Electrodermal Activity EDA

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Electrodermal Activity (EDA) Behavior

• Hieu Jayson

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EDA

• Whether it can distinguish between positive and
  negative emotion
• Relationship between EDA and response speed
• Motivational level
• Skin activity indicate a person is lying!

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Cont.

• Produce by physical and emotional stimuli through
  small current (Fere et al., 1888)
• Tarchanoff did not applied current, and observed
  that there were natural differences in electrical
  potential between two skin areas (1890)
• Two basic methods for the measurement of EDA
  recording of skin conductance and skin potential
• Changes in sweat glands have been strongly
  implicated

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Skin Anatomy Physiology

• 3 layers
• 1) epidermis (outer layer)
• - consists of 5 separate cellular layers
• - 1mm and less in thickness
• 2) dermis (inner layer)
• - ranges 0.5-6 mm
• - contains blood vessels, nerves, lymph
  vessels, hair follicles, smooth muscle, sweat
  glands, and sebaceous glands
• 3) hyperdermis
• - subcutaneous connective tissue (secretary
  portion of the sweat glands)

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Structure of the skin
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Sweat Glands

• Total number on the body ranges from 2 to 5
  millions (Fowles, 1986)
• - a square inch on the palm contains 3, 000
  sweat glands
• 2 types
• 1) apocrine
• - large, open into hair follicles, begin to
  function after puberty
• - found in genital areas and armpits
• 2) eccrine
• - tubular with a rounded secretory portion and
  a duct that leads to the skin surface
• - wide distribution over the body surface
• - most numerous palms of the hands, soles of
  the feet
• - intermediate densities on the head
• - least dense arms, legs, and trunk

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Nervous System control of EDA

• EDA is a complex reaction with a number of
  control centers in the CNS
• Controlled by three system
• 1) Limbic structures ( hypothalamus, cingulate
  gyrus, hippocampus)
• - involved in EDA activity related to
  emotional responses and thermoregulation
• 2) Motor cortex parts of basal ganglia
• - involved in locomotion
• 3) reticular formation
• - related to states of arousal

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Skin and Sweating

• Skin
• - protect organism it covers
• - role in thermoregulatory activities
• - blood dilation and increased sweating
  resulting in decreased temperature
• - blood vessels constriction and piroerectrion
  (goose bumps) causes an increased temperature
• Sweating
• - reflecting as changes in skin potential (SP)
  and skin conductance (SC) in a variety of
  situations
• - contributes to bodily efficiency in times of
  emergency

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Types of EDA

• Phasic responses
• Tonic level
• Terms abbrevation
• - Exosomatic (SRR, SRL, SCR, SCL)
• - Endosomatic (SPR, SPL)
• - nonspecific SCRs (NS-SCRs) vs. event-related
  SCRs (ER-SCRs)

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Skin Conductance

• SRR momentary fluctuations in skin response
• SRL indicates baseline skin response at any
  given time
• SCR SCL conductance unit measures of SRR SRL
• Conductance units are prefer over resistance
• - conductance values are more suitable for
  averaging and statistical manipulation
• - more logical
• Unit for conductance mho
• Some used microsiemen (µS) interchange for µmho
• Amplitude of SCR depends on electrode size and
  phasic change vary from 0.05 to 5 µmho
• Apperance ranges from 1.0 to 3.0 sec after
  stimulus presentation

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Skin Potential

• SPR changes in skin potential
• SPL level of skin potential at any point in time
• SPR can be biphasic or uniphasic wave
• - measured in millivolts
• SPR amplitude
• - difficult to meausure due to SPL is not easy
  to establish
• - negative wave about 2 mV
• - positive wave about 4mV
• Latency of the negative SPR is similar to SCR

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Origin of EDA

• Research relating performance and psychological
  factors to EDA found that measures of SC or SP
  reflecting changes in sweating activity.
• Wilcott (1967) found that the amplitude of palmar
  SCRs and SPRs and the amplitude of sweating
  responses are usually highly correlated
• Edelberg proposed sweat gland and EDA model
  relates standing level of sweat in the duct to
  tonic SCL and SCRs to increases in the level of
  sweat.

