Terry Stanard

Monocular optical constraints on collision control.

A simulated ball-hitting task was used to explore the optical basis for collision control. Ball speed and size were manipulated in Experiments 1 and 2. Results showed a tendency for participants to respond earlier to slower and larger balls. Early in practice, participants would consistently miss the slowest and largest balls. Experiments 3 and 4 examined performance as a function of the range of speeds. Performance for identical speeds differed depending on whether the speeds were fastest or slowest within a range. Asymmetric transfer between the 2 ranges of speeds showed that those trained with slow speeds were very successful when tested with a faster range of speeds. Those trained with fast speeds did not do as well when tested on slower speeds. The pattern of results across 4 experiments suggests that participants were using optical angle and expansion rate as separate degrees of freedom for solving the collision task.

Evaluating the Uncertainty in Various Measurement Tasks Common to Accident Reconstruction

When performing calculations pertaining to the analysis of motor vehicle accidents, this paper describes how investigators must often select appropriate values for a number of parameters. The uncertainty of the final answer is a function of the uncertainty of each parameter involved in the calculation. This paper presents the results of recent tests that were conducted to obtain sample distributions of some common parameters, including measurements made with tapes, measurements made with roller-wheels, skidmark measurements, yawmark measurements, estimation of crush damage from photographs, and drag factors, that can be used to evaluate the uncertainty in an accident reconstruction analysis. The paper also reviews the distributions of some pertinent data reported by other researchers.

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.

Collisions: Getting Them Under Control

Abstract In a control system, information about a current state is compared to a reference state in order to specify an action that will bring the current state and reference state closer together. This comparison process requires a common currency among the three sources of constraint: intention, action, and information. This chapter considers the possibility that structure in an optic array might be that currency. Performance for several tasks is represented in an optical state space that helps to illustrate the confluence of the multiple sources of constraints. The results suggest that the optical criteria for collision control vary to reflect the different sources of constraint.

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.

A Cognitive Task Analysis to Elicit Preliminary Requirements for an Automated UAV Verification & Planning System

A future vision for Unmanned Aerial Vehicles (UAVs) includes single operators managing multiple UAVs. Enabling operator management of multiple UAVs may be aided by automated planning systems that incorporate the strategies and constraints preferred by operators. To derive an understanding of these constraints, a table-top exercise was developed and a cognitive task analysis (CTA) was conducted with subject matter experts (SMEs) operating four UAVs in a dynamic mission scenario. Results indicated general consensus among SMEs on high level goals, prioritization of tasks, allocation of UAVs to tasks, and UAV flight paths and sensor parameters for fulfilling each task. These results will be directly incorporated into an automated verification and planning system. Participants also indicated preferred ways the automation would be most helpful, such as tracking and displaying mission details, and generating multiple, feasible plans that can be reviewed and modified before executing, echoing previous studies.

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).

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.

TESTING THE TAU HYPOTHESIS AGAINST ALTERNATIVE INFORMATION SOURCES USED FOR COLLISION AVOIDANCE

Research on the visual information used in collision avoidance has inappropriately attributed adequate task performance to the use of the visual variable tau (τ). We constructed a collision avoidance experiment where the τ hypothesis was tested against the use of other potential information sources, including expansion rate. Subjects viewed a head-on flight towards one or two barriers. During the first half of trials, a single barrier was present and subjects were instructed to approach it as closely as possible before ascending over it. During the second half of the trials, a second barrier was placed above the first and subjects flew through the resulting gap. The ascent dynamics were manipulated between subjects, such that a time-to-contact margin demarcated the collision boundary with one group, but a constant distance-to-contact margin with another group. Subjects in the time-relevant group responded in a manner more consistent with the use of expansion rate information, but neither a single critical expansion rate or τ strategy adequately explains performance in the two-barrier condition. Subjects in the distance-relevant group responded in a manner consistent with the use of relative distance information.