Effects of warned and unwarned demand transitions on vigilance performance and stress

The present study was designed to explore the effects of warned and unwarned demand transitions in vigilance on performance and self-reported stress. Twenty observers (10 women and 10 men) were assigned at random to each of six conditions resulting from the factorial combination of signal salience (high and low salience signals) and switching (no switch, switch with warning, and switch without warning). Performance metrics and self-reported stress state (Task Engagement, Distress, and Worry) were collected. While demand transitions did destabilize subsequent performance, increasing intra-individual variability, overall performance efficiency was uninfluenced by either switching or warning. Demand transitions, whether warned or not, increased self-reported distress. A dynamic model of performance stress may be necessary and research employing vigilance tasks in the future may be useful for developing this performance-stress model.     

Face processing: Human perception and principal components analysis

Principal components analysis (PCA) of face images is here related to subjects’ performance on the same images. In two experiments subjects were shown a set of faces and asked to rate them for distinctiveness. They were subsequently shown a superset of faces and asked to identify those that had appeared originally. Replicating previous work, we found that hits and false positives (FPs) did not correlate: Those faces easy to identify as being “seen” were unrelated to those faces easy to reject as being “unseen.” PCA was performed on three data sets: (1) face images with eye position standardized, (2) face images morphed to a standard template to remove shape information, and (3) the shape information from faces only. Analyses based on PCA of shape-free faces gave high predictions of FPs, whereas shape information itself contributed only to hits. Furthermore, whereas FPs were generally predictable from components early in the PCA, hits appeared to be accounted for by later components. We conclude that shape and “texture” (the image-based information remaining after morphing) may be used separately by the human face processing system, and that PCA of images offers a useful tool for understanding this system.     

Influence of task demand characteristics on workload and performance

Two experiments are reported that examined the influence of variation in task demand on performance and workload. The first experiment considered how the manipulation of prior level of task demand affected subsequent workload and performance. The second experiment examined the effects on performance and workload of increments in the level of task demand. Results from the first study indicated that prior level of imposed task difficulty did affect response in a manner consistent with a scaling of workload in relation to previous task conditions. The second study demonstrated the primacy of absolute demand level over increments in that demand as influencing operator response. Overall, our results indicate that workload and performance are sensitive to multiple characteristics of the task and not instantaneous demand level alone. These findings are important in explaining why association and dissociation occur between task demand, operator efficiency, and perceived workload in differing performance contexts. The importance of these findings for the aviation psychologist in assessing pilot and operator workload is articulated.     

Performance, workload, and fatigue changes associated with automation

The experiments discussed in this article addressed the influence of part-task automation on operator performance, workload, and fatigue in a multitask environment. The overall task environment included tracking, resource management, and multiple monitoring subtasks. Slower, more accurate monitoring and better resource management were observed when the tracking subtask was automated. Although lower workload was reported when tracking was automated, fatigue increased equally during periods of manual and automatic tracking. When participants could control workload by shifting between manual and automatic tracking, participants with 7 hr of training switched between automatic and manual tracking. Their performance during optional automation periods was superior to their performance in conditions in which only manual control or only automated control was available. The findings argue for the utility of discretionary control of automated systems.     

A note on the speed-amplitude function in movement control

An experiment is reported that documents the maximum average speed-amplitude relationship across the full range of motion for elbow flexion. Minimum movement time increased as a negative exponential within the movement range up to 94-97% of the maximum range of motion. At this point a discontinuity occurred with movement time increasing at an increasing rate probably due to anatomical and morphological constraints. These results suggest that the maximum average velocity-amplitude boundary to the movement speed-accuracy relationship is curvilinear. Kinematic analysis of the movements as a function of range of motion suggests that a simple pulse-step model of movement control cannot account for the present findings.     

Some variables affecting rate of key pecking during response-independent procedures (autoshaping)

Rate of key pecking by pigeons subjected to response-independent procedures in which a stimulus on the response key preceded food presentation was investigated in eight experiments. Color and shape of the stimulus, duration of the stimulus, probability of food following the stimulus, duration of the intertrial interval, and duration of food presentation were varied separately and in combination. All variables studied, except color and shape of the stimulus, had a reliable effect on pecking rate, but some variables had stronger effects than others. Rapid key pecking may be obtained with a variety of response-independent procedures, as well as by response-dependent reinforcement. The results of experiments in which food is both dependent on key pecking and correlated with stimulus conditions are not representative of simple operant effects. Key pecking is an ideal response for studying the simultaneous operation of response-reinforcer and stimulus-reinforcer effects.