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Spatial Updating in Human Cortex

Merriam, Elisha P. (2006) Spatial Updating in Human Cortex. Doctoral Dissertation, University of Pittsburgh. (Unpublished)

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Single neurons in several cortical areas in monkeys update visual information in conjunction with eye movements. This remapping of stimulus representations is thought to contribute to spatial constancy. The central hypothesis here is that spatial updating also occurs in humans and that it can be visualized with functional MRI.In Chapter 2, we describe experiments in which we tested the role of human parietal cortex in spatial updating. We scanned subjects during a task that involved remapping of visual signals across hemifields. This task is directly analogous to the single-step saccade task used to test spatial updating in monkeys. We observed an initial response in the hemisphere contralateral to the visual stimulus, followed by a remapped response in the hemisphere ipsilateral to the stimulus. Our results demonstrate that updating of visual information occurs in human parietal cortex and can be visualized with fMRI.The experiments in Chapter 2 show that updated visual responses have a characteristic latency and response shape. Chapter 3 describes a statistical model for estimating these parameters. The method is based on a nonlinear, fully Bayesian, hierarchical model that decomposes the fMRI time series data into baseline, smooth drift, activation signal, and noise. This chapter shows that this model performs well relative to commonly-used general linear models. In Chapter 4, we use the statistical method described in Chapter 3 to test for the presence of spatial updating activity in human extrastriate visual cortex. We identified the borders of several retinotopically defined visual areas in the occipital lobe. We then tested for spatial updating using the single step saccade task. We found a roughly monotonic relationship between the strength of updating activity and position in the visual area hierarchy. We observed the strongest responses in area V4, and the weakest response in V1. We conclude that updating is not restricted to brain regions involved primarily in attention and the generation of eye movements, but rather, is present in occipital lobe visual areas as well.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
Merriam, Elisha P.merriam@pitt.eduMERRIAM
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairOlson, Carl Rcolson@cnbc.cmu.eduOLSONC
Committee MemberColby, Carol
Committee MemberGenovese, Christopher
Committee MemberD'Esposito,
Committee MemberBehrmann,
Committee MemberKim, Seong-Gikimsg@pitt.eduKIMSG
Date: 20 March 2006
Date Type: Completion
Defense Date: 18 November 2005
Approval Date: 20 March 2006
Submission Date: 5 December 2005
Access Restriction: No restriction; Release the ETD for access worldwide immediately.
Institution: University of Pittsburgh
Schools and Programs: Dietrich School of Arts and Sciences > Neuroscience
Degree: PhD - Doctor of Philosophy
Thesis Type: Doctoral Dissertation
Refereed: Yes
Uncontrolled Keywords: Bayesian Statistics; Extrastriate Cortex; Functional Magnetic Resonance Imaging; Parietal Cortex; Spatial Constancy
Other ID:, etd-12052005-001608
Date Deposited: 10 Nov 2011 20:08
Last Modified: 19 Dec 2016 14:37


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