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1.1 What Is Psychophysiology?
Psychophysiology, as the term implies, is the study of the interrelationships between mind and body. Although clearly related to Behavioral and cognitive neuroscience, psychophysiology diﬀers from traditional neuroscience both methodologically and conceptually. Methodologically, psychophysiologists study primarily human subjects rather than lower animals, they usually measure physiological responses non-invasively, and the physiological responses are more molar as opposed to molecular. Conceptually, most psychophysiologists focus primarily on understanding psychological events and secondarily on understanding the underlying physiological events.
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1.2 Goals And History Of Psychophysiology
The notion that one can understand psychological states and processes by means of observing or measuring physiological changes dates from the origins of the human race (e.g., blushing indicates embarrassment, sweating is associated with fear, etc.). However, it was not until approximately 1960 that psychophysiology was deﬁned as a speciﬁc scientiﬁc discipline. The Society for Psychophysiological Research was founded in 1960 and the journal Psychophysiology was ﬁrst published in 1963 under the leadership and vision of Albert Ax. The stated purpose of the society was and continues to be ‘to foster research on the interrelationships between the physiological and psychological aspects of Behavior.’ Because only some of the highlights of psychophysiology can be identiﬁed here, the reader is referred to an introductory text by Hugdahl (1995), a more advanced handbook edited by Cacioppo et al. (2000), and the journals Psychophysiology and International Journal of Psychophysiology.
1.3 Typical Psychophysiological Measures
A great many physiological responses are used as psychophysiological measures. These fall broadly into four categories. The ﬁrst, and historically oldest, category includes responses of the autonomic (or involuntary) nervous system (ANS), that branch of the nervous system, which controls the actions of internal organs such as the heart, blood vessels, sweat glands, and digestive organs. It is divided into the sympathetic branch, which mobilizes body resources to prepare the organism to respond to the environment and deal with stressors and threat (e.g., by the increasing heart rate, respiration rate, and palmar sweating), and the parasympathetic branch, which acts to store and conserve energy by reducing heart rate and increasing digestive activity. As can be seen, the ANS controls many aspects of physiological function that serve as indicators of emotion or activation. Thus, a psychophysiologist might use heart rate or palmar sweating as a measure of how anxious a person felt in a particular social situation, such as having to give a speech to an audience.
The second category of psychophysiological measures reﬂects the activity of the skeletal nervous system, as indicated by motor activity. Of particular interest have been general measures of overall muscle tension, such as tension in the forearm muscles, which can reﬂect broad states of arousal and activation, and measures of the activity of facial muscle activity, which can indicate states of emotion.
The third category of psychophysiological measures consists of electrophysiological indices of central nervous system activity, primarily electroencephalogram (EEG) and evoked response potential (ERP) measures. For instance, one might use the amount of alpha (8–12 Hz) rhythm in the EEG as an index of relaxation, or the magnitude of a particular ERP component elicited by a stimulus as a measure of attention to that stimulus. The fourth category of measures is derived from brain scanning techniques, such as positron emission tomography (PET), magnetic resonance imaging, MRI, or functional MRI scans. For example, one could use a PET-derived measure of metabolic activity in the frontal lobes to examine diﬀerences in executive function between patients with schizophrenia and normal subjects.
2. Long-Lasting States
2.1 Alertness Arousal Activation
The terms alertness, arousal, and activation have a long and useful, albeit a bit checkered, history in psychophysiology. These terms generally denote a continuum of energy mobilization, from the low end of coma or deep sleep to the high end of excitement and extreme agitation. Primary psychophysiological indices of the state of arousal are levels of activity of the ANS, skeletal electromyographic (EMG) tension, and EEG. In keeping with the focus of this paper, we will limit our discussion to the ANS and EMG measures.
Arousal has been manipulated in psychophysiological laboratories in a variety of ways, including having subjects perform a diﬃcult arithmetic task; be threatened with impending electric shock; blow a balloon to bursting; and hold their hands in extremely cold water. In each of these tasks there is typically a signiﬁcant increase in activity of the sympathetic division of the ANS (e.g., increased palmar skin conductance and heart rate) and EMG. In more ‘real world’ situations, arousal has been observed in parachutists just before jumping from an aircraft, and from students just before taking critical exams. Again, there is evidence of increased activity in the sympathetic division of the ANS and EMG.
