Synaesthesia is a fascinating condition in which ordinary stimuli elicit extraordinary sensory experiences. For example, specific tastes may elicit unusual tactile sensations and standard black letters may elicit highly specific colour experiences. These unusual experiences have been shown to have substantial impact on cognition, emotion, perception, and covert attention. Two experiments are presented which show that synaesthesia also influences overt visual attention. In these experiments two grapheme-colour synaesthetes viewed coloured letters while their eye movements were tracked. Letters were presented in colours that were either congruent or incongruent with the synaesthetes' colours. Eye tracking analysis showed that synaesthetes exhibited a colour congruity bias – a propensity to fixate congruently coloured letters more often and for longer durations than incongruently coloured letters – in a naturalistic free viewing task. In a more structured visual search task, this congruity bias caused synaesthetes to rapidly fixate and identify congruently coloured target letters, but led to problems in identifying incongruently coloured target letters. The results are discussed in terms of their implications for perception in synaesthesia.

Some authors have argued that the primary function of the posterior parietal cortex is to control visual attention and awareness, whereas others have argued that the posterior parietal cortex is specialized for controlling actions. The purpose of the present thesis was to examine the influence of prism adaptation – a visuomotor adaptation technique – on visual attention deficits in patients with lesions of parietal cortex. Lesions to dorsal regions of the posterior parietal cortex lead to optic ataxia – a disorder in which visually guided reaching is disrupted. In contrast lesions to ventral (i.e. inferior) regions of the posterior parietal cortex of the right hemisphere lead to spatial neglect – a disorder in which patients are unaware of people or objects in contralesional (left) space. Chapter 1 presents an overview of the organization of the posterior parietal cortex, as well as an introduction to the disorders of spatial neglect and optic ataxia and the use of prism adaptation as a treatment for spatial neglect. Chapter 2 examined the influence of prism adaptation on attentional deficits in patients with right brain damage. Results demonstrated that prism adaptation reduced both the disengage deficit and the rightward attentional bias, two of the classic attentional deficits in neglect. Chapter 3 investigated the role of the dorsal posterior parietal cortex in controlling both reflexive and voluntary attention in two patients with optic ataxia. Lesions to the dorsal posterior parietal cortex led to both a disengage deficit and a rightward attentional bias, similar to patients with neglect, even though neither of the patients had any clinical symptoms of neglect. Contrary to previous work these results indicated that dorsal portions of the posterior parietal cortex – a region not commonly damaged in neglect – are important for controlling the orienting and reorienting of both reflexive and voluntary attention. Furthermore, these results indicated that optic ataxia is not purely a visuomotor disorder that is independent of any perceptual or attentional deficits as was previously assumed. Based on the results of Chapters 2 and 3 it was hypothesized that the beneficial effects of prism adaptation on attention may operate via the superior parietal lobe, a region which is typically undamaged in neglect, and is known to be important for controlling attention and action. Chapter 4 provided support for this hypothesis by demonstrating that a patient with lesions to the superior parietal lobe, who had the same attentional deficits as the right brain damaged patients tested in Chapter 2, failed to demonstrate any beneficial effects of prism adaptation on his attentional performance. Specifically, prism adaptation had no influence on his disengage deficit or his rightward attentional bias. Therefore, these data provide direct evidence that the beneficial effects of prisms on attention rely, at least in part, on the superior parietal lobe. Finally, Chapter 5 concludes with a summary of the research findings from the present thesis, and puts forward a new theory to conceptualize the mechanisms underlying the beneficial effects of prisms in patients with neglect.

