Fig. 9. Open-loop versus closed-loop responses to image expansion. (A) During open-loop presentation the position of the square was controlled externally, as opposed to the closed-loop paradigm in which the fly maintains control over the position of the square. The closed-loop wing responses (filled circles) are repeated from Fig. 4. The open-loop responses (open circles), also generated in response to an expansion at a rate of 500° s^-1, vary roughly with stimulus position as a square wave, in contrast to the open-loop responses, which vary sinusoidally. Thus, the ability to control the position of the square during the collision-avoidance reaction does affect the amplitude of the response. (B) The probability of landing is slightly reduced for open-loop presentations. (C) The latency of the collision-avoidance response is qualitatively similar for the closed- and open-loop stimuli, with slightly larger latencies in response to open-loop image expansion. (D) The open-loop landing response latencies were qualitatively similar to those seen during closed-loop presentations. Again, the latency is slightly shorter during closed-loop presentations. WBA, wing-beat amplitude.