g.EYEtracking Interface for SIMULINK

Human-Centered Research with BCI and Eyetracking

Eyetracking technology aims to measure the point of gaze or the movement of the eyes with eye tracking devices, often to study human behavior out of the lab. Researchers are challenged when subjects do not respond honestly or accurately due to artificial environments or discomfort. If the research aims to study real-world behaviors, lab situations or observations can change each subject’s behavior, reducing the ecological validity of the data. With eye tracking, researchers can measure behavior in natural environments and without monitoring the subjects, which lead to more valuable results.

Wireless EEG and biosignal acquisition systems are becoming more important in neurophysiological research, especially when studies tend to take part in the field instead of in the lab. Therefore, it is necessary to synchronize the eyetracking data with EEG and other biosignals such as pulse, skin connectivity, respiration rate or heart rate.

Real-time eye movement data using SIMULINK

The g.EYEtracking Interface for SIMULINK allows you to acquire eye gaze and x-, y-coordinates of the eye together with biosignal data. The signals can be visualized, stored and analyzed in real-time in SIMULINK and offline in MATLAB. The g.EYEtracking Interface for g.HIsys allows users to acquire biosignal data such as EEG, ECG, EMG, eyetracking information, and other signals in real-time. It provides a block to read gaze data from the eye-tracker simultaneously with other biosignal data coming from g.USBamp, g.HIamp or g.Nautilus wireless EEG system with dry or wet electrodes.

g.EYEtracker Interface can be used with the following fixed/cable eye trackers on the monitor or wearable/wireless eye trackers. The main advantage of wireless eyetrackers is that subjects can freely move in the experimental environment and are not tied to computer monitors.

Eyetracker fixed on the monitor

  • SR Research: EyeLink 1000 Plus
  • Tobii EyeX

Wearable Eyetracker with cables

  • Tobii X2-60
  • Arrington Research ViewPoint (ony 32 bit, Windows 7)

Wireless and wearable Eyetracker

  • Tobii Pro Glasses 2

Product Highlights

  • record and view x- and y-eye-coordinates, velocity, pupil width, ocular torsion, fixation duration in SIMULINK simultaneously with biosignal data
  • simultaneous data acquisition of biosignal using g.HIamp, g.USBamp or g.Nautilus
  • analysis of EEG and eye-tracker data in MATLAB SIMULINK
  • compatible with a range of Tobii Eyetracker: Tobii Pro Glasses 2, Tobii EyeX, Tobii X2-60
  • compatible with SR Research EyeLink 1000 Plus

How to use g.EYEtracking Interface

For tracking eye movements, an eye tracker (see eyetrackers in the sections below) with monocular or binocular cameras is required. The eye tracker is connected e.g. via USB to the computer. To simultaneously acquire biosignals, g.USBamp, g.HIamp, g.MOBIlab+ or g.Nautilus Highspeed Online Processing for Simulink must be installed. This package allows you to read in the biosignal data into Simulink. The specially developed g.EYEtracking Interface works together with the eye tracker software and allows you to acquire both the eye movements and the biosignals into one MATLAB data file, which makes offline analysis easy.

The g.EYEtracking Interface provides a Simulink library with blocks for the different eyetracking systems, that can be easily copied into every model to capture the eye-movements of the subject.
Furthermore, we provide basic example models for the different eyetracking systems. Below is an example that is using the g.USBamp with an Arrington Eyetracker. The model visualizes the EEG and eyetracking data, stores the data and runs an experimental paradigm.

How to use g.Nautilus wireless EEG and eyetracker simultaneously

Wireless devices open up many new application and research fields. Whether you study Marketing, Web Development, Sports, Driving, etc., you are able to use different eye tracker together with Brain-Computer Interface Technology. g.Nautilus is g.tec’s wireless EEG solution that is designed to be completely different from all other devices and sets a new standard of usability. The tiny and lightweight device with active electrodes is attached to the EEG cap to avoid cable movements and allows completely free movement.

Read more: The Unlimited Possibilities of Wireless EEG
Read more: Human-Centered Research with Eyetracking and BCI


Functional principle of Eyetracking

The infrared light source of the tracker illuminates the eye and also provides a specular reflection from the surface of the eye (from the smooth cornea) that is captured with a camera. Then, the computer system uses image segmentation algorithms to locate the areas of the pupil and the bright corneal reflection (glint). Additional image processing algorithms locate these areas and calculate a difference vector between the center locations. A mapping function transforms the eye position signals into coordinates. Additionally, the program can determine whether the gaze point is inside of any region of interest (ROI) that was previously defined by the user.

A scene camera captures the environment and allows you to project the eye movement on the real situations. A prerequisite is a calibration system that presents calibration stimuli to the user to measure the eye position signals for each stimulus point. These data are used to compute an optimal mapping function.


Tobii PRO Glasses 2

The Swedish company Tobii has developed the Tobii Pro Glasses 2 , a wearable eyetracker with wireless real-time view function that offers hardware synchronization of eye-tracking data with physiological data. 

