I think the contrast has a lot to do with it. Yes, to perceive motion you don't need many frames per second, but alternating frames of black and white at 60fps is easily noticeable. (your PC and/or monitor may totally ruin this though! My laptop displays at 60Hz) ... I guess that 60fps alternating frames should be called a '30Hz flicker', though. Left side of the screen is therefore 30Hz, right side is 15Hz. Make sure you're in full screen or manually set it to 1080p60.
Yes, that is very easily 'noticeable'. but there are so many 'electronic issues' in terms of getting it onto my screen, that I really don't know what to make of it - other than literally a demonstration of what happens if one tries to display 60Hz (or 30 Hz) 'flicker on a computer screen and then view it.
I used to know a lot about this stuff, but that was decades ago and therefore most has now faded (or vanished) - I'll see if I can find some of my dusty notes! In the meantime, a few comments, mainly about movies and TV ....
It might be related to brightness, rather than contrast. Persistence of vision is a purely photochemical phenomenon. Once a receptor in the eye has been stimulated, there is a finite time, dictated by the 'chemical recovery processes' before it can respond to further light, and nothing c an change that. However, it's possible that, at some brightness levels, some receptors may respond some times and other receptors at other times.
It's important to understand the difference between 'frame rate' and 'refresh rate'. Ever since the start of movies with sound (the sound required film movement rate to be standardised), right up to today, Movie film (movies) have always used 24 frames per second. Traditionally, a 2-bladed shutter result in each frame being projected twice, hence a 'refresh rate' (as perceived by viewer) of 48 per second. I think that modern projectors can project each frame three times, hence a refresh rate of 72 per second. It is the refresh rate that determines how often the image being seen changes.
Even with the traditional 48 per sec movie refresh rate if one was looking at a movie of something unchanging (like a static caption) one was unaware of any significant 'flicker'.
Similarly with TV. Frame rate was tied to the local electricity frequency - hence 25 per second (half of 50Hz) in Europe and 30 per second (half of 60Hz) in US. However, since nearly all TV systems used 'interlaced' frames (each transmitted frame containing only alternate lines), there were twice this number of frames transmitted- hence 50 and 60 per second respectively. Traditionally, each transmitted frame was displayed only once, hence refresh rates of 50 and 60 per second. However, we are now seeing TVs with higher refresh rates (e.g. 120 Hz), so that each transmitted frame is displayed two or more times, hence increasing the 'frequency' of what the viewer sees.
As I said, I'll see what I can remind myself about what I once knew about visual perception!
Kind Regards, John