The Scaling of Information to Action in Visually Guided Braking.

Braking to avoid a collision can be controlled by keeping the deceleration required to stop (i.e., ideal deceleration) in the "safe" region below maximum deceleration, but maximum deceleration is not optically specified and can vary as conditions change. When brake strength was manipulated between participants using a simulated braking task, the ratio of ideal to maximum deceleration at brake onset was invariant across groups, suggesting that calibration involves scaling information about ideal deceleration in intrinsic units of maximum deceleration. Evidence of rapid recalibration was found when brake strength was manipulated within participants, and the presence of external forces that affect brake dynamics resulted in biases in performance. Discussion focuses on the role of calibration, internal models, and affordance perception in visually guided action. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Perceiving curvilinear heading in the presence of moving objects.

Four experiments were directed at understanding the influence of multiple moving objects on curvilinear (i.e., circular and elliptical) heading perception. Displays simulated observer movement over a ground plane in the presence of moving objects depicted as transparent, opaque, or black cubes. Objects either moved parallel to or intersected the observer's path and either retreated from or approached the moving observer. Heading judgments were accurate and consistent across all conditions. The significance of these results for computational models of heading perception and for information in the global optic flow field about observer and object motion is discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Signaling, notetaking, and field independence–dependence in text comprehension and recall.

Experiment 1 involved having undergraduates take or not take notes while listening to two passages with or without signals (structural cues). When notetaking on signaled text, recall was maximized; on nonsignaled text, recall was minimized. Because notetakers appeared to rely on signals in processing text, it seemed that notetaking produced a structure-search process. Regression analyses suggested that notetaking in the presence of signals enhanced recall of field-dependent (FDs) but not field-independent learners (FIs). Experiment 2 directly examined this issue in a reading context. Increased high-level recall across passages of the same overall structure (a transfer of structure effect) was found for FIs only in the non-notetaking conditions and for the FDs only in the notetaking conditions. Thus, FIs seemed to spontaneously use a tacit structure strategy when left to their own devices and FDs appeared to immediately display powerful structuring skills when induced to do so via notetaking. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Behavioral dynamics of steering, obstable avoidance, and route selection.

The authors investigated the dynamics of steering and obstacle avoidance, with the aim of predicting routes through complex scenes. Participants walked in a virtual environment toward a goal (Experiment 1) and around an obstacle (Experiment 2) whose initial angle and distance varied. Goals and obstacles behave as attractors and repellers of heading, respectively, whose strengths depend on distance. The observed behavior was modeled as a dynamical system in which angular acceleration is a function of goal and obstacle angle and distance. By linearly combining terms for goals and obstacles, one could predict whether participants adopt a route to the left or right of an obstacle to reach a goal (Experiment 3). Route selection may emerge from on-line steering dynamics, making explicit path planning unnecessary. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perceiving circular heading in noncanonical flow fields.

Five experiments examined circular heading perception with optical flows that departed from the canonical form. Noncanonicity was achieved through nonrigidity of the environment (Experiments 1 and 2), oscillations of the point of observation (Experiment 3), and the bending of light (Experiments 4 and 5). In Experiments 1 and 2, perception was impaired more by nonrigidity of the ground plane than by nonrigidity of the medium. In Experiment 3, perception was unimpaired by noncanonical flows induced by the bounce and sway of observer locomotion. In Experiments 4 and 5, perception was not impaired when light paths were distorted by a spherical projection, but perception was impaired when they were distorted by a sine function. Results are discussed in relation to the hypothesis that the information for perceiving heading is the ordinal pattern of optical flow. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Calibration, Information, and Control Strategies for Braking to Avoid a Collision.

This study explored visual control strategies for braking to avoid collision by manipulating information about speed of self-motion. Participants watched computer-generated displays and used a brake to stop at an object in the path of motion. Global optic flow rate and edge rate were manipulated by adjusting eyeheight and ground-texture size. Stopping distance, initiation of braking, and the magnitude of brake adjustments were influenced by both optical variables, but global optic flow rate had a stronger effect. A new model is introduced according to which braking is controlled by keeping the perceived ideal deceleration, based in part on global optic flow rate, within a "safe" region between 0 and the maximum deceleration of the brake. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A Dynamical Model of Visually-Guided Steering,Obstacle Avoidance,and Route Selection

Using a biologically-inspired model, we show how successful route selection through a cluttered environment can emerge from on-line steering dynamics, without explicit path planning. The model is derived from experiments on human walking performed in the Virtual Environment Navigation Lab (VENLab) at Brown. We find that goals and obstacles behave as attractors and repellors of heading, the direction of locomotion, for an observer moving at a constant speed. The influence of a goal on turning rate increases with its angle from the heading and decreases exponentially with its distance; the influence of an obstacle decreases exponentially with angle and distance. Linearly combining goal and obstacle terms allows us to simulate paths through arbitrarily complex scenes, based on information about obstacles in view near the heading direction and a few meters ahead. We simulated the model on a variety of scene configurations and observed generally efficient routes, and verified this behavior on a mobile robot. Discussion focuses on comparisons between dynamical models and other approaches, including potential field models and explicit path planning. Effective route selection can thus be performed on-line, in simple environments as a consequence of elementary behaviors for steering and obstacle avoidance.     

Steering toward a goal by equalizing taus.

Steering toward a target can be controlled by equalizing the time-to-closure of the angle between the target and the direction of locomotion and the time-to-passage of the observer by the target. Two experiments required observers to steer through a computer-simulated environment toward a target depicted as either a floating cross that did not optically expand, a floating sphere that optically expanded or a grounded post that optically expanded. Experiment 1 revealed better performance in the post and sphere conditions, suggesting that steering is influenced by local optical expansion but not by perceived spatial target location or distance. Experiment 2 revealed differences in steering behavior between target types that suggested observers attempted to equalize time-to-closure and time-to-passage. (PsycINFO Database Record (c) 2010 APA, all rights reserved)