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L9: Attention & Workload (What is Workload? (Underload Effects…
L9: Attention & Workload
Understanding Attention and Workload in the Workplace
Problematic Workload Levels due to
Poor physical and mental design
Physical task design limitations (mismatches)
How Workload is Defined
Operator's interaction with a task > mentally
Not very visible > so we want to observe
Importance of Workload**
System Safety
Productivity
Impacts worker health
Cost
What is Workload?
Operator's Capacity (internal)
Mental Resources
(controlled by attention / extra MR = spare capacity)
Task Demands (external)
Divided Attention*
Extra task > similar resources shared by other task > performance decreases
Mental Resources: visual, manual, cognitive
Workload = Task demands + operator's capacity (attention mediates MR)
Operator capacity determined by > mental resources > mediated by attention
Task demands moderated by > situational factors
Underload Effects
Fatigue ^
Task engagement v
Vigilance v
Operator's capacity v (underload = spare capacity v)
Why Measure Workload?
Answers range of work design questions
3 Objectives for Measuring
Equipment Assessment
(optimise task demands)
Choose the Right Operators
(operator capacity - select for training to improve)
Workload Prediction
(workload acceptable limits)
WORKLOAD MEASURES**
Subjective Measures
(personal exp of WL)
Useful variables to
categorise
different rating techniques
Evaluation (absolute / relative)
Immediacy (interval asked)
Dimensionality (single / multiple)
NASA Task Load Index
(NASA-TLX)
Advantage
No interference
with pri task
Good reliability + validity
Cheap + simple to use
Huge literature
for comparison (NASA-TLX)
Disadvantage
People
aren't always aware
of WL
People find it difficult to not baseline WL (order of
exp diff for diff
ppl)
Not sensitive to moment-to-moment
changes
Alt Measure: Air Traffic Workload Input (ATWIT)
1 to to 10, how hard are you working (easy + quick to use in-between)
Physiological Measures
Ocular (pupil dilate)
Brain Activity
Event-related Potential (ERP) (distraction)
Cerebral Blood Flow (task demand)
Electroencephalogram (EEG) (attention)
Cardiovascular
Advantages
Objective
Many diff techniques available
Relatively
continuous
measure
Disadvantages
High cost
Obtrusive
> affects performance
Cannot
determine feelings
about the task
Performance Measures**
Secondary Task
(not work relevant - spare capacity)
Advantage
Collection of validated sec tasks available to use
Measures
spare capacity
/ good for lack of pri task data
Secondary task can be applied to other primary task (versatile)
Disadvantage
Increases workload
by adding extra task
Can
interfere
with primary task
Relevant if sec task + pri task >
share same mental resources
Primary Task
(work relevant - performance)
Advantage
Non-invasive and non-interfering
Tracks workload
dynamically
Workload
reflected directly to performance
outcome
Uncontaminated by memory
issues (e.g. questionnaire)
Disadvantage
Doesn't take
effort
into account
Might not have technology
available to monitor performance
Mental workload
isn't the only
influence on performance
Important Notes for Research
Dealing with High WL
Performance can degrade if safe to do so
Shed low priority tasks
Efficiency > mental shortcuts = less MR demand
Summary of WL Measures
Dealing with Low WL
Rmb consequences (vigilance, boredom, fatigue)
Implications in automation systems
Increased WL isn't so bad
Optimise Operator WL