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.