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Rationale

Eye tracking allows for monitoring of eye position during the course of a scan. Our tracker employs the bright pupil technique: under direct coaxial illumination, the eye acts as a retroreflector as infared light reflects off the retina to create a corneal reflection (CR). The position of the resulting contrast is monitored over time by the camera.

Equipment

The system is manufactured by Applied Science Laboratories (ASL) and is the LRO-6.

It operates by direct video imaging of the pupil, providing a near-continuous (60 Hz) x/y pupil location and pupil size.

Software and manuals for the device are stored on the CfN cluster at:

/jet/images/eyetrac

The control components are located outside the HUP6 Scanner Room. They include the following:

Acer Computer Control Unit EyeTracMonitor Stimulus Display Monitor Power Box
acercomputer.jpgASCII���{
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    FocusScan = "(0,21.79) (29,23.25) (56,31.13) (81,22.61) (105,27.49)
(127,31.46) (149,24.29) (169,21.84) 3.7s ago";
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    NoiseReduction = "S:20 C:11 Y:3";...ASCII���{
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(127,31.46) (149,24.29) (169,21.84) 8.7s ago";
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    FocusWindow = "350/300 300x400";
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    ISOSpeedRating = 615;
    NoiseReduction = "S:24 C:12 Y:4";... ASCII���{
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    AccelerometerDeltas = "(0.0055 0.0066 0.0108) @ 0.0200";
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(239,12.13) (255,12.13) 0.2s ago";
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    ISOSpeedRating = 1016;... powerbox.jpg

Scanning using eyetracking

The eye tracking equipment is currently setup to record data from the right eye. It is setup at the back of the scanner near the projector in HUP6 on a stand and is angled upwards to capture the eye. The configuration of the stimulus projection system and mirrors makes recording from the left eye difficult with the current equipment.

1. Subject preparation

  1. Remove any mascara or eye makeup; these pigments can reflect IR and degrade the tracking signal.

2. Setup control system outside of scanner

  1. Login to Acer computer (top panel-left)
    • ID: eye
    • Password: tracker6
  2. Make sure Control Unit and EyeTracMonitor are ON
  3. Turn on the Stimulus Display Monitor
  4. Load Program: Eye Trac6.Net User InterFace. The User Interface is displayed to the right.
    • In the “Upload to ASL Eye Tracker Control Unit” Window, click Upload to accept the pre-set FPGA and DSP files for calibration.
  5. Set up Dog-fMRI testing laptop
    • Connect the laptop to the blue VGA monitor out plug using the DVI-VGA adapter (included in the Dog-fMRI case)
    • Connect the USB wire to the laptop and tan TTL box (included in the Dog-fMRI case)
    • Connect the TTL box to the Eyetraker using the gray/black B/C-Parallel Wire:
      1. Plug the B/C end (circle plug with single central pin) to the left most outlet on the TTL box
      2. Remove the silver X-Dat wire from the parallel plug in front of the Acer monitor, behind the keyboard.
      3. Plug the Parallel end (wide multipin gray plug) into the same parallel plug (in front of the Acer monitor, behind the keyboard) which the X-Dat was connected to
    • Start Matlab, and navigate to →Users→iron→documents→Matlab. On the NIToolbox folder, Press CRTL+click, and select “add to path.”
    • In the command line, Type EyeT2 to start calibration
  6. The monitor will not mirrow the windows desktop but will mirror when running the script. The Eyetrac Stimulus Display monitor will autommatically mirror the script when it runs. (IF not, push thr PC/AV button on the Stimulus Display Monitor to toggle its input).

