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Thesis (MAppSc in Physiotherapy)--University of South Australia, 1996

Thesis (Ph. D.)--University of California, San Diego and San Diego State, 2002. / Vita. Includes bibliographical references (leaves 101-113).

Thesis (M.A.)--York University, 1998. Graduate Programme in Psychology. / Typescript. Includes bibliographical references (leaves 49-51). Also available on the Internet. MODE OF ACCESS via web browser by entering the following URL:http://wwwlib.umi.com/cr/yorku/fullcit?pMQ27383.

The overarching purpose of this work is to expand the utility of pupillometry as a non-invasive index of pupil-linked neuromodulatory systems, which are correlated with behavior states and are integral in carrying out complex behaviors, such as decision-making. The work characterizes tonic pupil dynamics and their relation to brain state and behavior (B. J. Schriver, S. Bagdasarov, & Q. Wang, 2018), characterizes the mechanisms and functional consequences behind phasic arousal linked pupil dynamics, and examines the causal role of the locus coeruleus in mediating the relationship between pupil dynamics, arousal, and ultimately behavior. For characterization of tonic pupil dynamics in the awake, behaving animal, rats were shown to be able to discriminate between directions of whisker deflections in a Go/No-Go behavioral paradigm with behavioral outcomes being associated with unique pupil dynamics. Furthermore, pupil baseline was inversely correlated with pupil dilation. Our work found that the behavior of rats performing the tactile discrimination task was highly dependent on pupil-indexed level of arousal. Pupil baseline exhibited an inverted U-shaped relationship with perceptual sensitivity and a U-shaped relationship with decision criterion. Shorter reaction times were also associated with higher perceptual sensitivity, more liberal decision criterion, and larger pupil baseline. We also found that behavioral outcomes influenced upcoming pupil dynamics and behavior. Altogether, we observed that there existed tight correlations between pupil dynamics, perceptual performance, and reaction time, all of which were influenced by fluctuating behavior state. For characterization of the mechanisms and functional consequences behind phasic pupil dynamics in the awake, behaving animal, task-evoked pupil responses were first shown to differ according to their underlying cognitive processes. Task-evoked pupil responses are composed of a superposition of elementary components and this work showed that individual responses could be decomposed into the sum of their weighted, time-locked generalizable pupil-linked phasic arousal inputs. These phasic arousal inputs were separate from inputs controlling baseline related arousal fluctuations. We found distinct contributions to phasic arousal were made by stimulus encoding and decision-formation. Looking at these independently suggested differences in the underlying phasic arousal related mechanisms in driving the animals towards outcomes contingent on stimulus identity. Furthermore, drift-diffusion modeling revealed that interplay between phasic arousal evoked by both stimulus encoding and decision formation had important functional consequences on forming behavioral choice in perceptual decision-making. We also observed a central role of the locus coeruleus-norepinephrine (LC-NE) system in modulating pupil-linked behavioral state. Both electrical and optogenetic activation of the LC-NE system mediated pupil dilation. Furthermore, trial-by-trial LC-NE system activation via channelrhodopsin-2 (ChR2) increased perceptual sensitivity in a difficulty dependent manner, with more pronounced improvement occurring when distracting stimuli were more similar to the target stimulus.

