Galvanic skin response (GSR) is a phenomenon where the conductivity of human skin fluctuates in response to a wide range of stimuli such as emotional responses or mental state to name a few. This phenomenon has been empirically studied since the 1800s when Emil du Bois-Reymond discovered that skin was electrical conductive.
How They Work
GSR sensors measure skin conductance by passing a weak current between two electrodes placed on the skin, typically one inch apart. When the person is subjected to stimuli, the skin conductance can fluctuate by several microsiemens. Due to how small the conductance values are, amplifiers and filters are added to remove noise and boost the signal.
GSR circuit by Drew Fustini
Keep in mind that skin conductance is affected by environmental factors such as temperature and humidity.
The GSR circuit on the MetaHealth board is designed entirely in house. Our GSR circuit has a resolution of 10nS with a 16bit ADC resolution and can measure conductance samples at frequencies up to 100Hz.
GSR sensors have a long history with psychological research, able to detect changes in emotional and cognitive states. They can be found in modern polygraph devices, providing an additional measurement to blood pressure, heart rate, and respiratory rate. They are also used in therapy where the sensor serves as an indicate of the patient’s stress level.
Drew Fustini has a post on the element14 community detailing a GSR circuit he worked on for a project.