http://www.dspace.cam.ac.uk:80/handle/1810/221774 Wed, 22 May 2013 01:24:31 GMT 2013-05-22T01:24:31Z http://www.dspace.cam.ac.uk:80/handle/1810/244104 Title: Episodic cognition: what is it, where is it, and when does it develop? Authors: Cheke, Lucy Gaia Abstract: Episodic Cognition (or “Mental Time Travel”) is the ability to mentally re-experience events from our personal past and imagine potential events from our personal future. This capacity is fundamental to our lives and has been argued to be uniquely human. The aim of this thesis is to use behavioural tasks developed in comparative cognition to integrate both the literature on different research subjects (animals, children, adults, patients) but also from different theoretical perspectives, with the hope of facilitating communication and comparison between these fields. The backbone of the thesis is the behavioural tasks themselves, along with their origins in theory. Specifically, the “What-Where-When”, “Unexpected Question” and “Free Recall” episodic memory tasks and the “Bischof-Köhler” test of episodic foresight. Each of these tasks stems from different theoretical approaches to defining episodic cognition. Whilst extensively studied, these four tasks have never been undertaken by the same subjects and have never been directly compared. It is thus unclear whether these different theoretical perspectives converge on a single “episodic cognition” system, or a variety of overlapping processes. This thesis explores these issues by presenting these tasks to previously untested animal (the Eurasian Jay), developing children (aged 3-6), and a sample of human adults (Cambridge Undergraduates). Finally, these findings are applied in the assessment of episodic cognition in a population that is thought to have mild hippocampal damage – the overweight and obese. It was predicted that if all these putative tests of episodic cognition were tapping into the same underlying ability, then they should be passed by the same animal species, develop at the same time in children, correlate in human adults and be impaired in those with damage to the relevant brain areas. These predictions were, to some degree, confirmed. While the novel animal model could not be tested on all paradigms, the jays performed well on Bischof-Köhler future planning test. However, the results of the What-Where-When memory test were equivocal. There was a relatively low degree of correlation between performance on all the tasks in human children, along with a suggestion that each had a distinct developmental trajectory. The study of human adults revealed that while performance on all the tasks were related to one another, this relationship was often nonlinear, suggesting the contribution of several different psychological processes. Finally, it was found that both memory and performance on the Bischof-Köhler future planning task were altered in individuals who are overweight. A potentially surprising theme throughout the results is that performance on the Bischof-Köhler tasks is in fact negatively related to performance on memory tests, and improves in patients thought to have mild hippocampal damage. It is concluded that there may be a significant degree of overlap in the processes tapped by different putative tests of episodic memory, but that they can not be considered to be equivalent. Furthermore, it is suggested that episodic cognition is a fundamentally ineffective system with which to predict future motivational states, because it is biased by current feelings. Tue, 13 Nov 2012 00:00:00 GMT http://www.dspace.cam.ac.uk:80/handle/1810/244104 2012-11-13T00:00:00Z http://www.dspace.cam.ac.uk:80/handle/1810/241706 Title: The sociality, ontogeny, and function of corvid post-conflict affiliation Authors: Logan, Corina Abstract: Humans and non-humans alike seek support after conflicts by making up with their former opponent (former opponent affiliation) or by affiliating with a bystander (thirdparty affiliation). Post-conflict behaviour has been studied in many mammals but only in two bird species: rooks and ravens. Consequently, the prevalence and function of avian post-conflict affiliation is unknown. My objectives were to expand the study of post-conflict affiliation to more bird species and examine two potential functions of this behaviour. I hypothesised that differences in sociality would influence corvid postconflict affiliation, and that this behaviour would change as individuals developed from juveniles to adults. I predicted that social rooks (Corvus frugilegus) and jackdaws (C. monedula), but not the less social Eurasian jays (Garrulus glandarius), should have post-conflict affiliation because this behaviour should be dependent on the presence of high quality social bonds. Affiliation should only occur with their mate because they are monogamous; the pair-bond being by far the highest quality relationship in the group. My results showed that the social species have third-party affiliation with their mate, while the less social jays have third-party