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Psychophysiological Methods
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Electrodermal Measurement
Galvanic skin response as indicative of the sympatheticbranch of the autonomic nervous system
Sweat glands provide a shunt between skin and deepertissues
Measures indicative of arousal, stress-strain, andemotion
Autonomic habituation provides a physiological measureof information processing capacity needed to complete a
task Used as measure of workload, mental strain, andemotional strain.
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Procedure
Sampling across various locations of the body
Typically 3-4 cm distance between electrodes
sampling dc current using a bioampifier
Sampling at 20hz sufficient to calculate SkinConductive Response (SCR)
Amplitude, rise time and recovery time are
measured May be used to determine tonic Electrodermal
Activity (EDA) to measure readiness for action
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Three-Arousal Method of
Measurement for the use of
Psychophysiology in Ergonomics
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Typical Epidermal Response
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Advantages/Disadvantages
Easy to measure and
interpret the physiological
signal
Pure measure of the
sympathetic branch of the
ANS
Sensitivity to workload
and emotional strain
Somewhat difficult to
record
Prone to artifacts in non-
laboratory settings
Indiscriminately sensitive
to any ANS activity
Several months of lab
training to be able to use
plus training for use in an
ambulatory setting
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Reliability/Validity
Short term reliability(within days) is fairly good(.80 to .90)
Longer term reliability is
more limited (.60) Tonic EDA more reliable
than SCL (test-retestcorrelations of .76 and.61 at one year)
Validity at or above .90for EDA-Emotionalstrength in LAB setting
No similar data for
applied settings Validity based more on
strength of emotionrelated to strain thanphysical relationship
Heart rate and BP areyield better validity thanEDA (.68 to .86)
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Electromyography
Studies muscle function using electrical analysis ofsignals emanating at muscle contraction
Motor activity Anterior horn of the spinal cord, transmitted via alpha motor
neurons to muscle
Each muscle fiber consists of multiple chains of contractilesarcomeres (actin-myosin-filaments)
These filaments create muscle contraction
Motor unit chemically activates the muscle fibers connected asmyoneural junction is depolarized (amplitude of about 100mVwith a 2-14msec duration
Muscle action potential causes sarcomeres to contract
Electrodes in tissue or skin can measure these action potentials(electrolytic response)
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EMG (continued)
Muscle force defined by motor units activated
EMG forms a quasi-randomly shaped spikes ofamplitude and duration but no identifiable
sequence Correlation between number and intensity of
generation of amplitude spikes and musclecontraction force
Remember, doesnt measure force, joint positionbut rather voltage associated with local musclerecruitment
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Use of EMG in the Workplace
Used for workplace and tool design
Muscle load (static and dynamic)
Local muscle fatigue due to overload
Muscle timing and coordination Motor-unit recruitment
EMGs complemented by use of measures of
external load, body posture, joint measurement
EMGs can be performed with needle electrodes
inserted into muscle or surface electrodes
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Procedure
Placement of electrodes or needles in muscles,signal passed to preamplifier, processed withband-pass filters for frequencies related tomuscular activity
Select muscles related to action (may depend onhow specific you want to be measuringpotential between muscle and ground
Amplify, filter and store results Signal Processing
Scaling
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Surface EMG Signal Processing
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Correlation between feedback control and
execution speed during learning an assembly task
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EMG Advantages/Disadvantages
Continuous and quantitativemeasured data
High temporal resolution withmarginal interference with taskexecution
Allows detection of muscle fatigue
at early stages providing objectivemeasure
Multi-channel EMG can identifymuscular bottle-necks
Surface EMG limited to musclesdirectly beneath area accessed byskin electrode
Only feasible for single muscles inindividuals not too obese
Requires careful calibration,
instrumentation, datamanipulation, and interpretation
Setup is fairly time consuming
Interpretation requires dataanalysis and data integration
Calibration lacks reliability
Requires individual calibration,poor reliability
Needle method more specific butinvasive and quite painful
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Heart Rate/Variability
Various Measures Electrocardiogram (ECG)
Duration between heartbeats (HR)
Mean heart period or Interbeat Interval (IBI)
Heart Rate Variability (HRV)
Normal Rhythm Cardiac Sinusoidal Mode Modulated by innervations from the sympathetic and parasympathetic
branches of the ANS
Heart Rate Controlled by nuclei in the brain stem and guided by the hypothalamus
and prefrontal cortical structures Two control modes Parasympathetic (Vagal) and Sypathetic output (Pores (1995))
Mediation of bororeflex activity
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Use of ECG
HRV related to changes inautonomic control
Vagal Gating
NSR is vagally determined
HRV and other cardiovascular
variables modulated bybaroreflex gain.
