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Working memory (WM) is often described as a mental workspace where information can be maintained and manipulated in the service of ongoing cognition. Theoretical accounts describe the focus of attention as a state within working memory where a limited number of items can be briefly maintained in a heightened status of awareness. Ongoing debate and conflicting empirical evidence surrounds the capacity and characteristics of the focus of attention. Substantial recency effects are reported in a group of WM studies, and these recency effects are interpreted as a marker of the focus of attention (e.g., Nee & Jonides, 2008; Oztekin, Davachi, & McElree, 2010). The present work considers whether these findings are specific to parameters of these particular studies or whether they generalize across a broader range of tasks. An initial behavioral experiment tested performance across two tasks (judgment of recency and judgment of primacy), two information types (verbal and spatial), and two self-reported strategies (maintenance-based and retrieval-based). Central analyses averaged trials by the serial position of the correct item, and compared the accuracy and speed of retrieval of trials in different serial positions. Results showed evidence of both recency effects and primacy effects in all four types of task (verbal judgment of recency, verbal judgment of primacy, spatial judgment of recency, and spatial judgment of primacy). Moreover, a significant task by effect-type interaction showed that the size of recency and primacy effects shifted with the demands of the task (e.g., larger recency effects in judgment of recency than in judgment of primacy). Some similarities and some differences were found between verbal and spatial domains, while no differences were found across self-reported strategy. A subsequent fMRI experiment examined the neural correlates of verbal judgment of recency and primacy. Again, behavioral results showed a task by effect-type interaction where there was a larger recency effect in judgment of recency and a larger primacy effect in judgment of primacy. FMRI results showed no distinct correlates of a recency effect. In other words, , contrasts comparing fMRI signal during retrieval of recency item trials and middle item trials did not reveal above threshold clusters of activation. In contrast, neural correlates of primacy were found in frontal lobe brain regions (BA 4, 6, 32) associated with active maintenance of information. Moreover, the precise neural correlates of primacy were task-specific. In sum, two experiments demonstrate that the behavioral and neural signatures of WM, specifically related to primacy and recency effects, are dependent on task-demands. Accounts of the architecture of WM should address these observations, which inform how competing claims are supported across studies of WM. / Psychology

The purpose of the current study was to explore the genetic and environmental association between working memory and different behavioral aspects of the attention network (i.e., executive attention, alerting attention, and orienting attention), using a twin design. Data were from 131 monozygotic (39% male) and 173 same-sex dizygotic (44% male) twins. Individual differences in working memory performance and behavioral measures of executive attention, alerting attention, and orienting attention were found to be moderately heritable. A modest nonshared environmental effect was found for all variables. Individual differences in working memory were significantly correlated with variability in executive and alerting attention, but not orienting attention. All of the association between working memory and executive as well as alerting attention was statistically mediated by genetic influences, indicating a common genetic mechanism or mechanisms underlying the links between working memory and certain behavioral indicators of attention. / Master of Science

The purpose of the current study was to examine the mediating role of language in explaining the relation between home environment and prefrontal functioning. Participants were 30 children from two preschool centers (Virginia Tech Lab School and Radford Head Start Center) representing a wide range of socio-economic status. Children's working memory was assessed through performing two verbal tasks, namely the Day/Night task and the Yes/No task and a non-verbal task, the Tapping task. Language, in turn, was assessed through the Peabody Picture Vocabulary Test (PPVT-III). The criteria proposed by Baron and Kenny (1986) were followed to test for the mediational hypothesis, as well as an alternative hypothesis stating that working memory might mediate the relation between home environment and language. Results indicated that language did mediate the relation between home environment and prefrontal functioning, particularly working memory. The alternative hypothesis did not prove to be successful. Theoretical and educational implications of these findings are discussed. / Master of Science

In all past research, iconic memory shows a significant benefit over visual working memory for storage capacity of visual items. However, this effect has only been studied on simple items such as colors and letters. The goal of this thesis was to determine whether an iconic benefit also exists for visual stimuli with higher visual complexity, such as shapes and faces. Five experiments tested iconic and working memory capacity for complex face stimuli, intermediate-complexity shape stimuli, and simple color stimuli, as well as examining feature binding of objects in iconic memory. Results from these five experiments indicated that increased visual complexity of stimuli negatively impacts the iconic capacity benefit. High- and intermediate-complexity items had little to no iconic benefit, unlike all previously tested simple stimuli. Iconic memory may only be able to represent simple features, or may not be able to transfer complex information into visual working memory as quickly as simple information. Additionally, results showed that feature representations in iconic memory were sometimes bound into complex objects. The results of these five experiments challenge the traditional characterization of visual sensory memory as a precise snapshot; this early memory store may be more complex than a simple visual icon.

