RIT’s Visual Perception Laboratory continues to innovate in the design, fabrication, and application of novel eyetracking systems. The RIT Wearable Eyetrackers are specifically designed to record eye movements as observers perform tasks in a natural environment – outside the laboratory.


The custom headgear on the 3rd-generation eyetracker uses an off-axis infrared illuminator and a miniature, IR-sensitive CMOS camera to capture a dark-pupil image of the eye. A second miniature camera is located just above the right eye and is used to capture the scene from the subject’s perspective. The tracker is designed for off-line analysis; raw video of the eye and scene are captured using the backpack or portable collection systems, while calibration and analysis are carried out later in the laboratory, making data collection ‘in the field’ more efficient.


3rd-generation wearable eyetracker and backpack


3rd-generation wearable eyetracker headgear


Portable data collection system for 3rd-generation eyetracker

Offline calibration and analysis

 

The 2nd-generation RIT Wearable Eyetracker is a valuable tool for investigating visual perception in a range of natural tasks outside the laboratory. Based on a pair of racquetball goggles and a backpack, the wearable eye tracker does interfere with natural eye, head, and whole-body movements.

The custom headgear uses an infrared illuminator, a miniature, IR-sensitive CMOS camera, and beam splitter to capture an image of the eye. The eye is illuminated by the IR along an optical path directed by a first surface mirror and hot mirror. The bright-pupil image is reflected back to the CMOS camera along the same path. A second miniature camera is located just above the right eye and is used to capture the scene from the subject’s perspective. Slightly above the scene camera is a small laser to be used for calibration. Finally, a battery is mounted on the left side of the goggles to power the cameras, and also to balance the weight of the optical components.

2nd-generation
Wearable Eyetracker

The headgear is wired to a customized Applied Science Laboratory (ASL) Model 501 controller unit contained in a backpack. The line of gaze is computed in real time, and is based on a vector difference between the center of the pupil and the first corneal reflection.

A crosshair representing the line of gaze is superimposed on the scene video. The video signals from the eye camera and ASL unit are passed through a picture-in-picture unit which superimposes the image of the eye in the corner of the scene. The combined image is then recorded onto a Sony digital video camcorder.


Custom-built headgear for the 2nd- generation wearable eyetracker

Backpack containing digital video recorder, picture-in-picture unit, ASL control unit, and batteries for the 2nd-generation wearable eyetracker

 

The head-mounted eyetracker used in the Visual Perception Lab is the ASL Model 501 system. The eye is tracked in the same fashion as in the wearable system, however, the head-mounted eye tracker can only be used in the laboratory because it is tethered to the control unit and video recorder.

 


ASL Model 501 headgear

 

A Polhemus 3-Space Magnetic Head Tracker (MHT) can be used in conjunction with the head-mounted eyetracker. By tracking head movements as well as eye movements, the gaze position on a pre-defined plane can be determined. This is useful in experiments where the subject is viewing stationary planes, such as a computer monitor.

The Polhemus system uses a fixed transmitter located behind the subject, and a receiver attached to the head-mounted optics to determine the position and orientation of the head. Multiple planes can then be defined in relation to the fixed transmitter.

The ASL system calculates gaze position at an effective temporal resolution of 133 msec. The intersection of the subject’s line of gaze with the plane is computed in real time, and a video record with a cursor overlay is created. Information about the eye, head, and gaze positions can also be logged to a data file for off-line analysis.


Experimental setup using the head-mounted eyetracker and magnetic head tracker


Pioneer 50" plasma display used with the integrated head and eye system for image display during experiments

The remote eyetracker used in the Visual Perception Lab is an ASL Model 504 Remote eyetracker. This system monitors eye position without any contact with the subject. The camera lens used to image the eye is surrounded by infrared emitting diodes (IREDs) providing illumination coaxial with the optical axis. The infrared, video-based eyetracker determines the point-of-gaze by using a video camera to extract the center of the subject’s pupil and a point of reflection on the cornea.