The present project aimed to characterize the role of serial order within the working memory and language domains by first addressing a) whether serial order processing is domain-general and then b) whether serial order processing underlies vocabulary acquisition. Experiment 1 revealed that order memory in the visuo-spatial domain is qualitatively similar to order memory for verbal memoranda by reporting visuo-spatial equivalents of two well-known effects in verbal STM for serial order, repetition inhibition (e.g., Crowder, 1968) and repetition facilitation (Crowder, 1968). The effects were, however, accompanied by critical differences that may be due to modality-specific processes. Experiment 2 directly investigated whether verbal and visuo-spatial STM rely on common ordering mechanisms using a delayed recall dual-task design that contrasted two types of visuo-spatial interference tasks during a concurrent verbal serial order memory task (digit sequence memory). The visuo-spatial tasks probed either serial order STM or non-serial order (item) STM. Serial-order specific interference effects with the concurrent verbal serial order STM task were found. In experiment 3, we replicated the investigations of Experiment 2 using a word-learning paradigm as a concurrent task in place of the verbal serial order STM task that was previously used. Again interference by a visuo-spatial STM task was found only when it required memory for serial order. In sum, the results suggest that verbal and visuo-spatial STM subsystems rely on common mechanisms for serial order processing. These in turn appear to communicate with domain-specific processing substrates involved in item-level memory representations. Furthermore, the results indicate that such domain-general serial ordering mechanisms are also involved in novel word-learning. Taken together, the present findings provide crucial constraints for modeling of order representations. They also offer insight into mechanisms shared by vocabulary acquisition and STM tasks. / Thesis / Doctor of Philosophy (PhD)

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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 aim of this project was to investigate the impact of language proficiency (represented in first and second language) on working memory capacity. A sample of 100 college students from Virginia Tech University completed an on-line survey, performed 2 computer-based working memory capacity tasks (the OSPAN and the Letter Rotation) and had their first language (L1) as well as their second language (L2) proficiency tested. All participants were classified on a five-point likert scale from "poor" to "excellent". Verbal WMC (as measured by OSPAN) was associated with L2 proficiency. However, the L2 "excellent" group did not differ in their OSPAN from the remaining four groups of L2 proficiency classification. No correlation was found between the two WMC tasks. / Ph. D.