title: Accommodation and vergence require effort-to-see.
abstract: OBJECTIVE
  Accommodation and vergence both appear to be influenced by multiple nonsensory factors. "Effort-to-see" is one of these factors. This study was designed to assess the extent to which effort-to-see affects accommodation and vergence.
  
  
  METHODS
  Nine volunteers participated in this study. Stimuli were chosen to stimulate selectively either accommodation or vergence. Accommodation and vergence responses were measured while observers viewed each stimulus with the instruction of "concentrate" or "space-out."
  
  
  RESULTS
  Both oculomotor adjustments were accurate when observers "concentrated," but regressed toward the resting posture during identical stimulus conditions when observers spaced-out. Interesting, individual differences in oculomotor behavior were apparent.
  
  
  CONCLUSIONS
  This study demonstrates that higher-level attentional factors play an important role in accommodation and vergence for active exploration of the three-dimensional environment.
authors.affiliation: Division of Ophthalmology, Children's Hospital of Philadelphia, Philadelphia, PA, USA.
authors.forename: Ellie L
authors.initials: EL
authors.lastname: Francis
authors.forename: Bai-chuan
authors.initials: BC
authors.lastname: Jiang
authors.forename: D Alfred
authors.initials: DA
authors.lastname: Owens
authors.forename: Richard A
authors.initials: RA
authors.lastname: Tyrrell
mesh_terms: D000065:Accommodation, Ocular / Q000502:physiology*; D000328:Adult; D001288:Attention / Q000502:physiology; D003290:Convergence, Ocular / Q000502:physiology*; D005133:Eye Movements / Q000502:physiology; D006801:Humans; D014796:Visual Perception / Q000502:physiology*