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Psychophysiological Methods. Electrodermal Measurement. Galvanic skin response as indicative of the sympathetic branch of the autonomic nervous system Sweat glands provide a shunt between skin and deeper tissues Measures indicative of arousal, stress-strain, and emotion

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electrodermal measurement
Electrodermal Measurement
  • Galvanic skin response as indicative of the sympathetic branch of the autonomic nervous system
  • Sweat glands provide a shunt between skin and deeper tissues
  • Measures indicative of arousal, stress-strain, and emotion
  • Autonomic habituation provides a physiological measure of information processing capacity needed to complete a task
  • Used as measure of workload, mental strain, and emotional strain.
  • 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 Skin Conductive Response (SCR)
  • Amplitude, rise time and recovery time are measured
  • May be used to determine tonic Electrodermal Activity (EDA) to measure readiness for action
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

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-retest correlations of .76 and .61 at one year)

Validity at or above .90 for EDA-Emotional strength in LAB setting

No similar data for applied settings

Validity based more on strength of emotion related to strain than physical relationship

Heart rate and BP are yield better validity than EDA (.68 to .86)

  • Studies muscle function using electrical analysis of signals 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 contractile sarcomeres (actin-myosin-filaments)
    • These filaments create muscle contraction
    • Motor unit chemically activates the muscle fibers connected as myoneural junction is depolarized (amplitude of about 100mV with a 2-14msec duration
    • Muscle action potential causes sarcomeres to contract
    • Electrodes in tissue or skin can measure these action potentials (electrolytic response)
emg continued
EMG (continued)
  • Muscle force defined by motor units activated
  • EMG forms a quasi-randomly shaped spikes of amplitude and duration but no identifiable sequence
  • Correlation between number and intensity of generation of amplitude spikes and muscle contraction force
  • Remember, doesn’t measure force, joint position but rather voltage associated with local muscle recruitment
use of emg in the workplace
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
  • Placement of electrodes or needles in muscles, signal passed to preamplifier, processed with band-pass filters for frequencies related to muscular activity
  • Select muscles related to action (may depend on how specific you want to be – measuring potential between muscle and ground
  • Amplify, filter and store results
  • Signal Processing
  • Scaling
emg advantages disadvantages
Continuous and quantitative measured data

High temporal resolution with marginal interference with task execution

Allows detection of muscle fatigue at early stages providing objective measure

Multi-channel EMG can identify muscular bottle-necks

Surface EMG limited to muscles directly beneath area accessed by skin electrode

Only feasible for single muscles in individuals not too obese

Requires careful calibration, instrumentation, data manipulation, and interpretation

Setup is fairly time consuming

Interpretation requires data analysis and data integration

Calibration lacks reliability

Requires individual calibration, poor reliability

Needle method more specific but invasive and quite painful

EMG Advantages/Disadvantages
heart rate variability
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
use of ecg
HRV related to changes in autonomic control

Vagal Gating

NSR is vagally determined

HRV and other cardiovascular variables modulated by baroreflex gain.

General cardiac response found in mental-effort studies characterized by increased HR and BP and decreased HRV and BP variability at all frequencies

Compatible with fight-flight reaction (lab studies, short-lasting tasks, challenging mental operations in working memory.

Mid freq. band most sensitive to variation in mental effort due to decreased vagal activation and increased sympathetic activation.

Use of ECG
  • Three or 7 lead methods
  • Sampling and R-peak detection
  • Artifact detection and Correction
  • Spectral procedures
  • HR, IBI or Normalized Values?
  • Logarithmic Transformation
HR and HRV used as indicators of mental effort

Higher invested effort, higher HR and lower HRV

Complex relationship between HR with baroreflex BP control and autonomous nervous activity

Most stable results only really found in lab settings

Restrictions in sensitivity for artifacts in obtained IBI series and sensitivity for changes in respiration

Artifact correction time consuming

Newer technologies are mitigating some of these limitations

reliability and validity
R and V of HR and HRV in short duration mental loading lab results usually high

Doesn’t hold for practical settings

Diagnostic validity and reliability debated

Sensitivity of the measure not very high

Difficult to distinguish levels of task load and related invested effort

Requires multiple data collection sessions on single subject

Validity affected by fight-flight mechanism versus compensatory mechanisms

Reliability and Validity
ambulatory eeg methods
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
  • 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)
procedure example
  • See text for in depth discussion of procedure for setup and use of EEG and EOG.
  • Example 12.1 shows EEG/EOG pattern in severe sleepiness performing a task and demonstrates beta activity, increased alpha activity, eye closure, slow eye rolling movements, and dozing off, reappearing beta activity, return of eye blinks
application training
Application takes 15-30 minutes minimum for electrode placement

