Optical illusion of car wheels, speeding up Perhaps it is some free moving spinner attached to the wheel, but as opposed to this question: Why does the wheel of a car appear to be moving in opposite direction?
I have seen car wheels that appear to spin backward both while speeding up, and moving at a constant rate. 
Am I just confused, or is there a reason for this?
 A: Your eyes and brain process images at a fixed sampling rate.  This means that you only see the world in a series of quick images.  If those images are taken at such a rate that the images are taken in synch or multiples of your eye's sample rate the tire can appear to be still.  When that tire moves at a rate that is slightly lower than a multiple of your eye's rate it appears to move slightly backwards.  Likewise if it move slightly faster than a multiple of your eye's sample rate it appears to move slightly slower.  This effect is known as aliasing.
Humans see about 10-12 frames per second (fps) (everyone's rate is a little different and different frames can be perceived at different rates).  If the tire spins at 1,000 frames per second our eye (if working at 10 fps) will only see 10 instances of that tire.  If they are in perfect synch it won't appear to have moved. Here's a youtube example.
In 2004 a newer theory has been proposed called Temporal Aliasing.  Temporal aliasing is caused by the sampling rate (i.e. number of frames per second) of a scene being too low compared to the transformation speed of objects inside of the scene. This causes objects to appear to jump or appear at a location instead of giving the impression of smoothly moving towards them.
