This definitely isn’t an area where we have as much experience as others (such as Karen Adolph, John Franchak, Chen Yu, Roy Hessels). But there were just a few things that I wanted to share about our head-mounted eyetracker, which we’ve had for a few years now (more on infant eyetracking data quality in general).
This is aimed particularly at people who’re thinking about buying one, but haven’t yet. These are some of the things that we hadn’t appreciated…
The first is that it’s practically difficult to use, particularly with older babies – because the video camera which comes in front of the child’s eye is so highly visible to the child. To start your head mounted eyetracking, you have to calibrate it before you can use it – by getting the participant to look at five set places – but what happened time and again for us is that you’d calibrate it and then, just as you’re ready to start recording, the infant notices the camera and reaches out to touch it – so you have to begin again.
Honestly as well, though, we haven’t used the data that we’ve collected from the eyetracker as much as we’d thought. One problem that we hadn’t anticipated is that you calibrate the head mounted eyetracker to one 2D plane, but then you lose accuracy when you move forwards or back from that – so it works best with experiments that all take place on one plane.
And another problem – that again we should have realised! – is that a fundamental difference between screen-and head-mounted eyetrackers is that the screen eyetracker can automatically analyse where they’re looking on each frame (because what they’re seeing is identical to each child). Whereas for a head-mounted eyetracker what they’re seeing isn’t identical – and so you can’t easily process it automatically. You get a video with cross-hairs showing where they are looking – which you then generally have to code by hand.
So overall – probably from not having thought it through properly before we bought it! – we haven’t used this nearly as much as I’d thought we would. Others have, though, done lots of fantastic work with it though – so don’t just take my word for it!!