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13.4 Physiological tools 383

13.4.1.1 Electrodermal activity or galvanic skin response
As many science-museum exhibits demonstrate, human bodies can act as conductors
for electricity. Glands in our hands and feet produce sweat in response to emotional
and cognitive stimuli. The salty sweat increases conductivity, allowing more electric-
ity to flow (Stern et al., 2001; Mandryk and Inkpen, 2004). Conductivity is a mea-
sure of how well electricity flows through a substance: higher conductivity means a
greater flow of electricity. Electrodermal activity is the measurement of the flow of
electricity through the skin. Electrodermal systems use a pair of electrodes on the
skin—usually connected to fingers—to measure the conductivity between two points
(Figure 13.4). Research efforts have linked conductance level to arousal, cognitive
activity (Mandryk and Inkpen, 2004), and frustration (Scheirer et al., 2002). Some
studies have established differences in the magnitudes of changes associated with
different emotions. For example, fear leads to smaller increases in skin conductance
than sadness (Cacioppo et al., 2000).

13.4.1.2 Cardiovascular signals
Anyone who has ridden a roller coaster or watched a suspenseful movie has first-
hand knowledge of how the heart responds to stimuli. Increased heart rate is one
part of a complex set of reactions that may involve changes in the variability of the
heart rate, blood pressure, and blood-volume pressure (BVP) (Scheirer et al., 2002).
Heart-rate variability has been used to measure mental effort and stress (Wastell and
Newman, 1996; Rowe et al., 1998; Mandryk and Inkpen, 2004) as well as emotional
responses including fear, happiness, and anger (Cacioppo et al., 2000).

FIGURE 13.4
Thought technology's skin conductance sensor attaches to two fingers or toes to measure
galvanic skin response (GSR).
From http://www.thoughttechnology.com/sciencedivision/pages/products/skinconduct.html (accessed 04.06.16)