Week 9 - attention and workload Flashcards
define workload
Mental workload (referred to as just workload) is a general term used to describe the cost of accomplishing task requirements
what does workload depend on?
1- Workload varies as a function of the task demands
placed on the human operator
2- The operator’s capacity to meet those demands
what are three task demands
1- task difficulty
2- task priority
3- situation
define operator capacity
- each operator has a supply of mental resources
- mental resources are limited in supply eg memory, planning, decision making
- Task performance generally improves as resources are directed to it
- Resources that are unused are referred to as ‘spare
capacity’
overload vs underload
- Generally, the focus is on the detrimental effects of overload (e.g. excessive workload)
- However underload (e.g. sustained low workload) is
just as much of a problem
what does underload cause
(1) Increased fatigue
(2) Lower task engagement
(3) Lower vigilance
(4) Generally reduces operators capacity to deal
with the unexpected (spare capacity)
what are three reasons to why you measure workload
Workload prediction • To maintain workload within acceptable limits Equipment assessment • Optimize the system to suit operator Choose the right operators • Employee selection or further training
explain workload prediciton
Safety • Often relies on predicting workload ahead of time • When will an operator struggle? Change management: • Know in advance what effect changes will have
explain equitment assessment
Designers may want to know what workload will be at
the design, production, or usage stages
• Identify problem areas where performance may
decline
• Compare workload between multiple systems
explain choosing the right operators
- Equipment design focuses on controlling task demands, but operator selection focuses on controlling operator capacity
• Can train to improve some capacity, but only up to a
point (and it may not be cost effective)
what are three major categories of workload measures?
- Performance
- Subjective
- Physiological
what are two ways performance can be divided into?
- primary task measures
- secoundary task measures
what is primary task performance advantages
• Workload reflected directly by performance outcome
• Non-invasive and non-interfering
• Tracks changes in workload dynamically. (i.e., as
performance proceeds)
• Uncontaminated by memory issues
what is primary task performance disadvantages
• Mental workload is not the only thing that can
influence performance
• Doesn’t take effort into account
• Might not always have the technology or interface
available to monitor performance
what is a secondary task purpose and what does it measure?
- To measure the spare capacity not being
used by the primary task
• Usually, an increase in primary task workload is
associated with a decrease in secondary task perf.
• Potential measures including: Rhythmic tapping task, Probe reaction tasks, Auditory monitoring
what is secoundary task performance advantages
• The same secondary task can be used with very
different primary tasks
• There are a collection of available (and validated)
secondary tasks
• Provide a measure of space capacity
• Useful when there is little primary task data available
(e.g. monitoring jobs, baggage scanner)
what is secoundary task performance disadvantages
• Only relevant when secondary task taps into the
same resources as the primary task
• It adds in another task to the work environment (could increase workload)
• Can interfere/interrupt primary task
what are subjecive measures
Where you ask someone to quantify their personal experience of workload • Dimensionality (single or multiple) • Evaluation (absolute or relative) • Immediacy (when queried?)
what is an example of a subjective measure
NASA Task Load Index (NASA-TLX
what are advantages of subjective measures
• Cheap and simple to administer
• No need to interfere with primary task
• Reasonably good reliability and validity
• NASA-TLX has a huge literature available for
comparison
what are disadvantages of subjective measures
- People aren’t always aware of workload
- People find it difficult not to baseline their workload
- Not sensitive to moment-to-moment changes
what are physiological measures
• The assumption is that biological functions can reflect mental work done. • Popular measures include: - Cardiovascular - Ocular - Brain activity
explain cardiovascular physiological measures
- Heart-rate variability shown to increase with workload
- Particularly relevant to emotional stress
- Potential issues:
- Need to establish a baseline
- Quite a range due to individual differences
- Only sensitive when stress is involved
explain ocular physiological measures
• Pupil diameter increases with workload
• Visual scanning patterns and pathways change with
workload
• Length of time spent fixating on items changes with
workload
explain brain activity physiological measures
• It is intuitive that brain activity will reflect mental workload
• Brain activity sensitive to different kinds of cognitive
demands (e.g. memory, vigilance, flexibility, etc.)
• Measures: Electroencephalogram (EEG), Eventrelated potentials (ERP), and Cerebral blood flow
advantages of physiological measures
- Provide a relatively continuous measure over time
- Objective
- Many different techniques available
disadvantages of physiological measures
- High cost
- Often obtrusive
- Cannot be used to determine how the operator feels about the task (can be important)
Explain attention in mutiple resource theory
• Can be directed voluntarily
• Attending to one thing often excludes others from
processing
• Can be divided, but not without cost
Explain resources in multiple resource theory
- A general term covering resources used to perform a task
* From the lecture on errors:
why do errors occur in mutpile resource theory
- Selective attention
- Working memory capacity
- Long term memory limited on storage and retrieval
- Decision-making biases
what is multiple resource theory
- There is a common, finite pool of resources that can be
flexibly allocated to tasks - Allocating more resources to a task speeds up the rate of
processing of that task - The quantity of resources made available can be increased or decreased
what happens if two tasks are similar - multiple resource theory
- If two (or more) tasks are similar they will draw on a
common resource pool
• This will affect performance negatively - If the two (or more) require different resources, then
performing the tasks at the same time will have little
negative consequence
Stage 1- Stages of processing (MRT)
1- perception
2- cognition
3- response
Stage 2- Codes of processing (MRT)
- spatial
- verbal
Stage 3- Modalities (only relevant for perception stage):
- Auditory perception (e.g. listening to radio)
* Visual perception (e.g. looking for a sign)
Visual channels (only relevant in visual modality)
- Focal channel (focus of attention, e.g. car in front)
* Ambient channel (peripheral vision, e.g. cars on either side)
what three resources do you need to drive safetly
- cognitive
- manual
- visual
what are the 4 stages resources can be shared across
1- stages
2- codes
3- modalities
4- channels
define interruption
An interruption involves the primary task being suspended
while the secondary task is completed
define distraction
A distraction (or multi-tasking) is performing both at the same time (or more accurately, rapid task switching)
what are the costs of an interruption
• Memory: We form PM intentions when interrupted, and these degrade over time
• Warning: Sometimes there is little/no time to form intention
• Duration: Length of interruption, frequency of
interruptions
• Content: Interruptions more disruptive if similar
what is a prospective memory requirement (PM)
- holding an intention is costly
- the longer you have to hod it the poorer the retrieval
- Primary task performance slower and less accurate (i.e. more errors) when primary task is resumed
how to solve the problem
- Aiding the Interrupt task alert stage: Provide information about the urgency of the interruption
- Aiding the Disengagement stage: Reduce the to-be-remembered information load
- Aiding the Resumption stage: Upon resumption, use memory aids created