Additional product highlights:

  • pupil center in x-/y-/z-coordinated of both eyes
  • pupil diameter of both eyes
  • gaze direction of both eyes
  • gaze position in relation to live scene video
  • gaze position 3D
  • gyroscope data
  • accelerometer data

Read more: Human Centered Research with Eyetracking and BCI

The following Simulink model shows the g.Nautilus and Tobii PRO Glasses 2 Interface blocks. These blocks are reading the data into the Simulink model with the same data rate. If, for example, the g.Nautilus biosignal amplifier is sampling EEG data at 250 Hz, then the eye-tracking information is aligned with the EEG data at the same sample rate. This allows users to analyze the eye-tracking and the biosignal data in real-time.

  • The Nautilus block acquires biosignal data from 1–64 channels at a sample rate of 250 or 500 Hz. Optionally, filters can be applied to the biosignal data for noise reduction.
  • The Tobii Pro Glasses 2 Interface block acquires data from the eye-tracker. The pupil’s center, diameter and gaze direction, position as well as the 3D position of the left and right eye are visualized in displays.

SR Research: EyeLink 1000 Plus

The g.EYEtracking Interface for Simulink, recently developed for EyeLink 1000 plus, provides a block for acquiring binocular gaze position and gaze diameter of the SR EyeLink 1000 Plus eyetracking systems. The EyeLink system consists of a Host PC with an EyeLink camera system connected to it. The Host PC samples the gaze with up to 1000 Hz and provides the acquired data to a Display PC via TCP/IP. The Display PC is running the experiment and visualizes the eyetracking data.

Additional product highlights:

  • acquire binocular gaze position and gaze diameter data of the SR EyeLink 1000 plus
  • acquire at 250, 500 or 1000 Hz sample rate
  • low latency: < 3ms (gaze detection @ Host PC– data available in Simulink)

  

The g.EYEtracking Interface for Simulink for EyeLink 1000 plus software is running on a 3rd PC, the Data Acquisition PC. This PC uses the data connection between the Host PC and the Display PC to acquire the eye tracker data or the EyeLink eye tracker using a so-called "broadcast" connection. The software could also be run on the Display PC.

g.Nautilus dry or gel-based wireless EEG can be used with SR Research EyeLink 1000 plus eye trackers. The EyeLink 1000 plus system samples the gaze at a sampling rate of 1000 Hz (see SR Research homepage for further information).

Read more: g.EYEtracking Interface for EyeLink 1000 Plus


Tobii X2-60 Eyetracker

The Tobii X2 Eye Tracker is an unobtrusive eye tracker for detailed research of natural behavior. Its large freedom of head movement allows the participant to move during recording while maintaining accuracy and precision. The Tobii X2 Eye Trackers offer maximum flexibility with numerous software and stimuli setup options.

Additional product highlights:

  • record and view x, y eye coordinates, pupil diameter, eye position relative to the camera in Simulink, simultaneously with biosignal data recording
  • the eye tracking system can be used without discomfort for long periods
  • calibration takes only seconds and maintains drift-free accuracy

  

During tracking, Tobii Eyetrackers use infrared illuminators to generate reflection patterns on the corneas of the participant’s eyes. These reflection patterns, together with other visual data about the participant, are collected by image sensors. Sophisticated image processing algorithms identify relevant features, including the eyes and the corneal reflection patterns. Complex mathematics calculate the 3D position of each eyeball, and finally the gaze point (that is, where the participant is looking).

Arrington Research: ViewPoint (32 bit, Windows 7)

The ViewPoint Eyetracker from Arrington Research provides a complete eye movement evaluation environment, including eye movement and pupil diameter monitoring. It provides several methods to map position signals extracted from the segmented video image in eye coordinates and calculate the participant’s point of view.

Additional product highlights:

  • record and view x and y eye coordinates, velocity, pupil width, ocular torsion and fixation duration in Simulink simultaneously with biosignal data
  • monocular and binocular options are available
  • size is adjustable and compatible with glasses
  • no calibration required
  • scene camera to track gaze position on real world scene videos
  • online signal analysis under SIMULINK

  

The program can determine whether the gaze point is inside of any region of interest (ROI) that was previously defined by the user. A scene camera captures the environment and allows you to project the eye movement on the real situations. A prerequisite is a calibration system that presents calibration stimuli to the user to measure the eye position signals for each stimulus point. These data are used to compute an optimal mapping function.

See some related products

Software

read more High-Speed Online Processing under Simulink: Specs & Features — read biosignal data directly into SIMULINK; highly optimized hardware-interrupt controlled device driver; data processing with maximum system speed; signal analysis blocks
product no.: 0111 read more g.RTanalyze: Specs & Features — real-time biosignal processing blockset under SIMULINK; real-time algorithms
product no.: 0101 read more g.BSanalyze: Specs & Features — advanced biosignal data processing toolbox; multi-modal Off-line Biosignal Analysis under MATLAB®

Related Media and Documents

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