I am working with Time to First Fixation data that was collected on a Tobii T60 and exported to an excel file. This project presented participants with four images at a time. Each image is designated as an area of interest. (passive viewing task)

Some of the time to first fixation values are blank (indicating missing data) while some of them are 0.

What does Time to First Fixation = 0 indicate?

I had initially assumed that it must indicate that the participant’s gaze was already in the area of interest when the image appeared. However, in some instances two images that were presented at the same time both have time to first fixation = 0. Does this simply mean that participants did not look at either of these images? What is the difference between a missing value vs. a value of 0?

Thank you so much for your help in advance!