Intelligence may be defined as the ability to learn and think and to adapt to the environment. There are many different theories of intelligence. How one conceives of the development of intelligence depends, in part, on the theory one accepts.
It used to be thought that infant intelligence represents some kind of sensorimotor program that is relatively distinct from the program that unfolds later on during childhood. The reason for this view was that infant intelligence (measured as sensorimotor abilities) does not much correlate with childhood and adult intelligence (measured as learning and thinking abilities). More recent work has shown, however, that there are ways of conceiving of infant intelligence that are more useful than the conventional one.
Although age of acquisition of sensorimotor abilities generally does not predict later intelligence, one thing that does so is an infant’s preference for novelty. This apparent preference for novelty is associated with the moderate-discrepancy hypothesis, according to which infants prefer stimuli that are moderately discrepant, or different, from what they already know.
The preference for novelty explains why infants learn about things only when they are ready to learn about them. They do not waste their time attending to completely familiar things, or to things so new that they are overwhelming. Indeed, it may be that infants who prefer some degree of novelty are more intelligent than are those who do not. Joseph Fagan and Marc Bornstein have found that infants who show stronger preferences for novelty at ages 2 to 6 months are more likely to have high scores on intelligence tests at ages 2 to 7 years. Thus, new methods of measuring intelligence in infants show that infant intelligence may predict later intelligence.
What, exactly, is ‘later intelligence’? Several different views have been presented about what it is, and how it develops.
The psychometric view
A traditional view of intelligence is a psychometric one, according to which intelligence can be understood in terms of a set of underlying mental abilities that, in combination, work together to produce intellectual performance. Charles Spearman (1863-1945), a British psychologist, proposed at the turn of the 20th century that intelligence can be understood largely as comprising a single, general ability (g), which he believed to be mental energy. Another theorist, the American Louis Thurstone (1887-1955), believed that the essence of intelligence is not in a single factor, but rather in multiple primary mental abilities, such as verbal comprehension ability (e.g., vocabulary), inductive reasoning ability, and spatial ability. Most recently, Carroll (1993) has suggested that a hierarchical model can well explain intelligence, with general ability at the top, multiple primary abilities hierarchically below this general ability, and specific abilities under those.
According to the psychometric view, intelligence can develop in several different ways. The number of abilities (measured as factors) can increase, or abilities that already exist can split off into more refined and differentiated abilities (the so-called differentiation hypothesis), or children’s efficacy in applying the abilities can increase.
Most existing tests of intelligence are loosely based on the psychometric view of intelligence. There are two major tests. One test, the Stanford-Binet (now in its fourth edition), dates back to the work early in the 20th century of Alfred Binet (1857-1941) and Theodore Simon (1873-1961). The other, more widely used test is actually a set of tests, the Wechsler Intelligence Scales. There are separate scales for preschool and primary-school children, and for children who are older. Both tests yield IQs, or intelligence quotients, which have a mean of 100 and a standard deviation of 16 (in the case of the Stanford-Binet) or 15 (in the case of the Wechsler). These tests measure higher-order knowledge and judgment skills, such as vocabulary, arithmetical reasoning, and spatial skills.
The genetic-epistemological view
During the 1960s and 1970s, views of the development of intelligence were dominated by the Piagetian approach. Although the approach is no longer as influential as it once was, no theory has been as important in thinking about the development of intelligence as that devised by Piaget.
Piaget, who had worked with Binet and Simon, revolutionized the study of children’s intelligence by proposing that researchers could learn as much about children’s intellectual development from examining their incorrect answers to test items as from examining their correct answers. Through his repeated observations of children, including his own children, and especially through investigation of their errors in reasoning, Piaget concluded that coherent logical systems underlie children’s thought. These systems, he believed, differ in kind from the logical systems that adults use. If we are to understand development, we must identify these systems and their distinctive characteristics.
