A letter to my professor

Professor ["C"],

In today's lecture we discussed frame rate, and they eye's ability to detect motion. I was a little concerned that some misconceptions were being fueled about the human eye's ability to detect motion. To say that the eye is "only capable" of seeing 12, 24, 30, or 60 "frames" is not correct. When I brought this up in class, you mentioned the example of a spinning wheel appearing to move backwards. I feel this example is flawed. Generally, this illusion applies to the wheel being captured on film at 24 hz, where we obviously have a stroboscopic effect causing the wheel to appear to turn backwards. It can also be observed in indoor lighting, particularly with flourescents, as the lighting itself operates at 60 hz.

There have actually been some real-world, sunlit experiments where people would perceive a wheel as rotating backwards, but I believe they are largely considered to be the result of eye fatigue, and not of some explicit limit in the brain's ability to interpret the data from the retina. I wonder if this may also be in part a result of our brains becoming so accustomed to strobic lights in modern life.

I found an interesting article on the subject:

"Illusory motion reversal is caused by rivalry, not by

perceptual snapshots of the visual field."

Keith Kline, Alex O. Holcombe, David M. Eagleman

http://wexler.free.fr/library/files/kline%20(2004)%20illusory%20motion%20reversal%20is%20caused%20by%20rivalry,%20not%20by%20perceptual%20snapshots%20of%20the%20visual%20field.pdf

Much of the article is technical neuroscience that I don't understand, but their conclusion is clear: motion reversal illusion cannot be explained by snapshots of the visual field.

Also, you posed the question in class today, "what does 'real-time' really mean?" I think it's a term that's become a little bit bastardized to mean "fast, snappy response time," but the technical definition is that a real-time system has a fixed amount of time allotted to complete a task.

Someone brought up the idea that a turn-based game like chess is not "real-time." Actually, in a tournament chess match with a hard timer, chess is a real-time game. Because the operation (selecting and executing a move) must be completed by a discrete moment, a computer opponent can be considered a real-time system. If no deadline is given, the operation can run as a simple batch process with no concern to the time it takes to complete.

Rigorously speaking, most game engines don't run in true real-time any more; it's just very important that we get really close, and handle things properly when we don't make our 16ms deadline :)