The processing of information within the visual system is limited by several cognitive and neural bottlenecks. One critical bottleneck occurs in visual working memory (VWM), as the amount of information that can be maintained on-line is limited to three to four items. While numerous theories have addressed this limited capacity of VWM, it is unclear how processing bottlenecks in the initial selection and perception of visual information affect the number or precision of representations that can be maintained in VWM. The purpose of this dissertation was to examine whether early competition for resources within the visual system limits the number or precision of representation that can be maintained in VWM. To establish whether competitive interactions affect VWM, Chapters 1 – 4 tested whether performance on VWM tasks was related to the distance between memory items. The results of these experiments reveal that when objects are presented close together in space, VWM performance is impaired relative to when those same objects are presented further apart. Using a three-component model of continuous responses in a recall task, Chapters 3 – 4 demonstrated that the distance between objects primarily affects the precision of responses, and increases the number of non-target errors. Chapter 5 extended these findings to distractors, demonstrating that multiple distractors affect the precision and accuracy of VWM responses. Chapters 6 – 7 tested how attentional selection can bias memory representations, revealing that objects that are given high attentional priority were reported with greater precision. Finally, Chapters 8 and 9 examined bias-signals as a potential source of individual differences in VWM performance, revealing that high-performers have more precise representations of sub-capacity representations than low-performers. Together, these results reveal that VWM performance is limited by competition for representation within the visual system, and that attention plays a critical role in resolving competition and consequently, determining the contents of VWM.

The processing of information within the visual system is limited by several cognitive and neural bottlenecks. One critical bottleneck occurs in visual working memory (VWM), as the amount of information that can be maintained on-line is limited to three to four items. While numerous theories have addressed this limited capacity of VWM, it is unclear how processing bottlenecks in the initial selection and perception of visual information affect the number or precision of representations that can be maintained in VWM. The purpose of this dissertation was to examine whether early competition for resources within the visual system limits the number or precision of representation that can be maintained in VWM. To establish whether competitive interactions affect VWM, Chapters 1 – 4 tested whether performance on VWM tasks was related to the distance between memory items. The results of these experiments reveal that when objects are presented close together in space, VWM performance is impaired relative to when those same objects are presented further apart. Using a three-component model of continuous responses in a recall task, Chapters 3 – 4 demonstrated that the distance between objects primarily affects the precision of responses, and increases the number of non-target errors. Chapter 5 extended these findings to distractors, demonstrating that multiple distractors affect the precision and accuracy of VWM responses. Chapters 6 – 7 tested how attentional selection can bias memory representations, revealing that objects that are given high attentional priority were reported with greater precision. Finally, Chapters 8 and 9 examined bias-signals as a potential source of individual differences in VWM performance, revealing that high-performers have more precise representations of sub-capacity representations than low-performers. Together, these results reveal that VWM performance is limited by competition for representation within the visual system, and that attention plays a critical role in resolving competition and consequently, determining the contents of VWM.

Emotional events are often better preserved in memory than events without an emotional component. Emotional stimuli benefit from capturing and holding the attention of a perceiver to a higher degree than more emotion-neutral stimuli. Arousal associated with experiencing emotionally valenced stimuli or situations affects every major stage in creating, maintaining and retrieving lasting memories. Presented in this thesis were models delineating the behavioral and neurological mechanisms that might explain arousal-induced effects on subsequent memory outcome. Based on a study of relevant literature, findings were presented in this thesis that highlight amygdala activation as crucial for the enhancement of memory generally associated with emotional arousal. The amygdala modulates processing in other areas of the brain involved in memory. Heightened levels of norepinephrine, stemming from sympathetic nervous system activation, underlies observable arousal-induced memory effects and seem to be a crucial component in enabling glucocorticoid augmentation of memory. Arousal seems to further amplify the biased competition between stimuli that favors the neural representation of motivationally relevant stimuli and stimuli of a sensory salient nature. The aim of this thesis was to outline the impact of emotional arousal on different stages of memory processing, including processes for memory formation, strengthening of memory traces, and eventual subsequent retrieval.

