This thesis explores the reported disparity between the concurrent think-aloud theory (Ericsson and Simon, 1984; 1993) and its application in usability practice. A tension exists between the classic approach and usability practitioners' desire to gather relevant data. This research is the first to specifically examine the impact of a number of methodological changes in the concurrent think-aloud method, on both the utility and validity of usability test data. Three empirical studies were conducted. Study One examined the impact of adding evaluator interventions to the classic think-aloud to make it an interactive think-aloud. The results showed that there were no differences between the types of utterances produced in the classic and interactive think- aloud styles, although the latter produced more utterances relevant to usability analysis, and more verbalised usability problems. However, the interactive think-aloud also produced a large number of low impact problems. The usefulness of interventions was low, and the types of interventions issued could affect the nature of the verbalisations elicited, their relevance and the quality of problems. Study Two examined the impact of using an explicit instruction that requests specific contents in the think-aloud. The results showed that the explicit instruction neither improved the utility of data nor facilitated the usability analysis process, compared to the classic instruction. However, it served to increase participants' mental workload and led users to be more critical about the system. The third study considered the use of dual elicitation by gathering both concurrent and retrospective think-aloud data. The results showed that by adding a minimal amount of time, this approach increased the explanatory power of the data, and facilitated problem discovery and understanding. These improvements were achieved without compromising the test's validity. The empirical work reveals that methodological changes that are divergent from their theoretical motivations may not work as effectively as practitioners anticipated. The risks of introducing invalid data are not worth the limited benefits obtained. The research suggests that researchers and practitioners should adhere to the classic think-aloud, but reinforce it by collecting additional retrospective data. This dual elicitation technique appears to be a more rigorous and useful usability evaluation tool.

Hemispheric asymmetries are a basic principle of human brain organization. Once thought to be unique to humans, hemispheric asymmetries have meanwhile been documented in a wide range of species, suggesting they contain an evolutionary advantage. However, there are a few theories as to why asymmetry confers such an advantage and, moreover, there is a paucity of empirical work which is chiefly limited to a small number of animal studies. The present thesis is concerned with directly testing theories about potential evolutionary advantages in humans. Because it is widely believed that hemispheric asymmetries generally enhance cognitive processing, the first study Investigated the general relationship between functional lateralization and cognitive performance using two visual half-field paradigms. The second study employed the same paradigms to test the notion that hemispheric asymmetries specifically enhance parallel processing. The final study tested the notion that high degrees of lateralization (determined with a dichotic listening test) are associated with enhanced left-right discrimination. It was hypothesized that in all studies highly lateralized participants would outperform less lateralized participants. In contrast to our hypotheses however, highly lateralized participants were consistently outperformed by less lateralized participants. Less lateralized participants showed higher cognitive performance and excelled at parallel processing and left-right discrimination. The results of the present thesis thus challenge a) the general notion that high degrees of lateralization are associated with enhanced cognitive processing, b) the specific notions that lateralization enhances parallel processing and left-right discrimination and c) the idea that hemispheric asymmetries are advantageous for cognitive processing per se. Taken together with previous studies, it is argued that advantages of hemispheric asymmetries depend on the degree of lateralization and situational requirements. That is, high, low and intermediate degrees of lateralization of the brain are each associated with distinct advantages (and disadvantages), depending on the demands placed upon it.

This major research project focuses on the possible influence that chronic substance use may have on prospective memory (PM) ability. Part one consists of a literature review examining the associations between recreational substance use and impairments in PM. This identifies 24 studies from 23 publications examining PM ability in recreational substance users. Although PM impairments are reported by most, the review highlights a number of methodological weaknesses in the existing body of research. These include an over-reliance on self report PM measures, the use of inadequate objective assessments, and limitations in internal and external validity. Suggestions are made for how methodological limitations may be overcome in future work. Part two is an empirical paper which describes a study that aimed to overcome the limitations highlighted in part one. This compared the performance of an alcohol dependent group to that of an age and premorbid ability matched control group, on an objective PM measure called the Virtual Week. It was found that the event based PM performance of alcohol dependents was strongly associated with indices of both alcohol usage and severity of alcohol dependence, and significantly impaired compared to that of controls. Furthermore, an imagining technique improved controls’ time based PM, but did not improve alcohol dependents’ PM. These findings are discussed in terms of the relevance of strategy application to successful PM functioning, and the implications this may hold for clinical practice. Part three consists of a critical appraisal of the research process, which explains why various methodological choices were made and how particular challenges were overcome as they arose. Certain conceptual issues are also reflected upon and their relevance to future research discussed.

