This article applies to:
E-Prime Extensions for Tobii 1.0
This sample experiment demonstrates the methods used to implement saccade tracking in an E-Prime/Tobii integration experiment.
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 saccadic amplitude (i.e., distance in pixels) between fixations, along with the saccadic latency (i.e., time) between when the stimulus appeared and the saccade took place.
The script runs through all of the points in the Tobii gaze point history. Fixations are tracked in the script, and saccades are determined based on these fixations. For example, the saccadic amplitude is logged as the distance between the last point in the previous fixations, and the first point in the current fixation. This distance is calculated using Pythagorean theorem and using the difference between X coordinates and Y coordinates in the respective Point variables for the last point in the previous fixation and the first point in the current fixation. Saccadic latency is always determined based on the onset time of the Stimulus object.
The data file logs saccadic amplitude, saccadic latency, total fixations, fixation length, the AOI being fixated upon, and the AOI looked at for the current gaze data point.