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Cone-based vision of rats for ultraviolet and visible lights

Gerald H. Jacobs^*, John A. Fenwick and Gary A. Williams

Neuroscience Research Institute and Department of Psychology, University of California, Santa Barbara, CA 93106, USA

View larger version (12K): [in a new window]   Fig. 1. (A) Template-based representations of the absorbance functions of two classes of cone found in the rat retina. The templates were derived for photopigments having peak absorbances of 359nm and 509nm (Palacios et al., 1996). (B) Relative spectral sensitivities for the two classes of rat cone. To derive relative spectral sensitivity, the absorbance functions at the top were scaled on the sensitivity axis to reflect the relative representation of the two cone types in the rat retina.

View larger version (14K): [in a new window]   Fig. 2. Rat electroretinogram spectral sensitivity function obtained for 12.5Hz flicker using an amplitude criterion of 3.2µV. The filled circles are mean values for three animals (±1 S.E.M.). The continuous line represents the best-fitting linear summation of the two cone-pigment template curves from Fig.1 (see text).

View larger version (14K): [in a new window]   Fig. 3. Increment-threshold spectral sensitivity functions for the rat. The thresholds are mean values (±1 S.D.) for three subjects as measured on an achromatic background [log(luminance)=1.12, where luminance is measured in cdm-2]. The curve is the best-fitting linear summation of the cone pigment templates.

View larger version (20K): [in a new window]   Fig. 4. Rat increment-threshold spectral sensitivity functions for four different achromatic backgrounds [from top to bottom: log(luminance=1.12, 1.43, 1.76 and 2.09, where luminance is measured in cdm-2]. The top curve is a replot of the mean results from Fig.3 and below that are spectral sensitivity functions obtained from an animal tested on three backgrounds that were progressively elevated in luminance. Each scale division on the sensitivity axis is equal to 0.5 log unit. The four spectral sensitivity functions have been best fitted with linear summations of the cone templates. The percentage of the 509nm component required in these best fits is (from top to bottom): 58%, 64%, 58%, 49%.

View larger version (13K): [in a new window]   Fig. 5. Effects of chromatic adaptation on visual thresholds in the rat. Increment thresholds for two test lights (510nm and 390nm) were measured on 560nm backgrounds of various intensities. Each plotted point is a comparison of the elevation in threshold produced for the two test wavelengths at a single background light intensity. Results are shown for three subjects. The straight line is the best-fitting linear regression (slope=0.71, r2=0.93, P<0.001). The broken line shows the relationship between the threshold elevations for the two test wavelengths expected if the two cone mechanisms had adapted univariantly.

View larger version (16K): [in a new window]   Fig. 6. Results from tests of wavelength discrimination by rats. The plotted points are the mean performance achieved by three rats (± 1 S.E.M.) for various test wavelengths versus a 370nm light (circles and broken line) and for various test wavelengths versus a 510nm light (triangles and solid line). The performance data are for pairs of lights that have been equated to be equally bright for the rat. The horizontal dashed line indicates chance performance for the number of test trials that were run.

View larger version (14K): [in a new window]   Fig. 7. An illustration of the effectiveness of the brightness controls used in the test of rat color vision. In successive experiments, a rat was required to discriminate between a test light of either 380nm or 510nm and a 510nm comparison light. Each of the test lights was presented an equal number of times at an intensity that had been pre-determined by the brightness equation procedure (see text) to be equally bright (arrow) to the comparison light as well as for values brighter (positive) or dimmer (negative) than the comparison light. Intensities are plotted in logarithmic units relative to the brightness match, and each plotted point shows performance over a total of 100 test trials. The broken line indicates the 99% confidence level. Note that the animal always successfully discriminates between 380nm and 510nm lights, but fails to discriminate between the 510nm test and comparison lights when the brightness cues are eliminated.