Piaget believed that the function of intelligence is to aid in adaptation to the environment. In his view (Piaget, 1972), the means of adaptation form a continuum ranging from relatively unintelligent means, such as habits and reflexes, to relatively intelligent means, such as those requiring insight, complex mental representation, and the mental manipulation of symbols. In accord with his focus on adaptation, he believed that cognitive development is accompanied by increasingly complex responses to the environment. Piaget further proposed that with increasing learning and maturation, both intelligence and its manifestations become differentiated (i.e., more highly specialized in various domains).
Piaget believed that development occurs in stages that evolve via equilibration, in which children seek a balance (equilibrium) between both what they encounter in their environments and what cognitive processes and structures they bring to the encounter, as well as among the cognitive capabilities themselves. Equilibration involves three processes. In some situations, the child’s existing mode of thought and existing schemas (mental frameworks) are adequate for confronting and adapting to the challenges of the environment; the child is thus in a state of equilibrium.
At other times, however, the child is presented with information that does not fit with the child’s existing schemas, so cognitive disequilibrium arises. That is, imbalance occurs when the child’s existing schemas are inadequate for new challenges the child encounters. The child consequently attempts to restore equilibrium through assimilation (i.e., incorporating the new information into existing schemas).
Under some circumstances, the child must somehow modify his schemas to allow for the new information, perhaps creating an overarching schema for animals into which he fits his existing schema for dogs. Piaget suggested that sometimes children modify existing schemas through accommodation (i.e., changing the existing schemas to fit the relevant new information about the environment). Together, the processes of assimilation and accommodation result in a more sophisticated level of thought than was possible previously. In addition, these processes result in the re-establishment of equilibrium, thus offering the individual higher levels of adaptability.
According to Piaget, the equilibrative processes of assimilation and accommodation account for all of the changes associated with intellectual development. In Piaget’s view, disequilibrium is more likely to occur during periods of stage transition. That is, although Piaget posited that equilibrative processes go on throughout childhood as children continually adapt to their environment, he also considered development to involve discrete, discontinuous stages. In particular, he divided cognitive development into three main stages summarized here: the sensorimotor, concrete-operational, and formal-operational stages. Others have added a preoperational stage, which may be better treated as a period of transition between the sensorimotor and concrete-operational stages. Because these stages are discussed elsewhere in this volume, they are not considered further here.
Neo-Piagetian theorists build upon a broad understanding of Piaget’s theory of cognitive development. Although each neo-Piagetian is different, most of them (a) accept Piaget’s broad notion of developmental stages of cognitive development; (b) concentrate on the scientific or logical aspects of cognitive development (often observing children engaging in many of the same tasks as those used by Piaget); and (c) retain some ties with the notion that cognitive development occurs through equilibration. Only a few neo-Piagetian theories are considered here.
Firstly, fifth-stage theorists do not posit an entirely different theory of cognitive development; instead, they build on the Piagetian four stages by suggesting a fifth stage beyond formal operations. Patricia Arlin proposed that a fifth stage of cognitive development is problem finding. In this stage, individuals come to master the tasks of figuring out exactly what problems they face, and deciding which problems are most important and deserving of their efforts toward solution.
Secondly, several theorists have suggested that logical reasoning beyond Piagetian formal operations might proceed to a fifth stage of dialectical thinking. Dialectical thinking recognizes that in much of life, there is no one final, correct answer, but rather a progression of beliefs whereby we first propose some kind of thesis, then later see its antithesis, and finally effect some kind of synthesis between the two, which then serves as the new thesis for the continuing evolution of thought. For example, adults use dialectical thinking when considering one extreme and then the other, subsequently incorporating only the best elements of each extreme.
The sociocultural view
In Piaget’s theory, cognitive development proceeds largely ‘from the inside out’ through maturation. Environments can foster or impede development, but Piaget emphasized the biological and hence the maturational aspect of development. Vygotsky’s (1978) theory takes an entirely different approach in emphasizing the role of the environment in children’s intellectual development. He suggested that cognitive development proceeds largely ‘from the outside in’ through internalization (i.e., the absorption of knowledge from context). Thus, social, rather than biological, influences are key in Vygotsky’s theory of cognitive development. According to Vygotsky then, much of children’s learning occurs through interactions within the environment, which largely determine what the child internalizes.