Learning to setup takes 10-20 hours for reliable recording

Scorring takes several months to learn

Requires repeated quality checks

reliability validity27
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/theta and slow eye movements

event related potentials erps
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 minimum latency with respect to discrete stimulus/response
  • Found to reflect perceptual, cognitive, motor processes
  • Useful to decompose processing requirements of complex tasks (Fabiani et al., 2000)
  • Experimental paradigm design
  • Subject preparation
  • Preparation of ERP data for analysis
  • Component definition and pattern recognition
  • Data analysis
advantages disadvantages30
We possess understanding concerning functional significance of different ERP components

Brain regions from which component generated are known

ERPs can be obtained in absence of operator action/performance

Motion artifacts

Require discrete stimulus or response

Substantial training required for recording, analysis, interpretation

training application times
Depends on whether you want to learn the basics (2 months) or become knowledgeable about the basis of ERP signals (advanced degree)

Application times from 15min for a few electrodes to 45min for large electrode array

Training/Application Times
reliability validity33
Validity of ERP components to specific cognitive constructs convincingly demonstrated

Reliability established through extensive replications

Split-half reliability high for P300 amplitude (.92) and latency (.83)

Test-retest reliability over several days for P300 amplitude .83 and P300 latency .63

eeg meg fmri
  • Neural activity generates currents outside the skull which can be monitored by their electrical and magnetic fields
    • Electroencephalogram (EEG)
    • Magnetoencephalogram (MEG)
    • Magnetic Resonance Imaging (MRI)
    • Functional MRI (fMRI)
  • Provide a basis for examining the neural substrate of specific cognitive processes
research areas amenable to meg fmri
Movement-related brain activation

Memory processes (encoding & retrieval)

Visual perception, attention, & selection

Auditory perception, attention & selection

Language production and processing

Perception of music

Learning and brain plasticity with respect to cognitive functions



Localization of epileptic foci based on specific brain areas spiking

Estimation of the impact of certain lesions on higher neural functioning

MEG preferred for temporal resolution; fMRI for spatial resolution; and maximum information when/where the two methods can be combined.

Limited to patients without ferromagnetic inserts

Research Areas amenable to MEG & fMRI
meg fmri mechanisms
Requires use of superconducting quantum interference devices (SQUIDs)

Exploit quantum mechanical “Josephson-effect”

Modern MEG systems monitor signals from 150-300 SQUIDs spread equally over the head surface

Variants of MEG sensors known as Gradiometers

Spin tilt of protons aligned with strong magnetic field is pertubated by a brief electromagnetic pulse

Protons emit burst of RF energy as they return to their initial aligned state

Strength of signal with particular RF signature allows determination of proton density

Helps define tissue characteristics at that location

MEG/fMRI Mechanisms
procedure meg
Procedure (MEG)
  • Helmet like gantry placed over subject’s head
  • Coils fixed on head provide weak magnetic sources known as anatomical sites.
  • Subject reclined on movable gantry, shifted into the bore of a magnet.
    • Structural scan
    • Repeated functional scans
experimental setup
Experimental Setup
  • During session, sequence of visual or auditory or other sensory stimuli is presented to the subject who has to process them according to a predefined task.
  • Often the same or similar stimuli are presented with slightly different task requirements
  • Differences between the BOLD responses in the different experimental conditions are evaluated to determine what brain regions are specifically activated by a particular task or sensory input
megdata analysis
Event-locked epochs initially averaged separately for each subject, 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 measurements determined for each component, task, subject.

Statistical analysis to ascertain significant differences which are localized to a region of the brain

Various co registration techniques possible using nonlinear parameters, algorithms from chaos theory

Analyzing continuous MEG data is based on chaos theory and beyond the scope of this class

MEGData Analysis
fmri data analysis
Continuously recorded fMRI/BOLD data sorted according to different stimulus/task condition

Any distortions are corrected by a processing algorithm.

