EyeLink
Introduction
SR Research EyeLink eye trackers allow for accurate gaze and pupil measurements.
Availability, support and advice
At FSW Leiden a few EyeLink 1000 (or EyeLink 1000 plus) eye trackers are used and one is available at the LIBC MRI scanner.
To check the specifications and a comparison of different eye tracking systems, see Eye Tracker Comparison.
Software
EyeLink eye trackers can easily be used with EyeLink software Experiment Builder for task presentation and Data Viewer for data analysis. SOLO supports EyeLink devices, however does not provide support for Experiment Builder or Data Viewer. EyeLink eye trackers can be used with other stimulus presentation software, see the OpenSesame and EyeLink and E-Prime and EyeLink pages.
EyeLink Setup
The EyeLink 1000/1000 plus system consists of an eye tracking camera, a host PC, accessories (mouse, keyboard) and a screen. The EyeLink host PC is connected with the stimulus PC on which the stimulus presentation software runs (e.g. OpenSesame, E-Prime, etc.) through ethernet cable.
Configure network connection on stimulus PC
The network of the stimulus PC needs to be configured so that communication with the EyeLink host PC is possible. For a Windows PC, the following instructions should be followed (full instructions can be found here, note that an SR-research account is necessary to view the thread).
- Connect the Host PC to the Display PC via an ethernet cable.
- Go to the Control Panel ⇒ Network and Internet ⇒ Network and Sharing Center ⇒ double click on the correct Ethernet.
- Click the Properties button to open the Ethernet Properties.
- Select the Internet Protocol Version 4 (TCP / IPv4) item.
- Click the Properties button to open the TCP / IPv4 Properties.
- Select the "Use the following IP address:" and enter 100.1.1.2 for IP address and 255.255.255.0 for subnet mask (leave the Default gateway blank).
Pupil size
Important information and further references about measuring pupil size can be found here: Learn About Eye Tracking for Pupillometry - Fast, Accurate, Reliable Eye Tracking (sr-research.com) and is highly recommended to read.
Use a chinrest
When recording pupil size, it is highly recommended to use the Head-Fixed mode (not Remote mode). This means that a chinrest is necessary to secure the participant's head. EyeLink provides more information about pupil size and the use of head support for example on their Forum: pupil size measurement in Head-free-move mode (sr-research.com) (you need to create an account to see the thread, which is highly recommended when you use EyeLink!).
Convert pupil size to mm
EyeLink reports pupil size in an arbitrary unit, which is based on the number of pixels the pupil consists of, as measured with the eye tracker's camera. After data collection, the pupil size can be converted to mm. This can be done by using an artificial eye, or by printing out a black circle with a known diameter. Note that the conversion steps can be done once, only if the data was collected with Head-Fixed mode (using a chinrest), and the camera was kept at the same distance for all participants. Below, links to instructions on how to convert pupil size to mm are given:
When using a printed out dot, instructions are provided on the EyeLink Forum: How can I convert pupil size to mm? (sr-research.com) (you need to register to be able to view forum threads, which is highly recommended when you use EyeLink). In order to collect the pupil size of the printed out dot, the FINAL.INI file on the host pc needs to be adjusted (and adjusted back after you are done), so that the pupil can be tracked without corneal reflection. The FINAL.INI file can be found in EYELINK D:\elcl\EXE after starting the Host pc in Windows.
When using an artificial eye, an instruction video can be found here: How to: Convert EyeLink Pupil Size Data into Millimeters.
Instead of Data Viewer, the EDF files can also be converted to ASCII and then opened in other software. See here for more info on SR Research's EDF to ASCII tool: EDF to ASCII Conversion / EDF2ASC (sr-research.com) and about the EDF file: An Introduction to EyeLink Data (EDF Files) (sr-research.com).
EyeLink lenses
The EyeLink eye trackers come with different sizes of lenses: 35 mm, 25 mm and 16 mm. Which lens you need to use, depends on the mode (remote/head stabilized, monocular/binocular) and model (1000 or 1000 plus) that is used. Please read Do I need to change the lens if I change tracking modes? (sr-research.com) for more information (you need to create an account to see the thread, which is highly recommended when you use EyeLink!).
Resources
- SR Research EyeLink website
- SR Research support forum. Here you can find manuals, webinars, FAQ, and much more. You need to register to be able to view the threads.