Galvanic Skin Response: What Is It and What Does It Measure?
The skin is an amazing and versatile organ. It’s not only smooth and often nice to look at, but also helps to regulate many functions of the body. It acts as a barrier against environmental threats, contains nerve cells that detect changes such as temperature and pressure, can heal itself, and (ideally) keeps your body at a steady 98.6 degrees.
Yet another great thing about the skin, and one that we are particularly interested in, is that the skin responds to changes, or stimulus, in a way that can be accurately measured via galvanic skin response. The term may sound a little geeky, but we think it’s pretty exciting, especially when we consider the amazing amount of information it can reveal about an individual.
Your skin is electric
Your skin, and much of the rest of your body for that matter, conducts electricity. If it didn’t conduct electricity, touching a high-voltage fence or sticking a knife in an electric socket would have no effect on you. We wouldn’t be alive without electricity because body functions are controlled by electrical signals.
The skin in particular is a good conductor of electricity, so even a weak electrical signal introduced to the skin can be measured. By applying a constant, unperceived level of voltage to the skin, we can get a baseline reading of the skin’s conductance. Skin conductance (SC) is a term that’s often used interchangeably with electrodermal activity (EDA) or galvanic skin response (GSR).
A measurable reaction
The baseline reading of skin conductance is referred to as tonic conductance. This conductance level is different for everyone, but it usually ranges from 10 to 50 very small units of conductance called microSiemens. Tonic skin conductance levels also vary based on the person’s psychological state and autonomic regulation at the time the measurement is taken.
While tonic skin conductance is a baseline measurement, phasic conductance changes are the result of the body responding to external stimuli. This increase in conductance compared to the baseline can be observed shortly after a subtle stimulus such as a smell, a sound, an image, or a question is introduced.
Phasic changes can be observed when the skin’s sweat ducts fill in response to a stimulus. After the sweat is deposited or absorbed by the skin, conductance returns to tonic levels. According to Edelberg’s widely accepted sweat circuit model, the extent of this increase can be measured by the amount of sweat and number of sweat glands activated.1
To tell the truth
Along with measuring heart rate, respiration rate, and blood pressure, the polygraph, or lie detector, measures galvanic skin response as questions are asked. A polygrapher is trained and qualified to interpret the responses to the questions, but standardized questioning procedures must be followed to get an accurate reading.
Initially, the polygrapher asks questions that are obviously true or false, such as “Is your hair blonde?” to establish a baseline reading. Questions with answers unknown to the polygrapher are then asked and the readings are compared to the baseline to determine whether the subject is telling the truth.
What else can galvanic skin response tell us?
The polygraph machine is the most well-known machine that uses GSR, but there are other applications of this technology that are even more significant. In the last hundred years or so, this technology has also proven its worth in a number of other fields, including:
- Psychological research
- Media and ad testing
- Usability testing
- Consumer neuroscience
- Health care
Making better wellness decisions with GSR
Similar to detecting truth and lies when hooked up to a polygraph machine, our biocommunication technology can determine if the body’s response to a digital signature of an actual stimulus is in range or out of range (and by how much) compared to the baseline reading. Digital signatures of specific nutritional products, for example, are posed as questions to the body, and the body responds directly via galvanic skin response. Because the computer communicates directly with the body, the subjectivity that occurs when questions are asked, perceived, and responded to (as with a polygraph test) is eliminated.
Thanks to GSR and the way we’ve integrated it into our biocommunication system, we are no longer limited to subjective interpretation when making decisions that impact personal wellness, and we think that’s something to get excited about.
1. “Experiment 33: The Galvanic Skin Response (GSR) and Emotion.” In Human Psychophysiology. Antipolygraph.org.