Numerous experiments have demonstrated that the activity of neurons can alter the strength of excitatory synapses. This synaptic plasticity is bidirectional and synapses can be strengthened (potentiation) or weakened (depression). Synaptic plasticity offers a mechanism that links the ongoing activity of the brain with persistent physical changes to its structure. For this reason it is widely believed that synaptic plasticity mediates learning and memory. The hypothesis that synapses store memories by modifying their strengths raises an important issue. There should be a balance between the necessity that synapses change frequently, allowing new memories to be stored with high fidelity, and the necessity that synapses retain previously stored information. This is the plasticity stability dilemma. In this thesis the plasticity stability dilemma is studied in the context of the two dominant paradigms of activity dependent synaptic plasticity: Spike timing dependent plasticity (STDP) and long term potentiation and depression (LTP/D). Models of biological synapses are analysed and processes that might ameliorate the plasticity stability dilemma are identified. Two popular existing models of STDP are compared. Through this comparison it is demonstrated that the synaptic weight dynamics of STDP has a large impact upon the retention time of correlation between the weights of a single neuron and a memory. In networks it is shown that lateral inhibition stabilises the synaptic weights and receptive fields. To analyse LTP a novel model of LTP/D is proposed. The model centres on the distinction between early LTP/D, when synaptic modifications are persistent on a short timescale, and late LTP/D when synaptic modifications are persistent on a long timescale. In the context of the hippocampus it is proposed that early LTP/D allows the rapid and continuous storage of short lasting memory traces over a long lasting trace established with late LTP/D. It is shown that this might confer a longer memory retention time than in a system with only one phase of LTP/D. Experimental predictions about the dynamics of amnesia based upon this model are proposed. Synaptic tagging is a phenomenon whereby early LTP can be converted into late LTP, by subsequent induction of late LTP in a separate but nearby input. Synaptic tagging is incorporated into the LTP/D framework. Using this model it is demonstrated that synaptic tagging could lead to the conversion of a short lasting memory trace into a longer lasting trace. It is proposed that this allows the rescue of memory traces that were initially destined for complete decay. When combined with early and late LTP/D iii synaptic tagging might allow the management of hippocampal memory traces, such that not all memories must be stored on the longest, most stable late phase timescale. This lessens the plasticity stability dilemma in the hippocampus, where it has been hypothesised that memory traces must be frequently and vividly formed, but that not all traces demand eventual consolidation at the systems level.

Learning and memory abilities decline with age; however collaborative learning with a familiar partner has been found to improve older adults’ performance on memory tasks and reduce these age-related differences. However it is unclear whether collaborating with a familiar partner is more beneficial to learning compared with collaborating with a stranger. Similarly, it is unclear whether older adults collaborate similarly with human and computer partners. The aim of this PhD thesis is to understand the role of collaborator identity on collaborative learning, and to investigate whether collaborative learning is as efficient and accurate with a range of learning partners. While collaborative learning is a socially-based memory task, the relationships between collaborative learning and social cognition have not yet been explored. The secondary aim of this thesis is to use experimental collaborative learning paradigms alongside standardised and experimental measures of social cognition to explore whether social cognition accounts for a significant amount of variance in collaborative learning performance with different partners. Two studies compare younger and older adults’ learning with familiar and unfamiliar partners on different collaborative learning paradigms. Two subsequent studies compare older adults’ learning on computerised versions of the collaborative learning tasks with partners they perceive to be humans or computers based on recordings of natural human or synthetic speech respectively. In all studies, measures of social cognition were used to assess whether social abilities affect learning outcomes with different partner types. When comparing older and younger adults’ results, familiarity had no effect on learning or immediate or delayed recall performance. Older adults initially took longer to complete the learning trials but performed with similar efficiency as younger adults by the final trials. Younger and older adults recalled collaboratively learned information with comparable accuracy after a delay of one hour, however after one week, older adults recalled the route less accurately than younger adults. Social cognition was not related to collaborative learning with familiar partners, but was related with unfamiliar partners, suggesting that those who are better able to take the perspective of another person may benefit during interactive learning. Social cognition was related to collaborative learning with perceived human partners but not perceived computer partners. This thesis offers a new perspective on the interplay between social and cognitive function in collaborative learning with different learning partners, and explores the differences between younger and older adults when learning collaboratively. The findings are discussed in relation to cognitive, social, and technological theories. On the whole, collaborative learning can result in older adults learning with similar speed and accuracy to younger adults; while familiarity does not improve learning outcomes, perceived human-ness does.

