Eye Tracking

Last modified by Iris Spruit on 2025/05/16 11:41

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Introduction

With eye tracking one can obtain information about a person's gaze (where someone is looking) and pupil size.

Availability, Support and Use-case

At the FSW Leiden mainly Tobii and EyeLink eye trackers are used. At the LIBC MRI Scanner an EyeLink eye tracker can be used.

Getting Started with Eye Tracking

Below you will find some useful further reading when starting out with eye tracking.

Eye tracker models/brands

At SSH Leiden various eye tracker models are in use. See for more information the Tobii and EyeLink pages and the Eye Tracker Comparison page.

Eye Tracking Procedure

The exact procedure differs quite a bit depending on the eye tracker brand and model, and the software that is used to present the stimuli.

Tobii

For Tobii eye trackers, please see the Tobii Academy for more information on the procedures for using Tobii eye trackers and Tobii Pro Lab. Additionally, see the Tobii website for user manuals and check-out the Tobii webinars.

Eye tracker setup

When using a Tobii Pro remote eye tracker (Fusion, Spark, X3-120, X2-60, Nano) the eye tracker needs to be configured after connecting it to a computer. This configuration needs to be performed each time the eye tracker is connected to another computer. See the Eye Tracker Manager for instructions how to configure the eye tracker. Only after this setup, the eye tracker can be used with the desired task presentation software. When the eye tracker stays connected to the same PC, this configuration only needs to be done once.

For EyeLink eye trackers, the EyeLink forum should definitely be the go-to for information on the EyeLink procedures. Note that you will need to create an account to be able to see the threads. As a start, check-out the Getting Started page and the Video Tutorials.

Calibrating an eye tracker

The calibration procedure is crucial for obtaining reliable gaze data. More information:

Pupil data

Recording and analyzing pupil data requires some special considerations. For more information, see:

Blink detection

Tobii

For Tobii eye trackers, the Eye Openness signal (only Spectrum and Fusion) or the Pupil Size signal can be used for blink detection. See for more information the Tobii webinar on blinks: Webinar: Catch every blink with eye tracking - Tobii, and a Github repo for blink detection: GitHub - marcus-nystrom/BlinkDetector.

Requirements for blink detection:

  • Tobii Pro Lab
    • version 24.21 or higher 
  • Eye tracker 
    • Tobii Pro Fusion (120 Hz) with Runtime version 2.5.4. Note: make sure you have the correct runtime version installed. This can be checked and changed in the Eye Tracker Manager. 
    • Tobiii Pro Spectrum with Firmware version 2.6.1

Blinks in Tobii Pro Lab: 

  •  In the Replay tab, switch on detect blinks in the eye openness data section. By default, the Blink detection settings (Nyström et al.) will be selected, which is an algorithm designed to detect blinks. You can also create a custom blink detection filter by selecting create new and changing the settings.
  • You will be able to see blinks in your recording in the Eye movements chart, Eye openness, Pupil diameter and Gaze data chart. 
  • To export blink data, go to Analyze - Metrics Export. There you will find a range of blink metrics that you can export. The available blink metrics are described in Table 1 here. 

EyeLink eye trackers report blinks by default. 

Tips & Tricks

  • Reporting guideline eye tracking: Follow the Minimal reporting guideline for research involving eye tracking (2023 edition) when publishing a study that involves eye tracking. It is highly advised to report data quality. Data quality can be reported in terms of accuracy and precision (see also Best practices in eye tracking research and Tobii article about accuracy and precision). The percentage of valid gaze samples can also be reported. Make sure that you know how your eye tracking data collection software saves this information, or how this information can be obtained.
  • Good calibration: A good calibration of the eye tracker is important when you want to obtain high quality data. Make sure to familiarize yourself with the calibration procedure, and adjust the calibration according to the participant (e.g. when calibrating the eye tracker with children, less calibration points and/or video's can be used for the calibration.
  • Light conditions: Most eye trackers use near-infrared light to obtain information about reflections of this light on the eye and then use this information to be able to track the eye. To obtain the best quality of data it is highly advised to not have direct light shining in the eye tracker or in the participant's eyes. Other than that, it is recommended that the space in which eye tracking is done is not very bright or very dark. Please contact labsupport@fsw.leidenuniv.nl if you want to borrow a luminance meter.
  • Mapping screen-based eye trackers to screen: The Tobii screen-based eye trackers (Fusion, Spark, Nano, X3-120, X2-60) need to be mapped to the screen, which is done with the Tobii Pro Eye Tracker Manager (see Tobii Pro Eye Tracker Manager for instructions).