The purpose of this thesis was to examine the influence of different characteristics of prospective memory (PM) cues and ongoing tasks on processes supporting PM retrieval. The first four experiments assessed the role of motivational enhancements on event- and timebased tasks. In the first experiment, it has been hypothesized that in a high-incentive condition, PM performance should be better compared with a low-incentive condition. In addition, in a negative reinforcement condition PM performance should be better than in a positive reinforcement condition. The second experiment extended these hypotheses by looking at individual differences, using skin conductance and personality questionnaires, while in the third experiment these hypotheses were used to assess order effect, using two successively low-incentive conditions. Finally, in the fourth experiment, these hypotheses have been tested on time-based PM tasks, including a punishment condition. The results from these experiments showed that high compared with low incentives influence retrieval processes on PM tasks. In addition, individuals differed in their performance to the negative and positive reinforcements on event-based tasks. Finally, performance was better under the punishment condition compared with the positive and negative reinforcement conditions on time-based tasks. The fifth experiment looked at how different types of PM cues and ongoing tasks influence retrieval processes when multiple cues were involved. Results showed that when the ongoing task was demanding and the PM cues were nonfocal, greater attentional resources were assigned to perform the PM task. In the final experiment, implicit and explicit encoding of PM intentions was investigated. It has been hypothesized that explicit encoding should lead to better performance compared with implicit encoding and that pre- and poststimulus neural activity, measured by electroencephalogram, will predict the retrieval of PM intentions. The overall results highlighted the influence of different components involved during encoding and retrieval of intentions, on PM performance.

The ultimate goal of language comprehension is to obtain meaning. However, this is difficult because many words are semantically ambiguous, mapping onto multiple meanings. Semantic ambiguity resolution has proven a useful tool to investigate language processing in general. However, the majority of research has focused on the initial encounter of an ambiguous word. Less work has investigated the processes occurring after an ambiguous word is encountered, when the initially understood meaning needs to be reinterpreted in light of subsequent inconsistent information. The first part of this thesis investigated the cognitive processes underlying semantic reinterpretation, examining how successful listeners are at this process as well as assessing the time course of suppressing and integrating the contextually inappropriate and appropriate meanings respectively. A semantic relatedness task was employed in which participants listened to ambiguous and unambiguous sentences and decided whether a following visual probe word was related or unrelated to the sentence. The results revealed that listeners are highly effective at reinterpretation but that suppression of the inappropriate meaning is delayed relative to integration of the appropriate meaning. The rest of the thesis examined the neural responses to these sentences by using functional magnetic resonance imaging (fMRI) and Transcranial magnetic stimulation (TMS). The fMRI study demonstrated ambiguity-elevated responses in left inferior frontal gyrus (LIFG) and posterior temporal cortex. These responses were modulated by the frequency of the ambiguous word’s meanings, such that activation was greater for sentences with a higher likelihood of reinterpretation. The final study developed a TMS paradigm to examine whether LIFG is necessary for this process, demonstrating evidence that this region may be important for sentence processing more generally. Together, this thesis has advanced understanding into the cognitive and neural processes underlying semantic reinterpretation that have various implications for models of ambiguity resolution and language comprehension in general.

No description available.

