title: Quantitative and functional influence of surround luminance on the letter contrast sensitivity function.
abstract: OBJECTIVE
  To determine the influence of surround luminance on the letter contrast sensitivity function.
  
  
  METHODS
  The binocular contrast sensitivities of 31 young and ocularly healthy individuals were measured with letters of sizes calculated to obtain the targeted fundamental frequencies of 3, 10, 20, and 30 c deg(-1), respectively; with surround luminances from 1 to 1000 cd m(-2), always with a test chart background luminance of 200 cd m(-2).
  
  
  RESULTS
  The letter contrast sensitivity increased with surround luminance up to 100 cd m(-2) and decreased when surround luminance increased from 100 to 1000 cd m(-2). These increments are larger for higher fundamental spatial frequencies, while decrements are similar for all frequencies. To analyse pupil size influence, results were compared with theoretical predictions obtained by combining different ocular MTFs with a typical neural function, where pupil size decrease leads to letter contrast sensitivity increments and veiling luminance causes the observed decrements. Other possible optical or neural factors that influence these values have also been considered.
  
  
  CONCLUSIONS
  Letter contrast sensitivity function depends on surround luminance and this influence should be considered in future standardized directives.
authors.affiliation: Departamento de Optica, Universidad de Valladolid, P. Prado de la Magdalena s/n, Valladolid, Spain. apa@opt.uva.es
authors.forename: Juan A
authors.initials: JA
authors.lastname: Aparicio
authors.forename: Isabel
authors.initials: I
authors.lastname: Arranz
authors.forename: Beatriz M
authors.initials: BM
authors.lastname: Matesanz
authors.forename: Juan G
authors.initials: JG
authors.lastname: Vizmanos
authors.forename: Lidia
authors.initials: L
authors.lastname: Padierna
authors.forename: Víctor R
authors.initials: VR
authors.lastname: González
authors.forename: Santiago
authors.initials: S
authors.lastname: Mar
authors.forename: José A
authors.initials: JA
authors.lastname: Menéndez
authors.forename: Luis
authors.initials: L
authors.lastname: Issolio
mesh_terms: D000328:Adult; D015350:Contrast Sensitivity / Q000502:physiology*; D005260:Female; D006801:Humans; D008029:Lighting; D008297:Male; D011680:Pupil; D014787:Vision Tests; D015348:Vision, Binocular / Q000502:physiology; D014792:Visual Acuity / Q000502:physiology; D055815:Young Adult