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Fig. 1. Experimental design. (A) Fly orientation was determined at 101 Hz with a
near-IR camera and realtime software. Visual stimulation was provided by a
32x64 matrix of LEDs wrapped in a cylinder around the tethered fly. N,
magnetic north; S, south. (B) Flies were glued to a steel pin, which was set
in a jewel bearing and held in a magnetic field so that the flies could rotate
only about their functional yaw axis. (C) Flies were stimulated with virtual
looming squares. The time course of the visual stimulus (
) was
proportional to x, the distance between the stimulus and the eye,
which was determined by the square's edge half-length (l=10 cm),
approach velocity v, and acceleration. (D) Time course of visual
stimulation for an approaching object with constant velocity (v=1.5 m
s-1, solid line), acceleration (vinit=0,
a=6.2 m s-2, dotted line), or deceleration
(vinit=3.4 m s-1, a=-5.3 m
s-2, broken line). The stimuli were discretized both spatially and
temporally due to limitations of the LED arena (visual refresh rate: 800 Hz;
pattern update rate: 50 Hz). The blue circles represent the approximate
discretization of the constant-velocity stimulus, sampled every 10 ms.
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