Ventral Optic Flow is a term used to describe what we would normally think of as ‘using landmarks and speed’ to determine where we are and were we have been.
The ventral Optic Flow (OF) of insects and airplane pilots is determined by the angular velocity of the underlying path with regards to a specific point[s].1
Cataglyphis ants, which live in the desert, have two modes of navigation. The first is Optic Flow which records angular velocity. The second is a built in pedometer. These are redundant systems, both of which record where they have been.
There are two types of these ants (disregarding the queen ant). One is a forager and the other is an interior worker. At times, when there is work to be done outside of the nest, the forager carries the interior worker. When being carried the interior worker has no pedometric feedback because it is not walking. However, the interior worker’s Optical Flow feedback remains active. If the two ants are separated, by experimental design, the interior worker can find its way back to the nest due to its OF capabilities. If the interior worker ant is blindfolded thus placing its OF out of commission, and then separated from the forager ant, it is totally lost and can no longer find its way back to the nest. It has neither OF or pedometric data stored.
Redundant systems are always a good choice; whether in biology or technology. The preference for redundant systems in some technologies, such as computers, is at least three (or any odd number) of systems. Action is taken in favor of the majority of results recorded by the systems; or voting, if you will.
1 “Flying Insects and Robots”; Dario Floreano, Jean-Christophe Zufferey, Mandyam V. Srinivasan,Charlie Ellington, Editors, Copyright Springer, 2009, page 29, Optic Flow Based Autopilots