affiliation with anyone. This behaviour became more frequent and lasted longer as jackdaws went from the pair formation stage to sexual maturity. Exploring the function of third-party affiliation, I found that it decreased the likelihood of receiving non-conflict aggression, thus buffering postconflict aggression for jackdaw and rook aggressors, as well as for rook victims. Hypotheses about post-conflict affiliation primarily concern former opponent affiliation and primates. I reviewed post-conflict affiliation across taxa and proposed a broad hypothesis that includes all forms of post-conflict affiliation: former opponent, thirdparty, quadratic, inter-group, and inter-species. Description: The full text of this thesis has been embargoed until March 2014 for publishing reasons. Tue, 07 Feb 2012 00:00:00 GMT http://www.dspace.cam.ac.uk:80/handle/1810/241706 2012-02-07T00:00:00Z http://www.dspace.cam.ac.uk:80/handle/1810/238959 Title: An Analysis of Functional Differences in Implicit Learning Authors: Brown, Jamie Abstract: This thesis analysed whether functional implicit learning differences existed in two areas that have produced promising, but equivocal, findings: individual differences in typical populations (e.g., Gebauer & Mackintosh, 2010) and group differences between Autism Spectrum Condition (ASC) and Typically Developing (TD) individuals (e.g., L. G. Klinger, Klinger, & Pohlig, 2007). Overall, the results from the four studies presented in this thesis emphasised a lack of functional differences in implicit learning between individuals. Study I investigated whether there were functional individual differences in implicit learning among a typical population by examining the inter-correlation between the performances of academic psychologists on three implicit learning tasks; the independence of those performances from IQ; the relationships between those performances, intuitive aspects of personality and occupational tacit knowledge; and, finally, whether the performances were related to occupational achievement. There was no evidence of inter-correlation between the implicit learning task performances, nor relationships between any of those performances, and occupational achievement, or personality. The study did replicate a finding that is important to the distinction between implicit and explicit learning: indices of explicit processing, but not performance on implicit learning tasks, were correlated with IQ (e.g., Gebauer & Mackintosh, 2007). Additionally, the study found that Academic Psychology and Business Management Tacit Knowledge Inventories measured knowledge that predicted occupational achievement in academic psychology incrementally to IQ and personality, and was general to both occupations. However, tacit knowledge appeared to be acquired primarily as a function of practice and experience, rather than individual differences in implicit learning. Overall, I asserted that a consideration of the results from Study I with the wider literature currently leads to the conclusion that there are minimal individual differences in implicit learning, which signifies that there is no general implicit learning ability that is critical to how much is learnt implicitly. In the absence of a general ability that determines how much is learnt implicitly, it was argued that there could still be general, prerequisite processes, which are always necessary for implicit learning but without those processes determining the variation in how much was learnt implicitly. Such prerequisite processes would not constitute a psychometric ability but could be SUMMARY vi conceptualised as general implicit learning processes. This conceptualisation of implicit learning would be supported by the existence of an atypical population who consistently demonstrated profound deficits on all implicit learning tasks and skills associated with an implicit acquisition. There is no convincing evidence of such a patient group, although the ASC population is a plausible candidate (e.g., L. G. Klinger, et al., 2007). Therefore, Study II compared IQ-matched ASC and TD individuals on a range of implicit learning tasks. The study, taken together with other recent reports (e.g., Barnes, et al., 2008), provided convincing evidence that implicit learning is actually intact in ASC and it was argued that deficits reported in previous studies must have resulted from differences in task procedures (e.g., L. G. Klinger, et al., 2007). In particular, the earlier studies used procedures that encouraged explicit strategies, which disadvantaged the ASC groups who had not been matched for IQ. A further analysis supported that interpretation: TD and ASC groups who were not matched for IQ exhibited differences on an explicit learning task, but not on the implicit learning tasks. In order to determine whether those previously identified implicit learning deficits in ASC resulted just from differences in IQ, or whether there was also a contribution from an ASC difficulty in explicit learning, Study III compared ASC individuals with