficiency of cerebral cortical activation and attentional reserve, while adaptive team environments enhance performance without such costs. Additionally, the final paper suggests that adaptive team environments may generate more optimal states of arousal, leading to performance enhancement. By comprehending the impact of team environments on brain dynamics, humans performing as members of teams in a variety of settings may be better equipped to maximize their performances.