The Neural Control of Vision
O. Illusions

A more extensive list of facts and inferences:

•  The illusion occurs over a large range of sizes and bar widths
  
  
•  The illusion is reduced by use of curvy lines and discontinuities
  
  
•  Using configuarations that increase center surround antagonism actually decreases the effect
  
  
•  The effect is enhanced with luminance differences of bars but occurs only when lesser contrast bars are in front
  
  
•  The actual spatial arrangement of the retinal ganglion cell receptive fields is in conflict with the theory
  
  
•  The illusion persists with contrast reversal

   Therefore the theory based on ON ganglion cell activity is invalid

•  Illusion not seen at isoluminance
  
  
•  Illusion is seen with brief presentation and is not altered by light and dark preadaptation

   Therefore simultaneous luminance contrast is essential

   Therefore eye tremor and afterimages are not a factor

•  The effect is strong under both scotopic and photopic conditions

   Therefore effect not due to rod/cone interaction

For earlier studies examining the Hermann grid and the possible underlying mechanisms of the illusion, see Lothar Spillman (1971) Pflugers Archiv, 326, 281-299 and Jeremy M. Wolfe (1984) Perception, 13, 33-40.