Measurement of Mental Workload Associated With Agricultural Spraying

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Measurement of Mental Workload Associated With
Agricultural Spraying

• Asit K. Dey and Danny D. Mann

Department of Biosystems Engineering University
of Manitoba
Winnipeg, MB R3T5V6
Prepared for 2008 Annual Meeting of CSBE,
Vancouver, BC, 13th -16th July
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Two Major Tasks of Agricultural Spraying

• Task 1 Steering a sprayer along a predefined
  path in response to a navigation device (PT)

Predefined Path
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• Task 2 Monitoring and controlling the rear-
• attached boom (ST)

Joystick
Boom
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Key findings of our previous study

• Agricultural spraying is a dynamic dual task
  (i.e. driving and monitoring) conducted under
  day, dusk, and night illumination levels.
• A sprayer operator sprays 16.5 h in a day that
  includes all the above changing environments.
• Moreover, various terrain conditions (i.e.,
  rolling, flat, or field with obstacle) imposes
  additional difficulty.

Dey, A and D. Mann. 2008. A complete task
analysis to measure the workload associated with
operating an agricultural sprayer equipped with a
navigation device. Submitted to Applied
Ergonomics.
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Key findings of our previous study (contd.)

• Most of the sprayer operators use a GPS lightbar
  to guide the sprayer along a pre-defined path.
• The modern cabs are equipped with a mapping
  display, application display, entertainment unit,
  and two-way radio communication unit.

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• Event detection and driving performance degrades
  whenever new information cues are introduced in
  the operators cab (Boer 2000).
• Degradation in driving performance will result in
  more skips and overlaps of crop inputs.
• Degradation in event detection may be linked to
  the safety of the operators.

Boer, E.R. 2000. Behavioral entropy as an index
of workload. In Proceedings of the IEA 2000/HFES
2000 Congress, 3/125-3/128, San Diego, CA.
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• The degradation of the driving performance can be
  minimized and operators comfort and safety can be
  enhanced by approaching a human centric design.
• The study of mental workload helps us achieving
  the above goal.
• Till today, there is no published literature that
  explored the effect of illumination, terrain
  difficulty, and task levels on the mental
  workload of an agricultural sprayer operators.

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Mental Workload

• Definition The proportion of mental resources
  invested to meet task demand.
• Excessive workload can affect selective
  attention, lead towards in-efficient sampling,
  and results in poor performance.
• Therefore, the role of a design engineer should
  be to keep the mental workload in an optimum zone
  below the workload redlines.

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• To investigate the effect of illumination (day
  and night), difficulty (low and high), and task
  levels (Single vs. Dual) on the mental workload
  of agricultural sprayer operators guiding a
  sprayer in response to a GPS lightbar.

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Agricultural Driving Simulator

• The participants drove a fixed-base agricultural
• driving simulator in response to a red commercial
  lightbar.
• The simulator was equipped with a torque and
  visual
• feedback unit

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• Participants
• 16 male university graduate students.
• Age Group
• lt25 (8), 26-30 (2), 31-40 (3), 41-60 (3)
• Training participants were trained to drive the
  above tractor simulator.

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Mental Workload Measurement

• Mental workload was measured by
• Driving performance lateral root mean square
  error (cm).
• Monitoring Performance Reaction Time (s)
• 0.1 Hz power of hear rate variability (a.u.)
• Dynamic Spectrogram
• P300 latency (s)
• Eye-glance behaviour ( time spent)
• NASA-Task Load Index and Simplified subjective
  workload assessment technique (SSWAT) (a.u.)

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Experimental Design
5 min
5 min

• Each participant received 12 randomized sessions.
  
• The experimental time was 3 h/participant.

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Percentage change in workload measures due to
change in illumination and difficulty levels
Da day, N night, L low, and H high
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Percentage change in workload measures due to
change in task levels
PT primary task, ST secondary task, DT dual
task, n.a. not applicable
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Percentage of time spent looking at various
sectors (outside, lightbar, left boom, right
boom) for day (DA) and night (N) illumination,
and low (L) and high (H) difficulty levels under
driving only condition
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Percentage of time spent looking at various
sectors (outside, lightbar, left boom, right
boom) for day (DA) and night (N) illumination,
and for low (L) and high (H) difficulty levels
under monitoring only condition.
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Percentage of time spent looking at various
sectors (outside, lightbar, left boom, right
boom) for day (DA) and night (N) illumination,
and for low (L) and high (H) difficulty levels
under dual task condition.
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Fig. 7. Dynamic spectrogram of average HRV data
under driving only (PT), monitoring only (ST),
and dual task condition (DT) for low (L) and High
(H) difficulty levels, and day (DA) and night (N)
illumination levels. PTDAL driving only task
under day driving and low difficulty levels.
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Conclusions

• The performance measures, P300 latency,
  subjective rating scales showed a trend that
  night illumination was more demanding. The main
  effect of illumination was significant for P300.
  
• Similarly, the above measures showed that high
  difficulty was more demanding. Only the P300 and
  SSWAT was able to differentiate between low and
  high difficulty at plt0.05.
• The 0.1 Hz HRV data showed driving under day
  illumination or under low difficulty were more
  demanding.

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Conclusions (contd.)

• Spectrogram showed that PT and DT under day
  driving, and ST under night driving was more
  demanding. Moreover, low difficulty was more
  demanding than day driving.
• All the measures significantly revealed that the
  dual task was more demanding than single task
  level.
• Under any illumination, difficulty, or task
  levels (except ST), participant spent more time
  looking at the lightbar. Therefore, lightbar is
  an important source of guidance information.

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• U of M Graduate Fellowship
• Department of Biosystems Engineering of the
  University of Manitoba.
• Participants

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Thank you