The most systematic and methodologically grounded approach to studies on temperament in children has been followed during the past two decades by Buss and Plomin. Among child-oriented conceptualizations on temperament their theory is the closest to fulfilling the requirements of a theory as postulated by Popper and Kuhn (see Chapter 2). Referring to the criteria depicted inTable 3.1, the child-oriented theory of temperament developed by Buss and Plomin may be characterized as a causal (behavior-genetic), multidimensional, and whole-behavior-oriented conceptualization. This theory, although centered from its very beginning on children, is one of the few that offers a broad developmental perspective, including conceptualizations and studies on adult temperament.
Reviewing Buss and Plomin's publications in the domain of temperament, it is not easy to gain a full picture of the origins of their temperament theory. Influential for their view on temperament was undoubtedly the comparative approach to temperament as represented by Diamond (1957), whom Buss and Plomin (1975) regarded as the initiator of modern temperament research. Diamond's idea that four basic temperaments—fearfulness, aggressiveness, affiliativeness, and impulsiveness—are shared by man and our mammalian predecessors was important for developing their conception of the nature of temperament. Also, G. W. All-port's (1937) popular definition of temperament, in which not only the emotional nature but also the constitutional component of temperament was underlined, played an important role in Buss and Plomin's theorizing about temperament.
At the time that Buss and Plomin started their studies on temperament, Eysenck's theory of extraversion and introversion and his pioneering behavior-genetic studies in this domain were already known to personality psychologists. Thomas and Chess's studies on children's temperament also created a favorable context for Buss and Plomin's research on the temperament domain of personality.
The authors' own experience also influenced the construction of the behavior-genetic-oriented theory of children's temperament. Arnold H. Buss (196l), from the University of Texas, conducted one of the most systematic studies on human aggression. This involved him in studying a personality/temperament dimension present in both humans and animals. His empirical investigations led him to elaborate a broad evolutionary and developmental perspective on personality research (Buss, 1988, 1989a; Buss & Finn, 1987). Robert Plomin was a student of Buss. His 1974 doctoral dissertation (cited in Buss & Plomin, 1975) was aimed at studying parent-child interaction, with temperament the main variable under study. From the very start of his academic career Plomin became involved in intensive behavior-genetic studies (DeFries & Plomin, 1978; Plomin, 1976; Plomin,
DeFries, & Loehlin, 1977) at the University of Colorado, one of the leading centers in this domain of research. The combination of Buss's interests in aggression and Plomin's concentration on behavior genetics led these investigators to begin thinking about those aspects of personality that might be most heritable, fundamental, and present in early developmental stages.
Buss and Plomin's theory of temperament has been described in detail in two monographs (Buss & Plomin, 1975, 1984) and in several papers (see Buss, 1989b, 1991; Buss & Plomin, 1986; Strelau & Plomin, 1992). The authors defined "temperaments as inherited personality traits present in early childhood" (Buss & Plomin, 1984). This short definition comprises the core elements of their theory.
According to Buss and Plomin (1984), two definitional and inseparable criteria must be fulfilled to classify behavior characteristics as belonging to temperament. They have to be present from early childhood (during the first 2 years of life), and there must be an essential contribution of the genetic factor to individual differences in these behavior characteristics. Thus, a trait that shows essential heritability but is not present in early childhood as, for example, conscientiousness, cannot be considered temperament. The same refers to a behavior characteristic present in early infancy, the variance of which is not genetically determined, for example, smiling or laughter.
