Doctor of Philosophy in Neuroscience (PhD)
Eye and Hand Coordination
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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.
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.