Neuromaturational theories (child development)

 

Introduction

Ontogenetic development occurs as a consequence of genetically determined structural changes in the central nervous system that can in turn give rise to orderly modifications in function. Thus, whatever the function, development conforms to an inevitable and invariable linear sequence of achievements (or milestones), with little or no assistance from the prevailing environment.

Redolent of the theory of the immortal germ plasm designed by August Weismann (1834-1914) to account for the genetic mechanisms of inheritance, this depiction of development continues to persist in text topics on human development that devote a section (rarely a chapter) to what has become known as neuromaturational theories. Typically, two names have been associated with such theories: Arnold L. Gesell (Fig. 1) and Myrtle B. McGraw (Fig. 2). Consequently, the history of so-called neuromaturational accounts of development is restricted to brief, and as a result distorted, descriptions of the research endeavors of these two eminent developmental scientists. Such descriptions inevitably go on to report the demise of neuromaturational theories of development, with the epitaph “of historical interest, but no longer relevant.” Nothing could be further from the truth, and it leaves one pondering whether some writers of developmental text topics have ever read the original (as in ‘source’ and ‘originality’) writings of Gesell and McGraw.

Previewing the conclusions

Scientists, unlike hermits, do not work in a vacuum divorced from contemporary and historical influences on their research interests. As Isaac Newton (1642-1727) wrote to fellow physicist Robert Hooke (1635-1703) in a letter dated February 5, 1675: “If I have seen further it is by standing on the shoulders of giants.” Who were the influential ‘giants’ with regard to the research and writings of Gesell and McGraw? Answers to this question lead to the conclusion that neuromatu-rational theories as depicted above are a caricature when applied to influences that motivated the wide-ranging works of Gesell and McGraw.

It becomes further evident that neither was a ‘neuromaturationist’ in the strictest sense when one considers what they actually wrote. Even though both frequently used the term maturation, they did so as a means of combating the excesses of behaviorism and its doctrinal insistence that the human newborn was nothing more than a tabula rasa. Thus, perhaps we should conclude that ‘neuromaturational’ is an inappropriate adjective with which to qualify their respective theoretical stances – a conclusion they reinforced by the fact that they not only converged, but also most noticeably diverged, in their speculations about the determinants of development.

Historical and contemporary influences

From Comenius to Dewey

The intellectual heritage implicit in the writings of both Gesell and McGraw can be traced back to Jean-Jacques Rousseau (1712-1778) and before him John Amos Comenius (1592-1670). Rousseau offered the first psychological theory of child development in his topic Emile (1762). While he portrayed development as an internally regulated process, he was by no means a strict maturationist as he emphasized that the spontaneously active child is ultimately a product of his own exploratory behavior and the environmental challenges it creates.

The intermediary link between Rousseau’s ideas on the nature of the child and those of Gesell and McGraw was John Dewey (1859-1952). Fascinated by the latter’s theory of enquiry and related research on infant and child development, the teenaged McGraw corresponded with Dewey from 1914 to 1918, and subsequently followed his courses at Columbia University. Dewey had a crucially important influence on McGraw’s research agenda and in turn his theorizing substantially benefited from her findings (Dalton & Bergenn, 1995b, pp. 1-36). As for Gesell, he was influenced by Dewey’s theory from two sources. Firstly, through the writings of G. Stanley Hall (Fig. 3) on child education, and secondly by his wife and some time co-author Beatrice Chandler who was a devotee of Dewey’s pragmatic philosophy.

Arnold Lucius Gesell (1880-1961).

Figure 1. Arnold Lucius Gesell (1880-1961).

Dewey’s rich and complex theory as expressed in his ideas on the development of judgment was an attempt to resolve the mind-body problem such that a static ‘being’ could be reconciled with a dynamical ‘becoming.’ Important in this respect were the related theories of Michael Faraday (1791-1867) and James Clerk Maxwell (1831-1879) on electrical and magnetic forces. Dewey believed that the laws of energy derived from these theories could be applied to the study of infant development. This step was taken by McGraw in one of her most detailed investigations on the development of bipedal locomotion, which for its time was technically sophisticated (Fig. 4).

For Dewey, and for McGraw, infants devote a considerable expenditure of kinetic energy in their first attempts at counteracting the gravitational field and subsequently in sitting, prehension, and the various forms of locomotion. For bipedal locomotion, at least, the dissipation of kinetic energy is expressed in a non-linear fashion, with the transition from unsupported to supported walking as shown by McGraw (Fig. 4). In general, however, development involves a gradual reduction in this expenditure through improvements in the transformation and redistribution of energy by the brain (and presumably by the musculoskeletal system in interaction with the central nervous system). The outcome is a series of overlapping phases during which there is a selective elimination of unnecessary movements in such actions. During these phases, movements become increasingly integrated and coordinated, thereby allowing more stable energy-efficient states of ‘being’ to be achieved.

