EyeLink
Introduction
SR Research EyeLink eye trackers allow for accurate gaze and pupil measurements.
EyeLink 1000 plus
Availability, support and advice
At SSH Leiden a few EyeLink 1000 (or EyeLink 1000 plus) eye trackers are available and one is available at the LIBC MRI scanner. To use an EyeLink eye tracker in one of the SSH labs, please contact labsupport@fsw.leidenuniv.nl. 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. To use these software packages, a dongle can be borrowed from SOLO, please e-mail labsupport@fsw.leidenuniv.nl. SOLO supports EyeLink devices, but 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, E-Prime and EyeLink and PsychoPy 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.
- For the EyeLink 1000 plus, see the for an overview of the setup (similar for EyeLink 1000).
- For the EyeLink Portable Duo, see the and for overviews of the setup.
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).
See for more information on EyeLink setup and participant setup: EyeLink 1000 Plus Setup and Usage Training Videos (create an account to view the thread).
Markers
When using EyeLink with stimulus presentation software such as E-Prime, OpenSesame, or PsychoPy, events are sent to EyeLink in the form of messages. These messages can consequently be used to segment the eye tracking data (for example pupil size with the PhysioData Toolbox).
Instead of messages, one can also send markers (see more about markers here: Markers and Events - XWiki). This can be useful for example when EyeLink is used in combination with BIOPAC or BioSemi. In this case, the marker signal to BIOPAC or BioSemi can be split and connected to both BIOPAC/BioSemi and the EyeLink.
To set up the EyeLink to receive markers, a DB25 cable must be connected from the stimulus PC to the EyeLink host PC. For SSH lab PCs, please contact labsupport@fsw.leidenuniv.nl, to modify or arrange a lab setup.
Importantly, the EyeLink host PC needs to configured to be able to properly receive the marker signal. To do so, the FINAL.INI file that is located on the EyeLink host PC needs to be modified. Make sure to leave other custom settings in the FINAL.INI file as is. If you do not know exactly how to do this, please contact labsupport@fsw.leidenuniv.nl to help out. How the FINAL.INI file needs to be modified, depends on the EyeLink model:
The marker signal is received by the EyeLink host PC on 8 input channels. When the state of each of these input channels changes, a message is recorded (e.g. INPUT_1_ON or INPUT_3_OFF). The digital marker signal is also saved in the EDF file in the input signal (rawEDF.FSAMPLE.input).
When using the marker signal, make sure to check beforehand how to use the marker signal, or input message events to segment the data in your analysis software, such as the PhysioData Toolbox or EyeLink Data Viewer. Double-check that the marker signal/messages you intend to use, can indeed be used the way you want in the analysis software!
Note that the EyeLink host PC can receive markers when the eye tracker is not actually recording any eye tracking (gaze/pupil) data. This happens for example when the EyeLink EDF file is opened, then markers are sent, and then the recording is actually started. Markers sent outside of the recording can be viewed and used in the PhysioData Toolbox, however, they are not recognized by EyeLink Data Viewer, where only markers sent during the recording can be viewed. To prevent sending markers when the eye tracker is not recording, make sure to only send markers after the recording is started and before the recording is stopped. Starting and stopping the recording can be done by third party software such as E-Prime or OpenSesame, or by the EyeLink host PC software.
It is important to always check on the EyeLink host PC whether the markers are correctly being received. When an input channel is turned on, the channel will appear in the recording screen on the EyeLink host PC in the lower-right corner, see image below. As a test, at the start of the task, it is advised to send marker 255, which will result in the image below (all input channels turned on), and check this on the EyeLink host PC.
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) (create an account to see the thread).
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:
An artificial eye can be borrowed from SOLO, please contact labsupport@fsw.leidenuniv.nl. When using an artificial eye, an instruction video can be found here: How to: Convert EyeLink Pupil Size Data into Millimeters.
Alternatively, a printed out dot can be used. Instructions are provided on the EyeLink Forum: How can I convert pupil size to mm? (sr-research.com) (create an account to see the thread). 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.
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 (create an account to see the thread).
EyeLink Mounting Options
EyeLink allows for different mounting options, such as Desktop mount, Tower mount, Arm mount, etc. See here for the options: EyeLink 1000 Plus - Fast, Accurate, Reliable Eye Tracking. At SSH Leiden, the standard Desktop mount is almost always used.
Configuration
On the EyeLink host PC, the correct configuration needs to be selected. Make sure this configuration is selected each time before you start your recording/task.
The configuration indicates which Mount is used, whether remote mode is used, whether a monocular or binocular recording is made and which lens is used. See the manual for more information: or EyeLink 1000 Plus - User Manual and Installation Guide (an account is required to view the thread).
Resources
- SR Research EyeLink website
- EyeLink Eye Tracker Learning Resources - Fast, Accurate, Reliable Eye Tracking
- 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, which is highly recommended for EyeLink users.
- EyeLink Hardware FAQs
- EyeLink 1000 Plus - User Manual and Installation Guide