title: Pointing at memorized targets during prolonged microgravity.
abstract: BACKGROUND
  Watt et al. (15) and Young et al. (17) have demonstrated that during prolonged microgravity, large errors can be made when pointing at memorized targets in the absence of vision. However, those experiments could not distinguish between errors caused by not knowing where the arm was pointed and errors caused by not knowing target location. The primary goal of this study was to determine the relative contribution of each of these potential sources of error.
  
  
  OBJECTIVE
  It was hypothesized that pointing errors would be greater than pre-flight controls if vision was continuously absent during testing, but not greater than pre-flight if vision was restricted only while pointing.
  
  
  METHODS
  Five subjects on Spacelab SLS-2 (Part A) pointed at targets while keeping their eyes closed continuously; (Part B) touched various body parts and estimated the position of their arms while the eyes remained closed; and (Part C) pointed at the same targets as in A but closed their eyes only while pointing.
  
  
  RESULTS
  On the ground, if the eyes were closed only while pointing, pointing errors averaged 4.5 degrees. After several days n space, errors averaged 7.0 degrees (p < 0.05). Again on the ground, if the eyes were closed continuously while pointing, an additional error of 4.0 degrees was measured. However, after several days in space, the additional error was 10.5 degrees (p < 0.0005).
  
  
  CONCLUSIONS
  The results of this study suggest that the major problem encountered when pointing at memorized targets in microgravity is a lack of knowledge of target, not limb, position.
authors.affiliation: Aerospace Medical Research Unit, McGill University, Montreal, Quebec, Canada.
authors.forename: D G
authors.initials: DG
authors.lastname: Watt
mesh_terms: D000222:Adaptation, Physiological; D006801:Humans; D008568:Memory; D011434:Proprioception; D013037:Spatial Behavior; D014785:Vision, Ocular; D018474:Weightlessness Simulation / Q000009:adverse effects*