Some problems with the simple global arousal concept were emphasized by Lacey (1967). Most important for the present discussion, he and his colleagues showed that the various psychophysiological indices of arousal (e.g., skin conductance and heart rate) were often not signiﬁcantly correlated and, even more embarrassing for a simple arousal concept, these measures would go in opposite directions in many situations. For example, when subjects watched colored lights or listened to tones, skin conductance would increase but heart rate would decrease. Thus, diﬀerent stimulus situations would reliably produce diﬀerent patterns of physiological responding (‘situational stereotypy’ or ‘stimulus speciﬁcity’).
To this day arousal is a useful descriptive concept, but psychophysiologists remain careful not to overgeneralize from one response system to another, or from one stimulus situation to another. There is a far greater degree of speciﬁcity of response systems and situational reactions than was recognized by the early global arousal activation concepts.
The study of emotion has also had a long history in psychology and psychophysiology. Advances with both EMG and ANS measures since the 1960s have shed new light on our understanding of emotions.
Movement of facial muscles is a common way of expressing and communicating emotion and therefore facial EMG oﬀers one measure of emotions. Even small covert changes in facial expression can be detected as small electrical changes with surface EMG recordings from various muscles of the face. Several researchers have found that the muscle that pulls up the corner of the lip as in a smile (zygomaticus major) is more active when subjects report positive emotion, whereas the muscle that pushes the eyebrows together as in a frown (corrugator supercilii) is more active when subjects report negative emotion. Whether facial EMG can distinguish various speciﬁc emotions (e.g., anger, fear, jealousy, disgust, etc.) is more controversial. Even more controversial is whether ANS responses can distinguish between diﬀerent speciﬁc emotions. It is generally agreed that ANS activity occurs during emotional states, but the degree of speciﬁcity of that activity to diﬀerent emotions remains an interesting and unsettled issue.
Another speciﬁc EMG measure that has proved useful in the study of emotions is the acoustic startle reﬂex. The acoustic startle response includes a series of involuntary muscle movements following a loud abrupt noise. One of the fastest and more reliable of these movements in humans is the eyeblink reﬂex. The eyeblink reﬂex can be measured easily by placing electrodes on the surface of the skin over the orbicularis oculi muscle just below the lower eyelid. For an overview of the methods and many implications associated with this measure, see Dawson et al. (1999). An important characteristic of the eyeblink startle reaction is that its magnitude is enhanced in the presence of unpleasant negative emotions and is diminished in the presence of pleasant positive emotions. This has been demonstrated many times by startling human subjects while they view unpleasant pictures (e.g., mutilated face) or pleasant pictures (attractive nude). It has been shown that changes in the acoustic startle eyeblink reﬂex can provide valid psychophysiological indices of the emotional state of the individual at the time that the reﬂex is elicited. A review of this literature and a proposed theoretical account can be found in Bradley et al. (1999).
3. Transient Stimulus-Elicited Responses
3.1 Orienting, Defensive, And Startle Responses
Psychophysiologists who focus on ANS and skeletal motor activity distinguish among three broad types of transient responses seen in reaction to a wide variety of stimuli: the orienting response, the defensive response, and the startle response (Graham 1992). The orienting response is the response to any novel or signiﬁcant, but non-aversive, stimulus. It is thought to signal a shift of attention to that stimulus and to facilitate stimulus processing. Its components include a transient increase in palmar skin conductance, heart rate deceleration, constriction of the blood vessels in the skin (usually measured in the ﬁngertips), and dilation of the blood vessels of the head. The defensive response is the response to aversive stimuli, including painful or threatening stimuli. Its components include an increase in palmar skin conductance, an increase in heart rate, and vasoconstriction in both the blood vessels of the skin and the head. The startle response is the reaction to unexpected stimuli that are intense and have a rapid onset. While there are ANS components of the startle response, the component that has been most investigated, because of its reliable occurrence and slow habituation, is the startle eyeblink, as discussed above.
