title: Determinants of contrast sensitivity for the tumbling E and Landolt C.
abstract: OBJECTIVE
  To compare the object spatial frequencies that underlie contrast sensitivity for the tumbling E and Landolt C across a range of optotype sizes and under conditions biased toward the magnocellular (MC) and parvocellular (PC) pathways.
  
  
  METHODS
  Contrast thresholds of two visually normal observers were measured using tumbling E optotypes that were either low-pass filtered or high-pass filtered with a two-dimensional Gaussian filter. Optotypes were presented using steady-pedestal and pulsed-pedestal paradigms to target the MC and PC pathways, respectively. Object frequencies essential for orientation judgments of the tumbling E were derived from plots of log contrast threshold vs. log filter cutoff frequency, and results were compared with those obtained previously for the Landolt C under identical testing conditions.
  
  
  RESULTS
  The object frequency used to judge the orientation of the tumbling E increased systematically with increasing target angular subtense, and the effect of target size differed depending on whether performance was mediated by the inferred MC or PC pathway. The overall pattern of results was similar for the tumbling E and Landolt C, but there was generally less dependence of object frequency on target angular subtense for the tumbling E.
  
  
  CONCLUSIONS
  The tumbling E and Landolt C are not equivalent in terms of the object frequencies that mediate orientation judgments. However, both optotypes show scale-dependent changes in object frequency, particularly under test conditions that favor the PC pathway. The scale dependence of these broadband optotypes can pose a challenge in interpreting test results using these targets. A potential solution is to use spatially filtered optotypes with limited, known object frequency content.
authors.affiliation: Department of Ophthalmology and Visual Sciences, University of Illinois at Chicago, Chicago, Illinois 60612, USA. kennalex@uic.edu
authors.forename: Kenneth R
authors.initials: KR
authors.lastname: Alexander
authors.forename: J Jason
authors.initials: JJ
authors.lastname: McAnany
mesh_terms: D000221:Adaptation, Ocular / Q000502:physiology*; D000328:Adult; D015350:Contrast Sensitivity / Q000502:physiology*; D006801:Humans; D008875:Middle Aged; D009949:Orientation / Q000502:physiology*; D010364:Pattern Recognition, Visual / Q000502:physiology; D010775:Photic Stimulation / Q000379:methods; D012684:Sensory Thresholds / Q000502:physiology; D014795:Visual Pathways / Q000502:physiology*