抄録
Age-related anatomical and physiological changes in the human visual system have been reported such as an increase in the density of the lens, a reduction of pupil size and loss of retinal ganglion cells. Although the retinal stimulus and neural signals are strongly affected by such age-related changes, color appearance is stable throughout the life-span because of parallel losses of cone sensitivities and other compensation mechanisms related to color constancy. On the other hand, there is a loss of sensitivity in color discrimination due, in part, to the reduction of retinal illuminance. The results of recent experimental studies by the author and colleagues indicate that this loss in discrimination is not only caused by the reduction of retinal illuminance, but also by a decrease in the signal-to-noise (S/N) ratio in neural pathways processing signals from S-cones and antagonistic signals from L- and M-cones. This change can be considered as a sort of a trade-off between maintaining a constant signal level from the cones through the life-span and decreasing the signal-to-noise ratio in the human visual system. These results suggest some possible methods for making safer and more comfortable visual environments for the elderly.
