No description available.

No description available.

No description available.

No description available.

No description available.

Eleven experiments are reported which examine the effects of 90 dB (A) white noise on the processes which govern orienting of attention in visual space. The selectivity hypothesis argues that noise alters the priorities which govern stimulus selection so that subjectively dominant aspects of the environment are attended to more fully than those which are non-dominant. The applicability of this hypothesis is examined with regard to attentional orienting. Three experimental paradigms are used. The first involves a central cue presented immediately prior to target onset. In the absence of eye movements reaction times to expected targets are faster than to unexpected targets, but noise has no effects on performance. It is concluded that the power of the central alerting cue is focussing attention in a maximal fashion and noise has no further effect on policies of allocation. A second task design involves the presentation of positional information prior to a block of trials. Under such conditions subjects fail to maintain orienting as trials continue. Noise enhances the ability to maintain orienting over time. This effect is discussed in the light of the selectivity hypothesis. It is argued that the inability to maintain orienting is not due to the inhibition which arises as a result of successive responding. Rather it is due to the difficulty involved in maintaining an active orientation. The third paradigm involves orienting to specific locations on the basis of information stored in short-term memory. When recall of this information is aided by a visual warning signal occurring prior to target onset noise has no effect on performance. Without this signal, noise alters performance and these data are compared to predictions based upon the selectivity hypothesis. These effects are discussed in terms of a noise-induced change in the strategy of performance, rather than an effect which is mechanistic.

Previous research on the relationship between emotion and attention has focused primarily on attention to emotionally valenced stimuli; trait anxiety and attentional biases for threat; or the relationship between emotion and attention in clinical contexts. Few studies have investigated the effect of emotion on attentional processing irrespective of the valence of the stimuli that is being attended. However, such studies are important as they shed light on issues central to emotions theory such as whether the experience of discrete emotions is associated with distinct patterns of attentional processing. In this thesis six experiments and one correlational study are described. The experimental studies investigate whether the experience of discrete emotions - specifically amusement, happiness, sadness and fear - influence attentional processing in comparison to a neutral condition. Film clips, emotional images and music were used to elicit a target emotional state. A modified version of the Attention Network Test (ANT) was used to assess three forms of attention – phasic alerting, covert exogenous orienting and executive attention. The correlational study required participants to complete a set of emotion-related questionnaires including the Basic Emotion Scale (BES) and to perform the ANT. The results suggest that: i) fear reduces executive attention costs, ii) sadness reduces intrinsic alerting, but does not influence alerting, orienting or executive attention, iii) amusement and happiness do not differentially influence alerting, orienting or executive attention, iv) individual differences in the tendency to experience high arousal negative emotions are associated with phasic alerting, i.e. faster mobilisation of attentional resources in response to an impending stimulus and v) exogenous orienting of attention may be impervious to the influence of emotion, at least in context of neutrally valenced stimuli. Results relating to anxiety, emotion regulation and attention network performance are also discussed. Taken together these findings provide only limited support for the broaden-and-build theory (Fredrickson, 1998) of positive emotions. Amusement and happiness did not result in broadening (as assessed by executive attention costs) in the present studies. An attentional narrowing effect was found for fear but not for sadness. It is proposed that fear, but not sadness, facilitates inhibition and reduces executive attention costs, indicative of more focused attention. The results here also suggest a relationship between negative emotions characterised by high arousal and phasic alerting – an aspect of attention which has received little coverage in emotions research to date. Implications relating to the use of the ANT as a measure of attentional performance, and the challenges associated with manipulating emotion in a lab setting are discussed.

Visual processing is not fixed, but changes dynamically depending on the spatiotemporal context of the presented stimulus, and the behavioural task being performed. In this thesis, I describe theoretical and experimental work that was conducted to investigate how and why visual perception and neural responses are altered by the behavioural and statistical context of presented stimuli. The process by which stimulus expectations are acquired and then shape our sensory experiences is not well understood. To investigate this, I conducted a psychophysics experiment where participants were asked to estimate the direction of motion of presented stimuli, with some directions presented more frequently than others. I found that participants quickly developed expectations for the most frequently presented directions and that this altered their perception of new stimuli, inducing biases in the perceived motion direction as well as visual hallucinations in the absence of a stimulus. These biases were well explained by a model that accounted for their behaviour using a Bayesian strategy, combining a learned prior of the stimulus statistics with their sensory evidence using Bayes’ rule. Altering the behavioural context of presented stimuli results in diverse changes to visual neuron responses, including alterations in receptive field structure and firing rates. While these changes are often thought to reflect optimization towards the behavioural task, what exactly is being optimized and why different tasks produce such varying effects is unknown. To account for the effects of a behavioural task on visual neuron responses, I extend previous Bayesian models of visual processing, hypothesizing that the brain learns an internal model that predicts how both the sensory input and the reward received for performing different actions are determined by a common set of explanatory causes. Short-term changes in visual neural responses would thus reflect optimization of this internal model to deal with changes in the sensory environment (stimulus statistics) and behavioural demands (reward statistics), respectively. This framework is used to predict a range of experimentally observed effects of goal-orientated attention on visual neuron responses. Together, these studies provide new insight into how and why sensory processing adapts in response to changes in the environment. The experimental results support the idea of a very plastic visual system, in which prior knowledge is rapidly acquired and used to shape perception. The theoretical work extends previous Bayesian models of sensory processing, to understand how visual neural responses are altered by the behavioural context of presetned stimuli. Finally, these studies provide a unified description of ‘expectations’ and ‘goal-orientated attention’, as corresponding to continuous adaptation of an internal generative model of the world to account for newly received contextual information.

