Developed and Maintained by the Visual Attention Lab at UMass Boston, led by Marc Pomplun
Welcome to the Homepage of Prexel!
News: As of September 2010, a new version of the eye-tracker extension, PresLink, using Presentation's Eye Tracker Interface 2, is included in the SR Research EyeLink Developer's Kit that can be downloaded for free. SR Research will provide the maintenance and customer service for the new interface. We recommend that you switch to the new interface, because it provides more functionality than Prexel and will be supported and further developed by SR Research. Prexel will no longer be supported, but will remain available for download on this site (below).
The current version (as of September 2010) of the Developer's Kit including PresLink can be downloaded here. Please check the SR Research forums for updates.
Prexel is an EyeLink (EyeLink I/II/1000/2K/Remote) eye-tracker extension for the Presentation software by Neurobehavioral Systems. Presentation is a widely used program for stimulus delivery and experimental control for behavioral and physiological experiments. Prexel allows the use of the EyeLink-II eye-tracking system (and its predecessor EyeLink), manufactured by SR Research, in Presentation experiments to collect eye-movement data.
The latest version is Prexel 1.1, updated for the EyeLink 1000/2K/Remote eye trackers by Marc Pomplun. It is still compatible with EyeLink I and II. The previous version was Prexel 1.0-Beta, written by Wisam Yacteen, Jing Dong, Shantanu Inamdar, and Marc Pomplun. It supports the entire functionality of the Presentation eye tracker interface, except for areas of interest (AOIs) and triggers. A shortcoming of all versions to date is that the EyeLink setup (camera setup, calibration, etc.) has to be controlled from the Operator PC. Moreover, while the EyeLink Button Box (game pad) can be used to register subjects' responses, only Presentation-specific means of input (keyboard, mouse etc. on the Subject PC) can control the flow of an experiment (start or end a trial, initiate a drift correction etc.). Please download the documentation below for details. These problems will be fixed in future versions of Prexel.
We are committed to making Prexel a highly reliable and convenient product that is useful for a large variety of purposes. Therefore, your feedback is very important to us. Please let us know your questions, problems, encountered bugs, and suggestions for improvement by sending an e-mail to email@example.com. We will answer questions promptly and use your input for the development of future versions of Prexel.
[Download Prexel 1.1]
This version has been compiled with the latest EyeLink libraries and fully supports the EyeLink 1000/2K/Remote eye trackers, including head target tracking for the EyeLink Remote, which is not supported by previous versions of Prexel. The documentation for Prexel 1.0-Beta still applies to version 1.1.
[Download Prexel 1.0-Beta]
This version contains several bug fixes, increased efficiency, and allows binocular eye tracking. Since Presentation does not currently support explicit commands for binocular eye tracking, we programmed a workaround that seems to work well without dropping any samples or events. Please download the 1.0-Beta documentation for further information. Also notice the new sample experiment "Gaze_Contingent_Binocular" that uses the new binocular tracking ability of Prexel. The installation instructions and list of implemented commands for Prexel 0.9-Beta still apply to 1.0-Beta.
[Download Prexel 1.0-Beta documentation]
This documentation in ASCII explains how to track the left, right, or both eyes with Prexel 1.0-Beta.
[Download Prexel 0.9-Beta]
Download the file prexel.dll to the Subject PC, then start Presentation (you need Version 0.80 or higher). Go to Tools -> Extension Manager -> Register New Extension -> Select Import DLL, then browse and select the prexel.dll file on your computer. The eye tracker extension should now show up in the list of Available Extensions. Click on the name "EyeTracker" and then on "Register Extension." You should now receive the message that the extension was successfully registered.
[Download Prexel 0.9-Beta documentation]
This documentation in PDF format lists the available functions and those that have not been implemented in the current version yet.
[Download Prexel sample experiment "Picture"]
The Picture sample experiment is an Presentation implementation of the experiment template with the same name that comes with the EyeLink-II system. It is a good demonstration of how to write eye tracking experiments under Presentation so that the resulting EDF files can be analyzed with the EyeLink software.
[Download Prexel sample experiment "Visual_Search_Eye"]
This is a simple visual search experiment with eye-movement recording. The subject has to decide whether displays contain a red item or not.
[Download Prexel sample experiment
Here, the possibility of programming gaze-contingent displays under Presentation is demonstrated. A red square is continually centered on the subject's current gaze position.
[Download Prexel sample experiment
Similar to "Gaze_Contingent_Monocular," except that both eyes are tracked and a red and a blue square are continually centered on the subject's current gaze position of the left and right eye, respectively. NOTE: This sample experiment requires Prexel 1.0-Beta or Prexel 1.1.
We would like to thank SR Research for the partial sponsorship of the Prexel project.
[UMass Boston Visual Attention Lab] [Marc Pomplun's Homepage]