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.

Anticipating the effects of visual gravity during simulated self-motion: estimates of time-to-passage along vertical and horizontal paths

“…In particular, participants anticipated on average the response during accelerated with respect to constant speed motions, and delayed it during decelerated motion. This behavior is in contrast with the predictions of the tau model (Tresilian 1999;1995) extended to time-to-passage tasks (Festl et al 2012;Capelli et al 2010;Kaiser and Hecht 1995;Lee 1980Lee , 1976, which assumes that second-order information (acceleration) is not used in predicting TTP. As a consequence, this classical model predicts that the duration of constant speed motions should be estimated correctly while it should be overestimated for accelerated and underestimated for decelerated motions.…”

“…Most studies indicate that human and non-human primates can visually detect accelerations, but the discrimination of acceleration is much poorer than that of speed (Orban 2008;Brouwer et al 2002;Werkhoven et al 1992;Snowden and Braddick 1991;Calderone and Kaiser 1989;De Bruyn and Orban 1988). In some self-motion studies, TTP estimation did not seem to take into account the deceleration signal, while the use of acceleration signal appeared to depend on stimuli parameters (Festl et al 2012;Capelli et al 2010;Kaiser and Hecht 1995).…”

Sound-evoked vestibular stimulation affects the anticipation of gravity effects during visual self-motion

“…In general, TTP estimates for self-motion are based on first-order optic flow and do not make use of retinal acceleration (Festl et al 2012). However, the acceleration due to gravity appears to be taken into account during visually simulated self-motion in the vertical direction: Observers trigger the motor response for passage at a landmark earlier during downward than forward motion, consistent with the a priori that downward but not forward motion is accelerated by gravity (Indovina et al 2013a).…”

The perception of ego-motion change in environments with varying depth: Interaction of stereo and optic flow

“…Ego-acceleration is an important variable in the control of movement because it can be used to stabilize egomotion by a simple feedback loop. Ego-acceleration can be perceived from optic flow but suffers from a perceptual confusion similar to the depth-velocity ambiguity, which may be called a narrowing-acceleration confusion (Festl, Recktenwald, Yuan, & Mallot, 2012): Subjects confuse the narrowing of a tunnel with ego-acceleration and the widening of a tunnel with egodeceleration.…”