3.2 Classical Conditioning
A paradigm in which stimulus-elicited responses are studied that has been of continuing interest to psychophysiologists is classical conditioning. In paradigms in which the conditioned stimulus (CS) is several seconds long, with the unconditioned stimulus (UCS) occurring at CS oﬀset, the form of the conditioned response (CR) is generally observed to be that of a heightened orienting response to the CS (Hugdahl 1995). A general question frequently investigated has concerned the relationship between classical conditioning, a very simple form of learning, and the more complex forms of learning of which humans are capable, including verbally mediated processes. For instance, Dawson and his colleagues (Dawson and Schell 1985) studied the relationship between acquisition of the conditioned skin conductance response and the human subject’s conscious awareness of the relationship between the CS and the UCS, asking whether a person who is unaware of the CS–UCS contingency will show conditioning. In a series of studies in which awareness of the CS–UCS relation was prevented or delayed by a distracting secondary task, they found that a CR was seen only in subjects who became aware of the CS– UCS relation. Moreover, CRs developed only at or after the point in time in a series of CS–UCS trials when subjects indicated awareness. Thus, these results indicate that conscious relational learning is necessary for human classical conditioning of ANS responses with neutral CSs. On the other hand, the relationship between awareness and conditioning may be diﬀerent with certain paradigms used to establish the skeletal eyeblink conditioned response (Clark and Squire 1999).
In most psychophysiological studies of classical conditioning, the CSs have been fairly neutral stimuli such as simple tones or colored lights. In contrast, Ohman and his colleagues (see Hugdahl 1995) conducted a series of interesting studies of a diﬀerent class of CSs, those variously characterized as potentially phobic, fear-relevant, or biologically prepared, such as pictures of spiders, snakes, or angry faces. Ohman and his colleagues have found that CRs (usually the conditioned skin conductance response) conditioned to potentially phobic stimuli (a picture of a snake) are harder to extinguish than are CRs conditioned to neutral stimuli (a picture of a ﬂower). They require more non-reinforced presentations of the CS, and are resistant to instructional manipulation. That is, while responses conditioned to neutral stimuli can usually be abolished by instructing the subject that the UCS will no longer be delivered, so that the subject no longer has any cognitive expectancy that the UCS will follow the CS, responses conditioned to potentially phobic stimuli remain after such instructions, even in the absence of conscious expectancy of the UCS. Thus, psychophysiological techniques can be used in the laboratory to study the dynamics of ‘irrational’ conditioned responses, such as one may encounter in clinical phobias where the patient fears an object while realizing rationally that the object is harmless.
Psychophysiology is particularly useful in the study of psychopathology because it oﬀers nonverbal measures of psychological states and processes. It thus opens a window onto events that psychiatric patients are unlikely to be able to report verbally. Many psychophysiological measures have been studied with psychopathological patients but space limitation requires that we mention brieﬂy only a few measures in schizophrenia and psychopathy. For a general review of a greater variety of measures and a greater variety of psychopathological conditions, see Keller et al. (2000).
Schizophrenia is a psychotic disorder characterized by hallucinations, delusions, and disorganized thinking and Behavior. With ANS measures, especially skin conductance activity, there is usually tonic sympathetic hyper-arousal. On the other hand, with phasic orienting response ANS measures, there is usually hypo-reactivity, at least in sizable sub-groups of patients (for a review see Ohman 1981). Among the many unsettled issues is whether these ANS abnormalities are state-related and/or trait related. That is, if ANS abnormalities are present even before the schizophrenia patients show symptoms, and persist after the symptoms disappear, they are considered trait measures. However, if the abnormalities are present only when the patients are exhibiting psychotic symptoms then they are considered state related. Although this issue is still unsettled, preliminary evidence suggests that tonic autonomic hyper-arousal is state related, whereas phasic autonomic hyporeactivity may be trait related, especially when it is expressed relative to their general arousal state (Dawson et al. 1994). These ﬁndings suggest that hypo-reactivity may be related to a continuing vulnerability to schizophrenia, whereas the hyper-arousal may be a separate phase associated with the development of symptoms.
Psychopathy is a serious personality disorder characterized by antisocial Behavior, untruthfulness, irresponsibility, and lack of remorse or empathy. It has been hypothesized that the psychopath is primarily deﬁcient in fear reactivity, and consistent with this hypothesis is the reliable ﬁnding that psychopaths show less fear conditioning as indicated by poor skin conductance classical conditioning (Lykken 1957).