This thesis examines how the context in which an item is studied affects the phenomenological experience of the rememberer. Previous research has extensively studied how the match between study and test context affect subsequent memory performance; however, little work has attempted to examine how visual context information provided at study affects later recollection when that context information is not re-presented at retrieval. In particular, the quality of the memory retrieved may be enhanced when highly meaningful visual context information is provided at study. In each of seven experiments in the current thesis, participants studied words presented with context information high or low in meaningful content, and on a later recognition memory test made a Remember, Know, or New response to the words presented alone. Experiment 1 showed that participants had better overall memory, specifically recollection, for words studied with pictures of intact as opposed to scrambled faces. In Experiment 2, these results were replicated and recollection was shown to be higher for words studied with versus without pictures of faces. Experiment 3 showed that participants had higher memory performance, and recollection in particular, for words studied with upright compared to inverted faces. In Experiment 4, participants showed equivalent memory for words studied with novel or familiar faces. These results suggest that recollection benefits when visual context information high in meaningful content accompanies study words, and that this benefit is not related to the novelty of the context. To further test the claim that participants engage in elaborative processes at study to bind item and context information, improving subsequent recollection, the subsequent set of experiments examined how normal, healthy aging affects participants’ ability to use context information provided at study to benefit subsequent recollection. Older adults have been shown to experience deficits both in memory for context and in recollection, suggesting that they might fail to use context effectively to increase recollection, in contrast to younger adults. Experiment 5 found that younger, but not older, adults showed higher recollection for words studied with faces as compared to rectangles. To determine the type of cognitive processing required to obtain recollection benefits, and to examine whether instruction could alleviate age-related deficits, in Experiment 6, the type of processing engaged during the encoding of context-word pairs was manipulated. Younger and older adults studied words presented with a picture of a face under a surface feature or binding feature instruction condition. Both age groups showed higher recollection in the binding than surface instruction condition. Results suggest that older adults do not spontaneously engage in the processes required to boost recollection when visual context information is provided at study, although instructional manipulation during encoding lessens this deficit. This is in line with the Associative Deficit Hypothesis (Naveh-Benjamin, 2000), suggesting that older adults’ recollection deficit involves a specific difficulty in binding item and context information. The final experiment used functional Magnetic Resonance Imaging (fMRI) to examine the neural correlates of recollection, specifically testing the hypothesis that sensory-specific reactivation of context information occurs during item recollection. In Experiment 7, brain activation for Remember responses given to words studied with and without meaningful context information was compared. Behaviourally, 8 of the 14 participants showed a higher proportion of Remember responses to words studied with faces than scrambled faces, and 6 did not. Whole brain analysis showed that, for only those participants who showed higher memory performance for words studied with faces, activation in the fusiform gyrus and hippocampus was higher, and a region-of-interest analysis showed increased activation in the functionally-defined FFA (identified in a localizer task), for Remember responses given to words studied with faces compared to scrambled faces. A regression analysis additionally showed that activation in the fusiform gyrus increased as the relative recollection benefit for words studied with meaningful (face) compared to non-meaningful (scrambled face) context information increased across participants. Results suggest that encoding context can influence the pattern of recollection responses on a recognition task and that sensory-specific reactivation is related to behavioural performance. The findings of these experiments suggest that participants can use context information high in meaningful content at study to improve subsequent recollection and I suggest that this involves the use of elaborative processes at encoding that integrates item and meaningful contexts. Such recollection benefits can also be observed in older adults when they are provided experimental instructions to bind item and context at encoding. In addition, the brain regions used to process context information are reactivated at retrieval and, importantly, that this neural pattern determines whether a boost in recollection, from the encoding manipulation, is observed. Participants can thus use context information provided at study to boost subsequent recollection, and I suggest that this involves cognitive processes that bind item and context information at encoding and the reactivation of sensory-specific brain regions at retrieval.

Additional cognitive deficits, including impairments in spatial working memory and/or saccadic remapping processes, have recently been implicated in unilateral neglect – a neurological condition classically characterized as a disorder of attention. The interactions between saccadic remapping and three memory processes (position memory, object memory and object-location binding) were investigated in healthy young (n=27) and elderly (n=20) participants to establish a baseline of comparison for future use with neglect patients and to study the effects of aging on these processes. In a computerized task, participants were instructed to first detect a target, and then hold in memory either its position, identity or both over a delay period. Subsequently, participants were tested on their memory for that particular task. The saccadic remapping component was introduced at the onset of the delay period with the fixation cross shifting either to the left, or right, requiring participants to remap the visual array into either right or left space, or remaining in the centre of the screen (i.e., no remapping condition). In the position memory and object-location binding task, a consistent cost to memory performance was found when remapping right only for the young participants. Overall the elderly did not perform any of the tasks involving a position memory component as well as the young participants and showed spatial asymmetries in the target detection task. The lack of an effect of remapping in the elderly group may be due to a general decrement in performance. These results are discussed in terms of hemispheric asymmetries and cognitive theories of aging.