This interactive form of learning relates to Vygotsky’s second major contribution to educational and developmental psychology: the construct of the zone of proximal development (ZPD), sometimes termed the zone of potential development. The ZPD is the range of potential between a child’s observable level of realized ability (performance) and the child’s underlying latent capacity (competence), which is not directly obvious. When we observe children, what we typically observe is the ability that they have developed through the interaction of heredity and environment. To a large extent, however, we are truly interested in what children are capable of doing – what their potential would be if they were freed from the confines of an environment that is never truly optimal. Before Vygotsky proposed his theory, people were unsure how to measure this latent capacity.
Vygotsky argued that we need to reconsider not only how we think about children’s cognitive abilities, but also how we measure them. Typically, we test children in a static assessment environment, in which an examiner asks questions and expects the child to answer them. Whether the child responds correctly or incorrectly, the examiner moves to the next question or task on the list of items in the test. Like Piaget, Vygotsky was interested not only in children’s correct responses, but also in their incorrect responses to questions.
Figure 1. The components of the triarchic theory of successful intelligence.
Thus, Vygotsky recommended that we move from a static assessment environment to a dynamical assessment environment, in which the interaction between child and examiner does not end when the child responds, especially not if the child responds incorrectly. In static testing, when a child gives a wrong answer, the examiner moves on to the next problem. In dynamical assessment, when the child gives a wrong answer, the examiner gives the child a graded sequence of guided hints in order to facilitate problem solving. In other words, the examiner serves as both teacher and tester. The examiner provides the scaffolding children need in order to go from wherever they are in problem solving to the next step beyond. In general, learning proceeds most efficiently when scaffolding is provided to ensure that children have the necessary prerequisites for advancing beyond their current understandings.
The ability to use hints is the basis for measuring the ZPD, because this ability indicates the extent to which the child can expand beyond her or his observable abilities at the time of testing. Two children may answer a given problem incorrectly. However, a child who can profit from instruction can potentially go far, whereas a child who cannot is unlikely to acquire the abilities needed to solve not only the problem being tested, but also related ones. Several tests have been created to measure the ZPD.
Two modern theorists have proposed theories of intelligence and its development that view intelligence as a system.
Gardner (1999) has proposed a theory of multiple intelligences, according to which there are eight intelligences: linguistic, logical-mathematical, spatial, musical, bodily-kinesthetic, naturalist, interpersonal, and intrapersonal. Gardner believes that each intelligence is modular and largely independent of the others. Thus, development of one intelligence proceeds relatively independently of development of the others. Complex behavior requires an integration of the intelligences. The mechanism for this integration is not clearly specified by the theory.
Sternberg (1997) has proposed a triarchic theory of intelligence, according to which there are three different aspects of intelligence: analytical intelligence, creative intelligence, and practical intelligence. The analytical aspect of intelligence is the kind measured by traditional tests of intelligence (Fig. 1). The creative and practical aspects of intelligence are not measured by such tests. Sternberg has offered a theory of intellectual development that emphasizes the role of information processing in development. In particular, children develop in terms of acquiring new processes, strategies, and ways of mentally representing information.
What constitutes intelligence and how it develops continue to be sources of much debate and disagreement among psychologists. We are now confronted with a range of theories about intellectual development, each with its own appeal, and each focusing on different aspects of what may constitute intelligence. Nevertheless, current theories do manifest some common ground (e.g., a concern with changes in information processing abilities in Sternberg’s theory and in the approach adopted by neo-Piagetians). It remains to be seen whether anything approaching a unified theory about the development of intelligence can ever be achieved. Future research needs to seek more measures of what might constitute precursors to childhood intelligence during infancy that arise from a well-articulated theory. In this respect, a concern for cortical brain development as is evident in the emerging field of developmental cognitive neuroscience has potentially much to offer. In addition, we need to know more about the mechanisms of developmental transitions in intelligence, in which this emerging field may play a vital role.