Myrtle Byram McGraw (1899-1988)

Figure 2. Myrtle Byram McGraw (1899-1988)

Granville Stanley Hall (1844-1924).

Figure 3. Granville Stanley Hall (1844-1924).

 Methodological aspects of the study by McGraw and Breeze (1941) on the energetics of unsupported and supported walking in fifty-two infants. (A) Infants walked across a glass-topped table covered in evaporated milk and on top of which was placed a rubber mat. Positioning a mirror below the table at an angle of 45° enabled images of footprints to be recorded. Black markers were attached to the lower legs and thighs and another to that "... corresponding to the level of the center of gravity as a whole" (p. 276). Successive footprints and displacements of the markers on both sides of the body were registered by means of a 16mm camera at a sampling rate of 32 frames per second. (B) An editing camera was used to to project recordings onto a screen so that single and double stance times as well as changes in marker displacements could be plotted frame-by-frame. (C) A frame-by-frame plot of footprints indicating single and double stance phases. (D) A frame-by-frame plot of paths followed by the centers of gravity of the whole body, thigh, and lower leg. A number of measures to capture the 'energetic efficiency of locomotion' were derived. One was based on translational kinetic energy: average kinetic energy of a projectile / average kinetic energy of the leg moving over the same horizontal distance. This ratio revealed little change throughout supported walking and a sudden increase with the onset of unsupported walking. Subsequently, there was evident variability, both between and within infants, in the amount of kinetic energy expended.

Figure 4. Methodological aspects of the study by McGraw and Breeze (1941) on the energetics of unsupported and supported walking in fifty-two infants. (A) Infants walked across a glass-topped table covered in evaporated milk and on top of which was placed a rubber mat. Positioning a mirror below the table at an angle of 45° enabled images of footprints to be recorded. Black markers were attached to the lower legs and thighs and another to that “… corresponding to the level of the center of gravity as a whole” (p. 276). Successive footprints and displacements of the markers on both sides of the body were registered by means of a 16mm camera at a sampling rate of 32 frames per second. (B) An editing camera was used to to project recordings onto a screen so that single and double stance times as well as changes in marker displacements could be plotted frame-by-frame. (C) A frame-by-frame plot of footprints indicating single and double stance phases. (D) A frame-by-frame plot of paths followed by the centers of gravity of the whole body, thigh, and lower leg. A number of measures to capture the ‘energetic efficiency of locomotion’ were derived. One was based on translational kinetic energy: average kinetic energy of a projectile / average kinetic energy of the leg moving over the same horizontal distance. This ratio revealed little change throughout supported walking and a sudden increase with the onset of unsupported walking. Subsequently, there was evident variability, both between and within infants, in the amount of kinetic energy expended.

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The notions of integration and coordination, according to Dewey, were evident in the continuing bidirectional relationships between motor and cognitive functions. Consequently, it was for him an artificial exercise, and thus biologically inappropriate, to compartmentalize development into separate functions. Doing so would undermine our understanding of how consciousness developed as it involves not just the mind, but also the mind in interaction with the body. To use Dewey’s terminology, the development of consciousness was the “awareness of difference in the making.”

Dewey, like Baldwin and Piaget, took account of Darwin’s impact on psychology in his theory building, as did Gesell through his exposure to the arch-Darwinist and avid supporter of recapitulation theory, Stanley Hall. While Dewey never fully ascribed to Darwin’s claim that development abided by a universal sequence, Gesell adopted it as a cornerstone of his theory. Apparently, McGraw displayed some hesitancy in applying Darwinian thinking to her work, feeling that it diverted attention away from a proper understanding of proximate mechanisms in development (Dalton & Bergenn, 1995a, pp. 207-214). Nevertheless, both she and Dewey can be read as subscribing to Darwin’s theory of natural selection, at least in terms of a metaphor applicable to development. Dewey’s selectionist account of development is echoed in McGraw’s (1935) conclusion that developing infants are engaged in a process of selecting and refining combinations of movements and postures best suited to gaining ascendancy over a new task or challenge. In this sense, they foreshadowed a key feature of Gerald Edelman’s theory of neuronal group selection.