The goal of this dissertation is to take initial steps towards understanding concealment behaviour and ultimately developing a theory of visual concealment. Since there are relatively few studies of concealment in the literature and given the natural relationship between search and concealment, five strategies used in the development of traditional visual search theory and scene-based search theory were applied to the study of concealment. These strategies are: 1) establish a methodology, 2) identify dimensions, 3) categorize dimensions, 4) prioritize dimensions, and 5) integrate results into a theoretical framework that may involve inferences about the mechanisms involved. In Chapter 2, participants placed target objects within luggage in locations that were easy or hard to find (i.e., the placement task). Participants’ subjective reports of their thought processes and strategies were analyzed to identify dimensions that are important during concealment in real-world settings. Once a list of dimensions was generated, the dimensions were then categorized into three categories: Stimulus Properties dimensions such as visual similarity, Embodiment dimensions such as confrontation, and Higher Order dimensions such as schema. In Chapter 3, the dimensions uncovered in Chapter 2 were used in a forced-choice task, and participants’ choices were evaluated to determine whether the dimensions affected hiding behaviour. To further develop the methodological techniques available to study concealment behaviour and to examine the generalizability of previous findings, in Chapter 4, the placement task was used in another context – an office environment – and the locations chosen by participants to make objects easy or hard to find were coded on relevant dimensions. In Chapter 5, an initial attempt was made to prioritize the dimensions. The forced-choice task was used in a new way to explore the relative importance of the dimensions by examining which dimensions participants chose to use over other dimensions. Finally in the General Discussion in Chapter 6, an attempt was made to integrate available results and previous theories and to make inferences about the mechanisms involved in visual concealment. Methodological considerations and future directions for the study of visual concealment are also discussed.

Beginning with a series of several self-report questionnaire studies I examine the potential for everyday attention lapses to create an inability to form connections to the external world, particularly through the experience of chronic boredom, and to subsequently lead to depression. In the first study I examine this process through the intermediate role of memory failures in the onset of boredom and depression, while in the second I examine the role of self-efficacy and in the third I add psychological stress as a further intermediate step between attention lapses and depression. For each study significant associations are found between self-report measures of attention lapses and attention-related cognitive errors, as presumed causes, and boredom proneness and depression as presumed outcomes. Structural equation modeling is then used to show these associations are well explained by an Attention-to-Affect model in which the attention lapses and attention-related errors predict the onset of boredom and depression, in part through their effects on memory failures (Chapter 1), perceived self-efficacy (Chapter 2), and psychological stress (Chapter 3). That these Attention-to-Affect models provide much better fit for the data runs contrary to the typical conception of attention and memory problems as consequences of emotional distress. Following from these models I examine in more specific terms the disconnect experienced as a result of attention lapses, through a laboratory study employing the Sustained Attention to Response Task. This study (Chapter 4) revealed a significant influence of attentional challenges on blinking behaviour, suggesting that whenever our attentional capacity is tested we have a tendency to momentarily direct our thoughts inwardly, perhaps to re-evaluate our attentional performance, and that the timeframe of this redirection is expanded following lapses of attention, and the commission of attention-related errors.