Thesis (Ph. D.)--University of Texas at Austin, 2001. / Vita. Includes bibliographical references. Available also from UMI/Dissertation Abstracts International.

No description available.

Thesis (MTchLn)--University of Canterbury, 2007. / Typescript (photocopy). "February 2007." Includes bibliographical references (leaves 139-147). Also available via the World Wide Web.

Diss. (sammanfattning) Stockholm : Karol. inst., 2005. / Härtill 8 uppsatser.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1969. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 136-140).

Thesis (Ph. D. in Neuroscience)--Vanderbilt University, Aug. 2009. / Title from title screen. Includes bibliographical references.

Thesis (M.A.)--Miami University, Dept. of Speech Pathology and Audiology, 2005. / Title from first page of PDF document. Document formatted into pages; contains [1], vii, 45 p. : ill. Includes bibliographical references (p. 36-41).

Following exposure to consistent stimulus–stop mappings, response inhibition can become automatised with practice. What is learned is less clear, even though this has important theoretical and practical implications. The main contribution of this thesis is to investigate how stimulus-stop associations are acquired and the conditions under which they influence behaviour. To this end, this thesis addressed several outstanding issues concerning the associative architecture of stop learning, the role of expectancies, and the specificity of learning in inhibition tasks. Experiments 1-4 provide evidence that participants can acquire direct associations between specific stimuli and the stop goal without mediation via a single representation of the stop signal. However, these experiments also suggest that the influence of stimulus-stop associations on behaviour depends on top-down attentional settings: if participants begin to ignore the stop-associated stimuli, the effects of stop learning are diminished or eliminated entirely. Across eight experiments, this thesis provides evidence that participants generate expectancies during stop learning that are consistent with the stimulus-stop contingencies in play. However, Experiments 5-6 indicate that there may be some differences in the relationships between stimulus-stop expectancies and task performance under instructed and uninstructed conditions; stimulus-stop associations that are acquired via task instructions or via task practice have similar effects on behaviour, but seem to differ in how they trigger response slowing for the stop-associated items. Experiments 7-8 investigated the role of signal detection processes during the acquisition of stimulus-stop associations. To distinguish between stimulus-stop learning and stimulus-signal learning, the contingencies between specific stimuli and the stop goal and the contingencies between specific stimuli and the spatial location of the stop signal were independently manipulated. Although these experiments showed evidence of stop/go (goal) learning, there was no evidence that participants acquired the stimulus-signal associations. Across four experiments, this thesis investigated the specificity of stop learning. Experiments 9-10 compared the effects of training on behavioural performance in inhibition (go/no-go) and non-inhibition (two-choice) tasks. The results of these experiments revealed that learning in inhibition and non-inhibition tasks could arise through similar associative mechanisms, but suggest that the effects of training in these tasks could also depend on top-down response settings and general non-associative processes. Experiments 11-12 investigated the neural specificity of stop learning. These experiments also revealed similar effects of training across the go/no-go and two-choice tasks adding weight to the claim that training in inhibition tasks primarily influences task-general processes. Combined, the overall conclusion of this thesis is that bottom-up control can influence response inhibition but what is learned depends on top-down factors. It is therefore important to consider bottom-up factors and top-down factors as dependent, rather than independent, influences on response inhibition.