title: Detection of linear ego-acceleration from optic flow.
abstract: 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 ρ, 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 updating of 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.
authors: Department of Biology, University of Tübingen, Tübingen, Germany. freya.festl@uni-tuebingen.de
authors: Freya
authors: F
authors: Festl
authors: Fabian
authors: F
authors: Recktenwald
authors: Chunrong
authors: C
authors: Yuan
authors: Hanspeter A
authors: HA
authors: Mallot
mesh_terms: D000054:Acceleration; D000328:Adult; D003867:Depth Perception / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D008959:Models, Neurological; D009039:Motion Perception / Q000502:physiology*; D057849:Optic Flow / Q000502:physiology*; D009949:Orientation / Q000502:physiology; D010775:Photic Stimulation / Q000379:methods; D012160:Retina / Q000502:physiology*; D014794:Visual Fields / Q000502:physiology