A length aftereffect from grating adaptation: now you see it ... now you don't.
Adaptation to a grating of short bars has the effect of increasing the apparent length of a subsequently viewed test bar, and adaptation to a grating of long bars has the effect of decreasing the apparent length of a subsequently viewed test bar. However, decreasing the interspace between the long adaptation bars has the effect of (1) negating the length aftereffect and (2) reducing the apparent width of the test bar viewed by the retina previously adapted to the grating of long bars.
D005366:Figural Aftereffect; D006185:Habituation, Psychophysiologic; D006801:Humans; D007088:Illusions; D009903:Optical Illusions; D012858:Size Perception