In partial fulfillment of the requirements for the degree of Doctor of Philosophy in Applied Physiology in the School of Biological Sciences Kyunggeune (Ted) Oh will defend his thesis “Contribution of visual experience, limb posture, and limb representation space in limb position sense and underlying brain activities”.

Thesis Advisor
Boris Prilutsky, Ph.D.
School of Biological Sciences

Committee Members
T. Richard Nichols, PhD (Biological Sciences)
Lewis Wheaton, PhD (Biological Sciences)
Thomas Burkholder, PhD (Biological Sciences)
Aaron Young, PhD (Mechanical Engineering)

Abstract
Position sense of the body limbs is critical for the accurate control of posture and movement and for the appropriate responses to sudden external perturbations. The lack of position sense due to illness has devastating consequences for the performance of even simplest motor tasks (Cole and Paillar 1998). Arm position sense has been the focus of extensive studies. It has been shown that many sensory systems (visual, vestibular, tactile, proprioceptive) and voluntary motor commands contribute to position sense. It is also known that the precision (random error) of arm position sense is not uniform in a horizontal workspace, i.e. the hand position is perceived more precisely in the radial than in azimuth direction and closer to the body than farther away. Although limb posture, muscle moment arms, and the biases of spindle and cutaneous afferent firing in specific movement directions have been considered as possible explanations for the non-uniform precision of arm position sense, there is no consensus in the literature. Visual experience might also affect the arm position sense due to the integration of proprioceptive, tactile and visual sensory information, especially if the arm position is defined with respect to the extrapersonal space (Tsay et al. 2016). For example, the blind persons respond differently to an imposed sensory conflict between joint-based sensory signals (proprioceptive and tactile) and sensory information that determines limb location in the extrapersonal space (visual, tactile, and auditory) (Nava et al. 2014; Petkova et al. 2012). That has led to the suggestion that the lack of visual experience could negatively affect remapping of the joint-based position information (somatosensory and tactile) onto the limb location information in the external space (Petkova et al. 2012). However, currently the role of prior visual experience in position sense is not clearly understood. The goal of my study is to investigate how prior visual experience affects the non-uniform limb position sense in joint and external space by comparing position sense and brain activities of the visually-impaired and normally sighted individuals.

My hypotheses are: (i) sighted individuals will demonstrate a better arm position sense than persons with impaired vision, (ii) the visually-impaired persons will demonstrated a better accuracy and precision of arm position sense in a joint angle matching task (in joint-based space) than in a hand position matching task (in external space), (iii) removal of tactile sensory input from the hand would decrease accuracy of arm position sense, (iv) the non-uniform precision of arm position sense is determined to a large extent by arm posture, (v) Electroencephalographic (EEG) activity over the parietal and visual cortices will be different between the blind and sighted subjects during arm matching tasks in both joint-based and external coordinate space, and (vi) the accuracy and precision of arm position sense in the visually impaired subjects will be positively correlated with the area and intensity of EEG activity in the visual cortex. These hypotheses will be addressed in the following specific aims: (1) Determine role of visual experience, limb posture, and limb representation space in the accuracy of limb position sense, (2) Determine role of visual experience, limb posture, and limb representation space in the non-uniform precision of limb position sense, and (3) Determine differences in EEG activities between arm position matching tasks in external and joint spaces in blind and sighted individuals.