‘What was I thinking ?!?’ – No matter age, intelligence or social status, we all experience moments like these. Perhaps it is walking into a room and forgetting what you went there to do or maybe failing to add sugar to your coffee due to an interruption. Regardless, even though many of our daily activities are accomplished through routines that require very little conscious effort, errors of attention or slips of action do occur. This collection of studies was designed with three main questions in mind: 1) can action slips be induced in a laboratory-based task (Slip Induction Task; SIT), 2) how well do currently established theories of action slips explain the errors that are induced within the SIT, and 3) what insight can be gained about preventing such errors? The first experiment was developed to replicate previous findings regarding the effectiveness of the SIT, as well as to determine the extent to which SIT performance correlates with other measures of attention failure. The study discussed in Chapter 3 expands on those results by investigating the effects of healthy aging on slip induction and finds that while older adults were better able to avoid action slips, they appear to sacrifice speed for accurate performance. The goal of the subsequent study was to determine whether young adult participants would also enjoy increased accuracy if they completed the task at a slower pace. Finally, the study discussed in Chapter 5 looks at whether changing the goal of the SIT would alter participants’ ability to inhibit unexpected cue information.

Memory and concentration problems are frequently reported long after experiencing a mild traumatic brain injury (mild TBI), though conflict with null findings of deficits on standard neuropsychological tests. Experimental research shows that these inconsistencies are, in part, due to the simplicity of neuropsychological tests. As well, past research suggests that when neuropsychological deficits are occasionally detected within this population, they could be influenced by diagnosis threat: an expectation bias for impaired performance when individuals are merely informed that cognitive problems may be experienced following a mild TBI. The main goal of this thesis was to specify the long-term cognitive effects of mild TBI, with the prediction that, while cognitive complaints may be over-reported due to diagnosis threat, significant deficits can be detected using sensitive measures in experimental paradigms. Experiment 1 sought to document whether diagnosis threat influenced self-report of everyday attention and memory problems and neuropsychological task performance in individuals with a remote history of mild TBI. We found that undergraduate students with a mild TBI were significantly more likely to report having attention and memory failures in their daily lives when exposed to diagnosis threat, compared to undergraduate students not exposed to diagnosis threat. These findings call into question the efficacy of using of self-report measures to identify long-term cognitive deficits following a mild TBI. In an attempt to further specify persistent significant cognitive deficits, we designed two different experimental paradigms that uniquely manipulated the demand place on executive processes, as past research suggested deficits emerge only when tasks require considerable cognitive resources. In Experiment 2a, we manipulated processing load on a visual working memory task, across two conditions, while also limiting the potential effect of diagnosis threat. While self-report and neuropsychological measures of attention and memory did not differentiate the groups, the mild TBI group took significantly longer to accurately detect repeated targets on our working memory task. Accuracy was comparable in the low-load condition and, unexpectedly, mild TBI performance surpassed that of controls in the high-load condition. Temporal analysis of target identification suggested a strategy difference between groups: mild TBI participants made a significantly greater number of accurate responses following the target’s offset, and significantly fewer erroneous distracter responses prior to target onset, compared to controls. In Experiment 2b we also examined whether manipulating executive processing demands would differentiate mild TBI from controls, this time on a routine action task that required participants to learn a sequence of hand movements to targets. While not significant, we found a trend such that mild TBI participants were slower to respond on trials with a large executive demand compared controls, while no differences were found on trials with relatively low executive requirements. Results from Experiments 2a and 2b provide stronger evidence for mild TBI-related slowing during a working memory task with an executive component compared to a skilled action task that also had an executive component, but placed minimal demand on memory. To more precisely identify the brain basis of this cognitive slowing, in Experiment 3 we administered a visual n-back task in which we systematically increased working memory demands from 0- to 3-item loads. We found that, compared to controls, mild TBI participants showed a reduction in P300 amplitude, conceptualized as an index of available cognitive resources for stimulus classification. While no late stage response differences were found between groups, P300 amplitude was negatively correlated with response times at higher loads in both control and mild TBI participants. Findings suggest that high functioning young adults who sustained a mild TBI in their remote past, have a reduced amount, or inefficient recruitment of, cognitive resources for target detection; a potential mechanism underlying mild TBI-related response slowing on tasks that place a heavy demand on processing resources. Similar to the effects of mild TBI, aging is also known to negatively impact cognition. In Experiment 4, we examined whether TBI-related deficits persist into older adulthood, and compound the negative effect of aging on cognition. We administered the same working memory task as in Experiment 2a, along with a variety of neuropsychological tests in order to investigate the effect of a TBI sustained an average of 50 years in the past. While no group differences emerged on our experimental working memory task, older adults with a history of 1 or 2 TBIs performed significantly worse than non head-injured older adults only on neuropsychological measures of attention that had an executive component. Such results suggest that a remote TBI sustained early in life further compounds normal age-related cognitive decline. Together, these experiments help specify the measures that best detect long lasting cognitive changes following TBI. Particularly, our findings provide a potential explanation for why long-term cognitive deficits are difficult to identify in the young mild TBI population: the majority of neuropsychological tests are insensitive to minor changes in information processing speed and, as a result, the execution of slowing strategies to maintain accuracy may go undetected. Our findings also demonstrate the importance of investigating longer-term effects of TBI, as they may be chronic and impact cognitive task performance in old age, amplifying normal age-related cognitive deficits.

