Abstract

David Stockman (1983) measured Stiles's Pi-4 color mechanism using tiny (3-min of arc) test flashes on tiny (7-8-min of arc) fields, and reported better isolation of the MW cone fundamental than Stiles had originally obtained with 1° tests on large fields. However, David Foster (1981) found spectral sharpening in the detection of tiny spots on combinations of large and tiny fields, consistent with R/G opponent site involvement in this case. We reasoned that if such opponency was influencing Stockman's results, red and green fields might be subadditive (they are additive in Stiles's: Reeves, 1987) in his conditions. We used either a 19- or 200-ms 3.6-min of arc test (530 nm) on either 8.6-min of arc or 10° fields (481 and 622 nm). Results for two observers show additivity (+/−0.06 log units) at ten times absolute threshold, as long as adaptation is complete (6 min).

© 1989 Optical Society of America