Using an ASL Eye Tracker with Inquisit

Versions 3.0.4.0 and later of Inquisit include a module that enables X-DAT markers to be sent from Inquisit to the eye tracker, and real time eye position data to be retrieved from the eye tracker for use in Inquisit experiments.

Sending Markers from Inquisit to an ASL Eye Tracker

Inquisit can send XDAT markers to the Eye Tracker in order to notify it of events in an experiment such as the onset of a stimulus or the moment at which a participant responds. The Eye Tracker then records these values into the data stream so that they can be used to analyze the tracking data. To send XDAT markers, follow these steps:

  1. Using the parallel cable labeled “XDAT” supplied by ASL, connect the parallel port of your Inquisit computer to the XDAT port on the back of Eye Tracker Control Unit.
  2. Start the Eye Tracker.
  3. To test your connection, start Inquisit, select the Tools menu, and select the “Parallel Port Monitor” command. Using the port monitor tool, select the port that the XDAT cable is plugged into, check all of the boxes in the Data section (pins 2-9), and click the Send Button. The XDAT value reported by the Eye Tracker software should change to 255.
  4. Open the sample script for “Sending Markers to ASL Eye Tracker” (this sample can be downloaded from http://www.millisecond.com/download/samples/). Run the sample by clicking on the “Experiment” menu and selecting the “Run” command. The script presents a series of pictures and sends a unique marker value at the onset of each one.

Figure 1: Inquisit's Parallel Port Monitor
Parallel Port Monitor

Sending Data from an ASL Eye Tracker to Inquisit

Inquisit allows a response to be defined as when the participant’s gaze falls within one or more predefined regions on the screen, such as the areas occupied by pictures, text, videos, or arbitrary shapes. Both the region that the participant looks at and the latency of their gaze can be recorded by Inquisit, reported back to the participant, and used to direct the branching and flow of the experiment.

The sample entitled “Retrieving Point of Gaze from ASL Eye Tracker” demonstrates how to use gaze points in an Inquisit experiment. To run the sample, download it from the Inquisit samples web page (http://www.millisecond.com/download/samples/) and follow these steps:

  1. Set up and test serial connection between Eye Tracker Serial Out port and the Inquisit computer as described in ASL SDK Appendix: Testing Serial Out Connection.
  2. Open the sample experiment in the editor.
  3. The sample script assumes that the serial out cable is plugged into the COM1, and the XDAT cable is plugged into LPT1. It also assumes that head tracking is off. If you are using different port numbers, you can change those values in the script by locating the <eyetracker> element in the script (see figure 2 below) and changing the numbers in the following two lines:
    / comportnumber = “1”
    / lptportnumber = “1”

    Figure 2: Eyetracker Element Example
    Eyetracker Element Example

  4. Run the experiment by clicking the “Experiment” menu and selecting the “Run” command.
  5. Inquisit will present a 9-point calibration bitmap on the screen. While this screen is displayed on the Inquisit computer, click the Set Target Points command on the Eye Tracker computer and set each of the target points so that the eye tracker can accurately map pixels on the Inquisit computer’s to Eye Tracker units. Press the space to bar to continue.
  6. Next, Inquisit will begin the process of calibrating the eye tracker to the participant’s eye. To begin eye calibration, select the “Standard Calibration” command on the Eye Tracker computer, and Inquisit will present the current calibration point. As the participant is looking at the point, click the “Save Current Point” button and the next point will appear on the presentation screen. When you are finished calibrating, press the space bar on the Inquisit computer.
  7. Inquisit will then present a single dot in the upper left corner of the screen. Instruct the participant to look at that point and press the space bar.
  8. Inquisit will then present a single dot in the lower right corner of the screen. Instruct the participant to press the space bar as they look at the dot.
  9. Inquisit will then present instructions for running the demo. The demo shows how to display a cursor on the screen at the current gaze point and report the current x and y pixel coordinates.

See the Inquisit documentation for more information on configuring the Eye Tracker and using gaze points in Inquisit.

Sending Markers from Inquisit 2.0 to Eye Tracker

Although Inquisit 2.0 does not support the ASL Eye Tracker module, it is nevertheless possible to send XDAT markers to the Eye Tracker using Inquisit’s generic parallel port signaling capabilities. To send XDAT markers, follow these steps:

  1. Using the parallel cable labeled “XDAT” supplied by ASL, connect the parallel port of your Inquisit computer to the XDAT port on the back of Eye Tracker Control Unit.
  2. Start the Eye Tracker.
  3. To test your connection, start Inquisit, select the Tools menu, and select the “Parallel Port Monitor” command. Using the port monitor tool, select the port that the XDAT cable is plugged into, check all of the boxes in the Data section (pins 2-9), and click the Send Button. The XDAT value reported by the Eye Tracker software should change to 255.
  4. Define your port signals using Inquisit’s <port> element. The <port> element is just another type of stimulus, similar to <picture>, <text>, <video>, and <sound>. As such, port stimuli can be presented using the same syntax that other stimuli can be presented.