3. Setup tracker system inside of scanner

  1. Turn out lights in the scanning room
  2. Plug in eyetracker
    1. Turn on black PowerBox outside scanning room, labelled “Eye Tracker Power Box” (top panel-right)
    2. Plug in eyetracker unit (located behind scanner) using the AC power cord (grey with white end with 3 holes) in closet inside scanning room
    • Be careful when walking past magent with the cord since it contains metal
  3. Turn on unit with Illuminator On switch.
  4. Turn on LCD monitor (with switch on left of screen). Do not move the LCD screen quickly because the magnetic field will interfere with its function.
  5. Bring the filters into the scanning room
    • The filters are stored in a styrofoam and felt wrapper, inside a cardboard equipment box in the control room ASCII���{
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    AWBGGain = 64;
    AWBRGain = 125;
    AWBStable = 1;
    AccelerometerDeltas = "(0.0065 0.0089 0.0035) @ 0.0200";
    ApertureValue = 3;
    BrightnessValue = -0.6679113102646765;
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    ExposureBias = 0;
    ExposureTime = 0.08316987826086956;
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    NoiseReduction = "S:20 C:11 Y:3";
    OneFrameAEMode = 0;...
    • The “thin” filter is used for alignment of the system. It allows the operator to see and align the attenuated light patch over the subject's eye. The “thick” filter is used for operation of the system in eye-tracking. The patch of light will be infra-red and not visible to the operator or subject.
    • PLace the filter in the slot labelled Filter in the center of the unit
  6. Align bright, yellow circle on the right side of bore (mostly) into the bore and over the subject's right eye
    • Will need to twist the unit and move the screen slightly to allow the light to pass into the bore
    • Use the thinner filter to setup the subject
    • Make sure to ask the subject to close their eyes if EVER removing the filter
    • Use knobs inside the right side of the eyetracker to move the circle (bottom knob - side to side)
    • Less important for pupils to be centered
    • More important for curve of MR head-coil to be minimally visible
    • Use adjustment levers on front of eyetracker to focus
    • Turn off LCD monitor on top of eyetracker before starting scanning because it will cause scanning artifacts
  7. Place thicker filter into eyetracker after alignment and before calibration

4. Calibration of system

Using EyeTrac6

  1. Select Standard Calibration from the Calibrate menu ?150
  2. Run EyeT2. Press any key to highlight the first region of positions 1-9. As the subject views each position, click the “Save Current Point <space>”. Press any key on the DOG-fMRI computer again to advance the position.
  3. Once this is complete, have the subject look around again at each of the points in order to check the quality of the calibration cross-hairs. If necessary, repeat the calibration process by running the Eprime script again and restarting the Standard Calibration in the Calibrate menu from the EyeTrac6 User interface.

5. Data Collection

  1. Click “File”
  2. Click “New Data File”
  3. Name File
  4. Close data file
  5. Copy to flash drive/e-mail/CD/etc.
  6. Exit program

6. Breakdown

Please leave everything as you found it

  1. Turn off and unplug Luminator/Eyetracker
  2. Take out Filter
    • :!: Be Careful!! Filter will be VERY HOT!! Allow to cool on top of projector while breaking down rest of setup
  3. Unplug & roll up cord to eyetracker. Put back in closet
  4. Turn off the black EyeTracker Powerbox
  5. Place filters back in covers and place back inside of eyetracking equipment box
  6. Place eyetracking equipment box back on top of shelves
  7. Power off TV monitor/Control unit
  8. Turn off Acer computer
  9. Reconnect the Silver X-Dat plug to the Parallel cable in front of the Acer monitor

Data analysis

Please describe the methods used to download the eye-tracking data, store, and analyze the results. General outline: - Pre-processing raw files to readable format - Running matlab program on resulting data files to denote time periods where fixation varied beyond 3 degrees

Key note: Final txt file, save as .EYE file. Copy said .EYE file(s) to PreScripts/Eyes folder.

Test of measurement precision

SP and GKA tested the precision of the eye-tracking measurement on 12/14/09. GKA was the subject in the scanner. Following standard calibration (see above) GKA was presented with a grid of 12 stimulus points (4 horiz, 3 vert) that tiled the screen. Every second a different randomly selected stimulus point blinked. GKA fixated the blinking stimulus while eye position was recorded. There were 3 runs of 72 trials each.

There were 18 trials at each horizontal position per run. The mean (and standard deviation) of eye position for one run across the 72 trials was:

Horiz Stim positionMean Horiz Eye positionStdev of horiz eye position
-9-9.000000.614120
-3-2.955220.442733
33.036950.400304
99.134680.741673

The units given are degrees visual angle, assuming a 18° separation between the two outer horizontal targets.

The plot below shows trace of horizontal eye position against stimulus position over 72 seconds (click to enlarge).

[Multiply the y-axis by ~30 to obtain degrees]

/var/www/html/aguirreg/html/wiki/data/pages/public/eye_tracking_during_fmri_scanning.txt · Last modified: 2011/09/24 21:46 by aguirreg