COLOR INFORMATION PROCESSING BY TURTLE CONES: Our preliminary intracellular findings suggest that turtle cones of differing spectral classes are coupled via excitatory chemical synapses. Even for small diameter test flashes, red and green cones are non-univariant. Further, the ratio of linear sensitivities measured with red and green flashes is a function of the intensity and color of large diameter chromatic adaptations. Preliminary anatomical studies suggest a pathway which might mediate this coupling; the telodendritic processes which radiate from the bases of one class of cone make synaptic contacts with neighboring cones of different spectral classes. We propose to extend these findings by: 1) determining the ratio of red to green inputs in red and green cones; 2) determining the spectral sensitivity of these additional chromatic inputs; 3) determining the nature of the synaptic pathways using chemical synaptic blocking agents; and 4) recording the consequences of this cone coupling on second order retinal neurons. All cells studied physiologically will be stained with Lucifer Yellow or HRP for subsequent anatomical studies of pathways which may mediate this coupling. TEMPORAL INFORMATION PROCESSING BY TURTLE CONES: Turtle cone photoreceptors manifest a """"""""linear range"""""""" where the cone response is linearly related to the number of quanta in the flash. One can use the """"""""linear impulse resonse"""""""" and linear systems theory to predict the cone's response to any temporal sequence of low intensity retinal illumination. These predictions have been made for a) pulses of various duration and b) sinusoidal modulations of various frequencies in both dark and light adapted cones. Sensitivity calculations based on these predictions relate to the psychophysical Bloch's Law and temporal modulation transfer function, respectively. The above predictions will be verified by intracellular recordings of turtle cone linear range responses to varying duration pulses and varying frequency sinusoidal modulations of low intensity. Linearity of the responses will be tested for each stimulus condition to ensure validity of the predictions. Preliminary intracellular studies of the dependence of the cone's response (kinetics and amplitude) on stimulus duration agree with the predicted behavior for both the dark and light adapted state.
