Fig. 1. Visual and olfactory stimuli were delivered to a fly tethered within a computer-controlled flight-simulator modified with odor delivery. (A) The tethered fly was suspended in the center of a cylindrical array of LEDs. Mass-flow-regulated water or apple-cider vinegar vapor was delivered to the antennae and removed continuously with a gentle vacuum to produce a continuous plume. (B) Flies were presented with wide-field patterns of rotation and expansion stimuli. Space-time plots indicate the movement in time of one representative horizontal row of the visual display. FOE, focus of expansion; FOC, focus of contraction.