Abstract: In experimental studies of visual performance, the need often emerges to modify the stimulus according to the eye movements performed by the subject. The methodology of Eye-Movement Contingent Display (EMCD) enables accurate control of the position and motion of the stimulus on the retina. EMCD procedures have been used successfully in many areas of vision science, including studies of visual attention, eye movements, and physiological characterization of neuronal response properties. Unfortunately, the difficulty of real-time programming and the unavailability of flexible and economical systems that can be easily adapted to the diversity of experimental needs and laboratory setups have prevented the widespread use of EMCD control. This paper describes EyeRIS, a general-purpose system for performing EMCD experiments on a Windows computer. Based on a digital signal processor with analog and digital interfaces, this integrated hardware and software system is responsible for sampling and processing oculomotor signals and subject responses and modifying the stimulus displayed on a CRT according to the gaze-contingent procedure specified by the experimenter. EyeRIS is designed to update the stimulus within a delay of 10 ms. To thoroughly evaluate EyeRIS' performance, this study (a) examines the response of the system in a number of EMCD procedures and computational benchmarking tests, (b) compares the accuracy of implementation of one particular EMCD procedure, retinal stabilization, to that produced by a standard tool used for this task, and (c) examines EyeRIS' performance in one of the many EMCD procedures that cannot be executed by means of any other currently available device.

A movie ( AVI 83MB) illustrates some possible applications to experiments in psychophysics and neurophysiology.
Results shown here were obtained with a RADEON 7000 AGP, a board with average performances. The PC used in the experiments is a dual Pentium III (600Mhz) with 756MB of RAM.

The following demos are shown:

1. Retinal Stabilization: Example with artificial eye movements. A model eye is moved to follow sinusoidal and square-wave trajectories with variable frequencies. The image on the display is shifted in real-time to keep the stimulus in the same position on the retina.
2. Foveated Image: Example with artificial eye movement. A model eye is moved to follow sinusoidal and square-wave trajectories with variable frequencies. The image is re-sampled in real-time so that the resolution changes with the angle of eccentricity.
3. Tracking Gaze: Example with eye movements recorded by a DPI eyetracker. The red dot indicates the gaze location.
4. Retinal stabilization: Example with eye movements recorded by a DPI eyetracker. The image shifts in real-time to maintain a constant position on the retina.
5. Eye Position Contingent Display: Example with recorded eye movements. Subject oculomotor activity is monitored by a DPI eye tracker. The stimulus on the display is changed to a square if the subject looks to the left; it is changed to a triangle if the subject looks to the right.
6. Blink Detection: Example with recorded eye movements. Subject oculomotor activity is monitored by a DPI eye tracker. The example shows how the system is able to detect blinks and conditions in which the eyetracker is not tracking.