Examining the neural correlates associated with the moment a stimulus enters or exits conscious awareness is one way to potentially identify the neural mechanisms that give rise to consciousness. In the present study, we examined neural activity using electroencephalogram (EEG) recordings while participants observed a bilateral shape-from-motion (SFM) display. While the display is in motion, the observer perceives an object that is immediately segregated from a noisy background. After the motion stops, the observer’s experience of the object remains momentarily in awareness, before it eventually fades out of consciousness back into the noisy background. Consistent with subjective reports of perceptual experience, we observed a prominent sustained posterior contralateral negativity (SPCN), but only in conditions associated with sustained awareness. Importantly, the amplitude of the SPCN was correlated with individual differences in visual awareness, suggesting that this activity plays a significant role in the maintenance of objects in consciousness.

The term working memory (WM) refers to a set of cognitive processes that allows for the temporary storage and manipulation of information. Neural correlates of the N- back task, a well-established WM measure used in neuroimaging, have been studied extensively in adults but less so in developmental populations. This thesis determines the effect of age on brain activations that mediate cognitive processes for remembering non- verbal/visual stimuli. Block-design fMRI was used to record activity in 84 subjects (6-35 years) during a visual-patterns 0- and 1-back task. Regions activated during the 1-back condition were largely common to all age groups, with adults displaying the largest extent of activations. Children and adolescents showed similar 0-back activations (distinct from 1-back) while adults engaged an analogous 1-back activation pattern during 0-back, suggesting that brain mechanisms underlying memory and attentional processes required for this task in children and adolescents are not yet mature and that strategy usage is still developing.

DOES A CONTINUOUS MEASURE OF HANDEDNESS PREDICT READING RELATED PROCESSES AND READING SKILLS ACROSS THE LIFESPAN? by Michele Harrison Brenneman The purpose of this research was to investigate the relationship between handedness, reading skills, and reading related cognitive processes. The research results with regard to handedness, specific reading skills, and reading related cognitive processes are ambiguous at best. The method in which handedness is measured contributes to these diverse research findings, therefore the present investigation addressed these methodological limitations. A large normative sample of up to 1383 participants that ranged in age from 4 to 80 completed the Woodcock Johnson Psycho-Educational Battery-Revised (Woodcock & Johnson, 1989a; Woodcock & Johnson, 1989b) or the Woodcock Johnson Psycho-Educational Battery-Third Edition (Woodcock, McGrew, & Mather, 2001) in combination with the Dean Woodcock Sensory Motor Battery (Dean & Woodcock, 2003) lateral preference scale, a continuous measure of handedness. Polynomial multiple regression analyses indicated curvilinear relationships between handedness and reading comprehension and basic reading skills, along with handedness and auditory working memory. Individuals towards the extremes of the handedness continuum performed lower on the reading related tasks. Therefore, just knowing a general classification of right, left or mixed handed will not provide significant knowledge regarding lateralization or potential cognitive and academic costs and benefits. One overarching implication of these findings is that laterality is an important predictor variable of reading skills and related reading processes, hence knowledge of an individual’s hand preference on a continuum may well be useful for evaluative purposes.

