The authors examined whether the learning and performance of dual tasks by young and old adults could be enhanced through training. Adults were trained with either a fixed-priority or variable-priority training strategy on a monitoring task and an alphabet–arithmetic task and then transferred to a scheduling and a paired-associates running memory task. Participants in the variable-priority condition learned the monitoring and alphabet–arithmetic tasks more quickly and achieved a higher level of mastery on these tasks than did those in the fixed-priority condition. Moreover, participants trained with the variable-priority technique showed evidence of the development of automatic processing and a more rapid rate of learning and higher level of mastery of the transfer tasks than did the fixed-priority participants. These results are discussed in terms of the mechanisms that underlie learning and performance of dual tasks and with respect to potential applications.

Magnitude judgments of the speed of self-motion were examined. The principal independent variables were edge rate, global optical flow rate, and the type of texture (grid or dot). Results indicated that edge rate and global optical flow rate had additive effects on magnitude judgments, with edge rate accounting for a larger portion of the variance. Effects were independent of texture type. Secondary variables examined were viewing condition and task load. Attempts were made to control the availability of flatness cues. Evidence indicates that the effectiveness of global optical flow rate varied with the control of flatness cues. A secondary running auditory Sternberg task was used to prevent edge counting; the presence of this task did not reduce the effect of edge rate. These results replicate and extend previous work by D. H. Owen and colleagues.

Two empirical studies are reported that examine active regulation of altitude as a function of the type of ground texture. Three ground textures were examined: lines perpendicular to the direction of motion, lines parallel to the direction of motion, and the combination (i.e., square or checkerboard texture). Although subjects only controlled altitude, disturbances were introduced on three axes: vertical, lateral, and fore-aft. The results show a clear advantage for texture parallel to the direction of motion. However, in considering these results in the context of previous research on altitude control, the argument is made that there is no compelling evidence that suggests either parallel (splay) or perpendicular (density) texture is privileged with regard to altitude control. Rather, the most effective display for altitude control will be the one that best isolates the optical activity associated with changing altitude from the optical activity arising from other sources of disturbance (such as forward locomotion). Such a display will make it easier for the observer to distinguish and respond specifically to the disturbances of altitude.Gibson, Glum, and Rosenblatt (1955) argued that "motion perspective" provided "a basis for the judgments required for the control of locomotion" (p. 385). Motion perspective refers to the flow of texture elements within the optic array of a moving observer. The research reported here focused on one aspect of the visual control of locomotion-regulation of altitude. Two sources of information within the optic array were examined: optical splay angle and global optical density (or optical depression angle). We begin by presenting an analysis of the optical geometry to show the linkage between altitude and optical splay angle and optical depression angle. Next, we review previous research where there is currently debate about the relative efficacy of these two sources of information. We then present two empirical studies that examined these two sources of information in an altituderegulation task. Finally, we attempt to integrate our results with those from previous studies and discuss the theoretical and practical implications. OPTICAL ANALYSISThe term optical splay was introduced by Warren (1982). Warren cites Biggs (1966), who noted that when an observer maintains a constant distance to a line on the ground plane (e.g., the curb of the road), despite the shifting optical positions of the individual points composing the line, the optical position of the line was invariant. For a straight line parallel to the direction of motion, the invariant optical position can be defined in terms of the angle at the vanishing point formed by the line and a second line perpendicular to the horizon along the ground trace of forward motion, as shown in Figure 1. Thus, it can be defined by the equation:where S is the splay angle, Y I is the lateral displacement of the line from the perpendicular, and z is the altitude (eyeheight) of the observer. This equation describes the projection onto the f...

We examined the ability of younger and older adults to selectively process moving items and ignore stationary items in a task that required the search for a target defined by a conjunction of movement and form (i.e., search for a moving X among moving Os and stationary Xs) in displays of 5, 9, 17, and 25 stimuli (Experiment 1) and displays of 5, 10, and 20 stimuli (Experiment 2). We also investigated subjects' performance in two feature search tasks, the search for a target defined by movement or form. Finally, we examined the influence of practice on feature and conjunction search. Younger and older adults searched the displays at similar rates in the feature and conjunction search tasks. Older and younger adults also benefited equivalently from practice. These data suggest age-equivalence in the processes which underlie feature search in dynamic environments as well as those processes responsible for the segregation of moving and stationary objects in the visual field.

Gibson (1966Gibson ( , 1979suggested that an important property of perception is that the observer is active. Two experiments were conducted to examine the benefits of active observation in determining dynamic spatial orientation. Subjects were presented with displays simulating locomotion through a three-dimensional environment. Active observers continuously controlled locomotion, whereas passive observers viewed the display. During the trial, the display was blacked out for a brief period, followed by a static image that was at either the correct or the incorrect orientation following the blackout. Subjects were required to indicate whether they were positioned at the correct extrapolated orientation. The presence or absence of orientation change, the type of change (changes in rotation about the depth axis [roll], horizontal axis [pitch], or forward translation), the duration of the blackout, and the consistency of change were varied. In addition, the experiments used either a compensatory or a pursuit tracking task Active observers had greater sensitivity than did passive observers in detecting a change for both tracking tasks. Subjects in both experiments exhibited greater sensitivity in detecting inconsistent changes (relative to consistent changes), suggesting that the dynamics specified by optical flow were incorporated in extrapolated orientation. In addition, sensitivity decreased with an increase in blackout duration. The results are discussed in terms of an extrapolation model of perception that incorporates the responses executed by active observers. 533An important characteristic ofthe ecological approach proposed by Gibson (1966Gibson ( , 1979 is that perception involves an active observer. According to Gibson, the observer is not a static organism in the environment but rather is engaged in action. Stimulation of the organism is obtained during action and not simply imposed on the organism by the environment. Gibson (1966, p. 31) further argued that action, and its effect on stimulation, can be considered as "a loop from response to stimulus to response again." This description captures the dynamic nature of control and perception that has typically been