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| The CBU currently has 4 eye trackers. One is in the MEG lab, one in the MRI (from May 2009), and we have two separate eye trackers for use in other locations. All eye trackers are made by SMI and use the same software for controlling the eye tracking hardware, for stimulus presentation and for analysis of the eye tracking data. In addition, all trackers can also be used with E-Prime, if needed. | The CBU currently has 3 eye trackers. One is in the MEG lab, one in the MRI scanner, and one separate eye tracker is in the eye tracking lab in room 443. All eye trackers are manufactured by [[https://www.sr-research.com/|SR Research]]. |
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| All 4 eye trackers use 'dark pupil' technology, where the gaze of the eye is tracked by identifying the pupil and the reflection of an infra-red light source on the cornea. | == Eye tracking fundamentals == [[EyeTrackingFundamentals|Fundamental information about eye tracking technology]] |
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| Eye trackers come in two variaties: 'contact' and 'remote'. With contact eye trackers the camera and light source are fixed to the head, or the head is on a chin rest to limit movements relative to the camera. In remote systems the camera and light source are in a fixed location, at some distance from the subject, enabling some head movements. Contact systems are more precise and reliable, in general. | [[http://www.eyemovementresearch.com|eyemovementresearch.com]] - A very good online resource for anything related to eye tracking |
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| Another important feature of an eye tracker is the frequency. To be able to follow the eye during saccades the minimum frequency is about 200 Hz. | == CBU Behavioural Eye Tracking Lab == The CBU Eye Tracking Lab is located in room 443 in the west wing. It contains the SR Eyelink 1000 tracker. |
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| All eye trackers are able to output the x and y coordinates of the screen location the subject is looking at, and the diameter of the pupil. That last value will be 0 during a blink. === MEG eye tracker === This is a 50 Hz system that should theoretically be called a remote eye tracker, but actually behaves more like a contact system as head movement is extremely limited in the MEG helmet. For that reason the camera can actually be zoomed in quite closely and the accuracy of the MEG eye tracker should be reasonably high. === MRI eye tracker === The MRI eye tracker will arrive in May. It will be a system comparable to that in the MEG. === RED eye tracker === RED stands for 'Remote Eye-tracking Device', and this is a remote system. For that reason the precision is limited, but this is a very easy system to use and very comfortable for the subject. The system is also relatively portable and consists of a monitor with added camera unit, a power supply box and a laptop. === Hi-speed eye tracker === This is a contact system that will allow frequencies of up to 1250 Hz for monoculair eye tracking and 500 Hz for binoculair tracking. The Hi-speed system is extremely precise and reliable, but requires the subject to put their head on a chin rest. == Eye tracking in general == |
== Using eye trackers == |
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| === Calibration === The first thing that needs to be done is a calibration. This is an automatic procedure that will adjust the main parameters to the specific subject. Calibration shouldn't take more that 20-30 seconds. If the subject leaves the setup, during a break, you will have to calibrate again at the beginning of the next block. |
[[SettingUpEyeTracker|Eye tracker setup]] |
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| === Problems === Mascara, drooping eye lids, left-right difference === Monoculair versus binoculair === Some of our eye trackers offer the choice between monoculair and binoculair eye tracking. There is no real consensus about which one is better. The RED system will always record binoculair data, and the MEG and MRI systems will usually record monoculair data. The hi-speed system can be switched between the two modes very quickly. When using an eye tracker in monoculair mode, the next question is which eye to use. There are two possibilities: using the same eye for all subjects, or using the dominant eye for each subject. |
[[EyeTrackingProblems|Common eye tracking problems]] |
Eye tracking
The CBU currently has 3 eye trackers. One is in the MEG lab, one in the MRI scanner, and one separate eye tracker is in the eye tracking lab in room 443. All eye trackers are manufactured by SR Research.
Eye tracking fundamentals
Fundamental information about eye tracking technology
eyemovementresearch.com - A very good online resource for anything related to eye tracking
CBU Behavioural Eye Tracking Lab
The CBU Eye Tracking Lab is located in room 443 in the west wing. It contains the SR Eyelink 1000 tracker.
Using eye trackers
Eye tracking is not as easy as it might look, and there's also quite a bit of variability between subjects. Most problems can be solved and with the vast majority of people you should be able to acquire decent quality eye tracking data.