Another psychophysiological measure of fear and negative aﬀect mentioned earlier involves the acoustic startle eyeblink reﬂex. Recall that normal subjects give enhanced eyeblink startle reactions while observing unpleasant pictures, compared to startle while observing neutral or pleasant pictures. This is not true of psychopaths, or at least of signiﬁcant subgroups of psychopaths (Patrick et al. 1993). This ﬁnding also is consistent with the hypothesized deﬁcit in fear in some types of psychopathy.
5. Applied Psychophysiology
In addition to their use in investigating many questions of broad theoretical interest in Behavioral and social sciences, psychophysiological techniques have also been used in a number of ways to deal with speciﬁc applied problems. The two most often encountered areas of applied psychophysiology are biofeedback and the detection of deception (lie detection).
In the early development of learning theory, it was generally believed that while responses of the skeletal motor system could be instrumentally conditioned, responses of the ANS could only be classically conditioned. Because they were not under conscious, voluntary control, ANS responses would not respond to operant reinforcement contingencies. However, beginning in the early 1960s, investigators such as H. Kimmel, B. Engel, N. Miller, and D. Shapiro began to demonstrate that rewarding organisms, including humans, for speciﬁc ANS activity increased the amount of such autonomic activity, and that this could occur whether or not a human subject was aware of the reinforcement contingency. Thus, it was demonstrated that people could learn to increase the size and number of skin conductance responses, or to increase or decrease heart rate or blood pressure, if they were rewarded for doing so by the arrival of pleasant stimuli or the avoidance of unpleasant ones. It was soon discovered that people could learn these things if their only reward was being told that they were acquiring a desired response or performing a task set for them by, for instance, lowering the pitch of a tone that was controlled by their heart rate, or moving the needle on a dial that indicated blood pressure.
These ﬁndings were soon applied to treating the symptoms of many psychosomatic disorders. Such disorders typically involve ANS dysfunction (migraine headache, hypertension, Raynaud’s syndrome) or loss of control of skeletal muscle tension (tension headache). In clinical biofeedback applications, the patient is given an external stimulus, such as a tone or meter reading, that indicates the level of muscle tension, cerebral vasoconstriction, blood pressure, etc., and the patient’s task is to lower the pitch of the tone, move the meter indicator to the left, etc. This approach has been used with varying degrees of success as a therapeutic method in a wide variety of psychosomatic disorders (Carlson et al. 1994), and the training parameters that maximize its eﬀectiveness have been widely studied.
5.2 Detection Of Deception
Use of psychophysiological techniques in the detection of deception began in the early part of the twentieth century. There are principally two diﬀerent techniques in use, each with its strong advocates and critics. Both rely upon the fact that stimuli or information that are of signiﬁcance or importance to a person will elicit greater ANS activity than will less signiﬁcant, important stimuli. The Guilty Knowledge Technique, developed by Lykken (see Lykken 1981), relies on there being information known to the guilty person in a crime and to the polygraph examiner, but not to the innocent person. Thus, if a victim were wearing a blue shirt, a guilty person will orient more to the word ‘blue’ than to other colors when asked the color of the shirt and presented with alternatives, whereas the innocent person will not show diﬀerential orienting. The Control Question Technique, ﬁrst well described by Reid and Inbau (1977) and extensively investigated by Raskin and his colleagues, compares responses to ‘critical’ questions about a particular crime (‘Did you steal that red Porsche last Friday’?) with ‘control’ questions that are presumed to elicit greater arousal among those innocent of that crime, and in fact that are presumed to elicit lying by the innocent, than do the critical questions (‘Have you ever stolen anything of value’?). Laboratory investigations with ‘mock crimes’ have indicated 90 percent or better accuracy rates with these techniques, with the most common error by far being the false guilty ﬁnding. However, a number of investigators have raised questions about the accuracy rate in real-world situations, particularly with respect to whether or not adequate control questions could be found when a person is accused of a serious crime.
Psychophysiology oﬀers potentially powerful nonverbal, noninvasive, methodologies with which to study psychological processes in real time. Cognitive processes and emotional processes are studied in both normal and abnormal populations using psychophysiological measures and concepts. Thus psychophysiology lies at the interface of cognitive science, clinical science, and neuroscience and oﬀers the capability to bridge these disciplines.
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- Lykken D T 1957 A study of anxiety in the sociopathic personality. Journal of Abnormal and Social Psychology 55: 6–10
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