Fig. 5. At starlight intensities of illumination, nocturnal hawkmoths of the species Deilephila elpenor learned to discriminate a training colour from eight different shades of grey and from two other colours but not from brighter or darker shades of the training colour. (A) The animal choosing one of the stimuli in the set-up. Discrimination occurred when the training colour was blue (B) or yellow (C). (Data from Kelber et al., 2002.)