The nature of the II1 colour mechanism of W.S. Stiles

Research output: Contribution to journalArticlepeer-review

57 Scopus citations


The Pi1 color mechanism was isolated by means of Stiles's auxiliary field technique: that it is Pi1 which is isolated is proven by both test and field action spectra. The fundamental mechanisms of human trichromatic color vision must satisfy Grassmann's law of additivity. The hypothesis that Pi1 is one of the three fundamentals is tested by experiments in which pairs (μ1, μ2) of monochromatic adapting fields are mixed. When two fields with wave lengths in the neighborhood of its primary mode (μ1, μ2 ≤ 500 nm) are combined, Pi1 is field additive, consistent with the hypothesis that this portion of the Pi1 action spectrum is that of the short wave length sensitive photoreceptors. When a short wave length adaptation field (μ1 ≤ 500 nm) is mixed with a longer wave length field (μ2 ≥ 550 nm) Pi1 is strongly nonadditive. This result proves that the long wave length portion of the Pi1 field spectrum is generated at least in part by a signal originating in the long or middle wave length sensitive cones. Analysis of the additivity failures supports a model of Pi1 in which the signal to be detected is generated in the short wave length cones, and must pass serially through two gain stages: the gain in the first stage is controlled by the short wave length cones alone; the gain in the second stage is controlled by a signal originating in the middle, or long wave length cones, or both.

Original languageEnglish (US)
Pages (from-to)713-747
Number of pages35
JournalJournal of Physiology
Issue number3
StatePublished - 1976
Externally publishedYes

ASJC Scopus subject areas

  • Physiology


Dive into the research topics of 'The nature of the II<sub>1</sub> colour mechanism of W.S. Stiles'. Together they form a unique fingerprint.

Cite this