  Brains and sensory systems evolved to guide motion. Central to this task is
controlling the approach to stationary obstacles and detecting moving
organisms. Looming has been proposed as the main monocular visual cue for
detecting the approach of other animals and avoiding collisions with stationary
obstacles. Elegant neural mechanisms for looming detection have been found in
the brain of insects and vertebrates. However, looming has not been analyzed in
the context of collisions between two moving animals. We propose an alternative
strategy, Generalized Regressive Motion (GRM), which is consistent with
recently observed behavior in fruit flies. Geometric analysis proves that GRM
is a reliable cue to collision among conspecifics, whereas agent-based modeling
suggests that GRM is a better cue than looming as a means to detect approach,
prevent collisions and maintain mobility.