General cardiac responsefound in mental-effort studiescharacterized by increased HRand BP and decreased HRVand BP variability at allfrequencies
Compatible with fight-flightreaction (lab studies, short-lasting tasks, challengingmental operations in workingmemory.
Mid freq. band most sensitive
to variation in mental effort dueto decreased vagal activationand increased sympatheticactivation.
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Procedure
Three or 7 lead methods
Sampling and R-peak detection
Artifact detection and Correction Spectral procedures
HR, IBI or Normalized Values?
Logarithmic Transformation
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Disadvantages
HR and HRV used asindicators of mental effort Higher invested effort,
higher HR and lower HRV
Complex relationshipbetween HR withbaroreflex BP control andautonomous nervousactivity
Most stable results onlyreally found in labsettings
Restrictions in sensitivity
for artifacts in obtainedIBI series and sensitivityfor changes in respiration
Artifact correction timeconsuming
Newer technologies aremitigating some of theselimitations
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Reliability and Validity
R and V of HR and HRVin short duration mentalloading lab results usuallyhigh
Doesnt hold for practicalsettings
Diagnostic validity andreliability debated
Sensitivity of the measurenot very high
Difficult to distinguishlevels of task load and
related invested effort Requires multiple data
collection sessions onsingle subject
Validity affected by fight-flight mechanism versuscompensatorymechanisms
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Ambulatory EEG Methods
Sleepiness linked with accidents (Comair 5191)
Sleep loss, long time awake, work at circadian trough
of physiological activation and alertness, monotony
Effects of drugs, alcohol, sedative, hypnotics,antihistamines all can have an effect.
Concept of sleepiness (various components)
Subjective
Behavioral
Physiological
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Methods
EEG sum of electrical brain activity
Recorded at scalp or needle electrodes
When alertness falls, frequency of EEG falls
and amplitude increases as more neurons
synchronized to fire by the thalamus (rational
behind EEG indicator of sleepiness)
Progression from Alpha (8-12Hz) to Theta(4-8Hz) to Delta (0-2Hz)
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Procedure/Example
See text for in depth discussion ofprocedure for setup and use of EEG andEOG.
Example 12.1 shows EEG/EOG pattern insevere sleepiness performing a task anddemonstrates beta activity, increasedalpha activity, eye closure, slow eye rollingmovements, and dozing off, reappearingbeta activity, return of eye blinks
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EEG/EOG Recording
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Application/Training
Application takes 15-30 minutes minimumfor electrodeplacement
Learning to setuptakes 10-20 hours forreliable recording
Scorring takesseveral months tolearn
Requires repeatedquality checks
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Reliability/Validity
No formal reliability
established for
ambulatory EEG methods
Hard to define due to the
definitions of the
measures and the
changing nature of the
measure
Several studies have
defined validity between
subjective sleepiness and
sleepiness-impaired
performance
Purposeful interaction
with the environment not
possible when EEG
dominated by alpha/thetaand slow eye movements
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Event Related Potentials (ERPs)
ERP Transient series of voltage oscillations
Recorded from the scalp
Response to direct stimuli and responses
Often defined in terms of polarity and minimumlatency with respect to discretestimulus/response
Found to reflect perceptual, cognitive, motor
processes Useful to decompose processing requirements
of complex tasks (Fabiani et al., 2000)
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Procedure
Experimental paradigm design
Subject preparation
Preparation of ERP data for analysis Component definition and pattern
recognition
Data analysis
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Advantages/Disadvantages
We possess
understanding
concerning functional
significance of different
ERP components Brain regions from which
component generated are
known
ERPs can be obtained inabsence of operator
action/performance
Motion artifacts
Require discrete stimulus
or response
Substantial training
required for recording,
analysis, interpretation
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Sample ERP Outputs
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Training/Application Times
Depends on whether
you want to learn the
basics (2 months) or
becomeknowledgeable about
the basis of ERP
signals (advanced
degree)
Application times from
15min for a few
electrodes to 45min
for large electrodearray
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Reliability/Validity
Validity of ERPcomponents tospecific cognitiveconstructs
convincinglydemonstrated
Reliability establishedthrough extensivereplications
Split-half reliabilityhigh for P300amplitude (.92) andlatency (.83)
Test-retest reliabilityover several days forP300 amplitude .83and P300 latency .63
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EEG/MEG/fMRI
Neural activity generates currents outsidethe skull which can be monitored by theirelectrical and magnetic fields
Electroencephalogram (EEG) Magnetoencephalogram (MEG)
Magnetic Resonance Imaging (MRI)
Functional MRI (fMRI)
Provide a basis for examining the neuralsubstrate of specific cognitive processes
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Research Areas amenable to MEG & fMRI
Movement-related brainactivation
Memory processes (encoding& retrieval)
Visual perception, attention, &
selection Auditory perception, attention
& selection
Language production andprocessing
Perception of music Learning and brain plasticity
with respect to cognitivefunctions
Uses
Neurosurgery
Localization of epileptic focibased on specific brain areasspiking
Estimation of the impact ofcertain lesions on higherneural functioning
MEG preferred for temporalresolution; fMRI for spatialresolution; and maximum
information when/where thetwo methods can be combined.
