Week 3 - Psychophysiological Methods

7/30/2019 Week 3 - Psychophysiological Methods

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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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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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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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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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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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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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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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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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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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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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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

Documents

Week 3 - Psychophysiological Methods