No description available.

In order to grasp an object in their visual field, humans orient their visual axis to targets of interest. While scanning their environment, humans perform multiple saccades (rapid eye movements that correct for a position error between eye and target) to align their visual axis with objects of interest. Humans are also able to track objects that move in their environment by means of smooth pursuit eye movements (slow eye movements that correct for any velocity error between eye and target, i.e. for any retinal slip). The appearance of a moving stimulus in the environment elicits smooth pursuit eye movements with a latency of around 100ms. Accordingly, the smooth pursuit system accounts for a change in the trajectory of a moving target with a similar delay. Due to this delay, the oculomotor system needs to develop strategies to avoid the build up of position error during tracking of a moving target. To do so, the oculomotor system uses prediction to try and anticipate the future target trajectory. However, this strategy is limited to conditions where target trajectory is predictable. Otherwise, primates have to combine pursuit and saccades in visual tracking of unpredictable moving targets to avoid large position error. This thesis focuses on both the prediction mechanisms and the interactions between saccades and pursuit. In order to investigate prediction mechanisms, we asked human subjects to pursue a moving target when it was transiently occluded. During occlusions, subjects continued to pursue the invisible target. This thesis demonstrates that this predictive pursuit response is based on a dynamic internal representation of target motion, i.e. a representation that evolves with time. This internal representation could be either built up by repetition of the same target motion or extrapolated on the basis of the pre-occlusion target motion. In addition, it is shown that during occlusions, saccades are adjusted in order to account for the large variability of the smooth pursuit response. As a consequence, it shows that the smooth pursuit command is used by internal models in order to predict future smooth pursuit response. These results demonstrate that both prediction and internal models are necessary to track the invisible and the visible.

<p>Smooth pursuit eye movements are movements of the eyes that are used to foveate moving objects. Their precision and adaptation is believed to depend on a constellation of sites across the cerebellum, but only one region’s contribution is well characterized, the floccular complex. Here, I characterize the response properties of neurons in the oculomotor vermis, another major division of the oculomotor cerebellum whose role in pursuit remains unknown. I recorded Purkinje cells, the output neurons of this region, in two monkeys as they executed pursuit eye movements in response to step ramp target motion. The responses of these Purkinje cells in the oculomotor vermis were very different from responses that have been documented in the floccular complex. The simple spikes of these cells encoded movement direction in retinal, as opposed to muscle coordinates. They were less related to movement kinematics, and had smaller values of trial-by-trial correlations with pursuit speed, latency, and direction than their floccular complex counterparts. Unlike Purkinje cells in the floccular complex, simple spike firing rates in the oculomotor vermis remained unchanged over the course of pursuit adaptation, likely excluding the oculomotor vermis as a site of directional plasticity. Complex spikes of these Purkinje cells were only partially responsive to target motion, and did not fall into any clear opponent directional organization with simple spikes, as has been found in the floccular complex. In general, Purkinje cells in the oculomotor vermis were responsive to both pursuit and to saccadic eye movements, but maintained tuning for the direction of these movements along separate directions at a population level. Predictions of caudal fastigial nucleus activity, generated on the basis of our population of oculomotor vermal Purkinje cells, faithfully tracked moment-by-movement changes in pursuit kinematics. By contrast, these responses did not faithfully track moment-by-moments changes in saccade kinematics. These results suggest that the oculomotor vermis is likely to play a smaller role in influencing pursuit eye movements by comparison to the floccular complex.</p> / Dissertation

共著者あり。共著者名:Yoshida Toshikazu, Fukushima Kikuro. / Hokkaido University (北海道大学) / 博士 / 医学

It is essential for the brain to keep track of self-movement in order to establish a stable percept of the environment. The major source of information about self-movement is vision. However, non visual (extraretinal) information can also contribute to the sense of motion. This thesis investigated the role of extraretinal signals to account for self-generated motion in the case of eye movements. The interaction of two types of eye movements, i.e. smooth pursuit and saccades, was used to investigate the system's capacity to keep track of self-motion. This work focused in particular on the ability of the saccadic system to account for smooth pursuit eye movements in darkness. A detailed analysis of the saccade metrics allowed the identification of a novel neural mechanism for smooth eye movement integration. As a result, the saccadic system could compensate for smooth eye displacements and thus was able to ensure space constancy across different eye movements. In addition to the experimental approach of this thesis, a mathematical model was developed that described all current findings.

It is essential for the brain to keep track of self-movement in order to establish a stable percept of the environment. The major source of information about self-movement is vision. However, non visual (extraretinal) information can also contribute to the sense of motion. This thesis investigated the role of extraretinal signals to account for self-generated motion in the case of eye movements. The interaction of two types of eye movements, i.e. smooth pursuit and saccades, was used to investigate the system's capacity to keep track of self-motion. This work focused in particular on the ability of the saccadic system to account for smooth pursuit eye movements in darkness. A detailed analysis of the saccade metrics allowed the identification of a novel neural mechanism for smooth eye movement integration. As a result, the saccadic system could compensate for smooth eye displacements and thus was able to ensure space constancy across different eye movements. In addition to the experimental approach of this thesis, a mathematical model was developed that described all current findings.