Limited to patients withoutferromagnetic inserts
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MEG/fMRI Mechanisms
Requires use ofsuperconducting quantuminterference devices(SQUIDs)
Exploit quantum
mechanical Josephson-effect
Modern MEG systemsmonitor signals from 150-300 SQUIDs spread
equally over the headsurface
Variants of MEG sensorsknown as Gradiometers
Spin tilt of protons alignedwith strong magnetic fieldis pertubated by a briefelectromagnetic pulse
Protons emit burst of RF
energy as they return totheir initial aligned state
Strength of signal withparticular RF signatureallows determination of
proton density Helps define tissue
characteristics at thatlocation
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Procedure (MEG)
Helmet like gantry
placed over subjects
head
Coils fixed on headprovide weak
magnetic sources
known as anatomical
sites.
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fMRI
Subject reclined on
movable gantry,
shifted into the bore
of a magnet. Structural scan
Repeated functional
scans
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Experimental Setup
During session, sequence of visual or auditoryor other sensory stimuli is presented to thesubject who has to process them according to apredefined task.
Often the same or similar stimuli are presentedwith slightly different task requirements
Differences between the BOLD responses in thedifferent experimental conditions are evaluatedto determine what brain regions are specificallyactivated by a particular task or sensory input
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MEGData Analysis
Event-locked epochs initiallyaveraged separately for eachsubject, channel (sensor), task,or condition
Epochs containing artifacts are
rejected or correlated Grand average waveforms are
scanned for components(peaks/troughs)(50-100msec)
Time/amplitude measurementsdetermined for eachcomponent, task, subject.
Statistical analysis to ascertainsignificant differences whichare localized to a region of thebrain
Various co registration
techniques possible usingnonlinear parameters,algorithms from chaos theory
Analyzing continuous MEGdata is based on chaos theoryand beyond the scope of this
class
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fMRI Data Analysis
Continuously recordedfMRI/BOLD data sortedaccording to differentstimulus/task condition
Any distortions arecorrected by a processingalgorithm.
Those functional imagesshowing significant
differences in activationlevels at the level of theindividual voxels
fMRI permits singlesubject statistical analysisdue to better signal tonoise ratios
Comprehensiveevaluation packages areavailable Statistical parametric
mapping (SPM) package
Also advanced applicationsthat deconvolve temporallyoverlapping BOLDresponses
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Sample MEG Data
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Sample fMRI Data
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Training
Predefined protocols performed by techs after two weektraining period
For more advanced/sophisticated applications, at leastone full time engineer or physicist should be available (6month training).
In clinical setting, support of a dedicated physician isrequired for data interpretation
Neuroscientists should have a sound background inexperimental design as well as neurophysiologicaleducation. Specific training per investigations being
conducted Joint program between Emory and Georgia Tech
provides degree and background in medical physics
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Test Times
Experimental run may require about 1.5
hours with 15 minutes additional subject
preparation
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MEG Reliability/Validity
MEG
Artifacts can be minimized but not eliminated
Raw signals, an experienced rater can
recognize these distortions Potential artifacts depend on s/n
Avoid misinterpretation of waveform
Reasonable solutions possible but not
foolproof.
Reliability and validity rely on usersexperience
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fMRI Reliability/Validity
fMRI Continuous maintenance should result in acceptable
raw images
Artifacts due to discontinuities in magneticsusceptibility can lead to low structural distortions andsignal loss
Easily detected but not readily corrected
Errors can be introduced to statistical analysis
Even with formal fMRI handling correct, erroneous
conclusions may be drown from data obtained usinginappropriate experimental designs
Reliability and validity of fMRI method also relies onuser experience
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Blood Pressure Measures
Strain affects mood and behavior
Performance and physiological effort have usedstrain analyses that are only psychological
Progress in ambulatory measurement hasallowed assessment of behavioral, emotionaland activational interaction with workload underreal work conditions.
