Looming by Luminance
Warning – this is a subtle effect.
What to observe
Observe the neighbouring figure. Does it appear to ‘breathe’ in for a second, out for a second? Does it move towards you (“loom”) when the yellow centre is a ‘+’, and recede when the centre is a yellow ‘–’?
This illusion of motion in depth is a somewhat subtle effect, it can be enhanced by slightly blurring the image. The effect may also be stronger when observed with one eye only.
The neighbouring figure is comprised of disks whose luminance changes over time in a sawtooth manner. For each disk the following rule holds: In the looming phase the luminance increases in small steps, and after the maximum value it drops to black (preferentially stimulating the off-system. In the receding phase the downwards ramp is slow, the rise is sudden, preferentially stimulating the on-system.
This illusion was developed by Frank Schäffel to stimulate accommodation without changes in focus and without actual motion. During our collaborative projects I saw it and was quite impressed. Based on data supplied by Frank, I programmed this somewhat slower on-line version.
Kremers J, Lee BB, Pokorny J & Smith V (1993) Responses of macaque ganglion cells and human observers to compound periodic waveforms. Vision Research 33:1997–2011
Crewther DP & Crewther SG (2002) Refractive compensation to optical defocus depends on the temporal profile of luminance modulation of the environment. Neuroreport 13:1029–1032
Weiss M, Seidemann A & Frank Schaeffel (2004) Stimulating human accommodation without changes in focus. Ophthal Physiol Opt 24:207–217