Subconcussions in sport is a growing field of interest and concern as deteriorative effects of these impacts have been shown in athletes without a diagnosed concussion. Detecting subconcussions is extremely difficult and there is no standardized method to recognize these injuries. A first step in identifying subconcussion is taking a closer look at concussions. The vestibular system has been shown to be negatively affected after concussive injuries which can be quantified via oculomotor function and pupillometry. Currently, King Devick (KD) style tests and Pupillary Light Reflex (PLR) are two popular tests that can be administered to athletes to gather clinical eye measures relating to oculomotor function and pupillometry. This study aimed to investigate how clinical eye measures change through serial in-season testing of Division 1 (D1) soccer athletes. Head impacts throughout a soccer season were recorded and we hypothesized that a greater number of head impacts would result in negative clinical changes even in the absence of a diagnosed concussion. No major trends were observed in soccer athletes that can be associated with trends seen in concussed populations. Soccer athletes were found to be slightly more likely to test abnormally than non-contact controls and soccer athletes with a greater number of head impacts were found to have slightly more abnormal tests than athletes with fewer head impacts. Overall, this study provides a dataset of pre and post-season measurements and uniquely includes multiple in-season measurements to provide a new perspective on oculomotor function and pupillary light reflex over the course of a sports season. / Master of Science / Subconcussions in sport is a growing field of interest and concern as deteriorative effects of these impacts have been shown in athletes without a diagnosed concussion. Detecting subconcussions is extremely difficult and there is no standardized method to recognize these injuries. The first step at identifying subconcussions is to more closely look at concussions. Eye movements and pupil response to stimuli can be affected after a concussive injury. Currently, King Devick (KD) style tests and Pupillary Light Reflex (PLR) are two popular tests that can be administered to athletes to gather clinical eye measures relating to eye motion and pupil response to stimuli. This study aimed to investigate how clinical eye measures change through repeated in-season testing of Division 1 (D1) soccer athletes. Head impacts throughout a soccer season were recorded and we hypothesized that a greater number of head impacts would result in negative clinical changes even in the absence of a diagnosed concussion. No major trends were observed in soccer athletes that can be associated with trends seen in concussed populations. Soccer athletes were found to be slightly more likely to test abnormally than non-contact controls and soccer athletes with a greater number of head impacts were found to have slightly more abnormal tests than athletes with fewer head impacts. Overall, this study provides a dataset of pre and post-season measurements and uniquely includes multiple in-season measurements to provide a new perspective on clinical eye measures over the course of a sports season.

The purpose of this study was to compare and contrast within and between participant performance on three different measures of listening effort: a dual-task paradigm, pupillometry, and skin conductance; participants also subjectively rated the difficulty of their experience. A repeated measures design was used to address the reliability and validity of each measure. 20 participants were recruited and attended two sessions; the second occurred a minimum of one week after the first. Participants listened to sentences presented in stationary noise at four different signal-to-noise ratios: quiet, 0, -3, and -5 dB SNR. The variables of interest were: change in peak-to-peak pupil diameter, change in reaction time from baseline, skin conductance response amplitude, and skin conductance response quantity. The results indicated that as SNR decreased, speech perception performance decreased and subjective listening effort increased. Participants accurately and consistently rated the more difficult conditions as requiring more listening effort. The change in reaction time from baseline, peak-to-peak pupil diameter, and skin conductance response quantity increased as SNR decreased; skin conductance response amplitude did not vary as task difficulty increased, but skin conductance response amplitude was larger for incorrect responses than it was for correct responses. There was a significant practice effect observed for the reaction time data. The dual-task paradigm and pupillometry measures had the greatest reliability and validity. This study demonstrated that listening effort can successfully be quantified both subjectively and objectively by using a variety of tasks. Future studies may be able to use these measures to further assess listening effort in the clinic and in the real-world.

It was the purpose of the present study to determine the shape of the TEPR function during a dichotic shadowing task when the imposed work load is beyond the capability of the subject.It was hypothesized that as the task became increasingly difficult, the plotted functions of the maximum TEPR and words/s produced would start out small, increase rapidly, then level off or decrease reflecting the amount of information processing actually done. Ratings of subjectively perceived effort would also follow this pattern, whereas ratings of perceived task difficulty would continue to increase. Analyses were performed on mixed between-subjects and within-subjects designs using Two-way Analyses of Variance for repeated measures. The Newman-Keuls Procedure was used for all post-hoc comparisons.The results clearly demonstrated that the maximum TEPR reflects information actually being processed rather than the imposed difficulty of the task. Subjective ratings of perceived effort appear to reflect the same. The TEPR is not a good indicator of perceived task difficulty since ratings of task difficulty continued to increase after the TEPR leveled off.

Thesis (Ph. D.)--University of California, San Diego and San Diego State University, 2009. / Title from first page of PDF file (viewed August 11, 2009). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 36-39).