The visual system extracts global (overall) motion estimates from natural scenes to construct representations of the visual world. Any moving image may be characterised by different local regions with distinct directions (or speeds), that might be independent from each other. Each point of the visual field only yields a piecemeal representation of moving objects and so conveys limited (local) information of the visual environment. To reliably estimate image motion, the visual system combines ('pools') these local signals into a global percept. Yet, it is equivocal whether the computational steps leading to human perceptual decisions are guided by statistical regularities present within the visual environment or whether they are better explained in terms of structured decoding of neural population activity. The purpose of this thesis was to investigate which strategies the visual system employs to combine local vectors of motion into a global percept. This pooling process was explored by using a combination of psychophysical techniques and computational modelling. A common assumption is that the pooling of visual motion signals is synonymous with averaging. However, this might only lead to a simplistic explanation of how local signals are combined by the visual system. The experiments outlined in this thesis explored whether or not global motion perception always adopts a strict averaging strategy. As observers often reported perceiving simultaneously overlapping (transparent) surfaces, the relationship between perceived global motion and transparency perception was also investigated and characterised. The findings described in this thesis have shown that perceived global motion does not always coincide with an averaging strategy. They also suggest that the mechanisms underlying global direction and global speed perception might be different. The spatiotemporal pooling of local direction signals was generally well predicted by a neural mechanism-based computation. By contrast, a geometric average oflocal speeds (that gives more weight to low speeds) was a good predictor of global speed perception. The results of these experiments have also shown that transparency perception strongly affects perceived global speed. Although observers' ability to discriminate between overlapping motion patterns was modulated by stimulus-based characteristics, the balance between integration and segregation of local motion signals appeared to mainly rely on the presence of relatively low and high speeds within a moving scene. Finally, these findings suggest that the visual system might encode transparent motion by employing multiple independent velocity-tuned channels.

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From an initial review of the literature on the superior colliculus it was apparent that there were a number of discrepancies concerning the effects of lesions upon general activity and discrimination performance in the rat. Subsequent experiments further investigated these effects. It was demonstrated that colliculectomised rats were transiently impaired in retention of multi-choice discriminations and that the deficit transferred to a two-choice task. In this task, it appeared that operated animals were unable to inhibit on-going responses. Initial learning of simple discriminations was normal. Later tests of the retention deficit demonstrated that operated rats performed faster than normals in the initial stages of a trial, but that simple running speeds were the same. This latency difference lasted throughout and after relearning. It was suggested that post-colliculectomy deficits in such tasks resulted from a locomotor disinhibition effect which caused animals to initiate responses before completing processes necessary for a successful outcome of the trial. In open-field tests, colliculectomised rats were hyperactive, but less responsive to novel visual stimuli than normals. Operated animals responded to novel auditory stimuli with startle whilst normal animals exhibited orienting responses. In the home cage, there was no difference in activity between the normal and operated rats, and there was no running speed difference in a simple runway. Operated and normal animals in the home cage responded differently to changes in the light cycle. A hypothesis was proposed to account for deficits in certain discrimination tasks in terms of locomotor disinhibition, which was also used to account for locomotor hyperactivity in the open-field. The hypothesis proposed that the rat tectum mediates orienting responses to novel stimuli, and that integral with this response is an inhibition of on-going locomotor activity. This hypothesis was reviewed in the light of previous literature regarding rats and other species.

The aim of this research was to develop a behavioural paradigm capable of quantifying action acquisition. It takes the form of a series of experiments in which human participants learn to produce new actions with a joystick. Research questions were focussed on the behavioural implications of Redgrave and Gurney's (2006) theory that dopamine neurons in the ventral midbrain play a pivotal role in the reinforcement and reselection of motor output that is essential to action learning. The first study looked at the effect of delayed audio and visual reinforcement on the ability to learn stable hand positions. Delays of 100 ms were found to impair acquisition in both modalities. This degree of temporal sensitivity supports the idea that dopamine neurons fire at low latencies to reduce the reinforcement of non-contiguous motor output. The second study investigated the effect of delay on the learning of hand movements. The movements produced during the delay period were analysed to address the question of whether the quantity of non-contingent output would impact on learning over and above the mismatch in temporal alignment. The results revealed that this was not the case, thus suggesting that timing is of primary importance to learning. The final study utilised a task requiring more complex movements, in an attempt to reduce the contribution of high-level, conscious, learning in favour of low-level non-declarative learning. Performance was compared across conditions, which differed in the quantity of spatial information provided. No evidence was found that the type of movements produced during learning impacted on later performance, thus indicating a tendency to use high-level spatial guidance of movements. All findings are discussed in terms of the value of the current paradigm and the extent to which they support the theory that action learning is mediated by a time-stamping mechanism in the midbrain.

