Our thoughts and behaviours can sometimes be influenced by stimuli that we are not consciously aware of having seen. For example, the presentation of a word that is blocked from entering conscious visual perception through masking can subsequently influence the cognitive processing of a further target word. However, the idea that unconscious cognition is sophisticated enough to process the semantic meaning of subliminal stimuli is controversial. This thesis attempts to explore the extent of subliminal priming. Empirical research centering on subjective methods of measuring conscious knowledge is presented in a series of three articles. The first article investigates the subliminal priming of negation. A series of experiments demonstrates that unconscious processing can accurately discriminate between two nouns beyond chance performance when subliminally instructed to either pick or not pick a given noun. This article demonstrates not only semantic processing of the instructional word, but also unconscious cognitive control by following a two-word subliminal instruction to not choose the primed noun. The second article investigates subliminal priming of active versus passive verb voice by presenting a prime sentence denoting one of two characters as either active or passive and asking which of two pictorial representations best matches the prime. The series of experiments demonstrates that overall, participants were able to identify the correct image for both active and passive conditions beyond chance expectations. This article suggests that individuals are able to process the meaning of word combinations that they are not aware of seeing. The third article attempts to determine whether subliminal processing is sophisticated enough to allow for the activation of specific anxieties relating to relationships. Whilst the findings reveal a small subliminal priming effect on generalised anxiety, the evidence regarding the subliminal priming of very specific anxieties is insensitive. The unconscious is shown in these experiments to be more powerful than previously supposed in terms of the fine grained processing of the semantics of word combinations, though not yet in terms of the fine grained resolution of emotional priming.

The following work presents an exploration of human search behaviour both from biological and computational perspectives. Search behaviour is defined as the movements made by an organism while attempting to find a resource. This work describes some of the principal procedures used to record movement, methods for analysing the data and possible ways of interpreting the data. In order to obtain a database of searching behaviour, an experimental setup was built and tested to generate the search paths of human participants. The test arena occupied part of a football field and the targets consisted of an array of 20 golf balls. In the first set of experiments, a random and regular distribution of targets were tested. For each distribution, three distinct conspicuity levels were constructed: a cryptic level, in which targets were painted the same colour as the grass, a semi-conspicuous level in which targets were left white and a conspicuous condition in which the position of each target was marked by a red flag, protruding one metre from the ground. The subjects tested were 9-11 year old children and their search paths were collected using a GPS device. Subjects did not recognise the spatial cues regarding the way targets were spatially distributed. A minimal decision model, the bouncing search model, was built based on the characteristics of the childrens search paths. The model produced an outstanding fit of the children's behavioural data. In the second set of experiments, a new group of children were tested for two new distributions obtained by arranging the targets in patches. Again, children appeared unable to recognise spatial information during the collection processes. The children's behaviour once again produced a good match with that of the bouncing search model. This work introduces several new methodological aspects to be explored to further understand the decision processes involved when humans search. Also, it illustrates that integrating biology and computational science can result in innovative research.

Two key questions underpin the research presented here. Firstly, how does altered higher order awareness contribute to hypnotic experience? Secondly, how do meditation and hypnosis differ in terms of the role of higher order awareness? These questions are addressed here in the form of four papers. In the first paper I review the literatures of hypnosis and meditation in order to consider the similarities and differences between meditation and hypnosis in terms of the role of attentional skill and the neural underpinnings of each. I then draw conclusions regarding the contrasting role of higher order awareness and metacognition in meditation and hypnosis. Paper two explores higher order awareness in hypnosis by comparing the effects of alcohol, compared to placebo, on hypnotisability and associated frontal lobe executive functioning. Paper three compares meditation and hypnosis by investigating differences in higher order thoughts, mindfulness, absorption and perceptual encoding style as revealed by self-report measures. The final paper takes a broader look at higher order awareness and its relation to the experience of agency and involuntariness in hypnotic suggestion using a Libet type paradigm.

In this thesis I explore functions of the neuromodulator dopamine in the context of autonomous learning and behaviour. I first investigate dopaminergic influence within a simulated agent-based model, demonstrating how modulation of synaptic plasticity can enable reward-mediated learning that is both adaptive and self-limiting. I describe how this mechanism is driven by the dynamics of agentenvironment interaction and consequently suggest roles for both complex spontaneous neuronal activity and specific neuroanatomy in the expression of early, exploratory behaviour. I then show how the observed response of dopamine neurons in the mammalian basal ganglia may also be modelled by similar processes involving dopaminergic neuromodulation and cortical spike-pattern representation within an architecture of counteracting excitatory and inhibitory neural pathways, reflecting gross mammalian neuroanatomy. Significantly, I demonstrate how combined modulation of synaptic plasticity and neuronal excitability enables specific (timely) spike-patterns to be recognised and selectively responded to by efferent neural populations, therefore providing a novel spike-timing based implementation of the hypothetical ‘serial-compound' representation suggested by temporal difference learning. I subsequently discuss more recent work, focused upon modelling those complex spike-patterns observed in cortex. Here, I describe neural features likely to contribute to the expression of such activity and subsequently present novel simulation software allowing for interactive exploration of these factors, in a more comprehensive neural model that implements both dynamical synapses and dopaminergic neuromodulation. I conclude by describing how the work presented ultimately suggests an integrated theory of autonomous learning, in which direct coupling of agent and environment supports a predictive coding mechanism, bootstrapped in early development by a more fundamental process of trial-and-error learning.

