Automation Technology and Human Performance: Current Research and Trends

By Mark W. Scerbo | Go to book overview

The Influence of Ascending and Descending Levels of Workload on Performance

Brooke Schaab U.S. Coast Guard Research and Development Center


INTRODUCTION

The influence of varying levels of workload on performance has been a prevalent topic in human factors and information processing research. The seminal law of Yerkes-Dodson proposed that both high and low levels of perceived stress degrade performance, with optimal performance occurring at some intermediate level. The findings reported in this study were obtained when a task was counterbalanced between increasing and decreasing levels of workload experienced during a simulated air traffic control task. It was found that performance differed depending upon whether participants experienced increasing or decreasing levels of workload.


TASK DESCRIPTION

Ninety-six undergraduates simulated radar "spotters" in a surveillance aircraft. Their task was to monitor a computer display and identify aircraft in the area as a "friend" or an "enemy." A representation of the task is presented in

Figure 1
. The center of the computer screen displayed a small red circle representing an aircraft carrier. Black squares, representing aircraft, traveled toward the carrier at a speed of .5 mm/sec. Participants used a mouse to click on these "aircraft." This produced a display box on the screen with four pieces of information: type of aircraft (Jet or Prop); altitude; speed; and identification number. The order of the information remained constant. The participant's task was to use either one, two, three, or four pieces of the information displayed to make a decision on whether the aircraft was a "friend" or an "enemy." For each participant the number of pieces of information used to make a decision (one, two, three, or four) remained constant throughout the task. A copy of the criterion used to make the decision and identify the aircraft was permanently displayed. The number "1" key was pressed if the criteria were met for identifying an "enemy." If the criteria were not met the number "2" key was pressed. Each respondent was exposed to 4, 8, 12, and 16 aircraft that were displayed on the screen for 3 min each, and the number of aircraft were presented in both ascending and descending order for every participant. The order, ascending or descending, was counterbalanced. After 12 min the participants experienced all 4 levels of the number of planes displayed (4, 8, 12, and 16 or 16, 12, 8, and 4). They took a short break and completed the NASA- TLX. The last 12 min of the task repeated the first but the number of aircraft on the screen was presented in reverse order. The TLX was readministered at the conclusion of the last 12 min segment.

Increases in workload were produced through the addition of the number of planes that required monitoring (within subjects). Information load was manipulated by increasing the number of criteria used for identifying the aircraft as "friend" or "enemy" (between subjects).


RESULTS

Significant order-by-number of planes-by-half interactions were found for the number of planes acquired (F(3,240)=92.31,p<.01); the number of planes acquired and identified correctly (F(3,240)=64.48, p<.01); and reaction time (F(3,240)= 93.03,p<.01). Overall, performance improved when the number of planes displayed increased in ascending order (4, 8, 12, then 16 planes displayed), with more planes acquired with each increase, more identified correctly, a larger percent correct of those acquired, and a decrease in reaction time. Performance showed a similar pattern in the first and second half, although overall

-218-

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