title: Crowding by invisible flankers.
abstract: BACKGROUND
  Human object recognition degrades sharply as the target object moves from central vision into peripheral vision. In particular, one's ability to recognize a peripheral target is severely impaired by the presence of flanking objects, a phenomenon known as visual crowding. Recent studies on how visual awareness of flanker existence influences crowding had shown mixed results. More importantly, it is not known whether conscious awareness of the existence of both the target and flankers are necessary for crowding to occur.
  
  
  RESULTS
  Here we show that crowding persists even when people are completely unaware of the flankers, which are rendered invisible through the continuous flash suppression technique. Contrast threshold for identifying the orientation of a grating pattern was elevated in the flanked condition, even when the subjects reported that they were unaware of the perceptually suppressed flankers. Moreover, we find that orientation-specific adaptation is attenuated by flankers even when both the target and flankers are invisible.
  
  
  CONCLUSIONS
  These findings complement the suggested correlation between crowding and visual awareness. What's more, our results demonstrate that conscious awareness and attention are not prerequisite for crowding.
authors.affiliation: Department of Psychology, The University of Hong Kong, Hong Kong Special Administrative Region, China.
authors.forename: Cristy
authors.initials: C
authors.lastname: Ho
authors.forename: Sing-Hang
authors.initials: SH
authors.lastname: Cheung
mesh_terms: D000221:Adaptation, Ocular / Q000502:physiology; D004192:Discrimination, Psychological; D006801:Humans; D009949:Orientation / Q000502:physiology; D013028:Space Perception / Q000502:physiology*; D014796:Visual Perception / Q000502:physiology*; D055815:Young Adult