This thesis is concerned with the problem of defining the processes by which a subject selects a response to a stimulus. Initially certain topics in two areas of research, sensory scaling and threshold measurement, are revived. In relation to the first the conflict between Fechner's law, which is derived from threshold measurements, and the more recent 'power law' given by 'direct methods' of scaling, is examined. It is shown that this conflict is due not to differences in the data from which the laws are derived, but to differences in the assumptions underlying the treatment of the data, and it is suggested that the logarithmic function may prove more useful for explaining a number of the findings in experiments on scaling, and that the same central effect of the stimulus say be considered to determine the response whether scales are being derived or thresholds measured. A short account of the development of models of the sensory discrimination process is then given, and evidence is reviewed which appears sufficient to justify applying the theory of signal-detection to the sensory threshold, and rejecting the neural quantum theory. To investigate the threshold mechanism further it was decided to examine the effect of an accessory stimulus given in controlled temporal relation to a critical stimulus on the threshold for the latter. The first experiment was an attempt to confirm Motokawa's finding (Gebhard, 1953) that sensitivity to an electric phosphene is affected a preceding flash of light, reaching a maximum 1-3 seconds after the flash, the exact time depending on the colour of the light. The absolute threshold for the electric phosphene was measured by the method of limits at intervals of 1-9 seconds after a flash of blue or white light. Motokawa found that sensitivity was maximal when the interval between the stimuli was 2 seconds for the white light, or 3 seconds for blue light. Neither particular could be confirmed. There was no peak of sensitivity in the range studied, nor was there any marked difference in the curves relating threshold level to inter-stimulus interval for the two colours of light. Instead a monotonic relation between threshold and inter-stimulus interval was found, for this range, the threshold falling as the inter-stimulus interval decreased, slowly at long intervals and more rapidly at the shorter ones. This raised two questions: why could Motokawa's findings not be confirmed? and what was the nature of the effect which had been found? The experimental technique of Motokawa and his colleagues is reviewed, and it is suggested that their findings mat be an artefact of certain features of their procedure, in particular the use of large steps where a threshold change is not expected, and small steps where a threshold is expected to appear. Two possibilities are considered for the threshold-lowering effect: it might depend on the use of two visual stimuli and reflect a peripheral interaction at the retina, or it might be a central effect, not specifically visual. To investigate this the light flash was replaced, in the second experiment, by the ring of a bell of the same duration and given at the same inter-stimulus intervals. The same threshold-lowering effect of the accessory stimulus was found as in the first experiment, showing that the effect could be produced by an accessory stimulus in another modality. Further support for this conclusion was provided by Experiment 3, in which both the light-flash and the bell were used, the former at the same intervals as in Experiment 1, but the latter always preceding the critical stimulus by 1 second. Here the threshold did not vary significantly: there was little or no residual effect of the light when the bell was given at a shorter inter-stimulus interval. It appeared that it was the interval of time since the most recent accessory stimulus, whatever its modality, that mainly determined the degree to which the threshold fell. In Experiment 4 the generality of the threshold-lowering effect was examined further. Using a visual accessory and auditory critical stimulus the possibility that the effect would occur only with visual critical stimuli was excluded. These findings raised two questions: What processes underlie the change in threshold? What determines the relation between threshold level and inter-stimulus interval? Possible answers to the first question were suggested in terms of the analysis offered by signal detection theory. In this theory it is assumed that the decision whether or not a stimulus has been administered is made by a process equivalent to comparing the afferent input with a criterion, and the criterion is computed in a way which may take account of the parameters, the variance (andsigma;²) and mean (M), of the 'noise' and 'signal + noise' distributions. The possibilities considered were that a change was produced in the functioning of the afferent paths at the time that the message from the critical stimulus was travelling along them, equivalent to a reduction in andsigma;_N or M_N, with a consequent change in the value of the criterion, c, computed by the subject (a 'distribution effect'), or that the computation of c was affected directly (a 'criterion effect'). Two hypotheses were proposed in answer to the second question (the relation between threshold level and inter-stimulus interval): (a) The accessory stimulus might have an 'arousing' or 'alerting' effect, causing an immediate central change with a small latency, which then decayed with time. (b) The subject might make use of the accessory stimulus as a 'temporal reference point' or 'warning'. By virtue of temporal information which he might possess he could use the accessory stimulus to determine when he could expect the critical stimulus to arrive. Here two subsidiary hypotheses might be suggested: (i) The subject lovers his threshold for the whole of the 'waiting time'. (ii) He may lover his threshold only when he expect the critical stimulus. Since his time-keeping ability is of limited precision, and the range of error will be greater for long times than for short, the 'range of expectation', if he allows for this, will be smaller the shorter the inter-stimulus interval. In either case, if the reduction in threshold is inversely related to the period for which it is reduced, a relation between threshold level and inter-stimulus interval of the sort found would be produced. In Experiment 5 an attempt was made to test the 'warning' hypothesis directly by using a small range of randomly varied inter-stimulus intervals instead of a single fixed interval as previously, in order to see whether a fall in threshold daring the 'range of expectation' could be demonstrated. Ranges of 0.5-1.5 seconds were used but no consistent effect was found. In Experiment 6 the same procedure was used but the inter-stimulus intervals were varied at random over a large range - 5 seconds - to prevent the accessory stimulus providing temporal information. Though it was found that the fall in threshold previously shown o^er this range disappeared, the possibility that this was due to 'habituation' of an 'arousal response' could not be excluded. The exact relation between the fall in threshold and the inter-stimulus interval was next considered.

