Abstract

Threshold summation indices were determined in a study of interrelations among Stiles π mechanisms. Test wavelengths of 630, 520, 475, and 420 nm were presented upon a 555-nm adapting field. The 630–520-nm test-stimulus combination showed very small summation indices compared to the index derived on the assumption of independence of the π₄ and π₅ mechanisms. We suggest that π₅ is not a single or unitary mechanism, but is comprised of two components, π_5r and π_5g, that may inhibit or cancel each other’s effects in producing the net response of mechanism π₅. The hypothesis also explains fairly well the observed small index for the combination 630–475 nm at low field luminance. The mechanisms π₁, π₄, and the composite π₅ seem to be independent, as shown by good agreement between the calculated and experimental indices at high field luminance for the combination 630–475 nm, and over the entire range of field luminance for the combination 520–475 nm. Complete summation is observed for the combination 475–420 nm at high field luminance, with which mechanism π₁ should be almost exclusively involved.

© 1970 Optical Society of America

Study of Interrelations between Mechanisms at Threshold*

Mitsuo Ikeda
J. Opt. Soc. Am. 53(11) 1305-1313 (1963)

Adaptation and Critical Duration for Stiles π Mechanisms

Toshio Uetsuki and Mitsuo Ikeda
J. Opt. Soc. Am. 61(6) 821-828 (1971)

Rod–Cone Interrelation

Mitsuo Ikeda and Mitsuo Urakubo
J. Opt. Soc. Am. 59(2) 217-222 (1969)

Stiles’s Π₅ color mechanism: Tests of field displacement and field additivity properties

C. Sigel and E. N. Pugh
J. Opt. Soc. Am. 70(1) 71-81 (1980)

Stiles’s π₅ mechanism: failure to show univariance is caused by opponent-channel input

Carl R. Ingling and Eugenio Martinez
J. Opt. Soc. Am. 71(9) 1134-1137 (1981)