The visual processing of a stimulus is facilitated by attention when it is at an attended location compared to an unattended location. However, whether attentional selection operates on the basis of visual features (e.g., color) independently of spatial locations is less clear. Six experiments were designed to examine how color information as well as location information affected attentional selection. In Experiment 1, the color of the targets and the spatial distance between them were both manipulated. Stimuli were found to be grouped based on color similarity. Additionally, the evidence suggested direct selection on the basis of color groups, rather than selection that was mediated by location. By varying the probabilities of target location and color, Experiments 2, 3 and 4 demonstrated that the use of color in perceptual grouping and in biasing the priority of selection is not automatic, but is modulated by task demands. Experiments 5 and 6 further investigated the relationship between using color and using location as the selection basis under exogenous and endogenous orienting. The results suggest that the precise nature of the interaction between color and location varies according to the mode of attentional control. Collectively, these experiments contribute to an understanding of how different types of information are used in selection and suggest a greater degree of flexibility of attentional control than previously expected. The flexibility is likely to be determined by a number of factors, including task demands and the nature of attentional control.

Perceptual rivalry refers to visual phenomena that are characterised by alternations between different percepts, despite an unchanging sensory input. Two common types of perceptual rivalry are (i) reversible figures — two-dimensional stable images that when viewed, are perceived to switch between different interpretations, and (ii) binocular rivalry — the alternations in image dominance resulting from the presentation of conflicting stimuli, one to each eye. Several investigators have suggested that these rivalling phenomena are mediated by similar neural mechanisms. Such a view, however, has not only been inadequately substantiated, but has also yet to be assessed in the context of a directly testable neurophysiological model. Miller and Pettigrew have proposed a novel, high-level interhemispheric switch (IHS) explanatory model of binocular rivalry. This model conceptualises the perceptual alternations as being mediated by alternations between one hemisphere’s selected image and the other hemisphere’s selected (rival) image. To assess their hypothesis, caloric vestibular stimulation (CVS) was used. CVS is a simple, inexpensive, and non-invasive brain stimulation technique that unilaterally activates high-level attentional areas. In accordance with the IHS model, CVS was found to significantly affect predominance (the duration that one image is perceived relative to the other, within a given viewing period) during conventional binocular rivalry with horizontal/vertical gratings and with orthogonal oblique gratings. The present thesis therefore aims, through the use of CVS, to extend this IHS model of binocular rivalry to reversible-figure alternations and propose a general IHS model of perceptual rivalry. Chapter 1 provides a detailed literature review of the field within the context of comparing both perceptual rivalries. In Chapter 2, investigations are presented on two different reversible figures — the perspective-reversing Necker cube and the figure–ground reversing Rubin’s vase–faces illusion. In these experiments, CVS was found to significantly change observers’ predominance compared to their baseline predominance. These results demonstrate that interhemispheric switching also mediates the alternations of these visual phenomena, in addition to binocular rivalry, thereby extending the IHS model to one of perceptual rivalry in general. Moreover, the findings are interpreted in a cognitive neuroscience context, including a novel proposal of a forebrain framework for the IHS model. Chapter 3 presents CVS experiments that address the issue of percept–to–hemisphere selection and the reproducibility of CVS effects, following Miller’s initial work on two types of conventional binocular rivalry. In planned analyses, significant predominance changes were not found in horizontal/vertical rivalry, oblique rivalry and Necker-cube rivalry. In post-hoc analyses that accounted for study-design differences between Miller’s original experiments and the present experiment, CVS was again not shown to induce significant predominance changes in any of the rivalry types. Assessment of directional predominance changes following CVS appeared to suggest an arbitrary selection of percept–to–hemisphere in all rivalry types, although no firm conclusions could be drawn from the obtained data on this issue. Nevertheless, the experiments further extend upon Miller’s earlier work by examining the inter- and intra-individual reproducibility of CVS-induced effects on predominance. Such reproducibility was found to be low and potential reasons for this are discussed. The experiments in Chapter 4 examine a type of binocular rivalry in which dichoptic presentation of Díaz-Caneja stimuli yields rivalry among four different stable images: half-field rivalry between the images presented to the eyes, and coherence rivalry in which aspects of each eye’s presented image are perceptually regrouped into rivalling coherent images. Each of these rivalries was found to occur for about half the given viewing time. Furthermore, CVS significantly shifted the predominance of perceived coherent images (coherence rivalry) but not half-field images (eye rivalry). This finding suggests that coherence rivalry (like conventional rivalry according to previous experiments) is mediated by interhemispheric switching at a high level, while eye rivalry is mediated by intrahemispheric mechanisms, most likely at a low level. In addition, it is proposed that Díaz-Caneja stimuli induce ‘meta-rivalry’ whereby these discrete high- and low-level competitive processes themselves rival for visual consciousness. The current thesis thus presents a novel meta-rivalry model of multistable binocular rivalry. It also presents the first direct evidence that interhemispheric switching mediates reversible-figure alternations, thereby supporting a generalised IHS model of perceptual rivalry. It is argued that both models provide a parsimonious exploratory framework within which specific predictions can be made and readily tested. Finally, the findings of all experiments in the current thesis are summarised.