The synchronisation of interpersonal behaviours in everyday life is essential to achieve joint actions tasks. Even in social interactions where there is no specific coordination goal, particular spatio-temporal relations are maintained between individuals unintentionally and are an important factor in social bonding. Two distinct approaches have been proposed to understand coordination in interpersonal movements during social interactions: the embodied simulation approach links behavioural matching to shared neural resources, which are activated both when an action is observed and when it is performed. Recent studies suggest that only biological stimuli evoke action imitation, as non-biological stimuli are processed elsewhere in the brain. An alternative approach, the coordination dynamics perspective, does not specify any neural substrate but views synchronisation as an emergent phenomenon of an underlying dynamical process, in which the components of a system self-organise toward a stable state. From this standpoint, the dynamic patterns of coordination are affected by attributes of the stimulus kinematics irrespective of whether this stimulus is biological or non-biological in nature. In this thesis, I investigate whether motion kinematics that are perceived as human will facilitate interpersonal coordination more readily than stimuli perceived as artificial. First, in two psychophysical experiments participants were asked to distinguish between real human movements and artificially produced movements. The findings provide insights into the features of one-dimensional cyclic movements that allow them to be identified as human; specifically, observers perceived movements of a particular range of smoothness and frequency as human, whereas both, very fast or very slow movements outside this range were reliably distinguished as artificial. Second, these distinct subsets of human and artificial movement kinematics were applied as stimuli in subsequent intentional and unintentional coordination experiments, and variations in both the strength and pattern of coordination response was observed. In contrast to expectations derived from the embodied simulation literature, experiments did not provide any evidence that the perceptual identification of a stimulus as human matters with regard to improving coordination. Instead, all modulations in coordination behaviour could be explained solely on the basis of direct effects of different stimulus kinematics on an underlying dynamical system. A subsequent modelling study showed that the same patterns of coordination occur with a system of coupled oscillators when the same stimuli are applied. The consistency between the theoretical model and empirical results suggests that the observed coordination behaviour in human subjects can be explained on the basis of an underlying dynamical system, in accordance with the coordination dynamics approach, without the need to incorporate perceptual factors or specialised neural networks. Future studies will have to clarify whether factors relating to the perception of stimuli, predicted by embodied simulation, might become more important in the absence of larger scale effects associated with stimulus kinematics or with a more ecological stimulus.

No description available.

Substantial evidence shows that attentional bias towards threat plays a fundamental role in anxiety and that deficits in frontal brain functioning might explain this. However, a paucity of research on anger related attentional bias leaves unanswered questions about whether similar mechanisms underpin aggression. This has led to a lack of theoretical explanations for anger related attentional bias and effective interventions to reduce anger. Electroencephalographic (EEG) evidence suggests that the hemispheric specialisation of the frontal brain predicts differential responding to emotional stimuli in anger and anxiety. Manipulating motivational direction, via unilateral hand contractions (UHCs), provides a means to explore the causal relationship between anger and attentional bias to threat. Previously, this method has only been used to change experiential and expressional aspects of emotion and its effectiveness in modulating attentional components of emotion regulation are unknown. Therefore, this Thesis aims to explore whether UHCs effectively modulate attentional bias to threat in relation to, and independent of trait anger. It also aims to discover the underlying neural effects of the UHC method to examine whether threat-related attentional changes reflect modulations in cognitive control and/or approach motivation. Finally, this Thesis aims to bridge the gap between the attentional bias and frontal brain asymmetry literature. These aims will be addressed by employing Emotional Stroop and Dot Probe paradigms as well as event related potentials measures. The findings provide evidence that UHCs provides an effective technique to modulate attentional bias to threat. Specifically, RHCs reduce attentional bias to threat independent of trait anger and in individuals with low trait anger but they do not modify attentional bias to threat in high anger individuals. In contrast, LHCs increase attentional bias to threat and this reduced task relevant processing, independent of trait anger. The implications of these novel findings and future directions of research are discussed.

