Interfacing the ViewPoint Eyetracker with g.USBamp

For many research experiments it is interesting and essential to acquire beside biosignal data also eye movements of one or both eyes. This is especially useful for usability investigations, for Virtual Reality, for physiological tests and many other applications.

g.tec developed therefore a g.EYEtracking Interface for Simulink that allows to acquire eye-movements directly in Simulink. Therefore the g.tec Highspeed On-line Processing for Simulink package is used to acquire the biosignal data from g.USBamp, g.MOBIlab+ or g.BSamp.

Running the g.EYEtracking Interface

The g.EYEtracking Interface provides a Simulink library with the Eyetracking block. This block can simply be copied into any Simulink model that contains a g.tec biosignal amplifier block. This means you can easily add the eye movement capturing functionality to all your current Simulink models.

The g.EYEtracking Interface provides a Simulink library with the Eyetracking block. This block can simply be copied into any Simulink model that contains a g.tec biosignal amplifier block. This means you can easily add the eye movement capturing functionality to all your current Simulink models.

Start e.g. the Simulink model gEYEtrackerwithgUSBamp which uses the g.USBamp to acquire 1 ECG and 1 EOG channel.

By double-clicking on the Eyetracking block the configuration can be performed. In this case the block is used to acquire the X- and the Y-Coordinates and the Fixation Time.

Both the biosignal data and the eye movement data is visualized with the Scope block and stored with the To File block in MATLAB format which makes the off-line analysis simple.

Experimental Paradigm

The Paradigm block presents the experimental paradigm in real-time on the computer screen. In this case 4 rectangles are positioned in a random order on the screen. The subject has the task to focus on the item as long as it is displayed. In total 12 items are visualized.

Performing the Experiment

1. Instruct the subject to sit relaxed in front of the computer screen and put the eye-tracker glasses, the ECG and EOG electrodes on
   
   
2. Go to the ViewPoint software and perform the calibration procedure
   
   
3. Instruct now the subject to fixate to the box that appears on the screen and to change as fast as possible to a new box
   
   
4. Then start the gEYEtrackerwithgUSBamp model by pressing the Start button. This will start the experimental procedure and all 12 boxes will be shown.
   
   
5. Finally Stop the Simulink model

Analyzing Data in g.BSanalyze

After acquisition load the data into g.BSanalyze. The Data Editor shows a time stamp signal in channel 1, the ECG in channel 2, the EOG in channel 3, the X-Coordinate in channel 4, the Y-Coordinate in channel 5, the Fixation Time in channel 6 and the appearance time point of the box on the screen on channel 7. A positive edge shows when the box appears and a negative slope shows when the box disappears on the screen. Each box is shown for 1.5 seconds and 3 times. This gives in total 12 trials.

g.Result2D opens with the results of the average calculation over trials and shows the mean of the X-Coordinate (left side) and of the Y-Coordinate (right side) of class 1. The red line indicates the time point when the box appeared on the screen. The subject needed some 100 ms to fixate the box and after 1.5 seconds the box disappeared again.

and 3

and 4

The left lower corner is considered as coordinate [0, 0], the right top corner as [1, 1].

In the g.Result2d plots the X- and Y-Coordinates are shown and are summarized in the table below. The correct solution for each class is shown in the right column.

This short example showed the data acquisition, the real-time experiment and the off-line analysis with the newly developed g.EYEtracking Interface.