Sometimes illusions are based on early sensory pro- cesses, subsequent processing, or higher-level assumptions made by the brain's visual system (Eagleman, 2001; Macknik et al., 2008). We've already discussed one visual illusion, color afterimages, which is due to opponent-processes in the ret- ina or LGN of the thalamus after light information has been detected by the rods and cones. Another postdetection but still rather early process has been offered for yet another illusion.