This article applies to:
E-Prime Extensions for Tobii 3.0
E-Prime Extensions for Tobii 2.0
E-Prime Extensions for Tobii 1.0
This sample experiment demonstrates the methods used to implement fixation tracking in a Tobii-enabled experiments.
The Prime and Stimulus objects display a cue (i.e., a hand pointing left or right) and two target areas. The cue appears for 200ms and then a ‘+’ is displayed at the left or right of the cue.
The script used for this experiment is a modified version of the script that comes with any of the samples installed with the E-Prime Extensions for Tobii. The modifications made are used to track when a fixation has been established and, if a fixation is present, when a fixation is potentially broken.
The script runs through all of the points in the Tobii gaze point history. The area of interest the participant is looking at during the current gaze point is always logged under AOI. If a valid AOI is looked at, the script records this as the potential beginning of a fixation. If the participant continues to look at this AOI for 100ms, a fixation is established and logged in the data file. If the participant then breaks this fixation, the duration of the fixation is logged. When a broken fixation is recorded, it is treated as a potential new fixation. Should the participant fixate on the cue and then immediately shift fixation to the target, this is reflected in the data file, and the participant does not have to re-establish the fixation for 100ms after breaking the previous fixation. Therefore, the participant does not have to look at the target for 100ms to break the fixation and then another 100ms to establish the new fixation. The 100ms to break the fixation is considered the start of a new fixation as well.
The data file logs total fixations, fixation length, the AOI being fixated upon, and the AOI looked at for the current gaze data point.
NOTE: Newer versions of E-Prime Extensions of Tobii Pro (i.e., 3.2 and later) log CurrentObject, ComponentName, and CurrentFixationDuration to the gaze data file automatically when TETGazeDataSave is called. Therefore, the contents of this article may not be as relevant to your study. E-Prime Extensions of Tobii Pro 3.1 does not contain the PackageFile routine TET_ConvertToMilliseconds which is used in the SaveGazeData InLine script in the sample experiments.