An individual`s eyes provide a wealth of information during social interactions. The present research investigates the social adjustment implications of one gaze behaviour, specifically, shared attention, which is the tendency to follow an interlocutor`s directed gaze to attend to the same object or location. Recent clinical research suggested that gaze control reflects the capacity to differentiate self from other at the attentional level, since patient populations with poor gaze control abilities (i.e., schizophrenic patients) were also found to exhibit difficulty in differentiating between the self and another agent. Four studies were conducted to examine whether flexible gaze following behavior, specifically the ability to inhibit gaze-following, when the situation warrants, would be positively linked with two markers of adaptive social functioning: sociocognitive abilities and self-close other(s) differentiation. Based on previous research that gaze cues linked to upright (but not inverted) faces trigger reflexive gaze following mechanisms, an upright face condition was used to assess social cueing mechanisms and an inverted face condition, as a control for non-social cueing mechanisms in a gaze control task with realistic (Study 2) and schematic faces (Studies 1, 3, and 4). Studies 1-4 showed that more flexible gaze following behavior predicted superior sociocognitive abilities, as indexed by higher capacity to infer the mental states of others in both young and older adults (Studies 1-3), as well as in clinical populations (i.e., Parkinson’s Disease [PD] patients, Study 4). Studies 2-4 further revealed that poorer gaze control predicted decreased self-close other differentiation in both younger and older adults. In Study 2, poorer gaze control performance characterized young adults from enmeshed family systems, which allow limited private space and emotional autonomy. In Studies 3 and 4, poorer gaze control predicted decreased cognitive-affective differentiation from one’s spouse and lower marital quality in healthy elderly couples (Study 3) and elderly couples, where one spouse had PD (Study 4). The present findings argue for the existence of a unified sociocognitive network, perpetually shaped by one’s interpersonal history, and which encompasses perceptual mechanisms, specialized for face and gaze processing and higher-order cognitive mechanisms, specialized for processing the meaning (s) of social environments.

Prior research has demonstrated that bilinguals outperform monolinguals on tasks requiring set shifting – that is, the ability to shift between different ways of thinking about an object or situation. For example, bilingual children have been shown to outperform monolingual controls on false-belief tasks and on the Dimensional Change Card Sort (DCCS) task. The present study aimed (a) to examine whether the bilingual advantage in false-belief and DCCS tasks can be replicated when accounting for languages/cultures and socio-economic status and (b) to determine whether inhibitory control, metarepresentation, and/or working memory underlie the advantage, if any exists. Three language groups (24 English monolingual, 24 French monolingual, and 24 English-French bilingual preschoolers) were tested on the following tasks: false-belief (FB) tasks, the DCCS task, an inhibitory control task (Stroop task), a metarepresentation task (Identity Statements task), a working memory task (Backward Word Span), and receptive language proficiency tests. Socio-economic status was measured through a parental questionnaire containing questions about parental income and education. Results showed that the three language groups were equivalent on socio-economic measures. Despite having significantly lower language proficiency scores, bilinguals’ raw scores on FB and DCCS tasks did not differ from monolinguals’ raw scores. After statistically controlling for language proficiency and age, bilinguals had significantly higher FB scores, but did not differ from monolinguals on DCCS scores. Analyses were then performed to determine whether inhibitory control, metarepresentation, and/or working memory help bilinguals “do more” in FB “with less” language proficiency. Working memory emerged as the likely candidate that compensates for the negative effect of bilingual children’s low language proficiency on FB performance because, after controlling for age and language proficiency, it was the only cognitive ability that fulfilled both criteria: (a) its measure correlated significantly with FB and (b) there was a bilingual advantage over both monolingual groups in the measure. A mediation analysis confirmed that the working memory measure significantly mediates the relation between bilingual status and FB while controlling for age and language proficiency. Both components of the working memory measure – that is, understanding of task instructions and maintenance/manipulation capacity – mediate this relation.

This study used pre-existing data to examine whether children with ADHD, with and without working memory (WM) deficits, differ in their academic achievement and clinical profiles. 73 children (26% female), aged 6-12 years, with a confirmed diagnosis of ADHD had completed standardized achievement tests of reading, mathematics, and written language. Six WM measures and three parent and teacher questionnaires probing behaviour and executive functioning were administered. Of the sample, only 26% met the criteria for a WM deficit. Children with WM impairments were found to perform significantly worse than those without WM impairment on all achievement clusters, with no clinical profile differences. Poor WM is not universal in ADHD, but its presence is associated with lower academic achievement scores. Clinicians and educators should consider that underlying impairments in WM may be the contributing factors to academic difficulties in children with ADHD. Interventions targeting WM skills need to be implemented.

