Rik Warren

The perception of egomotion.

Egomotion is defined as any environmental displacement of the observer. Twenty stationary observers viewed computer-generated films that simulated rectilinear egomotion of constant speed and altitude over an endless plain. The heading point could be 0 degrees, 15 degrees, 30 degrees, 45 degrees, 60 degrees, 75 degrees, or 90 degrees to an observers right of the screen center. The screen was 53 degrees wide. Hence, there was a constant heading toward a point on the horizon, but the heading point was not always in view. The typical observers mean pointing bias was 5.56 degrees to his right and his SD pointing error was 5.18 degrees. The results indicate that these abstract view samples of a pure egomotion ambient optic array are equally effective in giving rise to a compelling perception of egomotion. The results also indicate that observers can perceive the direction of their heading whether or not the heading point is in the view, although accuracy did vary slightly with the specific view. A pointing control using linear perspective scenes whose vanishing points fell off-view showed the same pattern of pointing errors with an overall rightward pointing bias of 3.19 degrees and with an SD pointing error of 3.04 degrees.

Perception and control of altitude: splay and depression angles.

In 3 experiments altitude control was examined as a function of texture type and forward speed. Four texture types were used: grid (rectangular grid with neutral colored cells); dot (small triangles distributed randomly on the ground surface); splay (rows of colored texture parallel to the direction of motion); and depression (rows of colored texture extending perpendicular to the direction of motion). The first 2 experiments required participants to track a constant altitude. Experiment 3 required participants to descend as low as possible without crashing. Results showed an interaction between texture type and forward speed. At low speeds, there was little difference between performance with the depression and splay textures. However, performance with the depression texture deteriorated with increasing forward speeds. Performance with the splay texture was independent of forward speed.

Psychophysical methods for equating performance between alternative motion simulators

Abstract Psychophysical matching techniques were employed to equate the subjective experience of motion in two roll-axis motion simulation devices: the RATS, a whole-body motion environment, and the dynamic seat sub-system of the ALCOGS, presenting motion cues through a moving seat pan. Two psychophysical techniques, cross-modality matching and magnitude estimation, yielded similar results. These results indicated that motion sensitivity increased with roll angular frequency for both simulators. However, the rate of increase at high frequencies was greater for the RATS than for the dynamic seat. These results were used to design a filter for the dynamic seat which enhanced high-frequency signal components. Tests in a roll-axis tracking task showed that performance in the dynamic seat using this filter was both quantitatively (in terms of r.m.s. error) and qualitatively (in terms of frequency characteristics) similar to performance in the whole-body motion environment.

Visual information use in collision avoidance tasks: the importance of understanding the dynamics of action

The tau hypothesis predicts that observers initiate collision avoidance actions based on an integration of speed and distance. We constructed an experiment to test whether human subjects are sensitive to the critical boundary of imminent collision, even when this boundary is not defined by an integration of speed and distance. Subjects were asked to perform a simulated flight towards a barrier surface and initiate an evasive ballistic ascent response at the last possible moment before collision. The between-subjects manipulation was the flight ascent dynamics. In one flight dynamic condition, the boundary of collision was defined by an invariant distance to arrival across the different forward speed conditions. In the other flight dynamics condition, the boundary was defined by an invariant time to arrival across forward speeds. Subject performance in the two groups indicated a sensitivity to the appropriate information defining the critical boundaries, although there was also a conservative distance bias and response variability that increased with forward speed. This bias is explained as a functional scaling of the response with the response variability present.

Cockpit Automation Technology: A Further Look

Cockpit automation is receiving much attention for both commercial and military applications. In particular, Aretz (1984) presented an overview of a United States Air Force Advanced Development Program aimed at developing a structured human factors crew station design methodology. In the past year, lessons have been learned, thinking has matured, and as is inevitable, new questions have arisen. This paper discusses several of these questions and issues. These further thoughts indicate that a well human factored methodology is no simple matter, yet remains important to develop.

Active Control vs. Passive Perception of Heading: Evidence for Different Perceptual Mechanisms

Traditional psychophysical research on perception of heading is characterized by an observer passively viewing a self-motion display. However, some studies suggest that active observers form different perceptions than passive observers, which challenges the relevance of traditional studies of heading to issues of vehicular control. The present study examined whether observers who actively control their self-motion perceive heading differently than those who passively view a self-motion display. We examined heading performance during both active control of yaw and passive observation using a manual control paradigm. The results indicated that observers who actively controlled their yaw perceived heading in a manner that was qualitatively different than observers who passively viewed a self-motion display. Moreover, the results suggest that active observers learn to use relevant display information that passive observers overlook. These results cast doubt on the relevance of traditional psychophysical research on heading to the issue of vehicular control.

Learning to Avoid Collisions: A Functional State Space Approach

Two experiments examined performance in collision avoidance situations. In both experiments participants were asked to initiate a discrete maneuver to avoid a collision at the last possible moment. The affordances of the situations were varied as a function of vehicle dynamics and the functional consequences associated with responding too late or too early. The results were examined in the context of a 2-dimensional functional state space with dimensions associated with optical angle and optical expansion rate. The patterns of performance showed that the actions were consistent with decision rules that could be specified in terms of linear functions of the two optical variables. In most cases, performance at early stages of learning suggested that people were using an Expansion Rate Criterion. With practice, people would tune to a decision rule that was appropriate for the specific vehicle dynamics tested. The results are discussed in relation to the role of three factors in shaping ultimate performance: (a) tasks constraints (i.e., affordances), (b) information constraints (i.e., optical structure), and (c) experience (i.e., learning).

Judgments of Speed of Self-Motion: Modeling the Relative Effects of Speed and Altitude Change

Empirical studies consistently show that judgments of the speed of self-motion are influenced by changes in the altitude of an observer. In general, a given actual speed is judged to be relatively faster from a lower altitude and relatively slower from a higher altitude. Similarly, loss of altitude can be accompanied by a false perception of increasing speed, while increases in altitude can be accompanied by a false perception of loss in speed. The direction of these effects is consistent with the Global Optical Flow Rate (GOFR) Hypothesis. However, the pattern of effects is not proportional to the ratio of velocity to altitude as predicted by the GOFR Hypothesis. An alternative model is presented that predicts additive effect of speed and altitude changes on speed perception.

The Basis for the Perception and Control of Altitude: Splay & Depression Angle Components of Optical Flow

This study evaluated subjects ability to track a constant altitude as a function of the structure in the optical flow field. Optic flow was manipulated by using four different types of ground texture (splay angle, depression angle, random dot, and block textures) crossed with two global optical flow (GOF) rates (0 and 3 eyeheights/s). The subjects were asked to maintain a constant altitude while wind disturbances randomly perturbed them on vertical, lateral, and fore-aft axes. The critical independent variables were texture type and GOF rate. Texture type was a within-subjects variable while GOF rate was a between-subjects variable. The main dependent variables included RMS height error and the correlation between subjects stick activity and the three wind disturbances. For both dependent variables, an interaction was found in that the depression angle texture provided superior performance in a hover or 0 GOF rate condition. The splay angle texture provided a constant level of performance for both GOF rates, being superior to depression angle in the higher GOF rate. These results are consistent with Flach et al.s (1992) hypothesis that the ability to pick-up altitude information from the optic flow field depends upon the amount of optical activity that is specific to changes in altitude (signal) rather than specific to changes in lateral or fore-aft position (noise). This hypothesis provides a higher order explanation for previous results on the control of altitude which had been thought to be inconsistent.