Fig. 2. Flies respond to mechanical, visual and concurrent oscillations with sinusoidal modulations of wingbeat amplitude. Rotational stimuli were applied around the roll axis. Each trace represents the time-averaged response to six trials for a single fly. (A) Concurrent visual and mechanical oscillations phase shifted by 180° elicit strong responses (R_m+v) that are approximately equal to the sum of the responses to each stimuli presented separately (R_m+R_v). (B) When visual and mechanical stimuli are presented with a 0° phase offset, flies display almost no response. (C) At a 270° phase offset, responses are intermediate in amplitude. L, left; R, right; , phase offset; , position. Wingbeat amplitude (WBA) is plotted in normalized units.