Detection of linear ego-acceleration from optic flow
Human observers are able to estimate various ego-motion parameters from optic flow, including rotation, translational heading, time to collision (TTC), time to passage (TTP), etc. The perception of linear ego-acceleration or deceleration, i.e. changes of translational velocity, is less well understood. While time-to-passage experiments indicate that ego-acceleration is neglected, subjects are able to keep their (perceived) speed constant under changing conditions, indicating that some sense of ego-acceleration or velocity change must be present. In this paper, we analyze the relation of ego-acceleration estimates and geometrical parameters of the environment using simulated flights through cylindrical and conic (narrowing or widening) corridors. Theoretical analysis shows that a logarithmic ego-acceleration parameter, called the acceleration rate, can be calculated from retinal acceleration measurements. This parameter is independent of the geometrical layout of the scene; if veridical ego-motion is known at some instant in time, acceleration rate allows to update ego-motion without further depth-velocity calibration. Results indicate, however, that subjects systematically confuse ego-acceleration with corridor narrowing and ego-deceleration with corridor widening, while veridically judging ego-acceleration in straight corridors. We conclude that judgments of ego-acceleration are based on first order retinal flow, and do not make use of acceleration rate or retinal acceleration.
F. Festl, F. Recktenwald, C. Yuan, and H. A. Mallot
Journal of Vision, 12(7), 1-12, 2012.