Eye tracking has been a consistent player in the physiological research field for a number of years, and more recently a “mobile” variation of this technology has become increasingly widespread. But just what is mobile eye tracking and how does it work? Unlike eye tracking studies tethered to a lab, where a participant visually follows an object on a computer screen, mobile eye tracking data can be acquired outside of the lab. All that is required, in fact, is a pair of glasses. Not just any glasses, but ETVision glasses, capable of recording not only multiple parameters of a participant’s “eye image” but also the scene the participant is gazing at and responding to. Let’s look briefly on how eye tracking glasses work. The lightweight ETVision glasses are equipped with two eye-facing cameras combined with a pair of LEDs for recording the various components of the “eye image,” such as pupil size/position, gaze path, fixation (when the participant’s eyes lock onto an area of interest), internal and external data markers, vergence angle (angle between the eyes), and corneal reflections (CRs). The cameras also look at the contrast between the pupil and the surrounding iris. This constant real-time feedback is recorded every 5.5 milliseconds and the eye images are rendered at 180 frames per second.
In addition to eye cameras, a built-in forward-facing 720p scene camera records the viewable area in front of the participant. This enables the landscape or scenery the participant is looking at to be combined and synchronized with the eye image data (say, if the participant is driving a car or riding a mountain bike).
Did I say riding a mountain bike? Yes. Full eye tracking data can be collected and stored in a 256 GB SD card and the logged data exported to a .*csv file, which in turn can be imported into AcqKnowledge software along with other logged physiological data. The glasses also have a coated visor for reducing glare. (Glare causes squinting and the eye tracking cameras do not perform as well on eyes that are squinting or closing due to excessive light or reflections.)
In addition, a small microphone built into the eyeglasses enables two-way audio between the investigator and the participant. Already wear glasses? No problem. Eye tracking glasses can be worn over corrective lenses without issue. However, contact lenses should be cleaned before wearing them under eye tracking glasses. The glasses are connected to a small controller via a standard HDMI cable, and the controller houses a 256 GB SD card. In addition to the SD card used for logging remote data, the controller can also be connected to a host computer via WiFi or LAN. The lithium-polymer battery will run the eye tracking glasses for 5.5 hours on a full charge.
Using the AcqKnowledge software’s Media feature, the eye tracking video data can be replayed with a tight correlation to other physiological data collected during the experiment by the BioNomadix Logger. (Other data acquisition hardware types, such as MP160 or MP36R, can be used within the lab.) The eye tracking video and graph data can be displayed side-by-side on the screen. Placing the I-beam cursor at any point in the AcqKnowledge graph takes you to the corresponding point in the eye-tracking video (say, during activities such as driving a car). Eye tracking data for vertical position, horizontal position, pupil diameter, and more can be imported as channels into the AcqKnowledge graph. This data will be synchronized with the eye tracking video, along with any added event markers.
Interested in more details about ETVision Eye Tracking Glasses and AcqKnowledge software? To see it all in action, we invite you to view our free on-demand Mobile Eye Tracking Webinar.
BIOPAC offers a wide array of wired and wireless equipment that can be used in your research. To find more information on solutions for recording and analyzing signals such as ECG, heart rate, respiration, and more using any platforms mentioned in this blog post, you can visit the individual application pages on the BIOPAC website.
Photo by Amanda Dalbjörn on Unsplash
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