Prospective Graduate Students / Postdocs
This faculty member is currently not actively recruiting graduate students or Postdoctoral Fellows, but might consider co-supervision together with another faculty member.
This faculty member is currently not actively recruiting graduate students or Postdoctoral Fellows, but might consider co-supervision together with another faculty member.
Dissertations completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest dissertations.
Adaptive behaviour in a highly dynamic and complex environment necessitates the ability to transform sensory input into motor output at different timescales. The goal of this dissertation was to probe the sensorimotor processes that underlie precise movement control in rich sensory environments. In four experimental studies, I studied different types of tracking eye movements in response to stimuli that mirror some of the complexities found in the natural environment (complex pattern motion, target acceleration, and audiovisual signals). In the first study, I investigated the dynamic motion integration processes that give rise to the coherent perception of 2D pattern motion. Comparing eye movements to observers’ perceptual experience revealed shared motion integration mechanisms that drive continuous tracking and motion perception (Chapter 2). Accurate sensing of complex motion signals is a fundamental ability that allows humans to interact with objects moving along complex trajectories. In Chapter 3, I investigated how observers track and manually intercept accelerating targets. Results showed that observers continuously monitor the changing target speed but fail to account for acceleration to predict and intercept targets. Natural interaction with moving visual objects typically involves multiple senses. In two studies, I demonstrated profound and rapid effects of audiovisual integration on goal-directed actions. I found that auditory and visual signals were weighted according to their uncertainty to guide interceptive movements (Chapter 4). Finally, presenting audiovisual distractors during continuous visual tracking revealed multisensory response enhancement of reflexive movement inhibition at short latencies of ~100 milliseconds (Chapter 5). These findings were obtained using eye movements as a continuous indicator of human sensorimotor integration, highlighting the use of eye movements as a model system to study adaptive sensorimotor behaviour in dynamic environments. I propose a model that describes how eye movements at different timescales are affected by the dynamic processing of complex visual and audiovisual signals. The present findings can be used to inform training protocols for interceptive sports athletes and to assess sensorimotor deficits in clinical populations.
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We live in a dynamic visual environment, which requires perceiving moving objects around us and acting accordingly. However, we do not yet fully understand how visual information informs perception and motor actions. This dissertation examines the perception-action link by testing how motion and expectation signals are processed for perception and for eye movements as an example of human motor action. I focus on two types of human eye movements triggered by distinct brain mechanisms: ocular torsion, the eyes’ rotation about the line of sight triggered by rotational motion, and smooth pursuit, the eyes’ continuous tracking of translational motion. Torsion is mostly controlled by subcortical brain areas, but might share early-stage cortical processing of sensory signals with perception. In contrast, smooth pursuit is controlled by subcortical and cortical areas and might therefore be more closely linked to perception, sharing both motion and expectation signal processing with perception. To test the torsion-perception link, I utilized a perceptual illusion induced by visual rotational motion. Results show that torsional velocity correlates with the perceptual illusion, potentially suggesting shared motion processing (Chapter 2.1). However, anticipatory torsion can only be elicited by trial repetition, but not by cognitive cues that induce expectation (Chapter 2.2). These results show that similar visual motion signals might drive reflexive torsion and perception. Expectation signals appear to be less effective in driving torsion. Probing the pursuit-perception link, I found dissociations between how each system processes motion and expectation signals. When integrating diverse motion signals across space, pursuit was biased to the average motion direction, whereas perception showed no consistent bias (Chapter 3). When investigating the role of expectation, I found that anticipatory pursuit followed the expected direction, whereas perception was biased in the opposite direction (Chapter 4). Overall, this dissertation reveals that perception and eye movements likely share early-stage motion processing, even for reflexive eye movements such as torsion. But perception and eye movements differ in how they utilize higher-level motion or expectation signals. The dissociations might indicate how each system optimally meets different functional demands: Perception relies on object segregation, whereas eye movements rely on signal integration.
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Natural tasks, such as catching a ball, involve the decision whether, when, and where to act. This dissertation examines the relationship between eye and hand movements during goal-directed manual interceptions that require rapid sensorimotor decisions. Human observers viewed and predicted the motion path of a briefly presented moving target and intercepted it at its assumed end position. Observers naturally tracked the moving target to guide interceptive hand movements. To probe the tight eye-hand link, I investigated the effect of perceptual-motor training on eye and hand movement quality (Chapter 2). Results indicate a mutual benefit of training eye and hand movements concurrently. Eye movement training alone was not sufficientto improve hand movement accuracy. However, training that required an active sensorimotor decision (eye or hand interception) enhanced eye movement quality.Next, I tested the role of eye movements during go/no-go decisions. Observers predicted whether targets passed through (go required) or missed (no-go required) a strike box. Observers' eye movements differentiated between decision outcome (go vs. no-go) on a trial-by-trial basis with an overall accuracy of 76% (Chapter 3). Moreover, I found that different eye movement phases were linked to a two-stage decision process. Whereas eye velocity during pursuit initiation corresponded to go/no-go decision accuracy, pursuit maintenance was related to successful interception timing (Chapter 4).Finally, I investigated the role of movement constraints on decision accuracy by manipulating response modality (button press vs. interceptive hand movement) and eye movements (free viewing vs. fixation; Chapter 5). Decision formation occurred earlier but less accurately when an interceptive hand movement had to be planned and executed. Eye movements (compared to fixation) enhanced decision accuracy regardless of response modality. These results indicate that perceptual decision formation occurs dynamically, relying on the continuous updating of sensory information until an action is required.In sum, this dissertation provides evidence that eye movements are directly related to neural signatures of perceptual decision making. Furthermore, eye and hand movements show interdependencies during visual predictions and manual interception. This work highlights the potential of studying eye movements as continuous readouts of ongoing sensorimotor and cognitive processes during natural tasks.