IQ-matched TD individuals on an implicit learning task, the Serial Reaction Time (SRT) task, with a procedure that encouraged explicit strategies. The SRT procedure was combined with a contextual cueing task that provided an indirect, ongoing index of the extent to which sequence learning was explicit (Jiménez & Vázquez, in press). Study III indicated a difference in initial explicit sequence learning in ASC, which was independent of IQ. Study IV replicated the difficulty and by using a pre-task manipulation the study was also able to elaborate the nature of that difficulty: ASC individuals were able to learn sequence information explicitly, but they had a specific difficulty with learning to apply that explicit information. Thus, there was good evidence that implicit learning is intact in ASC and that instead ASC individuals have more difficulties with aspects of explicit learning. These findings refute the idea that ASC individuals successfully compensate for implicit deficits with explicit compensatory strategies. Instead, together with the ASC propensity for using explicit strategies, an ASC difficulty with explicit processing might explain some ASC deficits in a range of learnt skills, although I acknowledge that there are also plausible alternatives. More generally, these SUMMARY vii findings and ideas accord with ASC literature concerning impairments in executive functions, which require flexible and intentional processing (e.g., Russell, 1997a) and emphasise that future research is focused on how explicit, executive differences emerge and affect behaviour. In conclusion, the thesis provided no evidence for the proposal that there are functional differences between individuals in implicit learning. I propose that, taken together with the equivocal evidence discussed in my reviews of the wider literature, it is parsimonious to conclude that there is neither a general implicit learning ability, nor general, prerequisite implicit learning processes. However, in line with previous literature, the thesis did support functional distinctions between implicit and explicit learning: explicit, but not implicit, learning was related to IQ; and ASC individuals have difficulties with explicit but not implicit learning. Therefore, I assert that a descriptive distinction between explicit and implicit learning remains both useful and valid. This is true even though implicit learning seems to be defined by the absence, or minimal influence, of explicit processing rather than the general presence of an implicit learning ability or processes. Beyond the issue of functional differences, I argue that these findings and conclusions make modest, but not decisive, contributions to some of the other fierce debates in the wider implicit learning literature. Finally, I propose some recommendations, and directions, for future research. Mon, 31 May 2010 23:00:00 GMT http://www.dspace.cam.ac.uk:80/handle/1810/238959 2010-05-31T23:00:00Z http://www.dspace.cam.ac.uk:80/handle/1810/238772 Title: Peak Shift in Pigeon and Human Categorisation Authors: Aitken, Michael R F Abstract: In a series of experiments, both pigeon and human subjects were trained to categorise two groups of confusable stimuli, with each category being made up of distortions of a ‘Prototype’. Once the subjects had successfully learned to categorise the training stimuli, they were tested on their responding to a variety of previously unseen stimuli: these were distortions of the Prototypes towards (‘Closer’ exemplars), or away from (‘Further’ exemplars), the other category, and the Prototypes themselves. Pigeons responded more to positive Further exemplars that were close to the Prototype than to the Prototype itself, or to exemplars even further away from the category boundary. This result is an example of the peak shift (Hanson, 1959), and can be explained by interacting excitatory and inhibitory generalisation gradients (Spence 1937). When the pigeons were autoshaped using stimuli from the positive category before learning the categorisation, they failed to show a peak shift; greatest response rates on test were elicited by the positive Prototype. This result could be explained by the interaction of the autoshaping producing a ‘prototype effect’, i.e. a generalisation gradient with a maximum at the Prototype of the positive category, which masks the development of the peak shift. Further experiments showed that a similar abolition of the peak shift occurred when the pigeons were given prior experience of the negative category in an extra-dimensional discrimination designed to produce an inhibitory analogue of the prototype effect. A connectionist model of categorisation learning is presented, based on representation of the stimuli as sets of independent features. Simulations conducted using this model showed that, with few assumptions, such an analysis was capable of accounting for all the results found with pigeon subjects, some of which present a problem for alternative instance theories of categorisation (e.g. Pearce, 1984). Human