Saccadic oculo-motor control chip

Abstract

The present chapter describes an integrated circuit intended to control the same light deflection system (oculo-motor system) as described in Sect. 5.2, but in a different operating mode. Instead of shifting the direction of gaze incrementally under permanent visual control as in Chap. 5, this chip computes directly the final prism orientations matching a specified direction of gaze picked somewhere within the accessible field, and generates a saccade (quick shift of the prism orientations) making this point the center of the retina image. The target point is specified in a fixed coordinate system tied to the rigid mechanical structure which the oculo-motor system is mounted onto. This coordinate system will be called head-centered by analogy with animal anatomy. This chip and the incremental control chip (Chap. 5) differ in accuracy and speed, and are intended for different purposes. The saccade control chip implements an inverse model of the oculo-motor system, and computes the required prism orientations open-loop. Thereby, the final prism orientations are known even before motion is initiated, therefore the mechanical parts can move at top speed. However, accuracy limitations of the model affect directly the final deflection angle. The chip has been designed to ensure that the target point is visible after a saccade, but its maps are not fine-grained to pixel accuracy.