Psychophysically derived visual mechanisms in turtle. I—Spectral properties

Abstract

Two-color increment thresholds were measured in turtle using a behavioral avoidance paradigm. Four visual mechanisms were isolated, and their spectral sensitivities were compared to action spectra of photoreceptors known to occur in this animal. One visual mechanism appears to be mediated by rods and red-sensitive cones at low background intensities, a second mechanism by coupled red- and green-sensitive cones at intermediate levels, a third and fourth mechanism by red-sensitive, and green-sensitive single cones, respectively, acting alone at high background intensities.