When multiple objects are present in a visual scene, salient and behaviorally relevant objects are selectively processed at the expense of less salient or irrelevant objects. Here I used three lateralized components of the event-related potential â " the N2pc, Ptc, and SPCN â " to examine how objects compete for representation in our limited capacity visual system, and how task-relevant objects are selectively processed. Participants responded to the orientation of a color singleton target while ignoring a color singleton distractor. Competition between the objects was manipulated by presenting visual search arrays that contained only a target, only a distractor, or both objects together. In Experiment 1, observers did not know the color of the target in advance, whereas in Experiment 2 this information was provided. Experiment 3 was a control experiment to rule out low-level sensory explanations of the effects. The results suggest that the N2pc component indexes capture of attention by salient objects which is modulated both by competition between the objects and top-down knowledge. The Ptc component may index inhibition of return so that once an object is processed it is not selected again. The SPCN component may index enhancement of goal-relevant objects once task-irrelevant objects have been suppressed. Together these lateralized event-related potentials reveal the temporal dynamics of competition and selectivity in the human visual system.

xii, 55 p. : ill. A print copy of this thesis is available through the UO Libraries. Search the library catalog for the location and call number. / Selective attention refers to perceptual selection and working memory refers to the active maintenance of mental representations. Selective attention and working memory are believed to be two of the most important functions in human cognition and have been intensively investigated in cognitive psychology. However, it is quite recent that the link between attention and working memory has been systematically researched. One question that remains controversial is the effect of working memory on attentional control with inconsistent results reported in the human psychophysical literature, despite clear and strong evidence from physiological studies with nonhuman primates that working memory is the main source of top-down attentional control. The main goal of the current study is to provide a plausible solution to the puzzle of attentional control by introducing the concept of goal-specificity and competition between working memory representations. I hypothesized that the strength of the biasing effect of working memory on attention depends on the specificity of representations in working memory, and developed an experimental paradigm (the goal-specificity paradigm) to test this hypothesis using psychophysical and neuroimaging methods. One of the most important manipulations in the goal-specificity paradigm is how specifically targets in different tasks are defined. The results demonstrate that there is competition between items in working memory for attentional control that is influenced by the specificity of each representation as well as task relevancy. Also, it is shown that the effect of goal-specificity is present in both spatial and temporal domains as revealed by visual search and rapid serial visual presentation tasks. The results suggest the possibility that the negligible effect of working memory in some previous studies may be due to insufficient specificity of the objects in working memory or to the presence of other specifically-defined information in working memory. Furthermore, based on the implication from the current study that goal-specificity has a significant influence on attentional control, I expect that the experimental paradigm introduced in the current study can be utilized as an objective psychophysical measure of attentional control. / Committee in charge: Margaret Sereno, Chairperson, Psychology; Scott Frey, Member, Psychology; Michael Wehr, Member, Psychology; Richard Taylor, Outside Member, Physics

Cette thèse portait sur l'attention visuelle sélective, dans le domaine non-spatial, c'est-à-dire la capacité à favoriser le traitement perceptif de certains objets de la scène visuelle au détriment des autres. En particulier, l'objectif était d'étudier, à l'aide de tâches de recherche visuelle, les différentes interactions possibles entre les processus endogènes (liés aux intentions et connaissances du sujet) et les processus exogènes (liés aux caractéristiques perceptives des objets). Une première série d'expériences démontrait que la saillance pouvait présenter des effets relativement durables. Cependant, ces effets de saillance pouvaient être favorisés ou contrecarrés par des processus endogènes (induits par indiçage portant sur la taille), et modulés par l'amorçage perceptif. Une seconde série d'expériences démontrait que la résistance à l'interférence induite par un distracteur saillant dépendait de ressources attentionnelles centrales, et était modulée par la charge perceptive. Enfin, la troisième série d'expériences validait l'hypothèse d'une intégration entre des signaux endogènes et exogènes compatibles mais strictement distincts. La falsification de l'inégalité de Miller (1982) précisait que cette intégration reposait sur une coactivation effective, non sur une simple facilitation statistique entre signaux strictement indépendants. Le locus cognitif de cette intégration semble être le système perceptif. L'ensemble des données présentées souligne la flexibilité du contrôle attentionnel, et invite à développer un modèle général de l'attention visuelle sélective basé sur l'hypothèse de compétition biaisée (Desimone & Duncan, 1995). / This thesis was about visual selective attention, toward non-spatial features, that is, the ability to favour the perceptual processing of some objects in the visual scene, at the expense of others. In particular, the aim was to study, through visual search experiments, the various possible interactions between endogenous (linked with incentives and knowledge of subjects) and exogenous (linked with perceptual properties of the objects) processes. The first series of experiments showed long-lived salience effects. These salience effects could, hewever, be favoured or overriden by endogenous processes (induced by cueing the target size), and modulated by perceptual priming. The second series evidenced that resisting the interference induced by a salient distractor depended on central attentional resources, and was modulatted by perceptual load. Finally, the third series demonstrated that separate endogenous and exogenous signals could genuinely integrate. This integration could not be accounted for by a race between strictly independant signals, as evidenced by the falsification of the Miller's (1982) inequality. This integration might occur in the perceptual system. Theglobal set of data highlighted the flexibility of endogenous attentional control, and invited developping a general model of visual selective attention, on the basis of the biased competition hypothesis.

