Human cones appear to adapt at low light levels: Measurements on the red—green detection mechanism

• Published in: Vision research (Oxford) 1995-11, Vol.35 (22), p.3103-3118
• Main Authors: Chaparro, A., Stromeyer, C.F., Chen, G., Kronauer, R.E.
• Format: Article
• Language: English
• Subjects: Adaptation, Ocular - physiology; Anatomical correlates of behavior; Behavioral psychophysiology; Biological and medical sciences; Color Perception - physiology; Cone-selective adaptation; Fundamental and applied biological sciences. Psychology; Humans; Lighting; Psychology. Psychoanalysis. Psychiatry; Psychology. Psychophysiology; Red-green detection; Retinal Cone Photoreceptor Cells - physiology; Second-site adaptation; Sensory Thresholds - physiology; Spectrophotometry
• ISSN: 0042-6989; 1878-5646
• DOI: 10.1016/0042-6989(95)00069-C

Recent physiological evidence suggests that cones do not light adapt at low light levels. To assess whether adaptation is cone-selective at low light levels, the red-green detection mechanism was isolated. Thresholds were measured with a large test flash, which stimulated the L and M cones in different fixed amplitude ratios, on different colored adapting fields. Thresholds were plotted in L and M cone contrast coordinates. The red-green mechanism responded to an equally-weighted difference of L and M cone contrast on each colored field, demonstrating equivalent, Weberian adaptation of the L and M cone signals. The L and M cone signals independently adapted for illuminance levels as low as 60 effective trolands (e.g. M-cone trolands. Since this adaptation is entirely selective to cone type, it suggests that the cones themselves light-adapt. The red-green detection contour on reddish fields was displaced further out from the origin of the cone contrast coordinates, revealing an additional sensitivity loss at a subsequent, spectrally-opponent site. This second-site effect may arise from a net “red” or “green” signal that represents the degree to which the L and M cones are differently hyperpolarized by the steady, colored adapting field. Such differential hyperpolarization is compatible with equivalent, Weberian adaptation of the L and M cones.