Perceptual rivalry refers to visual phenomena that are characterised by alternations between different percepts, despite an unchanging sensory input. Two common types of perceptual rivalry are (i) reversible figures — two-dimensional stable images that when viewed, are perceived to switch between different interpretations, and (ii) binocular rivalry — the alternations in image dominance resulting from the presentation of conflicting stimuli, one to each eye. Several investigators have suggested that these rivalling phenomena are mediated by similar neural mechanisms. Such a view, however, has not only been inadequately substantiated, but has also yet to be assessed in the context of a directly testable neurophysiological model. Miller and Pettigrew have proposed a novel, high-level interhemispheric switch (IHS) explanatory model of binocular rivalry. This model conceptualises the perceptual alternations as being mediated by alternations between one hemisphere’s selected image and the other hemisphere’s selected (rival) image. To assess their hypothesis, caloric vestibular stimulation (CVS) was used. CVS is a simple, inexpensive, and non-invasive brain stimulation technique that unilaterally activates high-level attentional areas. In accordance with the IHS model, CVS was found to significantly affect predominance (the duration that one image is perceived relative to the other, within a given viewing period) during conventional binocular rivalry with horizontal/vertical gratings and with orthogonal oblique gratings. The present thesis therefore aims, through the use of CVS, to extend this IHS model of binocular rivalry to reversible-figure alternations and propose a general IHS model of perceptual rivalry. Chapter 1 provides a detailed literature review of the field within the context of comparing both perceptual rivalries. In Chapter 2, investigations are presented on two different reversible figures — the perspective-reversing Necker cube and the figure–ground reversing Rubin’s vase–faces illusion. In these experiments, CVS was found to significantly change observers’ predominance compared to their baseline predominance. These results demonstrate that interhemispheric switching also mediates the alternations of these visual phenomena, in addition to binocular rivalry, thereby extending the IHS model to one of perceptual rivalry in general. Moreover, the findings are interpreted in a cognitive neuroscience context, including a novel proposal of a forebrain framework for the IHS model. Chapter 3 presents CVS experiments that address the issue of percept–to–hemisphere selection and the reproducibility of CVS effects, following Miller’s initial work on two types of conventional binocular rivalry. In planned analyses, significant predominance changes were not found in horizontal/vertical rivalry, oblique rivalry and Necker-cube rivalry. In post-hoc analyses that accounted for study-design differences between Miller’s original experiments and the present experiment, CVS was again not shown to induce significant predominance changes in any of the rivalry types. Assessment of directional predominance changes following CVS appeared to suggest an arbitrary selection of percept–to–hemisphere in all rivalry types, although no firm conclusions could be drawn from the obtained data on this issue. Nevertheless, the experiments further extend upon Miller’s earlier work by examining the inter- and intra-individual reproducibility of CVS-induced effects on predominance. Such reproducibility was found to be low and potential reasons for this are discussed. The experiments in Chapter 4 examine a type of binocular rivalry in which dichoptic presentation of Díaz-Caneja stimuli yields rivalry among four different stable images: half-field rivalry between the images presented to the eyes, and coherence rivalry in which aspects of each eye’s presented image are perceptually regrouped into rivalling coherent images. Each of these rivalries was found to occur for about half the given viewing time. Furthermore, CVS significantly shifted the predominance of perceived coherent images (coherence rivalry) but not half-field images (eye rivalry). This finding suggests that coherence rivalry (like conventional rivalry according to previous experiments) is mediated by interhemispheric switching at a high level, while eye rivalry is mediated by intrahemispheric mechanisms, most likely at a low level. In addition, it is proposed that Díaz-Caneja stimuli induce ‘meta-rivalry’ whereby these discrete high- and low-level competitive processes themselves rival for visual consciousness. The current thesis thus presents a novel meta-rivalry model of multistable binocular rivalry. It also presents the first direct evidence that interhemispheric switching mediates reversible-figure alternations, thereby supporting a generalised IHS model of perceptual rivalry. It is argued that both models provide a parsimonious exploratory framework within which specific predictions can be made and readily tested. Finally, the findings of all experiments in the current thesis are summarised.

