A visual learning study of brightness perception in two mutants ofDrosophila melanogaster

Aspects of brightness perception in two visual mutants ofDrosophila melanogaster were investigated in avoidance conditioning experiments: 1. The eye colour mutantwhite (w) and the phototransduction mutanttransient receptor potential with eye colour pigments missing (w; trp) could be conditioned to discriminate intensity differences of 2 log units over a light intensity range of approximately 6 log units (Fig. 2). 2. w; trp mutants could be conditioned to discriminate intensity differences even under high light intensity conditions which largely eliminate the sustained component of the photoreceptor potential. Under these illumination conditions no significant differences betweenw andw; trp mutants in visual memory or in the discrimination of small intensity differences (Fig. 3) could be found. 3. In thew mutant functional inactivation of photoreceptors R1–6 by PDA induction increased the threshold for intensity discrimination of monochromatic 406 nm light stimuli in the conditioning experiment by 2–3 log units (Fig. 5). 4. Brightness perception as determined by conditioning experiments was compared to phototactic choice behaviour forw andw; trp flies (Figs. 4 and 6). Implications for the interpretation of phototaxis experiments are discussed.