subjects also categorised the Further exemplars better than the Prototypes, but did not show a peak shift. Performance increased with greater distance from the category boundary, consistent with subjects having abstracted and applied a cognitive strategy. When trained in an incidental learning paradigm, designed to minimise the opportunity for using such a strategy, subjects showed evidence of learning without any knowledge of the categorisation ‘rule’. The performance in this ‘implicit’ task had some similarities to the results of the studies with pigeon subjects, suggestive of a peak shift. These results indicate that similar associative processes may underlie categorisation in both humans and non-humans, although higher-level ‘symbolic’ processes may control human performance in laboratory studies. Mon, 01 Jan 1996 00:00:00 GMT http://www.dspace.cam.ac.uk:80/handle/1810/238772 1996-01-01T00:00:00Z http://www.dspace.cam.ac.uk:80/handle/1810/237273 Title: Neural systems involved in delay and risk assessment in the rat Authors: Cardinal, Rudolf N Abstract: This thesis investigated the contribution of the nucleus accumbens core (AcbC) and the hippocampus (H) to choice and learning involving reinforcement that was delayed or unlikely. Animals must frequently act to influence the world even when the reinforcing outcomes of their actions are delayed. Learning with action–outcome delays is a complex problem, and little is known of the neural mechanisms that bridge such delays. Impulsive choice, one aspect of impulsivity, is characterized by an abnormally high preference for small, immediate rewards over larger delayed rewards, and is a feature of attention-deficit/hyperactivity disorder (ADHD), addiction, mania, and certain personality disorders. Furthermore, when animals choose between alternative courses of action, seeking to maximize the benefit obtained, they must also evaluate the likelihood of the available outcomes. Little is known of the neural basis of this process, or what might predispose individuals to be overly conservative or to take risks excessively (avoiding or preferring uncertainty, respectively), but risk taking is another aspect of the personality trait of impulsivity and is a feature of a number of psychiatric disorders, including pathological gambling and some personality disorders. The AcbC, part of the ventral striatum, is required for normal preference for a large, delayed reward over a small, immediate reward (self-controlled choice) in rats, but the reason for this is unclear. Chapter 3 investigated the role of the AcbC in learning a free-operant instrumental response using delayed reinforcement, performance of a previously learned response for delayed reinforcement, and assessment of the relative magnitudes of two different rewards. Groups of rats with excitotoxic or sham lesions of the AcbC acquired an instrumental response with different delays (0, 10, or 20 s) between the lever-press response and reinforcer delivery. A second (inactive) lever was also present, but responding on it was never reinforced. The delays retarded learning in normal rats. AcbC lesions did not hinder learning in the absence of delays, but AcbC-lesioned rats were impaired in learning when there was a delay, relative to sham-operated controls. Rats were subsequently trained to discriminate reinforcers of different magnitudes. AcbC-lesioned rats were more sensitive to differences in reinforcer magnitude than sham-operated controls, suggesting that the deficit in self-controlled choice previously observed in such rats was a consequence of reduced preference for delayed rewards relative to immediate rewards, not of reduced preference for large rewards relative to small rewards. AcbC lesions also impaired the performance of a previously learned instrumental response in a delay-dependent fashion. These results demonstrate that the AcbC contributes to instrumental learning and performance by bridging delays between subjects’ actions and the ensuing outcomes that reinforce behaviour. When outcomes are delayed, they may be attributed to the action that caused them, or mistakenly attributed to other stimuli, such as the environmental context. Consequently, animals that are poor at forming context–outcome associations might learn action–outcome associations better with delayed reinforcement than normal animals. The hippocampus contributes to the representation of environmental context, being required for aspects of contextual conditioning. It was therefore hypothesized that animals with H lesions would be better than normal animals at learning to act on the basis of delayed reinforcement. Chapter 4 tested the ability of H-lesioned rats to learn a free-operant instrumental response using delayed reinforcement, and their ability to exhibit self-controlled choice. Rats with sham or excitotoxic H lesions acquired an instrumental response with different delays (0, 10, or 20 s) between the response and reinforcer delivery. H-lesioned rats responded slightly less than sham-operated controls in