title: Apparent afterimage size, Emmert's law, and oculomotor adjustment.
abstract: The apparent size of an afterimage viewed from distances between 5 cm and 580 cm was matched to that of a size-adjustable stimulus at a fixed distance (20, 30, 90, and 200 cm). The experiment was conducted under normal indoor illumination with a procedure that facilitated matching for angular size. The matched size was found to increase with focal distance within 1 m and very little beyond 1 m. Similar results were obtained with an equivalent series of real stimuli subtending a constant visual angle. These findings suggest a scaling in perceived angular size in proportion to the oculomotor adjustments for accommodation and convergence. The observations of perceived angular size of the afterimage complement what Emmert's law is meant to describe (perceived object size of the afterimage), even though as the focal distance decreases it may be increasingly difficult to tease out perceived object size and perceived angular size with the matching procedure.
authors.affiliation: Department of Psychology, Grand Valley State University, Allendale, MI 49401, USA. loul@gvsu.edu
authors.forename: Liang
authors.initials: L
authors.lastname: Lou
mesh_terms: D000065:Accommodation, Ocular / Q000502:physiology; D000360:Afterimage; D004215:Distance Perception / Q000502:physiology; D005133:Eye Movements / Q000502:physiology*; D006801:Humans; D009903:Optical Illusions / Q000502:physiology*; D011601:Psychophysics; D012044:Regression Analysis; D012858:Size Perception / Q000502:physiology*