Those functional images showing significant differences in activation levels at the level of the individual voxels

fMRI permits single subject statistical analysis due to better signal to noise ratios

Comprehensive evaluation packages are available

Statistical parametric mapping (SPM) package

Also advanced applications that deconvolve temporally overlapping BOLD responses

fMRI Data Analysis
  • Predefined protocols performed by techs after two week training period
  • For more advanced/sophisticated applications, at least one full time engineer or physicist should be available (6 month training).
  • In clinical setting, support of a dedicated physician is required for data interpretation
  • Neuroscientists should have a sound background in experimental design as well as neurophysiological education. Specific training per investigations being conducted
  • Joint program between Emory and Georgia Tech provides degree and background in medical physics
test times
Test Times
  • Experimental run may require about 1.5 hours with 15 minutes additional subject preparation
meg reliability validity
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 user’s experience
fmri reliability validity
fMRI Reliability/Validity
  • fMRI
    • Continuous maintenance should result in acceptable raw images
    • Artifacts due to discontinuities in magnetic susceptibility can lead to low structural distortions and signal 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 using inappropriate experimental designs
    • Reliability and validity of fMRI method also relies on user experience
blood pressure measures
Blood Pressure Measures
  • Strain affects mood and behavior
  • Performance and physiological effort have used strain analyses that are only psychological
  • Progress in ambulatory measurement has allowed assessment of behavioral, emotional and activational interaction with workload under real work conditions.
  • Low strain load has been used to investigate long term work (fatigue, boredom, vigilance) on health
ambulatory bp
Ambulatory BP
  • Developed clinically to measure physical work effects
  • Increased use for psychosocial work characteristics
  • Use of portable recorders for non-invasive recording
  • 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
  • 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
advantages disadvantages53
Can simultaneously record workload and subject’s strain experience & behavior

Work-strain-related effects on BP recovery can be investigated and assessed

ABPM can have an artifact effect on daily activity (Hawthorn type effect)

May have an effect on subject’s sleep

training application
Investigator experienced in principles of BP measurement and interpretation of readings

Main and artifact variables 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

eye blink measures
Eye Blink Measures
  • Issues related to alertness/drowsiness
    • Neurobiological products of interaction between endogenous circadian pacemaker and homeostatic need for sleep
    • Objective biobehavioral signs often require intrusive physiological monitoring
  • Growing use of these measures as humans subjected to 24 hour workdays
  • Technological improvements are making measurement more affordable and less obtrusive
  • Use infrared, retinal reflectance monitor
  • Uses CCD camera to record eye closure measurements in real time
  • General use of two cameras situated at 90 degree 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
advantages disadvantages59
Availability of on-line, near-real-time, automated slow eyelid PERCLOS system unobtrusive 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 in completion of task

Equipment may be too obtrusive in mobile real-world applied environment

Not ideal in low humidity environments (not able to differentiate moistening of eyes and fatigue based closure

Misuse in safety sensitive environment may generate risk.

training application60
No training required other than to teach operator to interpret feedback indicating drowsiness

Small, fairly easily applied and useful in many but not all environments

reliability validity61
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 validity must be established across dynamic range of performance

human respiration
Human Respiration
  • Respiration linked to a variety of functional psychological dimensions
    • Response requirements
    • Appraisal patterns
    • Mental effort investment
    • Various dimensions of emotion
    • Affect
    • Mood
respiratory measures
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
Can be used with verbal self report related to work

Task demands

System demands

Operator workload

Stressful/hazardous aspects of environment

Must remain cautious of respiratory changes not related to work environment

May be secondary or compensatory to respiratory volume changes

measurement procedure
Measure non-obtrusively motions 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

advantages disadvantages68
Valuable in applied studies of complex tasks/systems demands/effort investment

Combines easily performance-based and subjective methods

Demonstrates metabolic activity associated with task but may be affected by extraneous variables

Respiration is intricate interplay between brainstem, metabolic, volitional influences

Difficult to unravel

May not be a convenient measure when interested in monitoring oxygen consumption

Will the quantification of respiration answer the questions which researcher is interested in?

training application69
Considerable investment in time, effort, resources to familiarize oneself with the underlying physiology, measurement, analysis required

Basics in a few weeks, expert knowledge much more time

Application of sensors, calibration, signal quality verification varies from 10-30min.

reliability validity70
Problems with reliability related to posture changes, movement and respiration related movement

Possible to filter some of these out but probably too complex for automatic filtering

Measurement of PetCO2 may pose serious validity problems that need to be considered

Breathing can vary widely and it may be difficult to correlate these changes to changes in work requirements