Embryology

An important contemporary influence on Gesell and McGraw was the rise of experimental embryology, which reached a peak during their most research-intensive period (viz., the 1930s and 1940s). Figures in this field such as Ross G. Harrison (1873-1959) had already expressed the view that embryogenesis was not predetermined, but instead relied on interactions between cells and between them and the extracellular environment, a view in keeping with Gottlieb’s concept of probabilistic epigenesis. By the time Gesell and McGraw embarked on their respective programs of research, such a view had become a commonly held principle among embryologists. For certain, they were keenly aware of such embryological principles and readily incorporated them into their work. Thus, we find Gesell writing: “The organismic pattern of one moment, responsive to both internal and external environments, influences the pattern of succeeding moments. In a measure, previous environmental effects are perpetuated by incorporation with constitution” (Gesell & Thompson, 1934, p. 294). For her part, McGraw expressed her indebtedness to embryology in the following way: “… it is the experimental embryologists and not psychologists who deserve credit for formulating the most adequate theory of behavior development. It is they who are revealing the process of morphogenesis, and it is they who are bringing the most convincing experimental evidence to bear upon an evaluation of the intrinsic and extrinsic factors in the process of growth” (McGraw, 1935, p. 10). She then goes on to state in a manner equally applicable to Gesell: “In many ways development as manifest in the early metamorphosis of the germ cells is extraordinarily similar in principle to that shown in the development of behavior in the infant and young child” (p. 10). Undoubtedly, the embryologist with the greatest impact on Gesell and McGraw was  E. Coghill (Oppenheim in Dalton & Bergenn, 1995a, pp. ix-xiv). Coghill had embarked on an intensive study of changes in the swimming movements of salamander larvae and embryos in 1906, with the aim of identifying the neural mechanisms underlying their behavioral development. His theoretical approach and findings influenced Gesell and especially McGraw in a variety of ways (Fig. 5). Three of these relevant to both of them can be mentioned. Firstly, behavioral development stemmed from an orderly sequence of changes in the nervous system (a standpoint perhaps shared more by Gesell than McGraw). Secondly, from the beginning, behavior is expressed as a total integrated pattern and from which individual functions emerge during development (Coghill’s principle of the integration and individuation of behavior, according to which experience and learning make significant contributions to development). Thirdly, behavioral development does not originate in a bundle of reflexes triggered into a chain-like response to external stimulation. Instead, it commences as a coordinated pattern generated by a spontaneously active nervous system (another standpoint perhaps shared more by Gesell than McGraw). This last point reveals something about Coghill’s strong opposition to behaviorism and its close cousin in neurophysiology, reflexology (Fig. 6).

Behaviorism

If embryology, with its emphasis on reciprocal structure-function relationships during development, was a source of inspiration for Gesell and McGraw, then behaviorism posed a definite threat to the future of their research. Of course, we are not talking about just any sort of behaviorism, but rather the radical formulation promulgated by John B. Watson (1878-1958). Attaining the apex of its dominance during the 1930s and 1940s, Watson’s radical environmentalism banned not only the use of the introspective method, but also concepts having to do with the internal regulation behavior that were so essential to the visions of development held by Gesell and McGraw. Why he espoused such an extreme view is not entirely clear. His Ph.D. thesis (1903) concerned the issue of how behavior and cortical myelination co-developed in the rat, and subsequently he carried out ethological research together with his student Karl S. Lashley (1890-1958) on the behavioral development of terns. Perhaps the turning point was his justifiable dissatisfaction with the concept of instinct as could be found in the writings of William McDougall (1871-1938) at the time. Whatever the case, Watson never studied child development, except for an abortive attempt to classically condition the human newborn. He did manage, however, to divorce mainstream (American) developmental psychology from its roots in biology that had been established by the likes of Baldwin and Stanley Hall before him.

A specific instance of Coghill's influence on McGraw's research. (A) The S-stage in the development of swimming movements in the salamander larva, one of three stages identified by Coghill, with the prior two being termed the Early Flexure and Coil stages. (From Coghill, 1929, as cited in  E. Coghill, this volume.) These observations provided McGraw with the motivation for studying developmental changes in the swimming movements of human infants. (B) Phases in the swimming movements of the human newborn (A), at about 2-3 months (B) during which they become more variable, and approximately coinciding with the achievement of unsupported bipedal locomotion (C). The newborn movements, no longer present when the infant is placed in water after phase B, suggest that they are ontogenetic adaptations to the intrauterine environment, with their 'reappearance' at phase C having to do with practice effects as in her co-twin study. They also demonstrate the effects of decreasing gravitational constraints on the behavior of the newborn and McGraw considered them to be better organized than either neonatal crawling or stepping movements.  A specific instance of Coghill's influence on McGraw's research. (A) The S-stage in the development of swimming movements in the salamander larva, one of three stages identified by Coghill, with the prior two being termed the Early Flexure and Coil stages. (From Coghill, 1929, as cited in  E. Coghill, this volume.) These observations provided McGraw with the motivation for studying developmental changes in the swimming movements of human infants. (B) Phases in the swimming movements of the human newborn (A), at about 2-3 months (B) during which they become more variable, and approximately coinciding with the achievement of unsupported bipedal locomotion (C). The newborn movements, no longer present when the infant is placed in water after phase B, suggest that they are ontogenetic adaptations to the intrauterine environment, with their 'reappearance' at phase C having to do with practice effects as in her co-twin study. They also demonstrate the effects of decreasing gravitational constraints on the behavior of the newborn and McGraw considered them to be better organized than either neonatal crawling or stepping movements.

