Research in the Active Perception Laboratory
has led to the development of EyeRIS, a new system for gaze contingent display control.
Experiments in visual neuroscience often require modification of the stimulus according
to the subject's eye movements. Examples of these procedures are retinal stabilization
(in which the image translates with the eye to eliminate retinal image motion) and
space80-variant sampling (in which the stimulus is re-sampled with resolution
that varies with eccentricity).
Computational limitations and time delays presents serious challenges for systems
of gaze-contingent display control. EyeRIS is a general-purpose gaze-contingent
display control system, which operates on a Windows PC.
This system allows a wide range of stimuli to be generated, modified, and visualized within a delay
of less than two frames with refresh rates up to 200Hz
technical specifications and user's manual
EyeRIS consists of:
A dedicated board based on a Digital Signal Processor with analog
and digital interfaces. This board can be connected to the PC
either via a parallel or a USB port, or a PCI bus. It is
responsible for sampling eye movement data and subject responses,
performing real-time data analysis, and communicating with the
graphic card on the host PC
A C++ software library, the Eye Movement Integrated Library
(EMIL), specifically designed for conducting gaze-contingent
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 (
) 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:
Part I: Applications in Psychophysics
- 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.
- 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.
- Tracking Gaze: Example with eye movements recorded by a DPI eyetracker. The red dot indicates the gaze location.
- 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.
- 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.
- 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.
Part II: Applications in Neurophysiology
Limiting stimulation to the classical receptive field: An aperture moves with
the eye along the scanpath. Stimulation may be limited to a selected aperture over the image in a gaze-contingent
display. That is, at each time, the stimulus is visible only in the area covered by the aperture. Outside the aperture,
the image is set to a uniform gray that is the mean luminance of the scene.
A scanpath during viewing of a natural scene: The red dot shows the path of the fovea.