Smooth tracking and efficient reaching for moving objects require the ability to predict the velocity and trajectory of the object. This skill is important to be able to perceive human action and object motion in the world. This thesis explores early visual motor development in full term and preterm infants. Study I showed that horizontal eye tracking develops ahead of vertical (full term infants at 5, 7 and 9 months of age). The vertical component is also more affected when a second dimension is added during circular pursuit. It is concluded that different mechanisms appear to underlie vertical and horizontal eye movements Study II-IV compared the development of the ability to visually track and reach for moving objects in very preterm infants born &lt;32 gestational weeks to healthy infants born at term. The development of horizontal smooth pursuit at 2 and 4 months of corrected age was delayed for the preterm group (Study II). Some infants were catching up whereas others were not improving at all. A question raised by the results was whether the delay was caused by specific injuries as a result of the prematurity. However, the delays persisted when all infants with known neonatal complications and infants born small for gestational age were excluded (Study III), indicating that they were caused by prematurity per se. At 8 months corrected age preterm and full term infants were equally good at aiming reaches and successfully catching a moving object. Nevertheless, the preterm group used a bimanual strategy more often and had a more jerky and circuitous path than the full term group (Study IV). In summary, preterm infants showed a delayed visual motor development compared to infants born at term. The results of these studies suggest that there is additional diffuse damage to the visual motor system that is not related to neonatal complications as diagnosed today. Measuring smooth pursuit could potentially be a new method for early non-invasive diagnosis of impaired visual function.

In a rapidly changing visual environment, the delay between perception and action might impair the probability of survival of a prey or the efficiency of a predator. In order to compensate for delays associated with sensory-motor processing, primates often make predictions about future events and initiate anticipatory movements. To prepare an anticipatory movement, an estimation of when and where to a target is likely to move is necessary. Such an internal representation is often termed 'expectation'. The aim of this thesis was to investigate the gradual changes of a subject's expectation at the behavioral and electrophysiological levels. Anticipatory smooth pursuit was used in order to study temporal and directional changes in expectation. We found that temporal uncertainty strongly modulated the latency and the velocity of anticipatory movements suggesting that monkeys could estimate the hazard rate of target motion onset in order to decide when to initiate an anticipatory movement. In addition, we have shown that monkeys could use prior directional information in order to voluntarily initiate anticipatory responses in the direction of expected target motion. This prior directional information significantly affected the latency and velocity of these movements. Finally, we have shown that the majority of recorded supplementary eye field (SEF) neurons encoded expected target motion direction. The presence of a directional cue induced an increase of activity in the preferred direction of the neuron. Moreover, a large sub-population of neurons encoded the direction of future anticipatory movement. These results suggest that the SEF could be involved in the cognitive control of anticipatory pursuit eye movements when prior temporal and directional information is provided.

No description available.

Smooth pursuit is the movement that occurs when the eyes meticulously follow an object in motion. While smooth pursuit can be achieved with a stationary head, it generally relies on the head following the visual target as well. During smooth pursuit, a coordinating vestibular mechanism, shared by both the head and the eyes, is used. Therefore, smooth pursuit can reveal much about where a person is looking based on only the direction of the head. To investigate the interplay between the eyes and the head, an application was made for the augmented reality head-mounted display Magic Leap. The application gathered data of the head and eyes respective movements. The data was analyzed using visualizations to find relationships within the eye-head coordination. User studies were conducted and the eyes proved to be incredibly accurate and the head direction was close to the target at all times. The results point towards the possibility of using head direction as a model for visual attention in the shape of a cone. The users’ head direction was a good indicator of where they put their attention, making it a valuable tool for developing augmented reality applications for head-mounted displays and smart glasses. By only using head direction, a software developer can measure where most of the users’ attention is put and hence optimize the application according to this information. / Följerörelser är det som sker när ögonen noggrant följer ett objekt i rörelse. Följerörelser kan uppnås med ett stationärt huvud, men generellt används även huvudet för att följa det visuella målet. Ögonen och huvudet delar en vestibulär koordineringsmekanism som är aktiv under följerörelser och därför kan enbart huvudrörelser avslöja mycket om var en person har sin uppmärksamhet.För att undersöka samspelet mellan ögonen och huvudet gjordes en applikation för ett augmented reality headsetet Magic Leap. Applikationen samlade in data på ögonrespektive huvudrörelser. Den insamlade datan analyserades med hjälp av visualiseringar för att hitta förhållanden inom ögon-huvud koordinationen.Användarstudier utfördes och ögonen visade sig vara väldigt exakta och huvudets riktning var hela tiden i närheten av målet. Resultatet pekar mot möjligheten att använda huvudriktning som en modell för visuell uppmärksamhet i formen av en kon. Användarnas huvudriktning var en bra indikator på var de hade sin uppmärksamhet, vilket gör den till ett användbart verktyg för utveckling av augmented reality applikationer för headsets och smartglasögon. En mjukvaruutvecklare kan mäta var användarnas uppmärksamhet dras genom att använda huvudriktningen och kan därmed optimera applikationen utefter den informationen.