People have always been fascinated by the extent to which belief or will may influence<p>behavior. Proverbs, like “we tend to get what we expect,” and concepts, such as optimistic<p>thinking or self-fulfilling prophecy, reflect this intuition of an important link between one’s<p>dispositions and subsequent behavior. In other words, one’s predictions directly or<p>indirectly cause them to become true. In a similar manner, every culture, country or<p>religion has their own words for ‘expectation,’ ‘belief,’ ‘disappointment,’ ‘surprise,’ and<p>generally all have the same meaning: under uncertainty, what one expects or believes is the<p>most likely to happen. This relation between what caused a reaction in the past will<p>probably cause it again in the future might not be realistic. If the expected outcome is not<p>confirmed, it may result in a personal ‘disappointment’, and if the outcome fits no<p>expectations, it will be a ‘surprise’. Our brain is hardwired with this heuristic capacity of<p>learning the cause-effect relationship and to project its probability as the basis for much of<p>our behavior, as well as cognitions. This experience-based expectation is a form of<p>learning that helps the brain to bypass an exhaustive search in finding a satisfactory<p>solution. Expectations may thus be considered an innate theory of causality; that is, a set of<p>factors (causes) generating a given phenomenon (effects) influence the way we treat<p>incoming information but also the way we retrieve the stored information. These<p>expectancy templates may well represent one of the basic rules of how the brain processes<p>information, affecting the way we perceive the world, direct our attention and deal with<p>conflicting information. In fact, expectations have been shown to influence our judgments<p>and social interactions, along with our volition to individually decide and commit to a<p>particular course of action. However, people’s expectations may elicit the anticipation of<p>their own automatic reactions to various situations and behaviors cues, and can explain that<p>expecting to feel an increase in alertness after coffee consumption leads to experiencing<p>the consequent physiologic and behavioral states. We call this behavior-response<p>expectancy. This non-volitional form of expectation has been shown to influence<p>cognitions such as memory, pain, visual awareness, implicit learning and attention, through<p>the mediation of phenomena like placebo effects and hypnotic behaviors. Importantly,when talking about expectations, placebo and hypnosis, it is important to note that we are<p>also talking about suggestion and its modulating capability. In other words, suggestion has<p>the power to create response expectancies that activate automatic responses, which will, in<p>turn, influence cognition and behavior so as to shape them congruently with the expected<p>outcome. Accordingly, hypnotic inductions are a systematic manipulation of expectancy,<p>similar to placebo, and therefore they both work in a similar way. Considering such<p>assumptions, the major question we address in this PhD thesis is to know if these<p>expectancy-based mechanisms are capable of modulating more high-level information<p>processing such as cognitive conflict resolution, as is present in the well-known Stroop<p>task. In fact, in a recent series of studies, reduction or elimination of Stroop congruency<p>effects was obtained through suggestion and hypnotic induction. In this PhD thesis, it is<p>asked whether a suggestion reinforced by placebos, operating through response-expectancy<p>mechanisms, is able to induce a top-down cognitive modulation to overcome cognitive<p>conflict in the Stroop task, similar to those results found using suggestion and hypnosis<p>manipulation. / Doctorat en Sciences Psychologiques et de l'éducation / info:eu-repo/semantics/nonPublished

Restless legs syndrome (RLS) is a sensory-motor disorder characterized by abnormal circadian rhythm with an increase in the severity of sensory and motor symptoms at night. Even though many neurological diseases have shown a strong nexus between motor and cognitive symptoms, to date, cognitive functions especially cognitive control in RLS has been poorly understood. Given that cognitive control is a key to leading a self-serving and successful life, including many aspects of employment, social life, and attaining long-term goals, this thesis aimed to examine cognitive control and the underlying mechanisms in RLS. Thalamic gamma aminobutyric acid (GABA), which has been linked to RLS sensory-motor symptoms, also plays an important role in cognitive control. Therefore, the potential relationship between thalamic GABA level and cognitive control in RLS was examined (Study I). RLS patients displayed reduced working memory-based control performances as compared to healthy controls. Elevated thalamic GABA was found to attenuate the observed control deficits in RLS, even though changes in thalamic GABA levels might not be the ultimate causes of these deficits. According to the modulatory effect of thalamic GABA on thalamic activity and thalamo-cortical connectivity, relatively higher GABA levels may have helped RLS patients compensate for their pathological changes such as thalamic hyperactivity and hypoconnectivity, which may underpin the observed control deficits. The critical feature of RLS, abnormal circadian rhythm is thought to be related to nocturnal striatal dopamine deficiency. Concerning the dopaminergic modulation of cognitive control, the circadian variation of cognitive control processes has been investigated (Study II & III). RLS patients displayed reduced attentional control (Study II) and automatic response activation (Study III) at night, which resulted from decreased activation within the extra-striate visual cortex, the superior parietal cortex, and the premotor cortex. As there were no activity changes within the prefrontal cortex, it is likely that cortico-basal ganglia cognitive loops were less prone to RLS. Instead, striatal dopamine deficiency at night may have influenced the cortico-cortical functional connectivity and cortico-basal ganglia motor loops in RLS. These findings not only shed light on the underlying mechanisms of cognitive control, but also advance early clinical treatment possibilities for cognitive changes in RLS patients. Furthermore, recent insights into daytime-related cognition may help patients develop a suitable daytime schedule to minimize the detrimental effects induced by cognitive deficits.