The accuracy and timely execution of rapid saccadic eye movements are crucial for effective vision. Therefore, an accurate measure of where the eye is aimed is required to understand not only the effect on visual processing but also the neuronal mechanisms that underlie the generation of the eye movements themselves. For more than 40 years, much of our understanding of the oculomotor system has relied on the scleral search coil system. This system has the advantages of operating in real time and having low noise and high accuracy. However, it requires an invasive surgery to implant the eye coil and bulky high power AC electromagnetic field coils. Unfortunately, as far as we are aware, there are no longer manufacturers that supply the scleral search coil system. The shifting focus of the electronics industry toward digital switching technology obsoletes most linear parts required to build the power oscillator that feeds the field coils and the detector. The optical eye movement transducers, which do not require attachment to the eye, are limited by the long latency of their video processing. Also, the fast high-end devices suffer from ringing artifacts at the end of a saccade that may mislead the interpretation of saccade kinematics. These problems could be a barrier for a new oculomotor neurophysiology lab. With the recent development of optogenetics, a technique that allows light to manipulate the activity of specific neurons with high temporal precision and then examine the effects on eye movements, the availability of an eye tracking device with a real-time characteristics is necessary. This real-time, low latency requirement is necessary in a closed-loop optogenetics experiment in which the laser light pulse is triggered and modulated by the kinematics of the eye movement while a saccade is unfolding. To address the need for a non-contact eye movement transducer with high spatial and temporal resolution, we propose to develop an eye tracking device that senses the asymmetric geometry of the ocular globe. The device will be based on a capacitive sensor that measures the proximity between the globe and the sensor. A capacitive proximity sensor has a wide bandwidth in excess of 1MHz and the signal processing stage can be designed using small-signal analog/digital circuits that allow for real-time operation. The capacitance sensor is composed of a fractured carbon nanotube-paper composite (CPC). Unlike other planar capacitive sensors, the fractured CPC relies on the total surface area resulting from the stretching of numerous multi-walled carbon nanotubes (MWCNTs). The surface area of MWCNT networks can be large enough to provide measurements that are orders of magnitude more sensitive than that of planar capacitors. The performance of the proposed sensor will be evaluated in a non-human primate and compared to that of a scleral search coil system.
This proposal develops a novel non-invasive eye tracking device based on capacitive sensing. A successful completion of this proposal would open up the possibility of implementing the capacitive sensing eye tracking device for marmoset and other research animals, and for clinical applications, as well as applications on virtual/augmented reality system.