the absence of delays, but they became better at learning (relative to shams) as the delays increased; delays impaired learning less in H-lesioned rats than in shams. In contrast, lesioned rats exhibited impulsive choice, preferring an immediate, small reward to a delayed, larger reward, even though they preferred the large reward when it was not delayed. These results support the view that the H hinders action–outcome learning with delayed outcomes, perhaps because it promotes the formation of context–outcome associations instead. However, although lesioned rats were better at learning with delayed reinforcement, they were worse at choosing it, suggesting that self-controlled choice and learning with delayed reinforcement tax different psychological processes. Chapter 5 examined the effects of excitotoxic lesions of the AcbC on probabilistic choice in rats. Rats chose between a single food pellet delivered with certainty (probability p = 1) and four food pellets delivered with varying degrees of uncertainty (p = 1, 0.5, 0.25, 0.125, and 0.0625) in a discrete-trial task, with the large-reinforcer probability decreasing or increasing across the session. Subjects were trained on this task and then received excitotoxic or sham lesions of the AcbC before being retested. After a transient period during which AcbC-lesioned rats exhibited relative indifference between the two alternatives compared to controls, AcbC-lesioned rats came to exhibit risk-averse choice, choosing the large reinforcer less often than controls when it was uncertain, to the extent that they obtained less food as a result. Rats behaved as if indifferent between a single certain pellet and four pellets at p = 0.32 (sham-operated) or at p = 0.70 (AcbC-lesioned) by the end of testing. When the probabilities did not vary across the session, AcbC-lesioned rats and controls strongly preferred the large reinforcer when it was certain, and strongly preferred the small reinforcer when the large reinforcer was very unlikely (p = 0.0625), with no differences between AcbC-lesioned and sham-operated groups. These results suggest that the AcbC contributes to action selection by promoting the choice of uncertain, as well as delayed, reward. Tue, 23 Jan 2007 00:00:00 GMT http://www.dspace.cam.ac.uk:80/handle/1810/237273 2007-01-23T00:00:00Z http://www.dspace.cam.ac.uk:80/handle/1810/237034 Title: A psychological analysis of the effects of memory retrieval prior to extinction on the reacquisition of a conditioned fear association Authors: Wood, Melissa Allison Abstract: The successful reduction of fear is the aim of clinicians treating people with anxiety disorders such as post-traumatic stress disorder or phobias. Existing treatments for these conditions, however, require many treatment sessions and are prone to relapse. A new technique, first demonstrated in rats by Monfils, Cowansage, Klann, & LeDoux (2009) and later shown to be effective in humans (Schiller et al., 2010), provides a method of efficiently reducing fear in a manner which is resistant to various known triggers of relapse. This procedure involves a single presentation of the fear-inducing stimulus one hour prior to extinction training. This procedure produces extinction learning that is resistant to the return of fear resulting from a change of context, the passage of time, exposure to the unconditioned stimulus, and even further conditioning of the stimulus with an aversive stimulus. This dissertation focuses on one particular property of this procedure: that a stimulus extinguished using this procedure is resistant to subsequent retraining of the fear association. The first four experiments presented here are aimed at replicating this phenomenon and determining whether prediction error at retrieval is necessary for the effect to occur. Following on from these studies, the next chapter presents three experiments which investigate whether trial spacing effects could explain the enhanced extinction and highlights conditions under which the effect is weakened, or possibly reversed. The next three experiments compare the properties of a stimulus extinguished under these conditions with a stimulus extinguished under normal conditions. These studies focus on explanations involving inhibition, inattention and the disruption of stimulus representations. In the final three experiments, the possibility of reversing the effect is investigated. These studies look at the effect of memory retrieval prior to retraining of the stimulus to determine the conditions under which the stimulus can again come to elicit a fear response. Tue, 16 Nov 2010 00:00:00 GMT http://www.dspace.cam.ac.uk:80/handle/1810/237034 2010-11-16T00:00:00Z http://www.dspace.cam.ac.uk:80/handle/1810/236782 Title: The ins and outs of pleasure: roles and importance of hedonic value Authors: Laane, Kristjan Abstract: The focus of this thesis was the hedonic value of stimuli, which is more commonly known as pleasure or positive affect. First, the scientific meaning of hedonic value was dissected. Second, a