Figure 5. A specific instance of Coghill’s influence on McGraw’s research. (A) The S-stage in the development of swimming movements in the salamander larva, one of three stages identified by Coghill, with the prior two being termed the Early Flexure and Coil stages. (From Coghill, 1929, as cited in  E. Coghill, this volume.) These observations provided McGraw with the motivation for studying developmental changes in the swimming movements of human infants. (B) Phases in the swimming movements of the human newborn (A), at about 2-3 months (B) during which they become more variable, and approximately coinciding with the achievement of unsupported bipedal locomotion (C). The newborn movements, no longer present when the infant is placed in water after phase B, suggest that they are ontogenetic adaptations to the intrauterine environment, with their ‘reappearance’ at phase C having to do with practice effects as in her co-twin study. They also demonstrate the effects of decreasing gravitational constraints on the behavior of the newborn and McGraw considered them to be better organized than either neonatal crawling or stepping movements.

Given their affinity with Coghill and Dewey, it is not surprising that Gesell and McGraw also opposed radical behaviorism as a means of understanding development. Certainly, Gesell was more outspoken in this respect and both he and McGraw were forced by Watson’s polemics to defend and refine their own theoretical stances on child development. What were the defining features of their respective theories?

Table 1. Gesell’s seven morphogenetic principles, with their interpretations, examples taken from his own writings and analogous terms used by others. Most of them were derived from embryology and some of them have interdependent meanings. The overriding principle is that of self-organization.


Principle

Interpretation

Gesellian example

Similar terms

1. Individuating fore-reference

Two aspects: 1. organism develops as a unitary whole from which differentiated functions arise (i.e., ‘being’ is sustained in the face of ‘becoming’); 2. neural mechanisms present before they are functionally expressed

Neural ‘machinery* for locomotion is developed before the child can walk

Systemogenesis and environmentally or experience-expectant development of structures and functions

2. Developmental direction

Development proceeds in invariant cephalo (proximal) – caudal (distal) direction as well as following a proximo-distal trend

Infant gains control over muscles of the eyes, neck, upper trunk, and arms before those of the lower trunk and legs

Gradients in morphogenetic fields

3. Spiral

reincorporation

Loss and (partial) recurrence of behavioral patterns (regressions as well as progressions) that lead to emergence of new ones, with development appearing to repeat itself at higher levels of organization

As the infant changes from being able to move in prone, elevated, and finally the upright position, there is a partial repetition of previous forms of leg activity.

Repetition (of abilities at increasingly higher levels of organization)1

4. Reciprocal interweaving

Periodic fluctuations in dominance between functions, and between excitation and inhibition. Applied not only to the changing dominance between flexor and extensor muscles, but also to perceptual and emotional development. Similarity with Piaget’s concept of decalage and thus to the process of equilibration

Alternations in hand preference during infant development that include a period of no preference.

Heterochrony and systemogenesis

5. Functional asymmetry

Development begins in a symmetrical state that has to be ‘broken’ in order to achieve lateralized behavior

Symmetry is ‘broken’ initially with the appearance of the asymmetrical tonic neck posture in neonatal life, which forms the origin of a subsequent hand preference


Symmetry breaking (in physics)

6. Self-regulatory fluctuation

Developing system in state of formative instability in which periods of equilibrium alternate with periods of disequilibrium. Accordingly, development is a non-linear process

Evident in changes in the developing relationships between sleep and wakefulness

Self-organization

7. Optimal tendency

Achievement of end-states in development through the action of endogenous compensatory mechanisms, which serve to ‘buffer’ the developing organism from undue external perturbations

Most infants achieve independent bipedal locomotion without any specific training at about the same age, despite temporary setbacks such as illnesses

Canalization and the mechanism of homeorhesis, both of which stem from the concept of equifinality

1 Derived from T. G. R. Bower and J. G. Wishart, 1979. Towards a unitary theory of development. In E. B. Thoman, ed., Origins of the Infant’s Social Responsiveness. Hillsdale, NJ: Erlbaum, and a feature of Bower’s model of descending differentiation applied to both perceptual and motor development.

