What Is an Electrodermal Response?
An electrodermal response (EDR) is a change in the electrical properties of the skin caused by eccrine sweat gland activity controlled by the sympathetic autonomic nervous system. The EDR is the single most commonly cited physiological indicator in polygraph research and one of the three core channels recorded during every examination.
Measurement Methods
EDRs can be measured using exosomatic methods (applying external current/voltage to measure skin conductance or resistance) or endosomatic methods (measuring skin potential without external current). Modern instruments use the constant voltage exosomatic method measuring skin conductance through electrodes on the fingers.
Scoring Features
The electrodermal channel provides several scoring features: amplitude (size of the conductance increase), duration (how long the response lasts), and complexity (number of inflections in the waveform). These are evaluated at each analysis spot and compared between relevant and comparison question locations.
Why EDR Is Important
The electrodermal channel is often considered the single most diagnostic channel because it provides a relatively direct measure of sympathetic activation. Unlike cardiovascular and respiratory channels influenced by both sympathetic and parasympathetic activity, the electrodermal channel is driven exclusively by the sympathetic nervous system — there is no parasympathetic innervation of eccrine sweat glands. This makes the EDR a “pure” sympathetic measure and a particularly sensitive indicator of deception-associated arousal.
Historical Names
The EDR has been known by many names: galvanic skin response (GSR), psychogalvanic reflex, and skin conductance response (SCR). The umbrella term electrodermal activity (EDA) encompasses all measures.