TABLE 1.

Cone quantal catches were used to calculate the percentage of luminance and off-axis contrast in the chromatic stimuli^*

Stimulus	Threshold (% contrast)	Luminance Contrast	Off-Axis Contrast	Chromatic Contrast Necessary for Detection by Luminance Mechanism	Chromatic Contrast Necessary for Detection by Other Chromatic Mechanism
For younger observers
L-cone stimulus	0.00699	0.67	1.97	5.728	5.252
S-cone stimulus	0.10327	0	0.14	4175.01	5.104
For older observers
L-cone stimulus	0.01285	12.28	0.78	0.516	33.77
S-cone stimulus	0.26424	2.92	3.7	2.168	0.347

^*The chromatic contrasts necessary for either the luminance or other chromatic mechanism to detect the stimulus are higher than the chromatic thresholds obtained in all cases. Therefore, the luminance mechanism cannot have detected either the L-cone or the S-cone contrast stimulus in the younger or older observers. Similarly, the L-M mechanism could not have mediated the response to the S-cone contrast stimulus and the S-(L + M) mechanism could not have mediated the response to the L-cone contrast stimulus.