Arnold Gesell the theoretician and tester

On the possibility of a behavioral morphogenesis

The anchor point of Gesell’s theory of development was morphogenesis, the study of change in the physical shape or form of the whole organism by means of growth and differentiation across ontogenetic (or phylogenetic) time. In this respect, he was greatly influenced by the Scottish zoologist D’Arcy Wentworth Thompson (1860-1948) and his topic Growth and Form (1917). Today the mechanisms of growth and differentiation are couched in terms of symmetry breaking following the seminal work of Alan Turing (1912-1954) on modeling the effects of chemical gradients in morphogenetic fields, something that Gesell was aware of toward the end of his working life.

According to Gesell, behavior had a changing morphology, and development, like physical growth, was a morphogenetic process that was revealed in transformations of the “… architectonics of the action system” (Gesell & Amatruda, 1945, p. 165). Morphogenesis was more than just a metaphor for Gesell: behavioral development conformed to the same processes of pattern formation as for the growth of anatomical structures, and its study required a topographical approach (partly via cinematography) in order to capture age-related alterations in the patterns of movement (e.g., prehension) and posture (e.g., the asymmetrical tonic neck configuration of head, arms, and legs). He endeavored to encapsulate these processes in his seven morphological principles or laws of growth (Table 1) and to depict their most salient features with the aid of spatial-temporal illustrations (Fig. 7).

What is clear from reading the later publications of Gesell (e.g., Gesell & Amatruda, 1945) is that his theory of behavioral morphogenesis complied with one overarching principle: self-regulation or what is now referred to as self-organization in open systems. He, like McGraw, was acquainted with General system theory as propounded by Ludwig von Bertalanffy (1901-1972) in his attempt to provide a theoretical framework for the unification of biology and physics through the agency of irreversible thermodynamics. Gesell was also becoming familiar with the approach of Ilya Prigogine (1917-2003) to this branch of physics and thus to how living systems evade the maximum entropy created by the Second law of thermodynamics. One can only speculate how Gesell would have incorporated the non-linear dynamics of irreversible thermodynamics and related theories into his own morphogenetic theory, but it is indisputable that for him development was a self-organizing process.

On the meaning of maturation

If development was a process imbued with self-organizing capacities, what then was the mechanism of ontogenetic change in Gesell’s theory? It is in this regard that we confront the most persistent representation of his theory, namely, that the ‘motor’ driving such change was maturation. Originating in embryology, the meaning of maturation was restricted there to the formation of gametes (ova and spermatozoa) from the oogonia and spermatogonia of the female and male gonads, respectively. As such, it refers to the first of the major stages in metazoan embryological development that is followed by fertilization, cleavage, and the stages of the blastula and neurula. In Gesell’s theory, maturation was not only a formative agent in development, but also even more so a stabilizing mechanism that ensured the ontogenetic achievement of species-characteristic end states. Thus, it has considerable kinship with the notion of canalization as advanced by the geneticist-cum-embryologist Conrad H. Waddington (1905-1975).

The obdurate misrepresentation of Gesell’s theory stems not only from a neglect of how he conceptualized development, which he used to replace the by-then-outmoded instinct concept. What tends to be overlooked is that he accorded both learning and experience equality with maturation as is evident in the previous citation from Gesell & Thompson (1934). What united learning, experience, and maturation in Gesell’s theoretical edifice was his concept of growth (Oppenheim, 1992). Growth for him was the functional enhancement of behavioral adaptations that included responses to internal and external environments, with the rider that the distinction between ‘internal’ and ‘external’ was ultimately an inexpedient exercise. Over the years, and perhaps as a debating point to counteract the excesses of radical behaviorism, he subtly altered his stance on the maturation versus learning debate that came to replace the hereditary-environment controversy. So, by the middle of the 1940s, he expressed the following, much-quoted, statement: “The so-called environment, whether internal or external, does not generate the progressions of development. Environmental factors support, inflect, and specify; but they do not engender the basic forms and sequences of development” (Gesell, 1946, p. 313). Such a statement is strikingly reminiscent of the roles of experience in development delineated by Gottlieb: maintenance (cf., support), facilitation (cf., inflect), and induction (cf., specify).