One of the central tenets of the embodied theory of language comprehension is that the process of understanding prompts the same perceptuo-motor activity involved in actual perception and action. This activity is a component of comprehension that is not memory–dependent and is hypothesized to be intact in Alzheimer's Disease (AD). Each article in this thesis is aimed at answering the question whether individuals with probable AD, healthy older adults and younger adults show differences in their performance on tests where perceptual and motoric priming take place during language comprehension. The second question each article asks is whether language comprehension in AD can be facilitated by the specific use of this perceptual and motoric priming. Article I examines whether the way individuals with pAD represent verbs spatially matches the way healthy older and younger adults do, and how stable these representations are. It also explores in what way spatial representations may relate to verb comprehension, more specifically, whether representations matching the norms translate into a better quality of verb comprehension. Article II tests the interaction between the verbs' spatial representations taking place during comprehension and perceptual cues - compatible and incompatible to the representations - in order to investigate whether individuals with pAD show differences in susceptibility to perceptual cues, compared to healthy older and younger participants. The second aim of this article is to explore in what way performance on a word-picture verification task can be affected, with reference to the fact that in previous studies on young participants, both priming and interference have resulted from the interaction of linguistic and perceptual processing. Article III explores the Action Compatibility Effect (ACE) (Glenberg & Kaschak, 2002) with the aim of finding out whether the ACE exists for volunteers with pAD and whether it can facilitate language comprehension. The order of presentation of language and movement is manipulated to establish whether there is a reciprocal relationship between them. This information could be crucial in view of possible applications to individuals with pAD. These articles test, for the first time, the effects of the manipulation of the perceptuo-motor component during language comprehension in individuals with pAD; they are intended as a methodological exploration contributing to a better understanding of the potential of embodiment principles to support language comprehension changes associated with pAD. Embodiment effects need to be studied further with a view to putting them to use in either clinical or real-life applications.

It is often reported that after amputation people experience "a constant or inconstant ... sensory ghost ... faintly felt at time, but ready to be called up to [their] perception" (Mitchell, 1866). Perceptual abnormalities have been highlighted in amputees, such as sensations in the phantom when being stroked elsewhere (Ramachandran et al., 1992) or when observing someone in pain (Giummarra and Bradshaw, 2008). This thesis explored the perceptual changes that occur following amputation whist focusing on pain, vision and touch. A sample of over 100 amputees were recruited through the National Health Service. Despite finding no difference in phantom pain based on physical amputation details or nonpainful perceptual phenomena, results from Paper 1 indicated that phantom pain may be more intense, with sensations occurring more frequently, in amputees whose pain was triggerinduced. The survey in Paper 2 identified a group of amputees who in losing a limb acquired mirror-touch synaesthesia. Higher levels of empathy found in mirror-touch amputees might mean that some people are predisposed to develop synaesthesia, but that it takes sensory loss to bring dormant cross-sensory interactions into consciousness. Although the mirror-system may reach supra-threshold levels in some amputees, the experiments in Paper 3 suggested a relatively intact mirror-system in amputees overall. Specifically, in a task of apparent biological motion, amputees showed a similar, although weaker, pattern of results to normalbodied participants. The results of Paper 4 showed that tactile spatial acuity on the face was also largely not affected by amputation, as no difference was found between the sides ipsilateral and contralateral to the stump. In Paper 5 cross-modal cuing was used to investigate whether referred tactile sensations could prime a visually presented target in space occupied by the phantom limb. We conclude that perception is only moderately affected in most amputees, but that in some the sensory loss causes normally sub-threshold processing to enhance into conscious awareness.

