A Neurocomputational Model of Smooth Pursuit Control to Interact with the Real World

Whether we want to drive a car, play a ball game, or even enjoy watching a flying bird, we need to track moving objects. This is possible via smooth pursuit eye movements (SPEMs), which maintain the image of the moving object on the fovea (i.e., a very small portion of the retina with high visual resolution). At first glance, performing an accurate SPEM by the brain may seem trivial. However, imperfect visual coding, processing and transmission delays, wide variety of object sizes, and background textures make the task challenging. Furthermore, the existence of distractors in the environment makes it even more complicated and it is no wonder why understanding SPEM has been a classic question of human motor control. To understand physiological systems of which SPEM is an example, creation of models has played an influential role. Models make quantitative predictions that can be tested in experiments. Therefore, modelling SPEM is not only valuable to learn neurobiological mechanisms of smooth pursuit or more generally gaze control but also beneficial to give insight into other sensory-motor functions. In this thesis, I present a neurocomputational SPEM model based on Neural Engineering Framework (NEF) to drive an eye-like robot. The model interacts with the real world in real time. It uses naturalistic images as input and by the use of spiking model neurons controls the robot. This work can be the first step towards more thorough validation of abstract SPEM control models. Besides, it is a small step toward neural models that drive robots to accomplish more intricate sensory-motor tasks such as reaching and grasping

Incorporating Prediction in Models for Two-Dimensional Smooth Pursuit

A predictive component can contribute to the command signal for smooth pursuit. This is readily demonstrated by the fact that low frequency sinusoidal target motion can be tracked with zero time delay or even with a small lead. The objective of this study was to characterize the predictive contributions to pursuit tracking more precisely by developing analytical models for predictive smooth pursuit. Subjects tracked a small target moving in two dimensions. In the simplest case, the periodic target motion was composed of the sums of two sinusoidal motions (SS), along both the horizontal and the vertical axes. Motions following the same or similar paths, but having a richer spectral composition, were produced by having the target follow the same path but at a constant speed (CS), and by combining the horizontal SS velocity with the vertical CS velocity and vice versa. Several different quantitative models were evaluated. The predictive contribution to the eye tracking command signal could be modeled as a low-pass filtered target acceleration signal with a time delay. This predictive signal, when combined with retinal image velocity at the same time delay, as in classical models for the initiation of pursuit, gave a good fit to the data. The weighting of the predictive acceleration component was different in different experimental conditions, being largest when target motion was simplest, following the SS velocity profiles

Psychological and psychophysical aspects of spatial orientation.

These studies were undertaken to investigate the psychological and psychophysical factors that mediate spatial orientation/disorientation in both healthy and patient populations. PERCEPTION OF ANGULAR VELOCITY: Using a new method of examining perception of rotation this study found a similarity between the sensation and ocular responses following velocity step stimuli. Both decayed exponentially with a time constant of circa 15 seconds following rotation in yaw; circa 7 seconds following rotation in roll. Both the ocular and sensation responses were significantly reduced following repeated vestibular and optokinetic stimulation. The test was conducted with patients suffering from congenital nystagmus, ophthalmoplegia or cerebellar lesions, all of whom had markedly reduced post-rotational sensation responses of approximately 7 to 9 seconds. ADAPTATION TO OSCILLOPSIA: Labyrinthine defective subjects were found to prefer less self- motion when viewing a moving video-image than either ophthalmoplegia subjects or normal controls. The results suggest that adaptation to oscillopsia may be related to an active approach to recovery (i.e. high external locus of control) and also to increased tolerance to retinal slip. This serves to illustrate the coactive role of psychological and psychophysical mechanisms in adaptation to vestibular disorders. INVESTIGATION OF PSYCHOLOGICAL AND PSYCHOSOCIAL FACTORS: This questionnaire- based study aimed to examine adjustment to illness in patients with balance disorders and with congenital nystagmus. The study identified a greater use of emotion-focused coping strategies than problem-focused strategies. It highlighted the prevaience of anxiety and depression among these patients and pointed towards several psychosocial variables (locus of control, self-esteem and social support) that play a significant role in the coping behaviour of these patients. MENSTRUATION, MIGRAINE AND MOTION SICKNESS: The relationship between hormonal cycles and migraine and motion sickness is poorly understood. The study demonstrated that motion sickness and headache occurred independently although exposure to rough seas could be a specific migraine trigger in certain individuals who did not otherwise suffer attacks. Female subjects were more prone to motion sickness around the period of menstruation and less so around ovulation

Horizontal and vertical eye deviations in response to linear accelerations

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1983.MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERINGBibliography: leaves 48-49.by Brenda Joyce Kitchen.B.S

