3.4. Measurement of Electrodermal Activity (EDA)

It is implicit that processing health information leads to cognitive processes based on neural activity in a person’s brain. Furthermore, this cognitive processing is accompanied by autonomic nervous system correlates of emotions, leading to changes in electrical skin properties. To measure these electrodermal changes, two electrodes are placed on the skin, and a small electrical voltage is applied. By controlling the electrical current through the measuring device, the time course of the skin’s electrical conductivity can be determined, showing the electrodermal activity (EDA). The test subject has to be deprived and calm, usually sitting in a sound-reduced test cabin. Psychological, emotional–affective, and cognitive processes influence the vegetative changes in skin conductivity in such a way that both conscious and non-conscious (subliminal) processing can be detected.

In a similar way, emotional–affective topics of conversation can be detected by measuring the changes in the electrical properties of the skin [31,32]. By using two skin electrodes at palmar sites of the hand, the measurement of electrodermal activity can begin, for example, while the test subject listens to different health-informative statements. As with the other methods mentioned here, EDA measurements do not produce reliable results based on a single item measurement. Random effects are observed too often for this. However, if 10 to 15 matched stimuli within one participant are compared with an equal number of control stimuli, reliable statements can be made. Broadening the experiment to an additional 10 to 30 participants then also allows a generalization of the findings. According to Visser et al. [33], cancer patients forgot 20 to 80% of the information provided during oncological medical consultations. Since Vissen et al. [33] assumed emotional stress to be the cause of this forgetting, they measured psychophysiological arousal using skin conductance level and heart rate. In the first study, Vissen et al. [33] were unable to show any correlation between psychophysiological arousal, self-reported emotional stress, and memory limitation regarding cancer-related information. Further differentiated studies could close these research gaps. The use of these methods to measure health literacy-associated aspects such as engagement is discussed by D’Mello et al. [28].