Abstract

Fast flicker is detected on mesopic backgrounds by π0′, a rod mechanism with fast temporal response and bandpass temporal contrast sensitivity. The similar temporal properties of cone and π0′ mechanisms suggest a special relationship between cone pathways and π0′-mediated signals that is not shared with the more sluggish, π0 rod signals. This is also supported by field adaptation studies where both rod and M-cone mechanisms adapt π0′ and a single rod mechanism adapts π0. How π0′ and cone flicker signals combine in cone pathways was determined by measuring test additivity. Chromatic adaptation was used simultaneously to isolate rods and either M- and L-cones. Test additivity experiments then assessed the degree of additivity between mechanisms. The degree of additivity was substantially less for π0′ with M-cones (k = 3.8) than with L-cones (k = 2.2). This is consistent with π0′ signals combining L-cone signals according to vector addition and with M-cone signals weakly or not at all for flicker detection. The differential specificity of π0′ and M-cone and L-cones for temporal processing contrasts with the nonspecificity previously reported for these mechanisms for increment detection.

© 1991 Optical Society of America