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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 4 eye trackers. One is in the MEG lab, one in the MRI scanner, and we have two separate eye trackers for use in other locations. All eye trackers are manufactured by [http://www.smivision.com/ SMI] and use the same SMI 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 and other custom experiment presentation software. |
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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. | ==== Eye trackers at the CBU ==== [:MegEyeTracker:MEG eye tracker] - 250 hz 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. | [:MRIEyeTracker:MRI eye tracker] - 50 hz tracker, similar to MEG setup. |
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| === 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. |
[:REDEyeTracker:RED eye tracker] - Remote system for behavioural tests. |
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| === MRI eye tracker === The MRI eye tracker will arrive in May. It will be a system comparable to that in the MEG. |
[:HiSpeedEyeTracker:Hi-speed eye tracker] - High-speed tracking for more demanding behavioural tests. |
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| === 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 |
[:EyeTrackingProblems:Common eye tracking problems] |
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| === 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. |
==== Instructions for specific software packages ==== The SMI eye trackers come with their own stimulus presentation software, Experiment Center, and their own analyses tool, BeGaze. Experiments designed and executed in Experiment Center are very easy to analyse in BeGaze, as everything is recognised automatically. The trade-off is that Experiment Center only allows fairly simplistic experimental designs. |
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| 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. | If you want to use other experiment software, you will need to customise your scripts. [:EyeTrackingWithExperimentCenter:Eye tracking with Experiment Center] [:EyeTrackingWithEprime:Eye tracking with Eprime] [:EyeTrackingWithMatlab:Eye tracking with Matlab (Cogent / Psychtoolbox)] == Data Analysis == The eye tracking data can be analysed very easily with the SMI software package BeGaze. This will plot raw data, gaze paths, dwell times, heatmaps etc. at the click of a mouse. It cannot do statistical analyses, though, and you will have to export the data from BeGaze for that. BeGaze will allow you to create areas of interest, even moving ones in videos, and calculate total dwell time for all your AOI's. [:BeGaze:Analysing Eye tracking data with BeGaze] [:ExportingEyetrackingData:Exporting eye tracking data for custom analysis] |
Eye tracking
The CBU currently has 4 eye trackers. One is in the MEG lab, one in the MRI scanner, and we have two separate eye trackers for use in other locations. All eye trackers are manufactured by [http://www.smivision.com/ SMI] and use the same SMI 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 and other custom experiment presentation software.
Eye tracking fundamentals
[:EyeTrackingFundamentals:Fundamental information about eye tracking technology]
[http://www.eyemovementresearch.com eyemovementresearch.com] - A very good online resource for anything related to eye tracking
Eye trackers at the CBU
[:MegEyeTracker:MEG eye tracker] - 250 hz tracker.
[:MRIEyeTracker:MRI eye tracker] - 50 hz tracker, similar to MEG setup.
[:REDEyeTracker:RED eye tracker] - Remote system for behavioural tests.
[:HiSpeedEyeTracker:Hi-speed eye tracker] - High-speed tracking for more demanding behavioural tests.
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.
[:SettingUpEyeTracker:Eye tracker setup]
[:EyeTrackingProblems:Common eye tracking problems]
Instructions for specific software packages
The SMI eye trackers come with their own stimulus presentation software, Experiment Center, and their own analyses tool, BeGaze. Experiments designed and executed in Experiment Center are very easy to analyse in BeGaze, as everything is recognised automatically. The trade-off is that Experiment Center only allows fairly simplistic experimental designs.
If you want to use other experiment software, you will need to customise your scripts.
[:EyeTrackingWithExperimentCenter:Eye tracking with Experiment Center]
[:EyeTrackingWithEprime:Eye tracking with Eprime]
[:EyeTrackingWithMatlab:Eye tracking with Matlab (Cogent / Psychtoolbox)]
Data Analysis
The eye tracking data can be analysed very easily with the SMI software package BeGaze. This will plot raw data, gaze paths, dwell times, heatmaps etc. at the click of a mouse. It cannot do statistical analyses, though, and you will have to export the data from BeGaze for that. BeGaze will allow you to create areas of interest, even moving ones in videos, and calculate total dwell time for all your AOI's.
[:BeGaze:Analysing Eye tracking data with BeGaze]
[:ExportingEyetrackingData:Exporting eye tracking data for custom analysis]