At 240 Hz black-white swiching, i wouldn’t expect to see any flicker, just constant grey --flicker-fusion frquency and all that. If anything were wrong, PTB would flood the screen with warning messages, so if you don’t see that, and no/no many reported missed flips, then all is likely good. At a 4 msecs cycle time i could see the sawtooth being a bit deformed, hard to sample such short-period cycles perfectly anymore. VBLSyncTest can give you more asessments, but sounds to me like no cause for worries.
Sorry to hear that. Please let Tobii know that you’d like to have Linux support for that device, maybe they take customer feedback into account. I could imagine that this being a 60 Hz eye tracker, running it in a Windows VM may work well enough, just passing through the USB port to the VM.
One company that I learned about recently, which makes eye trackers with open-source software that work nicely on Linux is “Pupil labs” (https://pupil-labs.com/). My girlfriend currently uses one of these for her research under Linux and is so far happy with it. I think a commercial open-source eye tracking solution is something to endorse here.
Yeah, it is annoying that Tobii has variable OS support considering its high price, I’ve also complained to them about this… Tobii do have Linux drivers (at least for the commercial-use 4C), but they don’t maintain them. To be fair their SDK is cross-platform, which is better than some other eyetracking products.
Pupil labs are much much cheaper and their software seems very flexible, I also wish they made a display solution…
The whole state of eye tracking is such a mess. Neither the hardware nor software is particularly challenging to produce, yet like much scientific equipment low demand and high requirements results in crazy pricing. Tobii made a low-cost consumer device with great hardware that worked really well in a research setting and functioned cross-platform, but as this was priced hundreds of times less than their official research trackers, they ended up using licencing requirements and software restrictions to block its use.
 Gibaldi A, Vanegas M, Bex PJ, & Maiello G (2017) “Evaluation of the Tobii EyeX Eye tracking controller and Matlab toolkit for research.” Behavior research methods49 (3), 923-946 https://doi.org/10.3758/s13428-016-0762-9