Effects of Symbol Size and Workload Level on Status Awareness of Unmanned Ground Vehicles.

摘要

The objective of this study was to determine which size symbols should be used by the U.S. Army for an operator control unit to indicate the status of unmanned ground vehicles (UGVs). Twelve participants were asked to watch the symbols on a map display and touch one of four UGV symbols when it stopped moving. Different numbers of distracter symbols with the same height as the UGV symbols appeared during the experimental trials. The time to notice that a UGV symbol had stopped (recognition time) and to touch the screen (response time) were measured. Participants were asked for Subjective Workload Assessment Technique (SWAT) ratings for each combination of symbol size and number of distracter symbols. Errors committed while attempting to touch the correct symbol were counted. Results for the time and error measures were as expected for changes in symbol size. As symbol size increased, recognition time, response time, and extra touches decreased. Significant differences were seen in these measures. Also, as expected, subjective mental workload increased as symbol size decreased, with differences seen between all symbol size levels. No significant differences were observed for workload manipulation (number of distracter symbols) as measured by time and error. However, SWAT scores did show a significant difference as a result of number of distracters. The differences between 0 and 8 distracters and between 0 and 12 distracters were significant. There was no significant interaction between symbol size and number of distracters for any of the measures. Overall results suggest that symbols smaller than those recommended for keypads may be sufficient for interactive map displays. For static platforms with bare-handed operators, symbols that subtend 40 minutes of arc may be sufficiently large to ensure adequate touch screen performance under low to moderate workload conditions.