The goal of this dissertation is to take initial steps towards understanding concealment behaviour and ultimately developing a theory of visual concealment. Since there are relatively few studies of concealment in the literature and given the natural relationship between search and concealment, five strategies used in the development of traditional visual search theory and scene-based search theory were applied to the study of concealment. These strategies are: 1) establish a methodology, 2) identify dimensions, 3) categorize dimensions, 4) prioritize dimensions, and 5) integrate results into a theoretical framework that may involve inferences about the mechanisms involved. In Chapter 2, participants placed target objects within luggage in locations that were easy or hard to find (i.e., the placement task). Participants’ subjective reports of their thought processes and strategies were analyzed to identify dimensions that are important during concealment in real-world settings. Once a list of dimensions was generated, the dimensions were then categorized into three categories: Stimulus Properties dimensions such as visual similarity, Embodiment dimensions such as confrontation, and Higher Order dimensions such as schema. In Chapter 3, the dimensions uncovered in Chapter 2 were used in a forced-choice task, and participants’ choices were evaluated to determine whether the dimensions affected hiding behaviour. To further develop the methodological techniques available to study concealment behaviour and to examine the generalizability of previous findings, in Chapter 4, the placement task was used in another context – an office environment – and the locations chosen by participants to make objects easy or hard to find were coded on relevant dimensions. In Chapter 5, an initial attempt was made to prioritize the dimensions. The forced-choice task was used in a new way to explore the relative importance of the dimensions by examining which dimensions participants chose to use over other dimensions. Finally in the General Discussion in Chapter 6, an attempt was made to integrate available results and previous theories and to make inferences about the mechanisms involved in visual concealment. Methodological considerations and future directions for the study of visual concealment are also discussed.

Beginning with a series of several self-report questionnaire studies I examine the potential for everyday attention lapses to create an inability to form connections to the external world, particularly through the experience of chronic boredom, and to subsequently lead to depression. In the first study I examine this process through the intermediate role of memory failures in the onset of boredom and depression, while in the second I examine the role of self-efficacy and in the third I add psychological stress as a further intermediate step between attention lapses and depression. For each study significant associations are found between self-report measures of attention lapses and attention-related cognitive errors, as presumed causes, and boredom proneness and depression as presumed outcomes. Structural equation modeling is then used to show these associations are well explained by an Attention-to-Affect model in which the attention lapses and attention-related errors predict the onset of boredom and depression, in part through their effects on memory failures (Chapter 1), perceived self-efficacy (Chapter 2), and psychological stress (Chapter 3). That these Attention-to-Affect models provide much better fit for the data runs contrary to the typical conception of attention and memory problems as consequences of emotional distress. Following from these models I examine in more specific terms the disconnect experienced as a result of attention lapses, through a laboratory study employing the Sustained Attention to Response Task. This study (Chapter 4) revealed a significant influence of attentional challenges on blinking behaviour, suggesting that whenever our attentional capacity is tested we have a tendency to momentarily direct our thoughts inwardly, perhaps to re-evaluate our attentional performance, and that the timeframe of this redirection is expanded following lapses of attention, and the commission of attention-related errors.