Q1: How do we track a ferret’s eye movement?
Uncalibrated eye tracking only requires one camera and one infrared light source. Calibrated eye tracking requires at least two light sources and two cameras, and requires animal to be head fixed. Cameras track the pupil, the center of the eye, and 2 reflected spots of light sources. Based on several reference points along the curvature of the eye, Matlab program moves a model of ferret eye around to find the position and angle with least square fitting error. Detailed approach is modified from a previous publication (Barsingerhorn, Boonstra, & Goossens, Behavior research methods, 2018). Prior knowledge of the position of the camera and the light sources is required for calibrated eye tracking.
Q2: Do ferrets move their eyes a lot?
A: In head-fixed ferrets, the movement of the center of the pupil is small in a period of more than 10 minutes in awake adult ferret, even if drifting grating is shown.
Q3: How long can ferrets be head fixed?
A: Kristina Nielson lab developed ferret head-fixed paradigm (eNeuro 2019). Training is required for ferrets to adapt to the head-fixed setup. Typically, adult ferret could stay in the rig for about 30 min after 4 weeks of training (once a day, 4 days a week) under water restriction.
Q4: Can juvenile ferrets be head fixed?
A: Yes. Also, juvenile ferret does not require much training. But they tend to fall into sleep a lot.
Q5: How do we estimate the fixation point on the screen (for example, to map receptive fields)?
A: Currently, it’s still work in progress, but, with the information of the relative positioning between the monitor and the cameras, it shouldn’t be difficult to map the angle of the eye onto the screen. However, as it is common to move the screen around, it might be case-by-case.