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•Head
Mounted SystemOptions |
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Overview•Technical
Specifications•Software |
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| Overview |
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500Hz
Sampling Rate Binocular recording at 500Hz |
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| Accurate
Average gaze position error <0.5° |
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| Real-time Access to eye position data with only 3 msec delay |
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| High
Resolution 0.01° in pupil only mode; 0.025° in pupil - CR mode |
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| Versatile High quality computer based or scene camera eye tracking flexibility |
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| Easy
Switch between pupil only or pupil-CR modes |
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| Complete
Software Set Including experiment creation and data analysis tools |
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| Compatible with most eye glasses and contact lenses |
Video-based eye tracking systems have long been acknowledged as the simplest to set up and operate. However, these systems also had a reputation for low data rates, poor spatial resolution, high noise, and frequent loss of data. The EyeLink technology changed all of this with custom-built high-speed cameras and hyperacuity image processing. EyeLink II has the highest resolution (noise-limited at <0.01°) and fastest data rate (500 samples per second) of any other head mounted video-based eye tracker. This exceptional data quality results in very low velocity noise, making the EyeLink II ideal for saccade analysis and smooth pursuit studies. In addition, on-line gaze position data is available with delays as low as 3 milliseconds, making the system ideal for gaze-contingent display applications. |
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The EyeLink
II system consists of three miniature cameras mounted on a comfortable
padded headband. The entire system was designed to be lightweight
with a low center of mass for stability and minimal rotational inertia,
all of which contribute to subjective comfort and low fatigue. No
mirrors are used in the EyeLink II system, making it very robust and
easy to set up. Two eye cameras allow binocular eye tracking or easy
selection of the subject's dominant eye without the mechanical reconfiguration
required by most head-mounted eye trackers. Each camera has built-in
illuminators, digitally corrected for even lighting of the entire
field of view. Together with digital compensation for changes in ambient
lighting, this results in exceptionally stable pupil acquisition. More details are available on the EyeLink II Technical Specification page. |
| An optical head-tracking camera integrated into the headband allows accurate tracking of the subject's point of gaze without the need for a bite bar. The extremely low noise level of this optical tracker means that the noise level of computed gaze position data is comparable to that of the original eye position data, allowing gaze data to be used for saccadic analysis. In contrast, the magnetic head trackers used in other head-mounted eye tracking systems have high angular noise and therefore limit the usability of gaze position data. |  |
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The use of
corneal reflections in combination with pupil tracking permits very
stable tracking of eye position by reducing the errors caused by headband
slippage, muscle tremor, or environmental vibration. Pupil-only tracking
is also available if corneal reflection tracking is not possible,
and relies on the exceptional stability of the EyeLink headband-the
original EyeLink system used pupil-only tracking with great success. Compatibility with a wide range of subjects is an outstanding feature of EyeLink II. Dark pupil tracking and off-axis illumination allow tracking of subjects with almost all eyeglasses when using the pupil only tracking mode, eliminating the bright reflections that limit the use of other eye trackers. Eye camera sensitivity is high enough that even eyeglasses with heavy anti-reflection coatings that block up to 80% of infrared illumination are not a problem. The corneal reflection tracking of the EyeLink II system is also usable with some eyeglasses, but is less tolerant than the pupil only mode. |
| One of the outstanding innovations of the
original EyeLink was the integration of most eye tracking functions
into one intelligent system, relieving the experimenter of the need
to implement data collection, calibration, integration of head tracker
data, and saccade and fixation analysis as separate steps in data
analysis. EyeLink II integrates all of these into a single package,
allowing the experimenter to focus on stimulus presentation and data
analysis. This vastly expands the pool of researchers who can use
eye tracking as a research tool. In addition, the integrated processing
chain allows experimenters to view the subject's gaze position overlaid
on experiment graphics in real time, allowing validation of calibration
accuracy before recording and monitoring of data quality during data
collection. |
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