First time I recall the canceling-out Fred speaks of is noticing that a new refrigerator motor in my family home was quite audible at first, but over time became imperceptible. Until the thermostat would turn it off — at which moment someone might say, sincerely, "What was that?!" When I was away at college my parents moved to another town nearby. My first time home it was quite noticeable that a plane would fly overhead every 6 minutes. Pretty soon, whenever I was there, the planes became imperceptible — unless I thought about them, in which case they were suddenly there. ((( A different perceptual phenomenon is demonstrated by the short film De Duva (The Dove), at < https://www.youtube.com/watch?v=8X2QmLWWxq4 >, which is based on Ingmar Bergman films. I recommend not reading anything at that URL but just starting the video right away at full screen size. ))) Okay, so this frequency-canceling works for visual and auditory stimuli. What about taste, smell, and touch? ——Dan Fred wrote: ----- A quick search for "moving bar illusion" failed to find anything obviously relevant to RWG's impressively effective post. So I'll point out that it demonstrates very neatly the way our perceptive mechanisms filter out constant background frequencies, allowing through only changes in the signal spectrum --- visual, auditory, tactile, olfactory(?!). In this case, the subsequent apparent stretching of the text is patently opposite to that induced by the video, as our internal DPU continues to cancel out the assumed previous motion. I am reminded of an incident late one night when standing beside the Victorian clock in the hall of my home: completely unable to hear its normal loud tick, I inspected the pendulum to check whether it had stopped. As I watched in some bafflement, the tick gradually became perceptible, accompanied by the realisation that it had actually been present throughout. -----