Fig. 7. Optomotor responses vary with image contrast. (A) Mean responses for N=30 flies indicated for an unadapted treatment; flies had no prior exposure to the test stimulus. (B) Mean responses for N=40 flies indicated for a `same-contrast adapted' treatment; flies were presented with the test pattern contrast for 7 s prior to the open-loop test (see Materials and methods). Data are fit with the sigmoid function indicated. The three function variables were identified with a non-linear least-squares optimization algorithm (see Materials and methods). Within-subject design obviates the need for error bars. Variance across animals was similar to that of Fig. 2.