The brain is a highly complex network of nonlinear systems with internal dynamic states that are not easily quantified. As a result, it is essential to understand the properties of the connectivity network linking disparate parts of the brain used in complex cognitive processes, such as working memory. Working memory is the system in control of temporary retention and online organization of thoughts for successful goal directed behavior. Individuals exhibit a typically small capacity limit on the number of items that can be simultaneously retained in working memory. To modify network connections and thereby augment working memory capacity, researchers have targeted brain areas using a variety of noninvasive stimulation interventions. However, few existing methods take advantage of the brain's own structure to actively generate and entrain internal oscillatory modulations in locations deep within the auditory pathways. One technique is known as binaural beats, which arises from the brain's interpretation of two pure tones, with a small frequency mismatch, delivered independently to each ear. The mismatch between these tones is perceived as a so-called beat frequency which can be used to modulate behavioral performance and cortical connectivity. Currently, all binaural stimulation therapeutic systems are open-loop "one-size-fits-all" approaches. However, these methods can prove not as effective because each person's brain responds slightly differently to exogenous stimuli. Therefore, the driving motivation for developing a closed-loop stimulation system is to help populations with large individual variability. One such example is persons with mild cognitive impairment (MCI), which causes cognitive impairments beyond those expected based on age. Therefore, applying a closed-loop binaural beat control system to increase the cognitive load level to people with MCI could potentially maintain their quality of life. In this dissertation, I will present a comparison of algorithms to determine brain connectivity, results of open-loop based binaural stimulation, the development of a closed-loop brain network simulation platform, and finally an experimental study to determine the effectiveness of closed-loop control to modulate brain networks hence influencing cognitive abilities. / Ph. D. / In order to do complex tasks, such as creating a memory, multiple regions of the brain must interact to become a network. Specifically for this work, we are looking at working memory which is the system that allows us to remember and manipulate information in the presence of additional incoming information. Working memory capacity, which is the number of items we can remember, is dependent upon synchronization between particular regions of the brain, particularly the frontal and parietal lobes. Higher synchronization means that people will, on average, respond with higher accuracy during a working memory task. To modify the connections in the network and thereby augment working memory capacity, a non-invasive brain stimulation technique called binaural beats can be used. Binaural beats take advantage of the brain’s response to two pure tones, delivered independently to each ear, when those tones have a small frequency mismatch. The mismatch between the tones is interpreted as a beat frequency, which may act to synchronize brain waves. This research seeks to answer the question of whether binaural beats can be used to identify and control working memory. Currently, nearly all therapeutic stimulation systems are open-loop “one-size-fits-all” approaches. However, these methods can prove not as effective because each person’s brain responds slightly differently to external stimuli. Therefore, the driving motivation for developing a closed-loop stimulation system is to help populations with large individual variability. One such example is persons with mild cognitive impairment (MCI) which is considered a precursor to Alzheimer’s. Therefore, applying a closed-loop binaural beat control system to increase the cognitive load level to people with MCI could potentially maintain their quality of life. In this dissertation, we have showed that we can successfully increase the connectivity in the brain using binaural beats in a closed-loop system.

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

<p>The objectives of the present study were 1) to examine the effects of noise exposure on recall and recognition of orally presented text and 2) to examine the relation between working memory capacity and the performance of recall and recognition of orally presented text in noisy conditions. A total of 32 subjects, age 20-33, with no known hearing impairment, were paid to participate in the experiment. The hearing ability of all subjects was tested using recorded sentences with and without background noise. Their working memory capacity was tested using listening span, reading span and operation span tests measuring a) correctly recalled words of all three tests, b) the response latency in the reading span test and c) the processing time of the arithmetical operations in the operation span test. Finally all subjects took recall and recognition tests on texts presented orally with and without broadband background noise (white noise). The test results showed that 1) noise had no significant main effect on recall or recognition of the spoken texts, 2) ) the capacity of the central executive component of working memory, measured as the processing time of the arithmetical operations of the operation span test, correlated significantly with recall and recognition of the orally presented text in the noise condition, but not in the control condition, 3) noise exposure had a negative effect on the recognition performance of subjects with lower capacity of the central executive component of working memory.</p>