(A) Reflexology: a schematic representation of the chain-reflex model. When the first reflex associated with a muscle is elicited by external stimulation, its output triggers the next reflex and so on. With elicitation of the last reflex in the chain, its output serves to re-elicit the first one and thus the movement is repeated as in locomotion. Opposed by Coghill, this model was also severely criticized by Lashley in 1930 as an unrealistic model of motor control. (B) Coghill's approach to behavioral development was akin to the Preyer-Tracy hypothesis of autogeneous motility, which today is reflected in the central pattern generator (CPG) theory. A CPG is taken to be a network of of spontaneously active interneurons situated, for example, in the spinal cord and which emits modulated rhythmical electrical discharges that activate muscles in coordinated fashion, such as those involved in locomotion. With thanks to Hans Forssberg for both illustrations.  

Figure 6. (A) Reflexology: a schematic representation of the chain-reflex model. When the first reflex associated with a muscle is elicited by external stimulation, its output triggers the next reflex and so on. With elicitation of the last reflex in the chain, its output serves to re-elicit the first one and thus the movement is repeated as in locomotion. Opposed by Coghill, this model was also severely criticized by Lashley in 1930 as an unrealistic model of motor control. (B) Coghill’s approach to behavioral development was akin to the Preyer-Tracy hypothesis of autogeneous motility, which today is reflected in the central pattern generator (CPG) theory. A CPG is taken to be a network of of spontaneously active interneurons situated, for example, in the spinal cord and which emits modulated rhythmical electrical discharges that activate muscles in coordinated fashion, such as those involved in locomotion. With thanks to Hans Forssberg for both illustrations.

On developmental testing

Gesell was not only a psychologist, but also a pediatrician by training. The fusion of these two professions in his academic career led him inexorably to what has become his defining contribution to developmental psychology: the derivation of normative, age-based, criteria for use in developmental diagnosis, which culminated in his battery of tests referred to as the Gesell Developmental Schedules.

Gesell's depiction of the morphogenetic principles he proposed as giving rise to the formation of behavioral patterns and which he termed a 'time-space diagram' or 'dynamic map.' The shaded area refers to the 'corpus of behavior', which consists of potential and achieved expressions of the developing action system. The lower-case letters a, b, c, and d stand for traits or their parts, which overtime merge into a developed complex of traits (D). The numbers associated with these letters represent the enhancement or elaboration of a trait, either of itself or through its integration with a related one. The broken lines denote latent traits that still have to be expressed in behavior, while the solid lines indicate dominant ones, with the former serving as replacements for the latter should that be required (e.g., as a consequence of focal brain damage). The behaviors at the edge of the shaded area (b2, a4, etc.) are those that are overtly manifest. In particular, this map illustrates the principle of reciprocal interweaving.

Figure 7. Gesell’s depiction of the morphogenetic principles he proposed as giving rise to the formation of behavioral patterns and which he termed a ‘time-space diagram’ or ‘dynamic map.’ The shaded area refers to the ‘corpus of behavior’, which consists of potential and achieved expressions of the developing action system. The lower-case letters a, b, c, and d stand for traits or their parts, which overtime merge into a developed complex of traits (D). The numbers associated with these letters represent the enhancement or elaboration of a trait, either of itself or through its integration with a related one. The broken lines denote latent traits that still have to be expressed in behavior, while the solid lines indicate dominant ones, with the former serving as replacements for the latter should that be required (e.g., as a consequence of focal brain damage). The behaviors at the edge of the shaded area (b2, a4, etc.) are those that are overtly manifest. In particular, this map illustrates the principle of reciprocal interweaving.

As pointed out by others, there is curious tension between Gesell the theoretician and Gesell the tester. On the one hand, he had articulated a complex and subtle theory designed to capture the development of the whole child. On the other hand, his schedules appear to bear little relationship to his theory, with the ‘typical’ child’s development being disassembled into one of several functional domains that have been incorporated into subsequent scales of infant development. His test battery, which covered ten ages, was intended to serve two main purposes. Firstly, to identify signs of deviant development as early as possible, despite the fact that the norms for each item were appropriated from testing children from middle-class families of North European ancestry. Secondly, and resting on the embryological concept of competence, to provide an indication of ‘readiness for schooling.’ In pursuit of that purpose, it was never really made clear by Gesell whether it also implied a ‘readiness for learning.’

A maturationist?

The truncated overview of Gesell’s prodigious and diverse publications does not entirely justify his continuing categorization as a ‘maturationist’ who simply rendered an account of ontogenetic development within the restrictive confines of neural determinism. A careful reading of his more theoretically oriented publications (e.g., Gesell & Amatruda, 1945) should dispel the commonplace supposition that he held such a ‘one-cause’ theory of development. Gesell was a pioneering student of child development who had many ‘firsts’ to his name: the first to employ the co-twin method, the first to use one-way observation mirrors together with cinematography in recording infant and child behavior, and the first to employ these and other techniques to study systematically the development of sleep and wakefulness (and the transitions between them) in both preterm and fullterm infants. He was, however, not an experimenter (except perhaps within the context of his co-twin study) and thus left an incomplete theory of how brain and behavior co-develop. McGraw, in contrast, can be said to have gone further than Gesell in these respects.

