Eye Tracking and its Application in MRI and EEG Settings Marcus Johnson, Ph.D SR Research Ltd. Toronto - Ottawa, Canada

Agenda Discussion of eye tracking hardware components System cabling and integration for noise/artifact minimization Synchronization options Discussion of Recording/Messaging Options

System Hardware

Desktop Mount Useful in EEG Environment Remote Mode with Sticker on EEG Cap Chinrest Mode for More Precise Recording – One concern is Chinrest

Long Range Mount Camera Head Infrared Illuminator with Focusing Lens Camera Lens Different Lenses (75mm,50mm,35mm) for Different Distances (overall range: 60-150cm) Required for MRI, Potentially Useful with EEG

Typical MRI Configuration

MRI Mounting Options - Tripod (Picture from MEG setup) Difficult to find tripods with no ferromagnetic metals in them

MRI Mounting Options – Screen Mount No ferromagnetic metals Flexible positioning

MRI Mounting Options – Screen Mount No ferromagnetic metals Flexible positioning Works with most MRIs

MRI Mounting Options – Trio Tray Mount No ferromagnetic Metals Rests on Trio’s bed rails Optional built-in screen Works with Siemens 3T Trio

MRI Head Coil Mirrors Allows subject to see screen and for eye tracker to see subject Best to use front-surfaced mirrors to prevent ghosting and secondary reflections

Long Range System Cabling

Long Range System Cabling Camera Base Box on Side of Host PC Fiber Optic Data Cable Power Options Lemo Connectors (to Camera/Illum.) Patch Panel Connection Options (DB9 or BNC) Battery Option

Long Range System Cabling

Long Range System Cabling No detectable interference with proper cabling (Graph from system use in MEG)

System Synchronization

System Synchronization Pre-Experiment activities Check Tracker Settings (via Set Options Screen and sending commands from Display PC) Participant setup Calibration Validation

MRI/Eye Tracker Synchronization Running the experiment Blocks Trials MRI sends synchronization pulse (TTL) to Display PC – Display PC in turn sends Message to Host PC Pulse triggers Display screen onset – on screen onset Display PC sends Message to Host PC Pulse typically sent from MRI to Parallel Port or USB Device Can optionally be split and sent to Host PC Parallel Port Parallel Port status on Host recorded on every sample Optional drift correction/drift checking Usually between Blocks Can also enable online drift correction with mouse click

MRI/Eye Tracker Synchronization TTL Pulse Display PC Updates Screen Message When Pulse Received Message When Screen Updated Time

EEG/Eye Tracker Synchronization Running the experiment Blocks Trials Display PC draws to screen – at same time sends Message to Host PC and sync pulse (TTL) to EEG Message/Pulse occur at screen retrace event Pulse typically sent from Parallel Port or USB Device of Display PC to EEG – can also be sent from Parallel Port of Host PC Event types can be coded (32 different pulse values) Optional drift correction/drift checking Usually between Trials Can also enable online drift correction with mouse click

Analog Card Option for Host PC – usually used for devices like EEG Converts Digital Data to Analog Voltages Output to BNC connectors Voltage range configurable Three Channels per eye being tracked Horizontal Position Vertical Position Pupil Size Also allows for extra Digital In/Out (in addition to Parallel Port) Quick – Data can be inserted into empty EEG channels Allows for easy alignment with EEG data Dirty – Noise is added by D/A and A/D conversion Saccade/Fixation information is lost

EEG/Eye Tracker Synchronization Display PC Updates Screen Message When Screen Updated TTL When Screen Updated Within 1 msec Optional Constant Analog Out to EEG Time

EEG/Eye Tracker Synchronization Display PC Updates Screen Message When Screen Updated About 1 msec OR Optional Constant Analog Out to EEG TTL from Host PC to EEG Time

Recording and Messaging

Recording and Trials Messages are Not Just For Marking Stimulus Events Data Viewer Format: Trial Onset Messages TRIALID 1 (TRIALID2, etc.) Trial Event Messages DISPLAY_1_ON BUTTON_RECEIVED DISPLAY_2_ON Trial Variable Messages !V TRIAL_VAR trial_condition condition_1 !V TRIAL_VAR reaction_time 2364 Trial Interest Area Messages !V IAREA RECTANGLE 1 100 200 200 300 square Target Position Messages (for moving targets) !V TARGET_POS Targ1 (512, 384) 1 0 !V TARGET_POS Targ1 (512, 364) 1 0 Trial Offset Messages TRIAL_RESULT 0

Recording and Trials Messages are Not Just For Marking Stimulus Events Data Viewer Format: For full description of Data Viewer format see: Data Viewer User Manual (Help -> Contents) “Protocol for EyeLink Data to Viewer Integration”

Recording and Trials EyeLink Recording and Analysis Messages are Independent Scenario 1: Start Recording Start Trial Loop For Each Trial: Trial Onset Message Stimulus Event Messages Mark Every Event of Trials Trial Condition Messages Independent Variables Behavioral (non eye-based) Dependent Measures Trial Interest Area Messages Trial Offset Message End Trial Loop Stop Recording

Recording and Trials EyeLink Recording and Analysis Messages are Independent Scenario 2 (Like Experiment Builder): Start Trial Loop For Each Trial: Start Recording Trial Onset Message Stimulus Event Messages Mark Every Event of Trials Stop Recording Trial Condition Messages Independent Variables Behavioral (non eye-based) Dependent Measures Trial Interest Area Messages Trial Offset Message End Trial Loop

Recording and Trials EyeLink Recording and Analysis Messages are Independent Can Use Scenario 1 or 2 for Most Programming Environments e.g., Psychtoolbox (Matlab), E-Prime, Presentation, C, Python If using Experiment Builder, Must Stick to Scenario 2 Many Messages Sent Automatically with Experiment Builder

Thank you!

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