According to contemporary learning theory, instrumental actions are controlled, in a large part, by two dissociable systems. Whilst goal-directed actions are driven by an explicit awareness of an anticipated outcome, habitual responses are the product of previously reinforced associations between contextual stimuli and salient outcomes. Although experimental lesion studies and pathological disorders, such as drug addiction and Parkinson's disease, have advanced our knowledge of the brain circuitries important in the regulation of instrumental behaviour, we still do not have a full understanding of the executive mechanisms regulating the expression of these behaviours or the neural processes which underlie the shift from �exible goal-directed actions to stimulus-bound habits that occurs naturally following repeated practice. The present work focused speci�cally on the molecular mechanisms involved in this shift. The �rst experimental section, Chapter 3, established a protocol for modelling goal-directed and habitual instrumental responding in rats. Experiment 1 measured the sensitivity of lever press responding to changes in outcome value, as an index of goal-directed behaviour, in groups of rats sourced from either Charles River or Harlan. After three sessions of instrumental training, only rats sourced from Charles River and devalued in the same context that they were trained in, rather than in a di�erent context, reduced responding for a devalued outcome. Building on these �ndings, in Experiment 2 a separate group of rats, sourced from Charles River, was trained to level press over 10 sessions. In contrast to the �rst experiment, lever press responding at test in this group of animals was insensitive to outcome devaluation. These initial experiments demonstrated evidence consistent with a training-induced shift from goal-directed to habitual instrumental behaviour and were used to inform the design of a second set of experiments, described in Chapter 4, in which region-speci�c di�erences in gene expression were compared across groups of rats with di�erent levels of lever press experience. DNA microarray analysis of tissue samples from the dorsolateral (DLS) and posterior dorsomedial striatum (pDMS), using Rat Gene 2.0 ST A�ymetrix arrays, revealed both training group- and brain region-speci�c ef- fects. Evidence of a high proportion of non-linear regulation pro�les across the training groups was indicative of experience-dependent shifts in gene expression; further- more, the high degree of separation between the training-dependent expression pro�les of the DLS and pDMS points to the dynamic engagement of distinct, region-speci�c regulatory networks over the course of instrumental learning. The experiments presented in Chapter 5 went on to investigate the role of epigenetic mechanisms, speci�cally histone acetylation, in the regulation of instrumental behaviour by using the histone deacetylase inhibitor sodium butyrate (NaB) to interfere with endogenous chromatin remodelling processes. The e�ects of systemic injections of NaB on the sensitivity of lever press behaviour to changes in outcome value were assessed in three separate studies, each designed to target a di�erent stage of learning. NaB had no e�ect on the acquisition or consolidation of goal-directed behaviour. However, after three sessions of training, the instrumental behaviour of animals receiving an injection of NaB prior to exticntion test was less sensitive to reinforcer devaluation relative to controls, suggesting that histone acetylation may be involved in the retrieval phase of instrumental learning. In an attempt to address some of the limitations of systemic drug administration, the �nal experimental chapter, Chapter 6, describes an initial exploratory investigation into the e�ects of administering NaB directly into the brain using a microinfusion protocol. Western blot analysis showed an increase in histone H4 acetylation in the mPFC following infusions of NaB targeting the infralimbic cortex. Behavioural data suggested that NaB may act to ameliorate some of the damaging e�ects of the infusion procedure, with NaB-treated animals showing enhanced sensitivity to outcome devaluation relative to controls. These preliminary data act as proof of principle for the development of a microinfusion protocol for studying the role of histone acetylation in instrumental learning and highlight a number of practical issues which will be addressed in ongoing work. Taken together the experiments presented in this thesis provide evidence for the existence of discrete gene expression changes associated with minimal or extended training regimes, and for highly speci�c e�ects of a systemically administered HDACi on components of instrumental behaviour. These data o�er new insights into the molecular mechanisms involved in the regulation of instrumental learning in rodents and provide a starting point for further investigations into the role that epigenetic processes may play in the neural plasticity underlying the transition from goal-directed to habitual behaviour.

