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Measuring eye movement to remove artefacts and assess attention

Eye tracking image

Where you’re looking and how wide the pupil is can be crucial factors in the analysis of behavioural and brain imaging data. Muscles that control eye movement produce relatively large electric currents and magnetic fields, making electroencephalography (EEG) and magnetoencephalography (MEG) highly sensitive to the interference produced by eye movements. Information in the eye-tracker can be correlated with EEG or MEG signals and used to remove the artefacts (distortions) caused by eye movements.

We also use eye tracking data to confirm where participants are looking and when they blink: this lets us ensure that participants are looking at the right place in the task, and that they don’t blink at crucial points in the experiment (when stimuli are presented, or changing). Using eye-tracking we can also quantify how gaze patterns change as a function of attention, or expectations that we have stored in memory. Studies of conditions with unusual gaze patterns (e.g. Autism) may use eye-tracking to investigate such patterns, or control for them.

At OHBA we have three EyeLink 1000 systems capable of tracking the eyes at a rapid timescale. One system is integrated into our new 3-Tesla MRI system and allows us to measure eye movements and pupil diameter and correlate these with the BOLD signal that we record during functional MRI (fMRI) tasks. A second is integrated into the MEG facility to complement the high temporal resolution of the signal that we record there. The third can be used in combination with our EEG and/or TMS facility, or used on its own, to facilitate a wider range of behavioural experiments. All our eye-trackers are suitable for binocular recordings and can sample up to 2kHz, ideal for detecting micro-saccades.