| The first of the four objectives of the present study was to conduct a complete task analysis in order to document the tasks and associated workload as experienced by the operator of an agricultural sprayer equipped with a lightbar navigation device. Task analysis result showed that, on average, an operator sprays on different terrains for 15 h in a day which includes day, dusk, and night illumination. Moreover, lightbar and aiming cues were important sources of guidance information. The second objective investigated the change in mental workload while guiding a sprayer in response to a GPS lightbar under day and night illumination, low and high task difficulty, and three task levels (driving only, monitoring only, and dual task). Sixteen male university students were trained to drive a fixed-base agricultural driving simulator. Mental workload was measured by performance measures, physiological measures, and subjective rating scales. All the performance measures, the P300 latency, and subjective rating scales showed that mental workload increased significantly with the change in illumination from day to night, task difficulty from low to high, and task types from single to dual. Under night illumination, participants spent more time looking at the lightbar for guidance information. The third objective investigated the sensitivity and diagnosticity of three different variants of NASA-TLX and five different variants of simplified SWAT scale to assess the mental workload associated with agricultural spraying. The discrete variants of SSWAT showed highest sensitivity and diagnosticity, but also higher between-subject variability. The continuous variants of both scales had less sensitivity and diagnosticity, but also lower between-subject variability. Thus, the selection of a scale was a function of sensitivity, diagnosticity or between subject variability. The fourth objective evaluated the mental workload associated with operating an agricultural sprayer in response to a commercial GPS lightbar (LBR), a mapping display (MAP), and an integrated display (INT). The performance and physiological measures showed that the LBR display induced less mental workload followed by INT and MAP. Subjective rating scale showed an opposite trend due to the differential task engagement with various displays. Therefore, the MAP display should not be used as the sole guidance aid. |
