Patients with Alzheimer’s Disease (AD) demonstrate a sensitive and specific short-term memory impairment for visual bindings (e.g. the combination of shapes and colours) that is absent in healthy ageing (Parra et al., 2009) and other dementias (Della Sala et al., 2012). This impairment is also seen in cases of asymptomatic, familial AD (Parra et al., 2010). The visual short term memory binding (VSTMB) impairment in AD has clear clinical and neuropsychological implications which are investigated in this thesis. Firstly, the utility of the VSTMB paradigm was contrasted with the Free and Cued Selective Reminding Task with Immediate Recall (FCSRT-IR) – which has recently been posited as a useful diagnostic marker of AD pathology (Dubois et al., 2014). The results indicated that the former is not affected by age, where the latter is, suggesting that the VSTMB paradigm provides a suitable baseline to measure cognitive decline associated with AD. The development of a parallel version of the FCSRT-IR is also reported. Secondly, a 24-week longitudinal study of patients receiving treatment for AD (donepezil hydrochloride) revealed that patients who respond to this treatment on cognitive scales also experience change in VSTMB performance. These responders, however, did not significantly improve on the FCSRT-IR during the study. This suggests that anticholinergic treatment may have an effect on VSTMB performance. Additionally, a meta-analysis that investigates the effect of a study’s funding on donepezil RCT outcome showed that industry-funded studies report larger changes in cognition than independent studies. Lastly, an auditory binding experimental paradigm was developed, with a view to reveal a non-visual binding impairment in AD, investigating whether the binding impairment reflects a general or modality-specific memory impairment. The overall conclusions of this thesis confirm that the VSTMB impairment has significant promise as an index of AD. The auditory binding paradigm, by contrast, shares conceptual similarity with the VSTMB paradigm, but may have restricted clinical use within the AD patient population.

Working memory, or the ability to maintain and manipulate information in mind when it is no longer physically present, is a pervasive yet severely capacity-limited component of cognition. Visual working memory, also known as visual short-term memory (VSTM), is limited to three or four items on average, with individual differences that range from roughly two to up to six items. Despite agreement that capacity is functionally limited, the current literature is split with respect to the nature of VSTM representations on two key questions: (1) What information is maintained in VSTM? (2) How is information stored in VSTM? The studies presented here address these questions using an event-related potential (ERP) task and a series of behavioural experiments that incorporate attentional selection via retrospective cueing (retro-cues). Experiment 1 manipulated both the number of features and the number of locations to be remembered in a lateralized change-detection task, with differences in the amplitude and topography of the resulting contralateral delay activity (CDA) indicating separate stores for features and locations. Experiments 2a-c established the basic effects of retro-cues on change-detection tasks, showing that attentional selection operated on one system at a time, with overall shorter response times and increased capacity estimates once baseline capacity was exceeded. Experiments 3a-b demonstrated that retro-cues biased VSTM resources to the cued item at the expense of representational strength of the other, non-cued items, showing flexible reallocation of resources. Experiments 4a-b presented multiple retro-cues to further examine the flexible reallocation of resources in VSTM, showing that capacity benefits depended on spatial specificity of retro-cues and that VSTM weights could be reallocated multiple times before probe comparison. Experiment 5 discounted the potential role of a general alerting mechanism in boosting capacity estimates, showing again that the retro-cue benefit required specificity of the cue. Experiment 6 showed that flexible reallocation of resources within one system did not change the online maintenance of representations within the other system. Thus, the studies collectively address the questions of (1) what and (2) how information is stored by supporting a two-system model of VSTM in which (1) locations and features are stored (2) independently via flexibly allocated resources.

Thesis (M.S.)--Rutgers University, 2009. / "Graduate Program in Psychology." Includes bibliographical references (p. 32-34).

Thesis (Ph.D.)--Ohio University, June, 2009. / Release of full electronic text on OhioLINK has been delayed until June 1, 2011 Includes bibliographical references (leaves 165-181)

Thesis (Ph.D.)--Ohio University, June, 2009. / Title from PDF t.p. Release of full electronic text on OhioLINK has been delayed until June 1, 2011 Includes bibliographical references (leaves 165-181)

Title from PDF of title page (University of Missouri--Columbia, viewed on Feb 17, 2010). The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Thesis advisor: Dr. Nelson Cowan. Includes bibliographical references.

