title: Form from motion parallax and form from luminance contrast: vernier discrimination.
abstract: Some objects are perfectly camouflaged when stationary, but are clearly visible when moving; the boundaries of such an object are defined entirely by motion parallax. Little is known about the eye's ability to make spatial discriminations between motion-defined objects. In this study, subjects viewed a pseudo-random pattern of dots within which a camouflaged bar was made visible by relative motion of dots. Vernier acuity for the motion-defined bar was 27-45 sec arc for three subjects, much less than the interdot separation of 360 sec arc, much less than the 2 deg receptive field size for motion, and comparable with the foveal intercone separation of 30 sec arc. It is proposed that an opponent-orientation process and an opponent-position process can both contribute to vernier judgements for motion-defined objects. Real-world motion contrast commonly confounds the following cues for figure-ground segregation: (1) different texture velocities on either side of the figure's boundary; (2) in any given time interval, texture in figure and ground moves different distances; and (3) texture continually appears and disappears along the figure's boundary. When cues (2) and (3) were eliminated, thus ensuring figure-ground segregation was achieved entirely by motion-sensitive neural elements, vernier acuity was 44 +/- 5 sec arc compared with 36 +/- 8 sec arc for a dotted bar defined by luminance contrast.
  
  
  CONCLUSIONS
  Vernier acuity for a dotted bar whose boundary was defined entirely by motion-sensitive neural elements was similar to vernier acuity for a dotted bar whose boundary was defined by luminance contrast.
authors.affiliation: Department of Ophthalmology, Dalhousie University, Halifax, Canada.
authors.forename: D
authors.initials: D
authors.lastname: Regan
mesh_terms: D015350:Contrast Sensitivity / Q000502:physiology*; D005556:Form Perception; D006801:Humans; D008027:Light; D009039:Motion Perception; D015357:Vision Disparity / Q000502:physiology*; D014792:Visual Acuity