With any sympathetic nervous system activation, skin reacts and becomes a better conductor of electricity. This can result from emotional, cognitive or other psychological origin. The phenomenon is known as electrodermal activity (EDA) and it is widely adopted in psychological research (1). Other commonly used terms for this phenomenon are skin conductance response and galvanic skin response.
EDA is generated by the activity of the sweat glands. Moodmetric measures the palmar skin on your finger. The palmar skin is the recommended EDA measurement location, since it has the highest eccrine sweat gland density (2). You can measure EDA elsewhere as well but the reliability is not as high or as easily achieved.
The unconscious actions of the human body are regulated by the autonomic nervous system. It consists of the sympathetic and parasympathetic part. The parasympathetic part controls the body’s rest-and-digest functions and the sympathetic part controls the fight-or-flight reactions. By examining electrodermal activity we can understand the sympathetic nervous system reactions.
The sweat glands are exclusively innervated by the sympathetic nervous system. This makes EDA an ideal measure for sympathetic activation (2). Electrodermal activity correlates to cognitive and emotional arousal, and high responses are caused by e.g. stress, enthusiasm, anxiety, joy, anger (1, 3).
Mobile EDA devices have been used by scientists for some time (2, 4). The Moodmetric ring is an unobtrusive option to follow EDA responses real-time and in long term.
The signal accuracy has been proven in a study of 24 people by the Finnish Institute of Occupational Health by J. Torniainen et al.. The accuracy against a laboratory grade reference was found to be 83 %. They conclude:
“Clearly the ring sensor can be used to measure a valid EDA signal as indicated by the similarity of both event-related responses and the calculated features. The accuracy of the Moodmetric EDA Ring is adequate for psychological and physiological research when weighted against the advantage of conducting ecologically valid experiments outside laboratory conditions.”
The results were accepted for publication in the 2015 conference of the IEEE Engineering in Medicine and Biology Society (EMBC 2015, August 25-29).
The Moodmetric measurement accuracy has also been studied at the University of Tampere, Finland in 2014. The correlation with the reference equipment Nexus-10-MK II was good. Comparison details in charts below.
With skin conductance level (SCL) we refer here to raw measured skin conductance without any filtering. The figures below show the comparison of the two devices.
Further reading in an article by Jari Torniainen and Benjamin Cowley, published in August 2016:
1 Mendes, W.B. (2009). Assessing the autonomic nervous system. In: Harmon-Jones E. ja Beer J.S. Methods in social neuroscience. New York: Guilford Press. p. 118-147.
2 Setz C., Arnrich B., Schumm J. and La R. (2010) Discriminating Stress From Cognitive Load Using a Wearable EDA Device. IEEE Trans. Inf. Technol. Biomed. 14(2). p. 410-417.
3 Nikula R. (1991) Psychological correlates of nonspecific skin conductance responses. Psychophysiology. 28(1). p.86-90.
4 Poh M.Z, Swenson N.C. and Picard R.W. (2010) A Wearable Sensor for Unobtrusive, Long-Term Assessment of Electrodermal Activity. IEEE Trans. Biomed. Eng. 57(4). p. 1243-1252.