The skin on the palms of the hands (and the soles of the feet) contains a high concentration of sweat glands. These sweat glands are directly influenced by the sympa thetic nervous system, the branch of the autonomic nervous system that prepares the body for action—that is, the fight-o -flight mechanism. When the sympathetic nervous system is activated (such as during episodes of anxiety , startle, or anger), the sweat glands begin to fill with salty wate . If the activation is suf ficiently strong o prolonged, the sweat may actually spill out onto the palms of the hands, causing the person to develop sweaty palms. Interestingly, all mammals have a similarly high concentration of sweat glands on the friction surfaces of their hands/paws.
Even before the sweat is visible, however, it can be detected by the clever application of a small amount of electricity , since water (i.e., sweat) conducts electricity . The more water that is present in the skin, the more easily the skin carries, or conducts, electricity. This bioelectric process, known as electrodermal activity (dermal means "of the skin"), or skin conductance, makes it possible for researchers to directly measure sympathetic nervous system activity .
In this technique, two electrodes are placed on the palm of one hand. A very low voltage of electricity is then put through one electrode into the skin, and the researcher measures how much electricity is present at the other electrode. The difference in the amount of electricity that is passed into the skin at one electrode and the amount detected at the other electrode tells researchers how well the skin is conducting electricity. The more sympathetic nervous system activity there is, the more water is produced by the sweat glands in the skin, and the better the skin conducts the electricity. The levels of electricity involved are so small that the participant does not feel anything.
Electrodermal responses can be elicited by all sorts of stimuli, including sudden noises, emotional pictures with char ged content, conditioned stimuli, mental effort, pain, and emotional reactions such as anxiety, fear, and guilt (as in the so-called lie detector test, which uses skin conductance). One phenomenon of interest to personality psychologists is the observation that some people show skin conductance responses in the absence of any external stimuli. Imagine a participant sitting quietly in a dimly lit room who is instructed to just relax. Most people in this situation exhibit very little in the way of autonomic nervous system activity . However, some participants in this situation exhibit spontaneous electrodermal responses, even though there is nothing objectively causing these responses. Not surprisingly , the personality traits most consistently associated with nonspecific electrodermal responding are anxiet and neuroticism (Cruz & Larsen, 1994). A person who is rated as high in anxiety and neuroticism appears to have a sympathetic nervous system that is in a state of chronic activation. This is just one example of how electrodermal measures have been used by personality psychologists to ascertain dif ferences in personality between people.
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