  The movements of birds, bats, and other flying species are governed by
complex sensorimotor systems that allow the animals to react to stationary
environmental features as well as to wind disturbances, other animals in nearby
airspace, and a wide variety of unexpected challenges. The paper and talk will
describe research that analyzes the three-dimensional trajectories of bats
flying in a habitat in Texas. The trajectories are computed with stereoscopic
methods using data from synchronous thermal videos that were recorded with high
temporal and spatial resolution from three viewpoints. Following our previously
reported work, we examine the possibility that bat trajectories in this habitat
are governed by optical flow sensing that interpolates periodic distance
measurements from echolocation. Using an idealized geometry of bat eyes, we
introduce the concept of time-to-transit, and recall some research that
suggests that this quantity is computed by the animals' visual cortex. Several
steering control laws based on time-to-transit are proposed for an idealized
flight model, and it is shown that these can be used to replicate the observed
flight of what we identify as typical bats. Although the vision-based motion
control laws we propose and the protocols for switching between them are quite
simple, some of the trajectories that have been synthesized are qualitatively
bat-like. Examination of the control protocols that generate these trajectories
suggests that bat motions are governed both by their reactions to a subset of
key feature points as well by their memories of where these feature points are
located.
