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.

Although several studies have investigated the effects of aging on aspects of motor planning and control, there remains a lack of consensus about the underlying mechanisms responsible for the motor slowing associated with aging. This may, at least partially, be due to the fact that few studies have kinematically examined both the transport and grasp components in both younger and older adults, and furthermore, even fewer have examined these movements when the context of the task is changed, such as when the movement is performed in isolation compared to when it is embedded in a sequence. Therefore, the purpose of this thesis was threefold: 1) to investigate how aging affects performance on a single reach-to-grasp movement, 2) to examine how movement context affects performance on the reach-to-grasp movement when it is performed alone or as the first movement in a two-movement sequence- in other words, are older adults able to plan the first motor task movement in anticipation of performing a subsequent task, and 3) whether younger and older adults are able to plan, execute, and modify that movement in accordance with the extrinsic properties of the subsequent movement task (near versus far target for second movement). To address this, the movement profiles of both younger (N=14; mean age= 20.7 years; 4 males, 10 females) and older (N=11; mean age= 75.1 years; 3 males, 8 females) healthy right-handed adults were compared on performing a reach-to-grasp movement under 3 different movement conditions: single-movement task, two-movement sequence to near target, and two-movement sequence to far target. For the two-movement sequence conditions, participants were instructed to reach and grasp the object (like the single-movement task), but then to move and place it on either a closer (near condition) or farther (far condition) target location. Overall, the results from this study are in agreement with the literature showing older adults to have slower movements in general and consistently taking longer to both initiate and execute the reach-to-grasp movement than the younger adults for all conditions. There were no other differences between groups on the single-movement condition. For all participants, the reach-to-grasp movement took longer when it was performed in isolation than when it was embedded as the first part of a two-movement sequence. This finding can be explained by the movement termination effect and is consistent with findings from studies on aiming movements showing that when the movement plan involves stabilizing the arm at the first target (single-movement) as opposed to merely slowing it down (two-movement sequence tasks), the constraint of achieving a stabile position imposes a greater demand, thus requiring the movement iv to be made more slowly. The results obtained from the study indicate that the movement termination effect is also seen in the context of prehensile movements and furthermore, this effect on performance persists with age. Not only do the findings from this study show that this effect persists with age, but also that this effect increases with age, as revealed by a Group by Condition effect for reaction time, movement time, and relative timing of the velocity profile, indicating greater changes in reaching performance between single- and two-movement conditions for the older adults than for the younger adults. Upon further examination of the details of the movement, it is apparent this movement termination effect is reflected in the ballistic phase of the movement. This last notion is inconsistent with previous studies, which showed the increased movement time associated with the movement termination effect was the result of changes in the amount of time spent in the deceleration phase toward the end of the movement rather than the beginning of the movement. Lastly, when reach-to-grasp performance was compared between moving to a near- compared to a far-target in the two-movement conditions, no differences were found between any of the movement features for either group. This suggests that the increased proportion of time spent in deceleration for the dual-movement conditions compared to the single-movement condition in older adults is due to online feedback control for terminating the first movement rather than online planning of the second movement. Despite the changes seen in the transport component, the findings for the manipulation component indicate that the formation of the grasp and its relative coupling with the transport component remains intact with age.

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.

‘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.

The updating process, which consists of building mental models and adapting them to the changes occurring in the environment, is impaired in neglect patients. A simple rock-paper-scissors experiment was conducted in our lab to examine updating impairments in neglect patients. The results of this experiment demonstrate a significant difference between the performance of healthy and brain damaged participants. While healthy controls did not show any difficulty learning the computer’s strategy, right brain damaged patients failed to learn the computer’s strategy. A computational modeling approach is employed to help us better understand the reason behind this difference and thus learn more about the updating process in healthy people and its impairment in right brain damaged patients. Broadly, we hope to learn more about the nature of the updating process, in general. Also the hope is that knowing what must be changed in the model to “brain-damage” it can shed light on the updating deficit in right brain damaged patients. To do so I adapted a pattern detection method named “ELPH” to a reinforcement-learning human decision making model called “RELPH”. This model is capable of capturing the behavior of both healthy and right brain damaged participants in our task according to our defined measures. Indeed, this thesis is an effort to discuss the possible differences among these groups employing this computational model.