Despite what this blog may imply, we manage to get a lot of sciencing done around here. (In fact, a whopping 25% of all starcraft-related activities conducted in this lab are research-related, but I’ll let someone else fill you in on those details). In addition to struggling with big picture questions about human cognition, though, we also need to address the nitty-gritty details of – and problems with – collecting data with an eye-tracker.
Here in the cogslab we use four desk-mounted Tobii X120 eye-trackers for data analysis. These machines record the location of your eye-gaze 120 times in a single second – that is, once every 8.3 milliseconds. Wow! As you can imagine, a single participant generates thousands and thousands of data points. In an experiment with 480 trials that takes about 45 minutes to complete, for example, the average participant yields 201,200 samples. We use a modified dispersion threshold (Salvucci & Goldberg, 2000) to condense this raw data into “fixations” by identifying points on the screen the eyes pause at (or “fixate”). Fixations are essentially [x,y] coordinates and durations, and our average participant in the aforementioned experiment has only 4215 of these.