Exorcising the double-nail illusion: giving up the ghost.
The principles of visual direction explain the double-nail illusion, without the concept of a ghost image. Also, the stimulus arrangement for the illusion is not perceptually ambiguous for the visual system as Krol and van de Grind claim.
D003290:Convergence, Ocular; D005133:Eye Movements; D005403:Fixation, Ocular; D006801:Humans; D007088:Illusions / Q000502:physiology*; D009903:Optical Illusions / Q000502:physiology*; D013028:Space Perception / Q000502:physiology