- Tools for Non-Invasive Evaluation of Normal and Perturbed Visual SystemsMy research program aims to develop and apply models, instruments and signal-processing techniques for the non-invasive evaluation of normal and perturbed visual system functions. The primary goals of my research program are to develop better models for the oculomotor system and to obtain a better understanding of the interactions between the sensory and motor visual sub-systems.
Instrumentation that enables the accurate measurements of eye-movements and neurophysiological functions have been developed. Eye movements are recorded by high- precision eye-trackers that incorporate advanced opto-electronic detectors and novel adaptive signal-processing techniques.
Neurophysiological functions such as stereopsis and visual acuity are monitored through the use of Visual Evoked Potentials (VEPs). The VEP system that we have developed uses novel signal processing algorithms to enhance parameter estimation and offers an objective and reliable method to study the development of information processing capabilities in preverbal (infant) subjects.
- Eye-TrackersHead-mounted eye trackers that can record and analyze responses from the saccadic, smooth pursuit and fixation ocular control systems have been developed. The unique functional characteristics of the eye-trackers (high temporal resolution, non-contacting etc.) have resulted in the following research projects:
1. Objective perimetry: We are developing a novel perimetry system that uses eye-movement responses to peripheral stimuli to determine the differential light threshold sensitivity of the retina. This novel approach to perimetry is more accurate than standard perimetry and will allow perimetry in subjects who have difficulty maintaining steady fixation.
2. Fixation eye movements during eccentric fixation: Eye movements of normal subjects and patients with deficient smooth pursuit system are recorded and analyzed. Based on these recordings we are developing a more complete understanding of the mechanisms responsible for the stabilization of gaze during fixation.
3. VOR in patients with peripheral vestibular lesions: Eye movements and head movements in patients with peripheral vestibular lesions are measured under dynamic head-rotations. We are using these recordings to develop a more complete understanding of the plasticity and compensation mechanisms of the oculomotor system.
4. Torsion eye-movement: We are developing a novel torsion eye-movement recording system that will provide the basis for the development of non-invasive tests of the otolith system.
5. Area of Interest (AOI) displays: The principle of AOI display is to present high-detail visual information to the observer's central field of view. In cooperation with CAE Electronics Ltd. of Montreal, we have developed an eye-tracking system that controls the AOI display on CAE's fiber-optics helmet mounted simulators.
6. Scan path analysis: We are developing an image analysis system that will determine the scanning behaviour of a subject relative to objects in her/his field of view. In this project we emphasize real-time general purpose image processing algorithms that allow automated analysis of video images.
- Visual Evoked PotentialsCurrent Visual Evoked Potentials (VEP) analysis techniques have difficulties in estimating visual thresholds (ie, visual acuity, contrast sensitivity thresholds, etc.). We have developed a VEP analysis technique that is sufficiently sensitive to reliably detect threshold VEP responses. This system is particularly useful in estimating visual performance of infants. In our main VEP project, our objective is to determine if a defect in either the binocular sensory system or its projections to oculomotor pathways is the underlying reason for the development of congenital strabismus. Over the past four years we have recorded binocular VEP responses from more than 200 babies (1-8 months) and have developed insights into the development of the feedback control loop that links the sensory and oculomotor systems.
- Signal ProcessingOptimal structures and algorithms for the detection and estimation of random signals are being investigated. The concepts developed through this research are often transferred to ophthalmology and biomedical research. Work is concentrated in the areas of time-delay estimation and high-resolution multi-elements arrays. In time-delay estimation, several robust sub-optimal structures have been developed and their performance was compared with adaptive (LMS, Lattice) structures. We have developed optimal estimators for time varying delays which allows optimal estimation of mildly non-stationary processes. The research into array structures (multi-target environment) involves the optimization of array resolution while rejecting correlated and uncorrelated noises.
Affiliate Scientist, Krembil Research Institute (Krembil)
Professor, Institute of Biomaterials and Biomedical Engineering (IBBME), University of Toronto
Professor, Department of Ophthalmology and Vision Sciences, University of Toronto.
Professor, Department of Electrical and Computer Engineering, University of Toronto
Adjunct Professor, Department of Optometry, University of Waterloo