I. Handedness - Different types of handedness, Eyedness - the nature of eye-dominance. The relation between eye-dominance and handedness. Theories concerning this relationship. Left-handed children and those subnormal in reading. Possibility of connection between this subnormality and eyedness of the left-handed child. Possible nature of the connection between "eyedness" and retardation in reading (if such connection exists) Types of difficulties in reading experienced by left-handed children which may be due to "eyedness". II. Experiments with left-handed children; 1st set, with results and conclusions.(a) Description of experiments and subjects.(b) Results of experiments showing:- (1) Incidence of left and right eyedness in unselected group.(2) Incidence of left or right eyedness in group of left-handed children(3) Reversals of forms (in words and groups of letters) (4) Transposition of letters in words and groups of letters. (5) Children's remarks with any pertinent introspections. Suggestion of difficulty or orientation arising from these results. Further analysis and conclusions, III. Experiments with adults; 1st set, with results and conclusions. (a) Description of experiments, (b) Description of subjects as to eyedness and handedness,(c) Results of experiments analysed,(d) The prominence of reversals of forms in the case of left-eyed subjects,(e) Other results of the analysis:-(i) type of reaction to exposures. (ii) Subjects, introspections and suggestions arising from these. IV. Further experiments with children.(a) Left-eyed and left-handed group.(b) Left-eyed and right-handed group.(c) Right-eyed and left-handed group.(d) Left-eyed and left-handed group. These experiments are tachistoscopic in character. They are designed to reveal the disability (or otherwise) experienced by left-handed children as regards orientation of forms and position in space. V. Further experiments with adults.(a) Right-handed and right-eyed.(b) Left-handed and left-eyed. (c) Left-handed and right-eyed. These experiments should confirm the results of the first set of experiments as to the characteristics of form most frequently reversed. VI. (l) Experiments with adults and children to prove whether the incidence of reversals of form, or of orientation with regard to position in space, is affected when the objects perceived tachistoscopically are in motion. (2) Analysis of these experiments. VII. General observations and conclusions.

Pseudoneglect represents the tendency for healthy individuals to show a slight but consistent bias in favour of stimuli appearing in the left visual field. The bias is often measured using variants of the line bisection task. An accurate model of the functional architecture of the visuospatial attention system must account for this widely observed phenomenon, as well as for modulation of the direction and magnitude of the bias within individuals by a variety of factors relating to the state of the participant and/or stimulus characteristics. To date, the neural correlates of pseudoneglect remain relatively unmapped. In the current thesis, I employed a combination of psychophysical measurements, electroencephalography (EEG) recording and transcranial direct current stimulation (tDCS) in an attempt to probe the neural generator(s) of pseudoneglect. In particular, I wished to utilise and investigate some of the factors known to modulate the bias (including age, time-on-task and the length of the to-be-bisected line) in order to identify neural processes and activity that are necessary and sufficient for the lateralized bias to arise. Across four experiments utilising a computerized version of a perceptual line bisection task, pseudoneglect was consistently observed at baseline in healthy young participants. However, decreased line length (experiments 1, 2 and 3), time-on-task (experiment 1) and healthy aging (experiment 3) were all found to modulate the bias. Specifically, all three modulations induced a rightward shift in subjective midpoint estimation. Additionally, the line length and time-on-task effects (experiment 1) and the line length and aging effects (experiment 3) were found to have additive relationships. In experiment 2, EEG measurements revealed the line length effect to be reflected in neural activity 100 – 200ms post-stimulus onset over source estimated posterior regions of the right hemisphere (RH: temporo-parietal junction (TPJ)). Long lines induced a hemispheric asymmetry in processing (in favour of the RH) during this period that was absent in short lines. In experiment 4, bi-parietal tDCS (Left Anodal/Right Cathodal) induced a polarity-specific rightward shift in bias, highlighting the crucial role played by parietal cortex in the genesis of pseudoneglect. The opposite polarity (Left Cathodal/Right Anodal) did not induce a change in bias. The combined results from the four experiments of the current thesis provide converging evidence as to the crucial role played by the RH in the genesis of pseudoneglect and in the processing of visual input more generally. The reduction in pseudoneglect with decreased line length, increased time-on-task and healthy aging may be explained by a reduction in RH function, and hence contribution to task processing, induced by each of these modulations. I discuss how behavioural and neuroimaging studies of pseudoneglect (and its various modulators) can provide empirical data upon which accurate formal models of visuospatial attention networks may be based and further tested.