Fig. 4. Collision-avoidance and landing responses vary with the position of stimulus expansion. (A) The maximum change in value of the wing-beat amplitude (WBA) from the baseline level of both the right (R; red) and left (L; blue) wings varies sinusoidally with the position of the stimulus. (B) A similar variation occurs for the maximum change in the difference between the left and right wing signals. (C) The percentage change in wing-beat frequency (WBF) was largest for expansion occurring in front of the fly and decreases slightly for lateral positions. (D) The probability of eliciting a landing response is greatest for frontal positions. Data points represent the mean value of maximum change ± S.E.M. The number of trials at each position is different because it was determined by where the fly happened to position the object at the onset of expansion. Data are taken from 300 presentations of a square expanding at a rate of 500° s^-1 to a single fly.

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