McGraw the theoretician and experimenter

Reflexology and the cortical inhibition hypothesis

In a paper published in 1985, McGraw contends that she had never worked out her own theory of development (McGraw in Dalton & Bergenn, 1995a, pp. 57-64). If she did not have her own theory, then she certainly took guidance from those of Dewey and Coghill, and at least one of the tenets of reflexology, in formulating the theoretical underpinnings of her broadly based program of research.

While the doctrine of reflexology was evident in how she interpreted her findings, McGraw was selective in her use of it. She never accepted that newborn behavior amounted to just a bundle of reflexes (or a ‘mid-brain preparation’) that were somehow activated and chained together by the grace of external stimulation. Rather, it was predicated in the first instance on a spontaneously active brain.

What she did extract from reflexology was the cortical inhibition hypothesis. In the Introduction to the 1962 edition of McGraw (1943), she expressed regret at having given prominence to this hypothesis as providing an explanation for what she saw as a change from sub-cortical to cortical mediation of behavior occurring around 2-3 months after birth. It is recognized, also in her time, that cortical activity is both inhibitory and excitatory. Moreover, the hypothesis has been refuted by both animal and human developmental studies and in particular by the fact that movements in near-term anencephalic fetuses are qualitatively different from those of their healthy counterparts. Nevertheless, it still lingers on as an explanatory construct in some quarters of developmental psychology.

A reductionist?

Some recent evaluations of McGraw’s published work have led to the assertion that it bears the badge of a reductionist in the sense that she claimed that behavioral development was prescribed by changes in the brain. In the same breath, she is portrayed as being more of a ‘maturationist’ than Gesell. Her writings speak firmly against such an adumbration. Take, for example, the following conclusion about the nature of development in McGraw (1946): “… it probably is the interrelationship of a multitude of factors which determines the course of behavior development at any one time” (p. 369). As another example, consider this comment from her Psychological Review paper published in 1940:

In studying the development of reaching-prehensile behavior of the infant, for example, the object in the field of vision is just as much an integral part in the organization of the behavior as are the arms, fingers and eyes of the baby… One manipulates arms and fingers quite differently when picking up a bowl a water from the way one does when trying to catch a fly. In that the object determines the configuration of neuromuscular movements, and as such might be considered an “organizer” of behavior.

Does this sound familiar? It should do as it conveys the essence of organism-environment mutualism that is the foundation of J. J. Gibson’s affordance concept.

Structure and function

On the issue of structure-function relationships during development, McGraw was more explicit than Gesell. For example, in McGraw (1946), she writes:

It seems fairly evident that certain structural changes take place prior to the onset of overt function; it seems equally evident that cessation of neurostructural development does not coincide with the onset of function. There is every reason to believe that when conditions are favorable function makes some contribution to further advancement in the structural development of the nervous system … Obviously, rigid demarcation between structure and function as two distinct processes of development is not possible. The two are interrelated, and at one time one aspect may have greater weight than the other.

Similar commitments to a bidirectional model of development are dispersed throughout both her topics (McGraw, 1935; 1943).

Based on her studies concerned with the development of locomotion, McGraw (1943) went beyond Gesell in acknowledging that structure-function relationships emerged from ongoing interactions between the central nervous system (CNS) and the energy-converting musculoskeletal system (MSS). In McGraw’s case, the MSS was the interface between the CNS and the infant’s external environment (Fig. 8), an insight commonly accredited to Nikolai A. Bernstein (1896-1966).

Just motor development?

Beyond Bernstein, connections to Piaget’s theory of development are also to be found in her publications. McGraw (1935), in her co-twin study, regarded the attainment of dynamical balance not only as a necessary condition for persistent bipedal locomotion to be achieved, but also as contributing to the development of problem-solving abilities and thereby to the promotion of consciousness. This was another example of McGraw putting Dewey’s theory of development to the test. To do so, her famous twins Johnny (with practice) and Jimmy (without practice) Woods had to resolve balance problems in, for example, roller skating before they could walk habitually, climbing up inclines at various angles, and demounting from pedestals of different heights. Her ingenuity in devising such age-appropriate manipulations matches that of Piaget. Both still stand as exemplars in their attempts to link theory with apposite methods in studying development through presenting infants with challenges on the cusp of their current abilities. Allowing them to discover their own solutions when challenged in this way complies with Piaget’s assertion that the resolution of conflict is a motivating force in generating development.

