Electrodermal activity

Getting a pulse on our lizard brain

Most of this information came from Figner and Murphy (2010).

Sc Example

Sc Single Signal

  • skin conductance (SC) indicates autonomic nervous system (ANS) activity
  • the ANS does a lot, so SC indicates a lot
  • cheap, noninvasive, time domain of a few seconds

Interesting, the author cites an emotions revolution (Weber & Johnson, 2009) in neuroscience, which popularized a specific type of EDA: skin conductance.

  • SC reflects hidden processes affecting decision-making
  • SC is tricky, and there are some subtleties

Terminology

  • electrodermal activity (EDA) measures electrical properties of the skin
  • endosomatic = not using external current
  • exosomatic = using external current (e.g. SC)

Measures of EDA quantify electrical properties of the skin

  • skin conductance (SC) - DC - voltage held constant
  • skin resistant - DC - current held constant
  • skin admittance - AC - effective voltage held constant
  • skin impedance - AC - effective current held constant
  • SC measured in microsiemens ( )
  • skin conductance level (SCL) - the average trend of SC over minutes or 10s of minutes - indicates arousal
  • skin conductance response (SCR) - SC peak and fall lasting a few seconds - responds to events - "phasic"
  • tonic skin conductance (TSC?) - number of SCRs per minute
  • onset latency - time from stimulus to SCR
  • rise time - time between onset and max amplitude
  • amplitude - SC at max minus SC at onset
  • area bounded by curve of SCR - a more recent measure of the magnitude of an SCR

Process interpretation

  • SC changes are caused by sweating!

  • "sympathetic branch of ANS controls sweathing" thus?? "skin conductance reflects 'arousal' of the sympathetic ANS"

  • ANS is in hypothalamus and brainstem, but other parts of limbic and paralimbic networks are involved

  • the "Iowa group"

    • demonstrated SCL indicates affective processing before, during, and after making decisions
    • showed that SCL indicates expected affect

  • Reid and Gonzalez-Vallejo (2009)

    • showed that relative magnitude of SCRs is predictive of preferences

  • Krosch, Figner, & Weber

    • used SCL to show something about "the CCT" (???)

Doing experiments

  • equipment Biopac system, with SC and cardiovascular activity modules
  • software (AcqKnowledge) that comes with it enables analysis
  • author gives his whole set-up, down to each parameter - skip
  • deep breaths give clear SCRs, and indicates the system is working
  • because of SC's long latency, they used to long inter-stimulus periods, to let SC respond
  • until rapid event-related designs -- allow SC responses to overlap, as in BOLD, deconvolving statistically

Other resources