Behavioral adaptation and cognitive control are crucial for goal-reaching behaviors. Every creature is ubiquitously faced with choices between behavioral alternatives. Common sense suggests that errors are an important source of information in the regulation of such processes. Several theories exist regarding cognitive control and the processing of undesired outcomes. However, most of these models focus on the consequences of an error, and less attention has been paid to the mechanisms that underlie the commissioning of an error. In this article, we present an integrative review of neuro-cognitive models that detail the determinants of the occurrence of response errors. The factors that may determine the likelihood of committing errors are likely related to the stability of task-representations in prefrontal networks, attentional selection mechanisms and mechanisms of action selection in basal ganglia circuits. An important conclusion is that the likelihood of committing an error is not stable over time but rather changes depending on the interplay of different functional neuro-anatomical and neuro-biological systems. We describe factors that might determine the time-course of cognitive control and the need to adapt behavior following response errors. Finally, we outline the mechanisms that may proof useful for predicting the outcomes of cognitive control and the emergence of response errors in future research.

Behavioral adaptation and cognitive control are crucial for goal-reaching behaviors. Every creature is ubiquitously faced with choices between behavioral alternatives. Common sense suggests that errors are an important source of information in the regulation of such processes. Several theories exist regarding cognitive control and the processing of undesired outcomes. However, most of these models focus on the consequences of an error, and less attention has been paid to the mechanisms that underlie the commissioning of an error. In this article, we present an integrative review of neuro-cognitive models that detail the determinants of the occurrence of response errors. The factors that may determine the likelihood of committing errors are likely related to the stability of task-representations in prefrontal networks, attentional selection mechanisms and mechanisms of action selection in basal ganglia circuits. An important conclusion is that the likelihood of committing an error is not stable over time but rather changes depending on the interplay of different functional neuro-anatomical and neuro-biological systems. We describe factors that might determine the time-course of cognitive control and the need to adapt behavior following response errors. Finally, we outline the mechanisms that may proof useful for predicting the outcomes of cognitive control and the emergence of response errors in future research.

A substantial number of works have aimed at modeling the receptive field properties of the primary visual cortex (V1). Their evaluation criterion is usually the similarity of the model response properties to the recorded responses from biological organisms. However, as several algorithms were able to demonstrate some degree of similarity to biological data based on the existing criteria, we focus on the robustness against loss of information in the form of occlusions as an additional constraint for better understanding the algorithmic level of early vision in the brain. We try to investigate the influence of competition mechanisms on the robustness. Therefore, we compared four methods employing different competition mechanisms, namely, independent component analysis, non-negative matrix factorization with sparseness constraint, predictive coding/biased competition, and a Hebbian neural network with lateral inhibitory connections. Each of those methods is known to be capable of developing receptive fields comparable to those of V1 simple-cells. Since measuring the robustness of methods having simple-cell like receptive fields against occlusion is difficult, we measure the robustness using the classification accuracy on the MNIST hand written digit dataset. For this we trained all methods on the training set of the MNIST hand written digits dataset and tested them on a MNIST test set with different levels of occlusions. We observe that methods which employ competitive mechanisms have higher robustness against loss of information. Also the kind of the competition mechanisms plays an important role in robustness. Global feedback inhibition as employed in predictive coding/biased competition has an advantage compared to local lateral inhibition learned by an anti-Hebb rule.

A substantial number of works have aimed at modeling the receptive field properties of the primary visual cortex (V1). Their evaluation criterion is usually the similarity of the model response properties to the recorded responses from biological organisms. However, as several algorithms were able to demonstrate some degree of similarity to biological data based on the existing criteria, we focus on the robustness against loss of information in the form of occlusions as an additional constraint for better understanding the algorithmic level of early vision in the brain. We try to investigate the influence of competition mechanisms on the robustness. Therefore, we compared four methods employing different competition mechanisms, namely, independent component analysis, non-negative matrix factorization with sparseness constraint, predictive coding/biased competition, and a Hebbian neural network with lateral inhibitory connections. Each of those methods is known to be capable of developing receptive fields comparable to those of V1 simple-cells. Since measuring the robustness of methods having simple-cell like receptive fields against occlusion is difficult, we measure the robustness using the classification accuracy on the MNIST hand written digit dataset. For this we trained all methods on the training set of the MNIST hand written digits dataset and tested them on a MNIST test set with different levels of occlusions. We observe that methods which employ competitive mechanisms have higher robustness against loss of information. Also the kind of the competition mechanisms plays an important role in robustness. Global feedback inhibition as employed in predictive coding/biased competition has an advantage compared to local lateral inhibition learned by an anti-Hebb rule.