Workload
I. Key Ideas
A. Humans have limited capabilities; when the limits are approached, performance degrades
B. However:
1. Performance doesn’t always degrade
2. Sometimes performance (accuracy, speed) increases
C. Effect depends on:
1. Load on particular cognitive processes
2. Modality of input and output
3. Motivation
4. Experience
II. Research Paradigms
A. Observational
1. Observe work, correlate errors with task load
2. NASA TLX is common measure
B. Single task
1. Measure performance on task (accuracy, speed)
2. Add load (items, complexity)
3. Measure performance under added load
C. Multiple task
1. Measure performance on primary task
2. Add secondary task
3. Measure performance on both tasks
III. Multiple Resource Model
A. Workload induced performance degradation depends on:
1. Stages of Processing
i. Perception
ii. Attention – central, peripheral
iii. Storage – SIS, STM, LTM
iv. …
2. Codes of processing
i. Auditory
ii. Visual
iii. kinesthetic
3. Input/output modalities
i. Visual
ii. Auditory
iii. Motor
iv. Speech
IV. Analysis by Stages of Processing
A. Attention
1. To avoid requiring more attention than available, present some information visually, some aurally
i. EGPWS (Enhanced Ground Proximity Warning System)
a. Visual presentation of terrain
b. Aural alert when needed: “Terrain, terrain”
ii. TCAS (Traffic Collision Avoidance System)
a. Visual presentation of traffic
b. Aural alert when needed: “Climb, climb”
2. Problem:
i. Attention-grabbing devices can attract attention when it is needed elsewhere.
ii. Need to allow central executive to function once alerted
iii. So build in ability to silence alarms
iv. Pilot isolate switch to avoid distractions
3. Task switching
i. Switching costs
a. When one must perform multiple tasks in quick alternation (e.g., fly aircraft, navigate, solve problem) performance on each task may degrade due to:
b. Prospective memory failures
· Failing to remember to do something
ii. Task Prioritization
a. Central executive function – attend to one task instead of another.
b. Standard pilot prioritization sequence
· Aviate
· Navigate
· Communicate
B. Storage
1. SIS – Sensory Information Store
i. Iconic storage of sensory information
ii. Very limited storage; easily replaced by new information
iii. Example of pattern mask from laboratory research
2. STM – Short Term Memory
i. Limited capacity; 7 +/- 2 items (Miller, 1956)
ii. Somewhat separate capacities for:
a. Visual/spatial information (sketch pad)
b. Verbal/auditory memory
3. LTM – Long Term Memory
i. Once in LTM, no known capacity limitation
ii. However, “exponential” forgetting curve
iii. Need repetition / use to retain information
4. Encoding Effect
i. Meaningless information must be coded in smallest unique chunks
ii. Meaningful information can be remembered as link to LTM and provide ready access to much more information than can be held as chunks in STM
iii. Application: Expertise can shift resource requirements
iv. Approach clearance
a. “United 123: 5 miles from FRAKK. Turn right heading 180, intercept the localizer, maintain 2000 until established. Cleared for the ILS 16R approach. Contact tower on 118.9.”
b. Very difficult to hold this much information in memory as separate chunks. With experience, pilot can remember large quantities because items are meaningful.
c. Of course, can (should) write it down!
V. Summary
A. Workload is a function of task demands on particular cognitive functions
B. Workload that can be handled will vary on distribution of demands across cognitive functions.
C. If task requires excessive demands on a particular function, performance will degrade
D. However, if task demands are distributed across cognitive states, increased work can be sustained without performance loss
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