Low strain load has been used to investigatelong term work (fatigue, boredom, vigilance) onhealth
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Ambulatory BP
Developed clinically to measure physical
work effects
Increased use for psychosocial work
characteristics
Use of portable recorders for non-invasive
recording
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Procedure
Procure ABPM Device
Select work analysis objective methods
Develop prequestionnaire about normal activities
Maintain diary
Prepare BP monitor
Fit monitor to subject
Instruct subject
Subject resumes daily routine
Remove BP monitor, collect diaries
Transfer data
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Requirements
Must have information about body position
and motor activity at time of measurement
Also should combine measurement with
psychological data
Must assess the nature of strain
Include measures of perceived mental
load, perceived control, mood, motivation
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Advantages/Disadvantages
Can simultaneously
record workload and
subjects strain
experience &behavior
Work-strain-related
effects on BP
recovery can beinvestigated and
assessed
ABPM can have an
artifact effect on daily
activity (Hawthorn
type effect) May have an effect on
subjects sleep
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Example of Recorded Data
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Training/Application
Investigator experienced
in principles of BP
measurement and
interpretation of readings
Main and artifactvariables on BP
Fitting takes 15-20
minutes
Subject instruction about
inflation/deflation of cuff
Instruct subject on need
for written diary
Removal done by
investigator with follow up
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Eye Blink Measures
Issues related to alertness/drowsiness Neurobiological products of interaction between
endogenous circadian pacemaker and homeostaticneed for sleep
Objective biobehavioral signs often require intrusivephysiological monitoring
Growing use of these measures as humanssubjected to 24 hour workdays
Technological improvements are making
measurement more affordable and lessobtrusive
PERCLOS
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Procedure
Use infrared, retinal reflectance monitor
Uses CCD camera to record eye closure
measurements in real time
General use of two cameras situated at 90degree angle
850-nm filtered bright eye camera and a 950-nm
filtered dark-eye (dark pupil) image
Calculate the changes in brightness of pupil
based on average brightness
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Sample Pupil Imaging
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Advantages/Disadvantages
Availability of on-line, near-real-time, automated sloweyelid PERCLOS systemunobtrusive to user
Ideal if used with preset
thresholds versus self-report Can be used as an
investigative and applied tool.
May not work in all situations(requires restricted FOV)
May create artifacts incompletion of task
Equipment may be too
obtrusive in mobile real-worldapplied environment
Not ideal in low humidityenvironments (not able todifferentiate moistening of eyesand fatigue based closure
Misuse in safety sensitiveenvironment may generaterisk.
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Training/Application
No training required
other than to teach
operator to interpret
feedback indicatingdrowsiness
Small, fairly easily
applied and useful in
many but not all
environments
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Reliability/Validity
Loss of alertness,
drowsiness, and
hypovigilance must be
theoretically linked to
performance deficits
Two levels of validation
Biobehavioral parameters
Specificity of biobehavioral
measure used
Both reliability and validitymust be established
across dynamic range of
performance
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Human Respiration
Respiration linked to a variety of functional
psychological dimensions
Response requirements
Appraisal patterns
Mental effort investment
Various dimensions of emotion
Affect Mood
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Respiratory Measures
Assessment of how depth and frequency
of breathing contributes to ventilation
Expressed as tidal volume
Frequency is respiration rate (BPM)
Measurement of parameters associated
with gas exchange
Breathing cycle
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Applications
Can be used with
verbal self report
related to work
Task demands System demands
Operator workload
Stressful/hazardous
aspects ofenvironment
Must remain cautious
of respiratory
changes not related
to work environment May be secondary orcompensatory to
respiratory volume
changes
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Measurement/Procedure
Measure non-obtrusivelymotions of the rib cage
and abdomen using an
inductive respiratory
plethysmography device Calibration techniques
Often combined with
other measures
(accelerometry, ECG,oximetry, PetCO2
Research Design
Prepare Subject
Physiological Monitoring
Data Acquisition/Analysis
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Equipment
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Advantages/Disadvantages
Valuable in appliedstudies of complextasks/systemsdemands/effortinvestment
Combines easilyperformance-based andsubjective methods
Demonstrates metabolicactivity associated with
task but may be affectedby extraneous variables
Respiration is intricateinterplay betweenbrainstem, metabolic,volitional influences
Difficult to unravel
May not be a convenientmeasure when interestedin monitoring oxygenconsumption
Will the quantification of
respiration answer thequestions whichresearcher is interestedin?
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Training/Application
Considerable investmentin time, effort, resources
to familiarize oneself with
the underlying
physiology,measurement, analysis
required
Basics in a few weeks,
expert knowledge muchmore time
Application of sensors,calibration, signal quality
verification varies from
10-30min.
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Reliability/Validity
Problems withreliability related toposture changes,movement and
respiration relatedmovement
Possible to filter someof these out but
probably too complexfor automatic filtering
Measurement ofPetCO2 may poseserious validityproblems that need to
be considered Breathing can vary
widely and it may bedifficult to correlate
these changes tochanges in workrequirements
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