What is GSR (galvanic skin response) and how does it work?
The galvanic skin response (GSR), also known as Skin Conductance (SC), refers to changes in sweat gland activity, which reflect the intensity of participants’ emotional state – or ‘emotional arousal’. GSR provides an additional source of insight into the level of emotional arousal, to validate self-reports, surveys, or interviews of participants within a study.
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Our level of emotional arousal changes in response to the environment we’re in. If something is scary, threatening, joyful, or otherwise emotionally relevant, the change in emotional response that we experience also increases eccrine sweat gland activity. GSR measurements work by detecting changes in electrical (ionic) activity resulting from changes in sweat gland activity.
It is noteworthy that both positive (“happy” or “joyful”) and negative (“threatening” or “saddening”) stimuli can result in an increase in arousal – and in an increase in skin conductance. The GSR signal is therefore not representative of the type of emotion, but the intensity of it.
Example GSR time course during an episode of “Breaking Bad” as visualized in iMotions. (Photo courtesy: iMotions)
What you need to know about GSR sensors
Skin conductance is typically captured from the hand and foot regions, using easy-to-apply skin electrodes. Most modern GSR electrodes have an Ag/AgCl (silver-chloride) contact point with the skin. These electrodes are cheap, robust, safe for human contact, and accurately transmit the signal from the ionic activity.
Some electrodes come pre-packaged with ionic gel to increase the signal fidelity. Alternatively, ionic gel can be applied to achieve the same effect. The signal is sent through the electrode, to the wire (usually lead) that passes the information to the GSR device.
Data is acquired with sampling rates between 1 – 10 Hz and is measured in units of micro-Siemens (μS). Once the data is passed to the GSR device, it is either:
- stored within the device to be later uploaded;
- transmitted wirelessly to a computer system;
- or the signal is sent through a further wired connection to a computer.
Of course, different GSR sensors allow different means of transmission, and the choice of each depends on the kind of research you’re carrying out.
GSR signals explained
The time course of the signal is the result of two additive processes: a tonic base level driver, which fluctuates very slowly (seconds to minutes), and a faster-varying phasic component (fluctuating within seconds). Changes in phasic activity can be identified in the continuous data stream, as these bursts have a steep incline to a distinctive peak, and a slow decline relative to the baseline level.
Researchers focus on the latency and amplitudes of the phasic bursts with respect to stimulus onset when investigating GSR signal changes in response to sensory stimuli (images, videos, sounds). When there are significant changes in GSR activity in response to a stimulus, it is referred to as an Event-Related Skin Conductance Response (ER-SCR). These responses, otherwise known as GSR peaks, can provide information about emotional arousal to stimuli.
Other peaks in GSR activity that are not related to the presentation of a stimulus are referred to as Non-Stimulus-locked Skin Conductance Responses (NS-SCR). By using the skin conductance values, or the number of GSR peaks, it’s possible to add quantitative data to studies of emotional arousal. With more data at hand, it’s easier to uncover new findings and make new discoveries about human behavior.
This article is an edited version of ‘What is GSR (galvanic skin response) and how does it work?’ by Bryn Farnsworth, Ph.D., published on July 17th, 2018, at https://imotions.com/blog/gsr/.