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Measurement of EDA

• Skin Conductance Level (SCL)
• Bipolar placement of electrodes is preferred
• 2 basic types of circuit used to measure SCL
• 1) constant voltage (voltage is constant across
  the electrodes, current through the skin varies
  with conductance changes)
• - recommended current 8 µA/cm2
• 2) constant current (current is constant,
  voltage varies with resistance)
• - recommended voltage 0.75 to 1.0 V
• Most instrument for the measurement of SC use the
  constant-current technique

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Cont.

• Skin Potential
• Unipolar placement is essential to record SPL
• - Active electrode placed in the palm
  inactive electrode placed on the forearm

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Electrode Placements of Electrodes for measuring
SC and SP
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Electrodermal ActivityStudy of
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Applications

• Reaction Time
• Learning and Memory
• Music
• Observed Violence
• Eroticism
• Emotional Response
• Vigilance
• Unconscious facial recognition

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Reaction Time

• Freeman- 1940
• RT during various states of alertness
• Inverted U-shaped relationship between SCL and RT
• RTs slower at high and low SCL and faster at
  moderate levels
• Later experiments fail to replicate results

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Reaction Time (cont.)

• Andreassi (1966b)
• Measured SCL as he gave subjects random signals
• Highest SCL found to produce faster RT
• Linear, not U-shaped
• Subjects level of arousal not manipulated

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Reaction Time (cont.)

• Andreassi, Rapisardi, and Whalen (1969)
• Produced signals at either random or fixed
  intervals
• Response to fixed interval showed faster RT than
  random interval
• Subjects anticipated signal

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Learning and Memory

• Andreassi (1966a)
• Asked Navy men to learn nonsense syllables
• SCL and HR higher during learning of the easy
  list.
• Yuille and Hare (1980)
• Asked subject to recall word after 15 sec
• Best performance had increased SC and HR

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Music

• Zimny and Weidenfeller (1963)
• Played exciting, neutral, or calming music
• SCR occurred during exciting music only
• Interpreted results as indication that different
  kinds of music produce differential EDA

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Violence

• Green and Rakosky (1973)
• SCR of male subject was recorded during viewing
  of a brutal prizefight from a movie
• Subjects were told fight was staged and injuries
  were fake
• More SCRs were found after fight, less found
  after remarks emphasizing the fictional aspects
  of the scene
• Expressing the fictional aspect of the fight
  allowed subjects to dissociate the violence

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Eroticism

• Hamrick (1974)
• Women viewed erotic stimuli
• Increased SRC and decreased HR
• Subjects expressed ratings that indicated sexual
  arousal and positive affective reactions

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Emotional Expression

• Lanzetta, Cartwright-smith, and Kleck (1976)
• Tested if free expression will intensify
  experience.
• Subjects asked to conceal or exaggerate facial
  expression of anticipated electric shock
• Suppression led to smaller SCRs and lower pain
  ratings
• Keeping a cool response to a situation can help
  keep situation under control

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Vigilance

• Eason, Beardshall, and Jaffee (1965)
• Subjects were asked to watch a flashing light and
  report when it stayed on longer than usual
• Performance and SCL dropped as experiment
  progressed
• Drop in SNS activity created decreased SCL

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Unconscious Facial Recognition

• Tranel and Damasio (1988)
• Brain damaged patients
• Tested recognition of family and friends (knew
  prior to accident) vs. physians and psychologists
  (knew after accident)
• Showed EDAs to faces unrecognized
• Bilateral brain damage inhibits conscious
  recognition
• Stimuli registration takes place in the visual
  cortex and then shared with the hypothalamic
  structures, resulting in the autonomic response