This article applies to:
E-Prime Extensions for EyeLink 3.0
EyeLink experiments can be configured for use in fMRI environments. Due to the simplified nature of the available EyeLink PackageCalls, only minor modifications of an experiment need to occur to make it "fMRI compatible."
First, fMRI paradigms require the use of the ELStartBlockRecording and ELStopBlockRecording PackageCalls. ELStartBlockRecording starts the eye tracker recording at the block level of an experiment. ELStopBlockRecording stops the eye tracker recording at the block level of an experiment.
ELStartBlockRecording, like ELTrialBegin, has two parameters that the researcher may need to edit. These are vBackdrop and vHostMessage. Please refer to the PackageCall object documentation in E-Studio for more information. The attached experiment uses both of these parameters. vBackdrop is specified as the "HostBackdrop" Slide in Unreferenced E-Object and vHostMessage is an Attribute from the BlockList that indicates what types of trials are run (i.e., practice vs. non practice).
In the attached experiment, 2 Blocks are present: PracticeBlockProc and BlockProc. PraticeBlockProc runs 4 trials in which the purpose is to get the participant acclimated to the study. BlockProc runs 20 trials. At the beginning of both Blocks, recording is started with the ELStartBlockRecording PackageCall. Recording is continuous until the end of the Block whenever ELStopBlockRecording is called. Both Procedures begin with a simple TextDisplay (i.e., PracticeBlockIntro and BlockIntro) that tell the participant what is about to occur.
The contents of the Procedures in the Blocks are the same in terms of E-Objects except for ELGazeReplay. ELGazeReplay is omitted from the real trials as it is meant to assist researchers and participants with obtaining and assessing accurate gaze data during practice trials. This way, any issues with poor calibration can be addressed before real trials are run.
NOTE: Typically, Cumulative Timing is enabled on your Trial E-Objects. This helps promote consistent trial duration. You also want to synchronize with the scanner as demonstrated in the article below. ELTrialBegin and ELTrialEnd do take time to process. You may synchronize per trial after ELTrialBegin or synchronize before the trials and place E-Objects before and after to absorb the delay(s). ELTrialBegin and ELTrialEnd have optional vHandlePreRelease parameters which can be set to False to allow it to be processed while in an object's PreRelease.
NOTE: In fMRI paradigms with long recordings, we recommend clearing the eye tracker history so no data is lost or overwritten. ELTrialBegin has the optional parameter of vClearHistory If specified as True, it specified clears the history of accumulated eye tracking samples. Refer to Appendix D in the E-Prime Extensions for EyeLink 3.0 User Manual for more information on the buffer size.
NOTE: EyeLink does not support the use of NTP. To make sure data files are in sync, we recommend using chronos or a parallel port to set a trigger during each trial. Therefore, analysis and exported data in Data Viewer have a better sense of accuracy (see DEVICE: How To: Synchronize E-Prime with an incoming marker/press via an Input Mask ).