Estimating Middle-Wavelength and Long-Wavelength Cone Sensitivity with Large, Long-Duration Targets and Small, Brief Targets

Abstract

Incremental threshold versus field-intensity curves (tvi) and spectral sensitivity functions were measured for 500 nm and 667 nm test flashes, either under the standard two-colour threshold conditions of Stiles (target: 1.0 deg, 200 ms)—which are known to favour detection by the chromatically-opponent pathways—or with a smaller (0.1 deg), shorter-duration (10 ms) target—chosen to favour detection by the non-opponent (achromatic) pathway. The data reveal differences between the two conditions: for the small, brief target, the tvi curves were shallower and less dependent upon wavelength, and the spectal sensitivity functions were narrower than for the standard target.