A fresh look at visual sampling: How are fixational eye-movements optimised? [PhysFEM]

How should a sensory system, such as vision or hearing, optimally sample the world? Too much detail takes too long, and too much resource to acquire and process; too little risks failing to capture the vital information on what is going on around us. Human vision is a fascinating example - for even when the gaze is 'fixed' onto a target object or performing a specific task such as deciding which of two objects is higher, the eyes are in constant, apparently-random, motion that we do not understand. One might assume that such involuntary movements of the eye could only 'blur' vision, but there are reasons to believe that they might actually enhance it. One reason for suspecting this is that we know that many aspects of vision have evolved towards the best performance possible.

This project - the Physics of Fixational Eye Movements (PhysFEM) - addresses the challenge of these ever-present involuntary movements of our eyes by combining ideas, methods and people from theoretical physics of random motion, and from the life sciences of visual neuroscience and psychology. The combination is new and potentially powerful: there is almost no realm of physics that does not think about finding paths of trajectories that optimise something. Examples arise in complex classical mechanics, quantum mechanics, and the thermal physics of random processes. These ideas from physics provide a natural but fresh way of thinking about the possibility that fixational eye movements optimise some aspects of vision. More than that, they bring new calculation methods to find such paths, leading to empirically testable predictions about how the eyes might move to maximise the information available given particular task-demands. The objective measurement of human visual performance under controlled conditions - the domain of 'psychophysics' - completes the iterative cycles of model predictions and testing.

Physics enters the experimental mode of this project also in terms of the equipment used in in the Oxford Perception Lab to measure eye movements. The team use 'adaptive optics' - first developed for large astronomical telescopes to correct the optical distortions of the atmosphere - to image the retina at the back of the eye whilst correcting for distortions in the eye's fluid-filled optical components. Such correction permits high-resolution imaging of individual cells in the human retina without any invasive procedure. The Adaptive Optics Scanning Laser Ophthalmoscope (AO-SLO) will perform three simultaneous tasks in PhysFEM: (i) projecting controlled images onto the retina; (ii) imaging the retina at the resolution of individual light-detecting ('photoreceptor') cells; (iii) measuring eye movements with unprecedented accuracy, under a series of specific visual tasks.

The findings of the project will be built into a growing, open-access computational tool for vision science and technology, ISETBio, through a collaboration with its originator and director at the University of Pennsylvania, USA. ISETBio is an open-source set of software tools that characterise the sensory processes of early vision, and provides a platform for realistic computational implementation and evaluation of models for how neural processing incorporates FEMs, and transferring this to the international community of researchers in biological- and computer-vision and medicine.