Evaluation of the candidacy of the Π-mechanisms of stiles for color-matching fundamentals

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Linear combinations of small field color matching functions that yield best fits (minimum RMS deviations on a logarithmic scale) to the spectral sensitivities of Stiles's Π-mechanisms were found by a computer minimization technique. Good fits to Π3 (RMS = 0.039 log units, λ ≦ 533 nm) and to Π4 (RMS = 0.042 log units) and a surprisingly excellent fit to Π5 (RMS = 0.024 log units) were found. The same fitting technique was applied also to a large set of pigment spectra obtained from the Dartnall A1, nomogram and from Wald, Brown and Smith's iodopsin spectrum by varying (i) λmax, (ii) optical density (iii) lens and macular pigment corrections. None of these spectra were found to be better fit than Π3, Π4 and Π5. A formal analysis reveals that the apparently protanomaloas W.D.W. unit coordinates induced by Π5, Π4, Π3 could result from small deviations of these spectral sensitivities from the "true" underlying sensitivities.

Original languageEnglish (US)
Pages (from-to)317-330
Number of pages14
JournalVision Research
Issue number3
StatePublished - 1978
Externally publishedYes

ASJC Scopus subject areas

  • Ophthalmology
  • Sensory Systems


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