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Theses completed in 2010 or later are listed below. Please note that there is a 6-12 month delay to add the latest theses.
Parkinson’s Disease (PD) is a neurodegenerative disease characterized by motor impairments including bradykinesia, rest tremor, and postural instability. In addition, motor dysfunction appears in oculomotor abnormalities, specifically saccadic eye movement deficits. It is now recognized that PD extends beyond motor impairments and affects sensory and cognitive domains. PD alters a range of cognitive functions, but particularly affects response inhibition, even early in the disease course. The antisaccade task is an oculomotor paradigm used to evaluate response inhibition and is a sensitive indicator of PD. Antisaccade task performance has been well characterized in PD patients, but it is unclear what factors contribute to these deficits. Here we investigated whether antisaccade performance in mild to moderate PD is related to motor function, executive function, and or general cognitive ability. We evaluated pro- and antisaccade performance in 17 patients and 20 matched controls. Saccade latencies, amplitudes, and error rates were compared between groups, and were correlated to performance on a series of motor (Timed up and Go test) and cognitive tasks (Trail Making Task, Stroop Task, and matrices sub-test of the Kaufman Brief Intelligence Index). Relative to controls, patients showed smaller amplitude prosaccades, and more than double the frequency of errors when executing antisaccades (patients M=21.7% SD= 18.6%; controls M=10.5%, SD=11.43%; p=0.013; d= 0.72). However, patients performed equal to, or better than controls on the battery of motor and cognitive assessments. Our results cautiously suggest that PD patients show deficits in response inhibition despite an absence of cognitive dysfunction on standard neuropsychological tools. With additional investigation, antisaccade task performance has the potential to be a sensitive indicator of early changes in response inhibition in PD, to be used as a tool in compliment with clinical evaluation.
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Bipolar disorder is defined as a brain disorder characterized by extreme mood fluctuations that result in changes in energy and disability. Enhanced impulsivity is present in episodes of mania or hypomania in bipolar disorder, of particular importance are factors of impulsivity such as inability to predict or anticipate future events. Delineating trait versus state components of impulsivity helps identify risk factors for bipolarity and evaluate disease progression. Eye movements have been used to assess impulse control as well as predictive and anticipatory mechanisms. Here, we use a subsyndromal approach to relate eye movement measures to impulsivity and hypomania proneness in a cohort of young adults not previously diagnosed with a psychiatric disease. We assessed 60 participants (20 males, 40 females) in the antisaccade task, and a smooth pursuit battery that include a sinusoidal pursuit paradigm and a predictive pursuit task. Participants additionally completed the Hypomanic Personality Scale and Barrat Impulsiveness Scale. We found positive relationships of small effect size between mean number of express saccades in antisaccade trials and deceleration after target extinction in predictive pursuit with hypomania proneness. We also show a negative trend of small effect size between initial eye acceleration with hypomania proneness. Given that we tested healthy participants and assessed hypomania proneness, our results might suggest a state-related component of impulsivity. However, all results must be interpreted with caution as none are statistically significant.
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Accurate hand movements are important for many daily activities and we frequently use vision to help guide our interactions with our environment. Here we investigated whether smooth pursuit training transfers to hand movements by examining manual interception accuracy.We conducted three series of five-day perceptual-motor learning experiments. In a track-intercept task, observers were instructed to track a moving target on a screen and to hit it with their index finger as soon as it entered a “hit zone”. In each trial, only the first part (100-300 ms) of the trajectory was shown and observers had to extrapolate and intercept the target at its assumed position. In all three experiments, subjects were tested on an eye-hand coordination task on the first day (day 1, pre-test) and last day (day 5, post-test); the three experiments differed with regard to training on days 2-4. Further, subjects were invited to complete the eye-hand coordination task during a one-week follow-up session after the post-test (day 6). Experiment 1 (n=9) involved no hand movements during training; subjects only tracked the target with their eyes and received no visual feedback. Subjects in Experiment 2 (n=9) tracked and intercepted the target during training. Experiment 3 (n=9) served as a control and involved no training. Subjects in all groups were invited to come back one week after the post-test for a follow-up testing session.Results show that manual interception performance (finger position error) improves in all groups, but improves most following combined eye-hand training. Interestingly, this group also resulted in the greatest improvement in eye movements. This finding is particularly noteworthy because both training groups involved the same degree of eye-movement training, but eye movements improved only if combined with engaging the hand. Analysis of performance in the one week follow-up after the post-test revealed that training effects in the eye-hand group were particularly long-lasting and stable, whereas eye movements continued to improve through to the week follow-up.I will discuss implications of these results for our understanding of the brain pathways underlying eye and hand movement control, as well as practical applications in sports and clinical rehabilitation.
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