Around the turn of the twentieth century, researchers eagerly attempted to construct "thought-reading machines"
with what tools were then available. With the advent of the vacuum tube, these crude mechanical methods gave way to the sensitive electronic techniques that were critical for the advancement of cognitive psychophysiology. Thus, about 1921, primitive electromyographs for recording electrical components of muscle activity became available. The first recording of electroencephalograms was by Hans Berger in 1929, empirically establishing that the brain generates electrical signals (although Berger's findings were greeted with skepticism for many years). The galvanic skin response and other measures of autonomic activity during emotion had been initiated in the late nineteenth century (especially with Fere in 1888); such autonomic measures were important in the early development of cognitive psy-chophysiology, as they continue to be today.
There are four essential features of a cognitive psy-chophysiological laboratory for electrically studying covert bodily events: (1) sensors, usually electrodes placed over the brain and on the surface of the skin to detect electrical components of neural, muscular, and glandular phenomena; (2) amplifiers, which increase the amplitude of the body signal sensed; (3) readout devices, such as cathode ray oscilloscopes or recorders, which can display the covert body signals; and (4) quantification systems, which render numerical values for those signals.
Anumber of the more commonly measured psychophysiological events are classified in Table 1. The primary division is between responses of the muscular and glandular systems and neurophysiological processes of the central nervous system.
The first two response classes in Table 1, those of the skeletal musculature in the speech and somatic regions, are best measured electrically through electromyography. Myo, standing for muscle, and graph, for writing, form the term for recording electrical components of muscle activity. Covert eye behavior, the third response category in Table
Table 1. Covert Psychophysiological Events in Humans
I. Covert Responses (muscular and glandular events)
A. Covert speech responses: electromyographic measures from the tongue, lip, chin, cheek, laryngeal, and jaw regions
B. Covert somatic responses: electromyographic measures of the skeletal musculature from the fingers, arms, legs, etc.
C. Covert eye responses, principally through electrooculog-raphy
D. Covert autonomic responses
1. Cardiovascular measures such as heart rate, electrocardiogram, finger pulse volume, and blood pressure
2. Visceral muscle activity principally from the intestines, as the electrogastrogram
3. Electrodermal measures from the surface of the skin (galvanic skin response, skin conductance, etc.)
Electrical activity from the brain, recorded with electro-encephalography, through signal averaging, yields average evoked potentials, and the contingent negative variation.
1, is typically recorded through electrooculography, where oculo refers to the eyes.
The last response class, that for autonomic behavior, consists of a variety of subcategories. Common autonomic components include: (1) measures of heart (cardiac) activity through electrocardiography; (2) activity of the intestinal portion of the gastrointestinal tract, which, when electrically recorded, yields the electrogastrogram; and (3) electrodermal measures of skin (dermal) activity, most prominently the galvanic skin response measured with the psychogalvanometer.
The second major category in Table 1 is for electrical signals from the brain. These include such well-known events as alpha waves (large amplitude, cyclical waves) and beta waves (lower in amplitude than alpha waves but greater in frequency).
With the entrance of the small electronic computer into the laboratory, however, it became possible to average brain waves to expose intrinsic signals not discernible in the raw traces.
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