In the first version of their temperament theory, Buss & Plomin (1975) considered inheritance as the crucial criterion for deciding which trait should be referred to as temperament. Such criteria as stability over childhood, retention into maturity, adaptive value, and presence in primates and other mammals were considered secondary to inheritance. These criteria have not been treated recently as imperative, although they remain important in Buss and Plomin's theory. Thus, the authors assume that temperaments are characterized by some continuity that assures that "such early traits [temperaments] are likely to be the foundation on which later personality traits are built" (Buss & Plomin, 1984, p. 84). Temperament traits have an essential impact on personality development. Temperament, according to the authors, is a crucial part of human personality. In early childhood, characterized by lack of internal cognitive structures and limited experience, the child's temperament constitutes his or her whole personality, assuming that cognitive functioning (intelligence) is not included in the construct "personality" (Buss & Plomin, 1984; Buss & Finn, 1987). Buss and Plomin also postulated that temperament traits must be broad, referring to a wide class of behaviors and situations, Temperaments must show functional significance documented by the role they play in different kinds of human adjustment (Buss & Plomin, 1975).
Taking these criteria and considerations into account, as well as the data from many studies, Buss and Plomin (1984, 1986; Buss, 1991) distinguished three basic temperaments: emotionality, activity, and sociability—EAS, an acronym by which their temperament theory has often been labeled. The notion "temperament" has been used by Buss and Plomin in two different meanings. First, according to the definition just given, it refers to all three traits of which the structure of temperament is composed. Second, temperament is used as synonymous with temperamental trait; thus, according to the authors' view, there are three temperaments.
Emotionality. The authors defined emotionality as the tendency to be aroused easily and intensely; this tendency is expressed in a primordial emotion identified as distress. "Emotionality equals distress, the tendency to become upset easily and intensely" (Buss & Plomin, 1984, p. 54). Distress, which can be observed from the first day of life (the presence of crying), differentiates during infancy into fear (at the age of 2-3 months) and anger, the latter developing at the age of about 6 months. Fear is expressed in an attempt to escape (flight) from threatening (aver-sive) stimuli, whereas anger reveals itself in attacking and complaining as a response to annoying or frustrating stimuli.
Taking into account three components of emotions—expression, feeling, and arousal—the authors (Buss & Plomin, 1975, 1984) argued that the only component that makes it possible to measure genetically determined individual differences in intensity and temporal characteristics of emotions is arousal. The only emotions characterized by level of arousal exceeding the level of nonemotional states (e.g., orienting reaction) are distress, fear, and anger. Although a fourth emotion—sexual arousal—is high, it is not present in early childhood and, according to the authors, there is no evidence for genetic determination of individual differences in respect to sexual emotion. As can be seen, the authors did not include positive emotions in their emotionality temperament. The reason is simple. The level of arousal typical for positive emotions is below that of negative emotions and, moreover, they do not fulfill the definitional criteria of temperament. There are gender-specific characteristics of emotionality, boys scoring higher on the anger component of emotionality and girls scoring higher on the fear component. The authors hypothesized that these differences are determined by inherited gender differences as well as by gender role socialization.
Activity. According to Buss and Plomin (1975) the "level of activity refers to total energy output. . . . Activity is equivalent to movement" (pp. 31-32). Since movement refers to all behavior, it also means that activity may be expressed in any kind of behavior. The activity temperament in reference to individual differences in activity consists of two components: vigor and tempo, mostly positively correlated with each other. A very active person is strongly motivated to be energetic; that is, she or he expends energy in vigorous activity performed with rapid tempo. "The twin aspects of activity—vigor and tempo—are best seen in how a response is delivered (style)" (p. 33). In some individuals, or for some kinds of activity, the components of activity may not be correlated with each other.
Activity occupies a special place among the three temperaments. Every response is accompanied by expended energy, and thus varies in vigor (intensity) and tempo. This means that activity has a more diffused character as compared with the two other temperaments and so may be considered a stylistic trait. The authors' view on activity did not change in their revised theory of temperament (Buss & Plomin, 1984).