Introduction: Based on a theoretical integration of cognitive development psychology, psychoanalytic theory and attachment theory, Blatt and his colleagues formulated a systematic psychodynamic model of mental representation of self and other emphasizing internalization, differentiation and integration of self and object representations in normal and disrupted personality development. During the development process, adolescence is a critical transformational stage to determine either the construction of an integrated self-identity and more mature expressions of relatedness within a wider social context, or emergence or consolidation of many forms of psychopathology. This study used a twin design to examine the degree of articulation, differentiation and integration of representation of self and representations of self and parents in mid-adolescence in order to estimate the role of the environment and of genes in individual differences in these representations. Method: This study used 160 twin pairs including equal numbers of monozygotic and dizygotic twins reared together to examine the degrees of genetic and environmental influences on mental representation in adolescence. Representations of self and other were assessed using an adapted measure of the Differentiation-Relatedness Scale. The estimates of heritability of mental representations were calculated using model-fitting analysis. Results/Discussion: There were indications of approximately 38% heritability in mental representation of self-mother and 28 % in representation of self-father. The remainder of the variance was attributed to non-shared environmental influences and possible measurement error with no effect of shared environmental influences. No genetic influence or shared environmental influences was found in self-representation. Different pathways were discussed to interpret the results, which suggested complex gene-environment interactions at play affecting the levels of mental representations in adolescence. Furthermore, the mechanisms involved in representations of self and other in adolescence were compared and contrasted with attachment security, which may potentially provide us a fuller understanding of the links between childhood experiences and the development outcomes of cognitive, affective and interpersonal dimensions in personality development.

Constructing internal representations of the world is a fundamental aspect of cognition, allowing us to predict and control our environment. However, sensory observations are frequently noisy and incomplete, leading to the question of how such representations are acquired. We take a normative approach to this problem of inductive inference, or structure learning, asking what agents should believe about the world in light of their observations. We consider experiments from a variety of psychological domains, in each case proposing a rational structure-learning model and comparing real behaviour with model predictions. Firstly, we address the problem of rule learning in a memory-based maze task. We show that gating algorithms, a model-free approach to solving POMDPs, replicate rule acquisition in rats, as well as transfer of learning under rule reversal. Secondly, we consider the problem of behaving flexibly in environments composed of distinct behavioural regimes, or 'contexts'. Vile show that a novel decision-making model that discriminates between contexts captures a number of important animal learning phenomena including spontaneous recovery, partial reinforcement and overlearning effects, and serial reversal learning effects. Thirdly, we turn to perception and whether structure learning can explain participants' behaviour in a perceptual task. Assuming that participants aim to infer the structure underlying observed stimuli, we show that discounting of colour cues when estimating motion direction can be explained by a rational clustering model. Finally, we consider the effect of working memory capacity (WMC) on category learning. Treating category learning as a structure learning problem and modelling WMC as the quantity of inferential resources available, we replicate the positive association between WMC and both rate of learning and ability to switch between categorisation strategies. Our results suggest that the simple assumption that agents construct representations of their environments, combined with adequate modelling tools for representation and inference, can offer parsimonious explanations of behaviour in diverse areas of psychology.

This thesis explores whether a decision to withhold an impending motor action can be initiated unconsciously. There is much evidence to suggest that both voluntary actions and reactions to external events can be initiated without consciousness. However, there is some debate as to whether inhibition or control of behaviour can occur unconsciously. Libet et al. (1985) proposed that while consciousness is not required to initiate an action, it may be essential in allowing the action to be vetoed. Similarly, evidence from tasks involving response conflict points to a close association between inhibition/control of behaviour and conscious awareness. In particular, both fMRl and EEG correlates of control are seen to be absent when response conflict is unconscious. The research in this thesis aimed to clarify whether the no-go N2 and P3, ERP correlates of the no-go response, can be modulated by an unconscious prime. In each of five EEG experiments, target-related N2 and P3 components were significantly affected by the nature of the unconscious primes. More specifically, when the unconscious information coded for a no-go response, N2 and P3 amplitude was significantly reduced, suggesting that inhibition of the imminent response was primed by the unconscious stimuli. In addition, there was evidence that the unconscious primes were able to directly engage frontal inhibition/control mechanisms. In experiments 1, 2 and 5 early ERP differences were observed over frontocentral electrodes that were entirely dependent on the nature of the unconscious prime. Furthermore, experiment 5 showed that this early modulation of ERP activity was directly related to the extent to which the participants were influenced by the unconscious primes. These findings suggest that inhibition of an impending motor action can be initiated by an unconscious stimulus.