published_or_final_version / Psychology / Master / Master of Philosophy

Visual working memory (VWM) has long been considered to be limited in capacity, but the way in which it is limited remains unclear. One of the theoretical debates in visual working memory concerns whether the number of objects that can be stored is fixed (discrete slot models) or variable (flexible resource models). Recent research on the resolution of VWM has helped elucidate this debate by acknowledging an important trade-off between number and resolution: as the number of items stored increases, the resolution of representation declines. Yet, a different conception suggests that the number and resolution may represent distinct aspects of visual working memory, evidenced by both behavioral and neuroimaging data. In this thesis, I examined three theoretical questions regarding the relationship between the number and the resolution of items in VWM. First, how does set size affect high- & low-resolution representations (differentially)? If an item limit can be evidenced in the high-resolution measure, but not in the low-resolution measure, my second research question emerges. That is, how much resolution do we have for the remaining objects when the item limit is exceeded? Third, if both high- & low-resolution representations of an item exist in VWM, are they stored together or independently? In a series of five experiments, I addressed these questions using an adapted continuous report paradigm, in which participants were asked to remember a mixture of objects from two categories and respond firstly to the category of the item-to-report (low-resolution measure), followed by a second within-category response (high-resolution measure) which was contingent on the first. In Experiments 1-2, only performance in the low-resolution, but not in the high-resolution, measure was largely indifferent to set size, which was not compatible with either discrete slot or flexible resource models, but was largely consistent with predictions from the two-factor model and the neural object-file theory. In Experiments 3-4, precision of high-resolution representations declined monotonically until the set size reached around four items, fitting to the predictions from discrete slot models. The overall accuracy in low-resolution measure, however, remained relatively high, suggesting differential set size influence on high- and low-resolution representations. In Experiment 5, capacity comparison revealed no significant difference when the low-resolution task was absent. Taken together, I demonstrate that 1) both low-resolution ensemble representations and high-resolution individual item representations exist in VWM, and 2) high-resolution representations (i.e. object identity) and low-resolution representations (i.e. objects’ categories, configural information and perhaps some coarse feature information) of an object might be stored independently. / published_or_final_version / Psychology / Master / Master of Philosophy

In older children and adults, words are stored in the mental lexicon in an organized manner and processed in a systematic manner on the basis of their phonological structures. The processing of novel words is therefore more efficient. Young children may process a novel word in a holistic manner, and the words are not stored phonemically distinct with one another in the mental lexicon. Priming is a method often used in spoken word recognition studies. The effects of phonological primes on word learning would reflect the organization of mental lexicon in young children. At the same time, research has shown that there is a positive correlation between phonological short-term memory (STM) and word learning. But the mechanism of how both phonological STM and mental lexicon are involved in word learning is not clear. Forty-two five- to seven-years-old children with a mean age of 6;06 (SD = 0;10) participated in a spoken word learning task. They were presented with names of 18 novel cartoon characters in nine word learning blocks and the names were novel disyllables that are consistent with the phonotactics of Cantonese. In each block, children were exposed to two novel words along with two real words as primes, with the primes phonologically similar to one novel word (“PHONOLOGICAL” condition) but not with the other one (“UNRELATED” condition). They heard each novel word twice and the primes three times. These participants also took part in nonword repetition tasks and a serial order construction task as measures of the phonological STM. A significantly positive effect of phonological priming was observed in the cartoon character naming but not in the form identification and the referent identification. Further analysis of the naming results showed that only the same-onset-and-tone primes produced a significant priming effect. Among the various short-term memory measures, only nonword repetition of pseudosyllables (syllable score) was significantly and positively correlated with the cartoon character naming score after controlling for age. The findings of the present study presented some evidence that even five-year-old Cantonese-speaking children have already organized the lexical representations in neighbourhoods so that phonological primes could exert facilitatory effects on their spoken word learning. Even this young group of children was able to process novel words in a segmental manner. But there could still be some subtle differences between the younger and older children. A word learning model which integrates the involvement of phonological STM and mental lexicon could help to explain how these two memory components contribute to word learning and the word learning differences between the younger and older children. The preliminary findings of this study provided some evidence in children’s sensitivity to the phonological structures of novel spoken words. Cantonese-speaking children, similar to English-speaking ones, are sensitive to the phonological structures of novel words and phonological primes facilitate their spoken word learning. The results of this study further suggest long-term memory and phonological short-term memory are involved at the initial stage of word learning. However, the mechanism of interactions needs to be further investigated. / published_or_final_version / Speech and Hearing Sciences / Master / Master of Philosophy

published_or_final_version / abstract / Linguistics / Master / Master of Arts