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Superior parietal cortex has been implicated in visuomotor guidance and is proposed to be specialised for action in the lower visual field and peripersonal space. Two patients, one with a right superior parietal lesion leading to optic ataxia (ME), and one with a lesion affecting right inferior parietal cortex (LH), were compared to elderly controls (n=8) and young controls (n=8) on a reciprocal pointing task with movements made in the near-far direction (i.e., sagittal plane) or right-left direction (i.e., fronto-parallel plane). In contrast to both control groups, who demonstrated a speed-accuracy trade-off in movement time and peak velocity, neither of the patients did. When the time spent post-peak velocity (represented as a percentage of total movement time) was examined, both patients demonstrated larger times post-peak velocity than controls for all movement directions. Furthermore, while rightward movements of the right hand had higher times post-peak velocity than leftward movements there were no directional patterns for near-far movements which contrasted with controls who had larger times post-peak velocity for near movements. The patient with the more superior lesion (ME) had the greatest difficulty with movements made back toward the body suggestive of a role for superior parietal cortex in the fine tuning of movements made in this region of space (i.e., personal or peripersonal space). In contrast, all directions of movement seemed to be equally affected in the patient with a more inferior lesion. These results are discussed in terms of the different roles played by inferior and superior parietal cortex in the control of visually guided movements.

Superior parietal cortex has been implicated in visuomotor guidance and is proposed to be specialised for action in the lower visual field and peripersonal space. Two patients, one with a right superior parietal lesion leading to optic ataxia (ME), and one with a lesion affecting right inferior parietal cortex (LH), were compared to elderly controls (n=8) and young controls (n=8) on a reciprocal pointing task with movements made in the near-far direction (i.e., sagittal plane) or right-left direction (i.e., fronto-parallel plane). In contrast to both control groups, who demonstrated a speed-accuracy trade-off in movement time and peak velocity, neither of the patients did. When the time spent post-peak velocity (represented as a percentage of total movement time) was examined, both patients demonstrated larger times post-peak velocity than controls for all movement directions. Furthermore, while rightward movements of the right hand had higher times post-peak velocity than leftward movements there were no directional patterns for near-far movements which contrasted with controls who had larger times post-peak velocity for near movements. The patient with the more superior lesion (ME) had the greatest difficulty with movements made back toward the body suggestive of a role for superior parietal cortex in the fine tuning of movements made in this region of space (i.e., personal or peripersonal space). In contrast, all directions of movement seemed to be equally affected in the patient with a more inferior lesion. These results are discussed in terms of the different roles played by inferior and superior parietal cortex in the control of visually guided movements.

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.

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.

Successful recognition memory decisions depend on mnemonic and decision making processes that are computed by multiple, distributed brain areas. However, little is known about what computations these areas perform or how these areas are connected. Here, I collected behavioral and functional magnetic resonance imaging data from humans during the performance of an old-new recognition memory task with retrospective confidence judgments. Across runs, choice bias was successfully manipulated by providing rewards for correct responses that were either symmetric (equal reward for hits and correct rejections) or asymmetric (one response worth more than the other). Successful recognition memory was associated with activation in anterior prefrontal, parahippocampal, posterior cingulate, and parietal cortex. Resting state functional connectivity demonstrated that these brain areas are organized into two distinct networks. The first network includes parahippocampal cortex and angular gyrus. The second network includes lateral prefrontal cortex and intraparietal sulcus. The hippocampal-cortical network was most active during old vs. new decisions, did not differentiate hits from false alarms, and was differentially active during low confidence old and new judgments. In contrast, while the frontoparietal network was robustly activated by hits, it was not activated during either false alarms or low confidence old judgments. Thus, these two distinct networks can be distinguished by their relative connectivity to the medial temporal lobe vs. lateral prefrontal cortex and their responses during uncertain old judgments and errors. The choice bias manipulation had opposing effects on the parietal components of these networks, which further suggests these networks make distinct contributions to mnemonic decision making. / Psychology

The posterior parietal cortex (PPC) has been reliably implicated in visuospatial attention, such that the dorsal regions (dPPC) are associated with voluntary ‘top-down’ attention, whereas the ventral regions (vPPC) are associated with automatic ‘bottom-up’ attentional processes. The Attention-to-Memory model (AtoM: Ciaramelli, Grady, & Moscovitch, 2008) has suggested that it also plays a similar role in memory retrieval, suggesting that the PPC mediates a domain-general attentional process. Furthermore, domain-generality of attentional processes may account for differences in perception and memory function accompanying old age. This study examined domain-generality by determining the shared variance in performance of tasks thought to recruit top-down and bottom-up attentional processes mediated across both domains. Results clearly suggested generality across domains in top-down processing; and in bottom-up processing, depending on its operationalization. Ageing was characterized by an absence of shared variance across domains and slower reaction times during bottom-up attentional reorienting only in perception.

The posterior parietal cortex (PPC) has been reliably implicated in visuospatial attention, such that the dorsal regions (dPPC) are associated with voluntary ‘top-down’ attention, whereas the ventral regions (vPPC) are associated with automatic ‘bottom-up’ attentional processes. The Attention-to-Memory model (AtoM: Ciaramelli, Grady, & Moscovitch, 2008) has suggested that it also plays a similar role in memory retrieval, suggesting that the PPC mediates a domain-general attentional process. Furthermore, domain-generality of attentional processes may account for differences in perception and memory function accompanying old age. This study examined domain-generality by determining the shared variance in performance of tasks thought to recruit top-down and bottom-up attentional processes mediated across both domains. Results clearly suggested generality across domains in top-down processing; and in bottom-up processing, depending on its operationalization. Ageing was characterized by an absence of shared variance across domains and slower reaction times during bottom-up attentional reorienting only in perception.

Thesis (Ph.D.)--York University, 2006. Graduate Programme in Psychology. / Typescript. Includes bibliographical references (leaves 148-172). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:NR19801

Thesis (M.Sc.)--York University, 2008. Graduate Programme in Kinesiology and Health Science. / Typescript. Includes bibliographical references (leaves 69-81). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pqdiss&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&rft_dat=xri:pqdiss:MR51534