Second Order Motion


Early Study of Second Order Motion

I made this movie  clip in the 1970’s, when I had more hair than brains.  Randomly- spotted vertical rods were held in a frame so that they could move up and down along their own length but not sideways.  When I slowly pulled the rug out from under them, they fell in sequence, so that a contour (defined by vertical motion) moved to the left.

I then turned the machine upside down and cranked the handle.  The rods, resting on the barley-sugar twist table leg, moved up and down sinusoidally, producing a travelling wave of second-order motion.  Since this ‘motion grating’ was defined by texture, not by luminance, a Reichardt motion detector would be blind to it.  Observers could see it quite clearly.  I looked for a motion aftereffect but found none.