Face adaptation techniques have been used extensively to investigate how faces are processed. It has even been suggested that face adaptation is functional in calibrating the visual system to the diet of faces to which an observer is exposed. Yet most adaptation studies to date have used unfamiliar faces: few have used faces with real world familiarity. Familiar faces have more abstractive representations than unfamiliar faces. The experiments in this thesis therefore examined face adaptation for familiar faces. Chapters 2 and 3 explored the role of explicit recognition of familiar faces in producing face identity after-effects (FIAEs). Chapter 2 used composite faces (the top half of a celebrity's face paired with the bottom half of an unfamiliar face) as adaptors and showed that only recognised composites produced significant adaptation. In Chapter 3 the adaptors were cryptic faces (unfamiliar faces subtly transformed towards a celebrity's face) and faces of celebrity's siblings. Unrecognised cryptic and sibling faces produced FIAEs for their related celebrity, but only when adapting and testing on the same viewpoint. Adaptation only transferred across viewpoint when a face was explicitly recognised. Chapter 4 demonstrated that face adaptation could occur for ecologically valid, personally familiar stimuli, a necessary pre-requisite if adaptation is functional in calibrating face processing mechanisms. A video of a lecturer's face produced FIAEs equivalent to that produced by static images. Chapters 5 and 6 used a different type of after-effect, the face distortion after-effect (FDAE), to explore the stability of our representations for personally familiar faces, and showed that even representations of highly familiar faces can be affected by exposure to distorted faces. The work presented here shows that it is important to take facial familiarity into account when investigating face adaptation effects, as well as increasing our understanding of how familiarity affects the representations of faces.

In human fear conditioning 'resistance to extinction' occurs when the removal of the aversive outcome fails to produce a reduction in conditioned responding. This phenomenon is important to understanding the persistence of anxiety disorders such as phobias. The research presented in this thesis examines factors that promote the acquisition and maintenance of learned fear response and attempts to differentiate between different explanations of the resistance to extinction phenomenon. To investigate the impact of different conditioning procedures (evaluative or classical conditioning) on the durability of the conditioned response (CR), event-related potential (ERP) methodology was employed. In addition, the role of the fear-relevance of the conditioned stimulus (CS), in supporting the acquisition and resistance to extinction of the CR, was explored. Evidence suggested that extinction effects are likely to reflect procedural differences in conditioning rather than different underlying learning processes. Extinction effects were dissociable across procedures, supporting the role of the type of unconditioned stimulus (US) in explaining past demonstrations of extinction when responses were indexed by physiological measures. Verbally transmitted, threat information heightened aversive US-expectancies and fear beliefs without the need for conditioning. Additionally, fear-beliefs were reduced without the need for extinction training when positive information was provided. Contrary to Davey's (1997) expectancy bias model, the results do not support the hypothesis that verbal information interacts with direct contingency experience to create fear responses; instead, information appears to be a direct pathway to fear. ERP measures for fear responses did not echo the effects of verbal information and contingency on fear-beliefs. However, the comparability of our ERP data, to other research using physiological measures of response, is discussed regarding the number of trials required to calculate the average ERP response. Due to averaging over a large number of trials the ERP measure may not be sensitive to fluctuations in response that may be dependent on information or contingency manipulations. In conclusion our data suggests the importance of verbal information as a pathway to fear and the role of cognitive factors in the prevention and treatment of fears.

The extent to which conscious and unconscious mental processes contribute to our experiences of learning and the subsequent knowledge has been subject to great debate. Dual process theories of implicit learning and recognition memory bear many resemblances, but there are also important differences. This thesis uses subjective measures of awareness to explore these themes using the artificial grammar learning (AGL) and remember/know (R/K) procedures. Firstly, the relationship between response times associated with intuition and familiarity based responding (conscious judgment of unconscious structural knowledge) compared to rule and recollection based responding (conscious structural knowledge) in AGL were found to be strikingly similar to remembering and knowing; their R/K analogues. However, guessing (unconscious judgment knowledge) was also distinct from intuition and familiarity based responding. Secondly, implicit learning in AGL was shown to occur at test, which would not be expected in R/K. Finally, wider theories of cognition, unconscious thought and verbal overshadowing, were shown to have measurable effects on AGL and R/K respectively. The approach used in this thesis shows the merits of both in-depth analysis within a given method combined with the synthesis of seemingly disparate theories. This thesis has built upon the important distinction between conscious and unconscious structural knowledge but also suggests the conscious-unconscious division for judgment knowledge may be as important. Implicit learning and recognition memory tasks differ in the kinds of mental processes that subjective measures are sensitive toward; particularly so in situations where judgment knowledge is unconscious. Different theories and methods divide nature in different ways; the conscious-unconscious judgment distinction may prove an important one.

This thesis examines the relevance of Hegelian-Marxian theory to modern day philosophy of cognitive science. It is suggested that certain key Hegelian-Marxian ideas and themes, such as 'externalization', 'praxis' and 'dialectics', have parallels in modern day cognitive science and that, in some instances a direct connection can be traced from Marxian theory to recent cognitive science, via intermediaries such as Vygotsky, Merleau-Ponty and Levins & Lewontin. It is also suggested that the overarching trajectory of cognitive science is one that can be usefully understood in Marxian terms as a 'retreat from alienation.' Taking this as one's starting point enables one to unify otherwise disparate perspectives under a single banner. In addition it provides one with a means of evaluating individual accounts, such as Varela, Thompson and Rosch's 'Embodied Mind' and Clark and Chalmers' 'Extended Mind'. Conversely, some recent cognitive scientific accounts, such as Kirsh & Maglio's work on 'epistemic action', offer further illumination of ideas that are ambiguously expressed in Marxian theory.