Abstract

One of the early milestones in Bob Boynton's career was his work with Ikeda and Stiles which examined the degree of summation between π mechanisms at threshold (e.g., Boynton, Ikeda, and Stiles, 1964). They made early use of a technique now called the test-additivity procedure, in which thresholds for two test-stimulus wavelengths are compared when they are presented singly versus presented together. Their results show that despite the relative independence of "photoreceptor-based" π mechanisms in other situations, in joint detection of increments, they interact in complicated ways that suggest the action of opponent postreceptoral pathways. In this sense, Boynton, Ikeda, and Stiles link what are now termed "first" and "second" sites.

© 1992 Optical Society of America