Fig. 3. Flies respond to odor by flying at lower arena altitudes. Sample flight trajectories for visual and olfactory treatments viewed from the side. (A) random checkerboard, (B) uniform, (C) checkerboard plus odor and (D) uniform plus odor. Probability histograms show distributions for altitude in (E) random checkerboard, (F) uniform, (G) checkerboard plus odor and (H) uniform plus odor. Location of odor source indicated by white circles. Numbers of flies and total flight times are the same as in Fig. 2.