An individual`s eyes provide a wealth of information during social interactions. The present research investigates the social adjustment implications of one gaze behaviour, specifically, shared attention, which is the tendency to follow an interlocutor`s directed gaze to attend to the same object or location. Recent clinical research suggested that gaze control reflects the capacity to differentiate self from other at the attentional level, since patient populations with poor gaze control abilities (i.e., schizophrenic patients) were also found to exhibit difficulty in differentiating between the self and another agent. Four studies were conducted to examine whether flexible gaze following behavior, specifically the ability to inhibit gaze-following, when the situation warrants, would be positively linked with two markers of adaptive social functioning: sociocognitive abilities and self-close other(s) differentiation. Based on previous research that gaze cues linked to upright (but not inverted) faces trigger reflexive gaze following mechanisms, an upright face condition was used to assess social cueing mechanisms and an inverted face condition, as a control for non-social cueing mechanisms in a gaze control task with realistic (Study 2) and schematic faces (Studies 1, 3, and 4). Studies 1-4 showed that more flexible gaze following behavior predicted superior sociocognitive abilities, as indexed by higher capacity to infer the mental states of others in both young and older adults (Studies 1-3), as well as in clinical populations (i.e., Parkinson’s Disease [PD] patients, Study 4). Studies 2-4 further revealed that poorer gaze control predicted decreased self-close other differentiation in both younger and older adults. In Study 2, poorer gaze control performance characterized young adults from enmeshed family systems, which allow limited private space and emotional autonomy. In Studies 3 and 4, poorer gaze control predicted decreased cognitive-affective differentiation from one’s spouse and lower marital quality in healthy elderly couples (Study 3) and elderly couples, where one spouse had PD (Study 4). The present findings argue for the existence of a unified sociocognitive network, perpetually shaped by one’s interpersonal history, and which encompasses perceptual mechanisms, specialized for face and gaze processing and higher-order cognitive mechanisms, specialized for processing the meaning (s) of social environments.

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.

Prior research has demonstrated that bilinguals outperform monolinguals on tasks requiring set shifting – that is, the ability to shift between different ways of thinking about an object or situation. For example, bilingual children have been shown to outperform monolingual controls on false-belief tasks and on the Dimensional Change Card Sort (DCCS) task. The present study aimed (a) to examine whether the bilingual advantage in false-belief and DCCS tasks can be replicated when accounting for languages/cultures and socio-economic status and (b) to determine whether inhibitory control, metarepresentation, and/or working memory underlie the advantage, if any exists. Three language groups (24 English monolingual, 24 French monolingual, and 24 English-French bilingual preschoolers) were tested on the following tasks: false-belief (FB) tasks, the DCCS task, an inhibitory control task (Stroop task), a metarepresentation task (Identity Statements task), a working memory task (Backward Word Span), and receptive language proficiency tests. Socio-economic status was measured through a parental questionnaire containing questions about parental income and education. Results showed that the three language groups were equivalent on socio-economic measures. Despite having significantly lower language proficiency scores, bilinguals’ raw scores on FB and DCCS tasks did not differ from monolinguals’ raw scores. After statistically controlling for language proficiency and age, bilinguals had significantly higher FB scores, but did not differ from monolinguals on DCCS scores. Analyses were then performed to determine whether inhibitory control, metarepresentation, and/or working memory help bilinguals “do more” in FB “with less” language proficiency. Working memory emerged as the likely candidate that compensates for the negative effect of bilingual children’s low language proficiency on FB performance because, after controlling for age and language proficiency, it was the only cognitive ability that fulfilled both criteria: (a) its measure correlated significantly with FB and (b) there was a bilingual advantage over both monolingual groups in the measure. A mediation analysis confirmed that the working memory measure significantly mediates the relation between bilingual status and FB while controlling for age and language proficiency. Both components of the working memory measure – that is, understanding of task instructions and maintenance/manipulation capacity – mediate this relation.

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.