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Fig. 1. Illustration of the generation and properties of the visual looming
stimulus. (A) An LCD projector projects a black disk that grows in size with
time on to a translucent white screen. This produces a growing image on the
retina, and its size can be quantified as the view angle
=2xtan-1 (d/2xs), where
d is the diameter of the projected disk on the screen and s
is the distance from the screen to the eye. (B) Two looming stimuli 1 and 2,
plotted as
vs time. Both have the same final view angle, but
stimulus 2 grows more slowly than 1.