title: Diminished spatial summation contributes to the age deficit in the discrimination of low-contrast vernier oscillation.
abstract: OBJECTIVE
  This study sought to determine whether a decline in spatial summation contributes to age-related deficits on oscillatory displacement thresholds (ODT's). A secondary goal was to evaluate the extent of spatial summation on a dynamic version of vernier hyperacuity.
  
  
  METHODS
  The ODT's and contrast sensitivity functions (CSF's) of optimally corrected young and old observers were compared as a function of vernier target length (4, 8, or 32 min), contrast level (5 or 30%), and oscillation rate (2 or 8 Hz).
  
  
  RESULTS
  Age deficits on ODT's were related directly to rate of oscillation, but not target contrast. No age difference was seen in ODT's for short low-contrast targets; as target length increased thresholds improved more rapidly for young than old observers; this pattern was reversed at high contrast. ODT's were related strongly and consistently to contrast sensitivity for old but not young observers.
  
  
  CONCLUSIONS
  Diminished spatial summation appears to contribute to the aging visual system's loss of temporal discrimination for low contrast oscillating targets. Spatial summation contributes more importantly to the displacement discrimination of oscillating than to static vernier targets.
authors.affiliation: Department of Psychology, Pennsylvania State University, State College, USA.
authors.forename: N J
authors.initials: NJ
authors.lastname: Hiller
authors.forename: D W
authors.initials: DW
authors.lastname: Kline
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology*; D015350:Contrast Sensitivity / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012160:Retina / Q000502:physiology*; D012684:Sensory Thresholds / Q000502:physiology; D014792:Visual Acuity / Q000502:physiology