Role of the cerebellum in visuomotor coordination

The initiation of coupled eye and arm movements was studied in six patients with mild cerebellar dysfunction and in six age-matched control subjects. The experimental paradigm consisted of 40 deg step-tracking elbow movements made under different feedback conditions. During tracking with the eyes only, saccadic latencies in patients were within normal limits. When patients were required to make coordinated eye and arm movements, however, eye movement onset was significantly delayed. In addition, removal of visual information about arm versus target position had a pronounced differential effect on movement latencies. When the target was extinguished for 3 s immediately following a step change in target position, both eye and arm onset times were further prolonged compared to movements made to continuously visible targets. When visual information concerning arm position was removed, onset times were reduced. Eye and arm latencies in control subjects were unaffected by changes in visual feedback. The results of this study clearly demonstrate that, in contrast to earlier reports of normal saccadic latencies associated with cerebellar dysfunction, initiation of both eye and arm movements is prolonged during coordinated visuomotor tracking thus supporting a coordinative role for the cerebellum during oculo-manual tracking tasks.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46565/1/221_2004_Article_BF00230206.pd

Sensory interactions in balance and eye movement control

Eye and head movements were recorded during angular/linear motion of the head or neck. Four areas of sensory-motor interaction in human balance control were studied. In the cervico-vestibular section, eye movements elicited by neck torsion were shown to be weak in normal subjects but considerably enhanced in labyrinthine defective patients, in whom they may partly compensate for the lack of the vestibulo-ocular reflex. In the vestibulo-cervical section, experiments showed a diminished ability of patients with absent vestibular function to stabilize the head in space during trunk motion. Other experiments found vestibular abnormalities in patients with cervical dystonia (Spasmodic Torticollis) which could not be explained by the abnormal head posture per se; it was concluded that the vestibular system contributes to human head posture and that the hitherto unexplained neural processes provoking Spasmodic Torticollis interfere with vestibular signals. Under the otolith-canal interaction section, experiments showed that slow phase eye movements of high velocity can be elicited in response to combined angular-linear acceleration, obtained by placing the head eccentrically in an ordinary "Barany" rotating chair. The possibility that the procedure could become a clinically useful test of otolith function was preliminary studied in oto-neurological patients. The section on otolith-visual interaction examines slow phase eye movements in response to lateral linear acceleration of the head. In the presence of visual fixation these responses are strong and compensate for head motion at very short latency, allowing the eyes to maintain fixation on stationary objects. In the dark responses are weak and inappropriate for visual stabilization. The experiments combining angular acceleration or visual stimulation with linear acceleration suggest that/ in order to generate functionally meaningful eye movements, otolith-ocular responses are highly dependent on interaction with other sensory stimuli. This thesis is supported by a series of published papers

Otolith function in human subjects: Perception of motion, reflex eye movements and vision during linear interaural acceleration

The thesis investigates how the otolith organs of the vestibular system, specifically the utricles, assist motion perception and aid visual stabilization, during translational lateral whole-body acceleration. It was found that high gradients of acceleration facilitate the detection of motion and that, for low acceleration gradients, motion perception in normal subjects relies on a 'velocity' threshold detection process. Experiments in patients without vestibular function indicated that, for the stimuli employed, the somatosensory system could be as sensitive to linear motion as the vestibular system. The interaction between the horizontal linear vestibulo-ocular reflex (LVOR) and visual context was characterized in the following experiments. Subjects were accelerated transiently in darkness, or while viewing earth-fixed or head-fixed targets. From onset, the eye velocity response to head translation was enhanced with acceleration level and target proximity, but was only slightly reduced by fixation of head-fixed targets. This suggested that the gain of the LVOR pathway was adjusted before or immediately after motion onset by a parameter depending mainly on viewing distance and less on the knowledge of probable relative target motion. For high relative target velocities, LVORs improved ocular fixation over what would be attained by pursuit alone, although fully compensatory eye movements were not always produced. The LVORs of patients who underwent unilateral vestibular deafferentation suggested that the utricular area generating transaural LVORs is the macular region lateral to the striola. Psychophysical experiments based on a reading task established the functional role of the LVOR for stabilising vision during high-frequency sinusoidal whole-body acceleration. Unlike normal subjects, visual acuity in patients without vestibular function was not better during self-motion than during display oscillation. Finally, the LVOR interaction with canal-ocular reflexes was studied using isolated and combined translational/rotational stimuli. The results showed that, shortly after motion onset, canal stimulation enhances the LVOR evoked by head translation

Microgravity vestibular investigations (10-IML-1)

Our perception of how we are oriented in space is dependent on the interaction of virtually every sensory system. For example, to move about in our environment we integrate inputs in our brain from visual, haptic (kinesthetic, proprioceptive, and cutaneous), auditory systems, and labyrinths. In addition to this multimodal system for orientation, our expectations about the direction and speed of our chosen movement are also important. Changes in our environment and the way we interact with the new stimuli will result in a different interpretation by the nervous system of the incoming sensory information. We will adapt to the change in appropriate ways. Because our orientation system is adaptable and complex, it is often difficult to trace a response or change in behavior to any one source of information in this synergistic orientation system. However, with a carefully designed investigation, it is possible to measure signals at the appropriate level of response (both electrophysiological and perceptual) and determine the effect that stimulus rearrangement has on our sense of orientation. The environment of orbital flight represents the stimulus arrangement that is our immediate concern. The Microgravity Vestibular Investigations (MVI) represent a group of experiments designed to investigate the effects of orbital flight and a return to Earth on our orientation system

Linear acceleration and horizontal eye movements in man

Thesis (Sc. D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1990.Vita.Includes bibliographical references (leaves 156-164).by Mark John Shelhamer.Sc.D