Sociability. In contrast to the other temperaments sociability has a directional component: seeking other persons. "Sociability is the tendency to prefer the presence of others to being alone" (Buss & Plomin, 1984, p. 63). This tendency has its roots in intrinsic rewards which result from social interaction with other persons. Buss and Plomin (1984) postulated that there are five social rewards underlying sociability: (1) presence of others, (2) sharing an activity, (3) receiving attention from others, (4) mutual responsivity expressed in such responses as agreement, disagreement, surprise, and interest, and (5) initiation of social interaction. These social rewards can be characterized by their extremes—absence and excess of reward. Absence of reward is seen as lack of social stimulation and, thus, as a source of low level of arousal, whereas excess of reward may be regarded as highly intensive social stimulation (resulting in a high level of arousal). Individuals high on sociability are more reinforced by social rewards and more upset by their deprivation.
The authors emphasize that any social interaction can be rewarding, and it is not the content of social rewards, such as sympathy, respect, or praise that is linked to sociability. Sociability as expressed in social interaction is developmentally specific. In infancy it plays a role in mother-infant interactions; it affects the type of attachment. Once mobile, infants and older children enlarge the range of social interactions significantly, especially in behavior with peers. Buss and Plomin (1975, 1984) suggested that the sociability temperament may be considered one of the two crucial components of extraversion, as postulated by H. J. Eysenck (1970), when extraversion was measured by means of the EPI.
In the 1975 version of their temperament theory, Buss and Plomin (1975) postulated that there are four temperaments, with impulsivity added to the three presented earlier. Thus, the theory in its first version was labeled by the acronym EASI. The main reason impulsivity has been removed from the list of traits composing the structure of temperament was lack of sufficient evidence regarding the heritability of this trait. Furthermore, impulsivity came out as a complex trait composed of inhibitory control, decision time, persistence in ongoing tasks and sensation seeking. Some of these components—sensation seeking and inhibitory control-are not present in early childhood (Buss & Plomin, 1984).
Since inheritance became the most crucial criterion for treating a trait as a part of temperament, Buss and Plomin devoted some effort to examining the genetic contribution to trait variance. Five studies in which the three temperaments were measured in MZ and DZ children (average age 43 months to 7;6 years) provided unequivocal evidence for the contribution of the genetic factor to individual differences in all three temperaments (Buss & Plomin, 1984). Table 3.2, which contains the average twin correlations across the five studies in which inventories constructed by the authors were applied, summarizes these data. The authors explained the (too) low intracorrelations for DZ twins by referring to contrast effects. A contrast effect, strongly present in fraternal twins, is the tendency to be perceived and treated by others as different. More recent data which correspond with the findings presented in Table 3.2 are discussed in Chapter 5.
After distinguishing three levels of arousal—behavioral, autonomic, and brain arousal, Buss and Plomin (1984) referred to them in the context of the three temperaments. As regards behavioral arousal that may vary from deep sleep to high excitement, its most obvious aspect is activity. Individual differences in au-tonomic arousal refer mainly to emotional behavior. The authors hypothesized that the sympathetic dominance of the autonomic nervous system (ANS) is linked to emotionality. The two components ofemotionality, fear and anger, are probably indistinguishable on the basis of autonomic arousal indices. "What is inherited in emotionality is the tendency to become physiologically aroused (sympathetic reactivity) regardless of whether the particular emotion is distress, fear, or anger" (Buss & Plomin, 1984, p. 54). In the authors'publications there is no direct statement regarding the postulated biological correlates of sociability. The authors' remarks that Eysenck's extraversion has its physiological background in the physiology of brain structures, and that sociability has a part in regulating the level of arousal (Buss & Plomin, 1975), leads to the assumption that brain arousal is a physiological correlate of sociability. To conclude the discussion of the biological bases of temperament, it is noted that, while there is plenty of evidence regarding the genetic contribution of individual differences in EAS temperaments, Buss and
TABLE 3.2. Twin Correlations for EAS Questionnaires
Twin correlations for EAS Scales
TABLE 3.2. Twin Correlations for EAS Questionnaires
Twin correlations for EAS Scales
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