fixes the ratio of L:L0 or M0
:M in the deuteranomal and protanomal
respectively. It is possible that the level of stimulation produced in
the bipolar cells by cone excitation is determined purely by the
number of photoisomerizations in the cone outer segment. A cone
with high optical density will, then, be very much more sensitive
than one with low optical density. Fig. 6 shows data for the eight
Foster, Nascimento, and Amano (2004) scenes where the OD determines
the scaling of the cone sensitivity spectra. This scaling does
not alter the influence of OD on color vision across most of the
range of OD considered. An exception must be made where one
cone has a very low optical density compared to the other (i.e.
large OD disparities): further increasing the disparity in this condition
does not continue to increase the cell count as it does in the
fixed ratio conditions.
3.4. Effect of OD disparity on color vision
Figs. 4–6 show how optical density affects color vision as measured
with our cell-counting method. The troughs produced in the
three-dimensional plots run along constant OD disparities for a