PERSPECTIVES ON PSYCHOLOGICAL SCIENCE A Trio of Concerns Jerome Kagan Harvard University ABSTRACT—This essay assesses the two most significant areas and searching for the genetic contributions to psycho- changes in psychology over the past century: the attempt to logical properties. Although most scientists working within each localize psychological phenomena in restricted brain sites of these specialized areas are aware of the issues to be discussed, and the search for genetic contributions to behavior and investigators probing related domains and the public do not psychopathology. Although there are advantages to these always appreciate the conceptual problems that follow the new developments, they are accompanied by some ques- conclusions of this research. This article, by an aging member of tionable assumptions. Because the investigators in these this young, vital field, is addressed primarily to these latter two domains often relate variation in their biological measures groups. to variation in personality traits evaluated with question- The most significant change in psychology over the past naires, an analysis of the unique properties of the verbal- century is the search for biological, rather than experiential, report questionnaires is presented. It is suggested that contributions to human cognition, behavior, and emotion. There future research on human personality should try to com- are obvious advantages to the new biological perspective. Most bine semantic reports with behaviors and biological data psychologists working during the early decades of the last in order to arrive at more fruitful constructs. century were certain that experiences were the primary causes of change and variation in behavior, thought, and emotion and were generally unconcerned with where those experiences were It is useful to reflect occasionally on the current state of a life, represented in brain because there was no way to measure brain social institution, culture, or scientific domain and on the pos- activity. The extraordinary advances in technology over the past sible constellation of forces responsible for its transformation few decades have allowed the current cohort of researchers to over a period of time. Scientific disciplines are defined by the offer better answers to a pair of questions that have piqued relations they seek to discover and by the methods used to make human curiosity: How are experiences represented in the brain the discoveries. A large number of contemporary psychologists and to what degree does a person’s inherited biology interact have become interested in the relations between with their experiences to affect their behaviors and moods? biological states (primarily genetic features and brain states), on These questions have the same degree of mystery that used to the one hand, and behaviors, emotions, and cognitive processes, surround the puzzles of why like begets like, why some species on the other. However, contemporary research on the relation- become extinct, and why the sun and moon appear to change ship between biological processes and personality often rely on their locations on a regular schedule. Although the contempo- questionnaires to index the psychological concepts. Because rary enthusiasms have obvious advantages over past ideologies, these questionnaires assume a narrow and specific conceptu- they are not free of flaws. This should not be surprising. Psy- alization of these concepts, this issue deserves analysis. Second, chology is a young discipline, and the histories of biology, unlike physicists, chemists, and biologists, psychologists often chemistry, and physics reveal that most initial premises turned use the same concepts for observations that are based on out to be mistaken. Mars does not move at a constant velocity in a different sources of evidence before it has been shown that the circular orbit around the sun; the fertilized egg does not contain sources are compatible: for example, labeling a brain profile, a miniature human being. facial expression, avoidant action, and semantic report as ‘‘fear.’’ This practice can have misleading consequences, as the validity LOCALIZATION OF FUNCTION of a concept rests with the referential meaning of a term, as well as its sense meaning. This habit is common in two popular areas The search for restricted neuronal clusters that may be the of inquiry: localizing psychological functions in select brain foundations of equally specific psychological functions or rep- resentations of knowledge is not a novel pursuit but is part of a continuing effort to assess the biological contributions to all Address correspondence to Jerome Kagan, Department of Psychol- ogy, Harvard University, Cambridge, MA 02138; e-mail: jk@wjh. psychological phenomena (Campbell, 1905). The phrenologists harvard.edu. of the late 18th and early 19th centuries, who enjoyed sufficient Volume 2—Number 4 Copyright r 2007 Association for Psychological Science 361 A Trio of Concerns popularity to warrant the establishment of schools to train new cuits involving diverse areas of the cortex and brain stem members of this profession, argued that abstract psychological (Cabeza & Nyberg, 2000; Engels et al., 2007). An event as characteristics, including love, resided in specific places in the simple as the unexpected sound of a whistle activates 24 brain. Freud, who also believed that the id, ego, and superego different brain areas (Kiehl et al., 2005). The acquisition of a were instantiated in nervous tissue, was friendly to Wilhelm conditioned eyeblink reflex in mice generates activity in Fliess’s assertion that vascular changes in nasal tissue were a different genes and brain sites during the early phases of con- valid sign of genital arousal (Sulloway, 1979). The following ditioning but not during the later phases (Park, Onodera, discussion does not address the philosophical debate over the Nishimura, Thompson, & Itohara, 2006). feasibility of replacing psychological terms with biological ones. The argument against a strict interpretation of localization Rather, this discussion deals with an issue that empirical evi- does not deny that some properties of sensory events are pro- dence can inform: Could any psychological function be medi- cessed in particular neuronal sites; for example, the perception ated by a single restricted set of neurons? The answer to this of contour, motion, high frequency tones, the fragrance of roses, question is independent of whether or not psychological phe- and the taste of sugar is dependent on activity in restricted areas, nomena can be ‘‘reduced’’ to a biological vocabulary. even though every visual perception requires both the thalamus It is worth noting that the attraction to localization is enhanced and the visual cortex. But the more abstract psychological by the wish to find a single cause for each distinct event. During functions and representations that are constructed from these the years following the initial positing of the gene a century ago, elementary sensory components are usually mediated by many most biologists were friendly to the premise that each biological sites and do not appear to be seriously localized. function could be localized in a specific gene. The Nobel Lau- The error in the argument for localization is the assumption reate Herman Muller penned an oft-cited phrase, ‘‘One gene, that if a select area of the brain is reliably activated by an event one enzyme.’’ One possible basis for this bias to attribute each or task, then the psychological process being engaged by the effect to a single cause is the universal experience of noting that event is probably localized in that same area. For example, the the conscious awareness of a particular object, say a spoon, is presentation of pictures of objects that are associated with almost always caused by the actual presence of a spoon in the well-learned motor movements activate both the brain areas visual field; hallucinated spoons are rare events. There is a mediating motor behavior (e.g., premotor cortex) and the areas perfect correlation between the perception of a white lawn in the activated by the visual perception of objects (e.g., fusiform area in morning and of a snowfall during the previous night. the posterior cortex; Weisberg, van Turennout, & Martin, 2007). However, the histories of the natural sciences have repeatedly The nucleus accumbens is usually activated when animals or taught scholars that many intuitions that originate in everyday humans prepare to make a response in order to gain a reward. experience are flawed guides to the most powerful explanatory However, that empirical correlation does not require the con- ideas. Aristotle thought that emotions were localized in the chest clusion that this structure contributes to the hedonic component area because this was the apparent location of strong feelings. of reward, as one must distinguish between the effort expended to Nothing in Murray Gell-Mann’s experiences could have led him obtain a reward and the sensory experience of reward (Baldo & to posit the concept of quarks. Darwin could not have imagined Kelley, 2007; Salamone, Correa, Farrar, & Mingote, 2007). In that the extraordinary variation among animals is traceable to addition, other areas, especially the orbitofrontal prefrontal cor- the different arrangements of only four bases. tex, are necessary for evaluating the reward value of an event Nonetheless, the idea of localization met little resistance (Jensen et al., 2006). Adults showed increased blood flow to six when