classification identifying core causes of positive affect was created. The classification was derived from specific positive moments reported by individuals throughout a day (collected through experience sampling methodology). Seventeen triggers of positive affect were identified, which were extracted from the data rather than originating from theory. Third, affective influences on reflexive-like motor responses were investigated using an approach-avoidance task. Contrary to previous studies, approach reaction times were not speeded by highly affective stimuli. Instead, a novel non-emotional effect was found on reaction times, which could directly explain the current results, and those of previous studies, in non-affective terms. Fourth, the propagation of hedonic reactivity from pleasurable to neutral stimuli was investigated. Contrary to expectations, the evaluative conditioning procedure utilised did not exhibit a phenomenon called blocking. Instead, 'liking' spread non-selectively to all stimuli co-occurring with the source hedonic stimulus. Fifth, the positive effect of pleasure on goal-directed motivation was established: participants were found to press a food trigger harder for highly palatable snacks compared to bland snacks, even though participants were not informed about the hidden measurement of forces. Additionally, the impact of hedonic value on actual food intake was quantified with best-fit equations that predicted consumption at both the group and individual level. In the last study, hedonic habituation, or the inhibitory effect of pleasure on itself, was demonstrated: eating pleasant snacks, as compared to bland ones, reduced the hedonic ratings of test foods that were consumed afterwards. Finally, these inputs and outputs of hedonics were integrated into a model specifying principal roles of pleasure in human behaviour. This pleasure-incentive model explains the effects of pleasure on incentive motivation, and makes important predictions about the mechanisms of pathological conditions such as over-eating and drug addiction. Description: Pagination differs from hard bound copy. Index missing from e-thesis. Tue, 08 Feb 2011 00:00:00 GMT http://www.dspace.cam.ac.uk:80/handle/1810/236782 2011-02-08T00:00:00Z http://www.dspace.cam.ac.uk:80/handle/1810/236348 Title: Neuropsychology of reinforcement processes in the rat Authors: Cardinal, Rudolf N Abstract: This thesis investigated the role played by regions of the prefrontal cortex and ventral striatum in the control of rats’ behaviour by Pavlovian conditioned stimuli, and in their capacity to choose delayed reinforcement. First, the function of the anterior cingulate cortex (ACC) in simple Pavlovian conditioning tasks was addressed. The ACC is a subdivision of prefrontal cortex that has previously been suggested to be critical for the formation of stimulus–reward associations. It was found that lesions of the ACC did not prevent rats from learning a simple conditioned approach response to a conditioned stimulus (CS) predictive of food reward, or from utilizing that CS as a conditioned reinforcer subsequently. Additionally, these subjects successfully acquired a conditioned freezing response to a CS predicting footshock. However, the same animals were impaired at the acquisition of autoshaped behaviour, an impairment that has been demonstrated previously. An autoshaping deficit was also observed when lesions were made following training. The phenomenon of Pavlovian–instrumental transfer was intact in these subjects. The hypothesis was developed that the ACC is not critical for the formation of stimulus–reward associations per se, but is critical when multiple stimuli must be discriminated on the basis of their differential association with reward. In support of this hypothesis, animals with lesions of the ACC were impaired on a version of the conditioned approach task in which a second, neutral stimulus, perceptually similar to the CS, was added; the lesioned subjects exhibited reduced discrimination. Second, the role of the nucleus accumbens (Acb) in Pavlovian–instrumental transfer was investigated. The nucleus accumbens core, together with a larger amygdalar–striatal network of which it is a component, has previously been shown to be necessary for the expression of ‘simple’ Pavlovian–instrumental transfer. Rats with lesions of the nucleus accumbens core (AcbC) and shell (AcbSh) were tested on a ‘response-specific’ Pavlovian–instrumental transfer task, in which a Pavlovian CS selectively enhances instrumental responding for the outcome with which the CS was originally paired. AcbC lesions impaired the response specificity of this effect, while AcbSh lesions abolished Pavlovian–instrumental transfer entirely. These results are consistent with some — but not all — previous results in suggesting that the shell provides ‘vigour’ and the core provides ‘direction’ for the potentiation of behaviour by Pavlovian CSs. Third, an attempt was made to train rats on a task for assessing preference for delayed reinforcement, using the ‘adjusting-delay’ paradigm. It was not immediately apparent that the rats reacted to the contingencies operative in this task, and mathematical analysis of their behaviour was conducted to establish whether their behaviour was sensitive to the delay, and what ‘molar’ features of performance on this task could be explained by delay-independent processes. Fourth, a different delayed reinforcement choice task was developed, modifying a previously published task in which the subject is repeatedly offered a choice, in discrete trials, of a small reward delivered immediately, and a large reward delivered after a delay, with the delays systematically varied by the experimenter. Rats were trained on versions of this task in which the large, delayed reinforcer was or was not explicitly signalled by a cue present during the delay. The behavioural basis of performance on this task was examined, and d-amphetamine, chlordiazepoxide, and alpha-flupenthixol were administered systemically. It was found that the effects of d-amphetamine depended on whether the delayed reinforcer was signalled or unsignalled, increasing preference for signalled delayed reinforcement at some doses, but decreasing preference for unsignalled delayed reinforcement. These results may resolve contradictions in the literature, and are suggested to reflect the known effect of amphetamine to potentiate responding for conditioned reinforcers. Fifth, rats that had been trained on this task (with no explicit signals present during the delay) were given lesions of the ACC, AcbC, or medial prefrontal cortex (mPFC). ACC-lesioned rats were no different from sham-operated controls in their ability to choose a large, delayed reinforcer. Lesions of mPFC reduced the tendency of subjects to shift from one lever to the other during the course of a session, but mPFC-lesioned subjects responded normally to removal of the delays, suggesting a loss of stimulus control. However, rats with lesions of the AcbC were severely impaired on this task, preferring the small, immediate reward, even though they discriminated the reinforcers. Additionally, the effects of intra-Acb amphetamine were assessed using a different version of the delayed reinforcement choice task, and found to have slight but inconsistent effects to reduce preference for the delayed reinforcer, though this effect did not depend on whether the delayed reward was signalled or unsignalled. These results suggest that the AcbC contributes significantly to the rat’s ability to choose a delayed reward, a finding that has important implications for the understanding of Acb function. It is suggested that dysfunction of the AcbC may be a key element in the pathology of impulsivity. Mon, 16 Jul 2001 23:00:00 GMT http://www.dspace.cam.ac.uk:80/handle/1810/236348 2001-07-16T23:00:00Z http://www.dspace.cam.ac.uk:80/handle/1810/224472 Title: Attention and awareness in human learning and decision making Authors: Aczel, Balazs Abstract: This dissertation presents an investigation of the modifying role of attention and awareness in human learning and decision making. A series of experiments showed that performance in a range of tests of unconscious cognition can be better explained as resulting from conscious attention rather than from implicit processes. The first three experiments utilised a modification of the Serial Reaction Time task in order to measure the interaction of implicit and explicit learning processes. The results did not show evidence for an interaction, but did exhibit an effect of explicit knowledge of the underlying rules of the task. Subsequent studies examined the role of selective attention in learning. The investigation failed to provide evidence that learning inevitably results from the simple presentation of contingent stimuli over repeated trials. Instead, the learning effects appeared to be modulated by explicit attention to the association between stimuli. The following study with a novel test designed to measure the role of selective attention in prediction learning demonstrated that learning is not an obligatory consequence of simultaneous activation of representations of the associated stimuli. Rather, learning occurred only when attention was drawn explicitly to the association between the stimuli. Finally, the Deliberation without Attention Paradigm was tested in a replication study along with two novel versions of the task. Additional assessment of the conscious status of participants’ judgments indicated that explicit deliberation and memory could best explain the effect and that the original test may not be a reliable measure of intuition. In summary, the data in these studies did not require explanation in terms of unconscious cognition. These results do not preclude the possibility that unconscious processes could occur in these or other designs. However, the present work emphasises the role conscious attention plays in human learning and decision making. Tue, 12 Jan 2010 00:00:00 GMT http://www.dspace.cam.ac.uk:80/handle/1810/224472 2010-01-12T00:00:00Z