Pseudoneglect is the tendency to be biased towards the left side of space in tasks of a spatial nature. A non-visual form of the bias referred to as ‘representational pseudoneglect’ has been observed when people generate a mental representation of a stimulus in the complete absence of visual input - participants pay more attention to the left-hand side of the mental representation. The aim of this thesis was to advance our understanding of representational pseudoneglect by exploring the bias across lifespan using different modes of non-visual presentation (touch vs. audition vs. visual imagery). In Experiments 1 and 2 healthy participants aged 3 to 96 years used touch alone without vision to bisect wooden rods at the perceived centre. All participants (with the exception of some adolescents) showed leftward biases on tactile rod bisection and significant gender and age effects were found. In Experiments 3 to 10 healthy young adults listened to aural-verbal descriptions of abstract patterns or real-world scenes without vision and formed a mental representation of the spatial layout that was described. A leftward bias was consistently found for a relative judgement task along with a significant effect of monaural presentation and start side, but no lateralised bias for memory recall regardless of ‘mental mapping’ ability or method of response. In Experiment 11 participants eye movements were recorded while they visually processed and then memorised natural real-world scenes; again there was no lateralised memory or eye movement bias. Experiment 12 showed that a secondary task increased the magnitude of visuo-spatial pseudoneglect for children and adults under certain conditions. This thesis argues that purely representational forms of pseudoneglect clearly exist in healthy participants and that: 1) the results can be explained in terms of contralateral attentional orienting by the right hemisphere, 2) extraneous variables (gender; physical or imagined starting position) can mediate representational pseudoneglect, and 3) current models of cognitive ageing need to provide for a cognitive bias that can be enhanced by age.

L’objectif principal de mon travail de thèse est l’extraction de la direction du regard (attention visuelle) d’une personne à partir de la vidéo. Cette analyse est effectuée dans un environnement composé d’une scène cible et d’une zone d’observation. La scène cible est une région d’intérêt définie pour être analysée (e.g. un écran plasma large, une image projetée sur un mur, une affiche publicitaire, un linéaire dans un magasin, ou la vitrine d’un magasin). La zone surveillée quant à elle est l’emplacement d’où les personnes regardent la scène cible (e.g. la rue, un couloir ou bien les allées d’un supermarché). Les connaissances qui sont extraites sont alors utilisées pour comprendre le comportement visuel de personnes ainsi que pour la réorganisation de la scène cible. Pour atteindre cet objectif, nous proposons une approche basée sur l’estimation de l’orientation de la tête et la projection du champ visuel pour localiser la région d’intérêt. Nous avons utilisé une méthode d’estimation de l’orientation de la tête basée sur l’apparence globale et sur un modèle cylindrique, et une méthode de projection géométrique pour extraire les régions d’intérêts basée sur les données physiologiques de la vision humaine. L’analyse du comportement visuel des personnes a été effectuée à l’aide d’un ensemble de métriques. Les méthodes proposées ont été validées sur des données vidéos et images. / The aim of this thesis is to analyze the behaviour of the people passing in front of a target scene. We consider an environment composed of a so-called target scene (a specific scene under analysis, such as a large plasma screen, a projected image, an advertising poster, a shop window, etc.) and a monitored area (place from which people look at the target scene, such as a street or shopping mall). Computer vision provides promising techniques enabling to obtain such information by analyzing videos captured by cameras monitoring this area. Such information are useful in order to simplify technologies that uses the output of the studies about a target scene. In this thesis, we propose an approach that estimates the visual gaze of a person in a controlled environment. The visual gaze of a person is estimated from the head pose. It is followed by its projection on the target scene that allows to estimate the approximate location of interest. Finally, an analysis of the region of interest allows an accurate explanation of the human activity and interest.