The central nervous system (CNS) interacts with the musculoskeletal system (MSS) throughout development. Moreover, the latter functions as the interface with the external environment (ENV), with which it also interacts. In a very simplified way, this figure illustrates some of the features of Bernstein's (1967) approach to resolving issues about motor control and coordination which he applied to the development of upright walking in infants. McGraw (1943) also treated motor development, and specifically locomotion, as consisting of bidirectional influences between the CNS and the MSS, and between the MSS and the ENV. The arrow labeled (1) signifies the common interpretation imposed on neuromaturational theories (structure ^ function), which therefore can be seen as omitting the many interactions between intrinsic and extrinsic factors considered by McGraw. The one labeled (2) refers to an interesting proposal by Bernstein (1967) that has implications for understanding (motor) development, which he communicates as follows:"... the reorganization of the movement begins with its biomechanics ... ; this biomechanical reorganization sets up new problems for the central nervous system, to which it gradually adapts" (pp. 87-89). Thus, according to this rather radical viewpoint, developmental transformations occur not just because the brain changes, but rather the opposite, namely, there are changes in the biomechanical properties of the body segments (i.e., the MSS) to which the developing brain adjusts.

Figure 8. The central nervous system (CNS) interacts with the musculoskeletal system (MSS) throughout development. Moreover, the latter functions as the interface with the external environment (ENV), with which it also interacts. In a very simplified way, this figure illustrates some of the features of Bernstein’s (1967) approach to resolving issues about motor control and coordination which he applied to the development of upright walking in infants. McGraw (1943) also treated motor development, and specifically locomotion, as consisting of bidirectional influences between the CNS and the MSS, and between the MSS and the ENV. The arrow labeled (1) signifies the common interpretation imposed on neuromaturational theories (structure ^ function), which therefore can be seen as omitting the many interactions between intrinsic and extrinsic factors considered by McGraw. The one labeled (2) refers to an interesting proposal by Bernstein (1967) that has implications for understanding (motor) development, which he communicates as follows:”… the reorganization of the movement begins with its biomechanics … ; this biomechanical reorganization sets up new problems for the central nervous system, to which it gradually adapts” (pp. 87-89). Thus, according to this rather radical viewpoint, developmental transformations occur not just because the brain changes, but rather the opposite, namely, there are changes in the biomechanical properties of the body segments (i.e., the MSS) to which the developing brain adjusts.

Gesell and McGraw: similarities and differences

There are similarities, but even more so differences, between Gesell and McGraw in terms of the theoretical assumptions and associated methods they assimilated into their research programs. Some similarities have been mentioned previously. Others that stand out are:

1. Reciprocal interweaving: McGraw, like Gesell, envisaged development to consist of alternating and overlapping phases, which resulted in both progression and regression. It seems to be the case that McGraw (1935) used weaving as a metaphor to capture the non-linearity of development some four years before Gesell introduced into the literature his related principles of reciprocal interweaving and spiral reincorporation (Dalton in Dalton & Bergenn, 1995a, pp. 134-135).

2. The role of movement: for both Gesell and McGraw, movement was a ‘final common pathway’ for the enhancement of all aspects of development (e.g., cognitive, social, emotional, etc.). While Gesell (& Thompson, 1934) alluded to movement as an essential ingredient in the development of exploration (or what he considered to be movement-generated ‘sensory experience’), he also included posture in this context. He went so far as to say that “Posture is behavior,” by which he meant “… the position of the body as a whole or by its members, in order to execute a movement or to maintain an attitude” (Gesell & Amatruda, 1945, p. 46). In Gesell’s view, the asymmetrical tonic neck (ATN) posture, or what he termed “This new visual postural visual-manual-prehensory pattern” (Gesell & Amatruda, 1945, p. 458), exerted a formative influence on the development of handedness. This conjecture brings us to the first of the differences between Gesell and McGraw.

1. Antecedent-consequence relationships: a consistent theme in Gesell’s writings is that mature expressions of behavior can be observed in incomplete forms earlier in development, with both being part of the same developmental sequence. His Developmental Schedules reflect this point of view. McGraw did not share such an ontogenetic scenario. This is exemplified in her interpretation of the ATN posture: it was not an antecedent condition for the acquisition of a hand preference, but instead forms part of an age-appropriate righting response that later becomes incorporated into prone locomotion (Dalton in Dalton & Bergenn, 1995a, p. 144). While neither of them referred to ontogenetic adaptations as such, it is clear McGraw envisaged development as being more of a discontinuous process than Gesell.

2. Heterochrony: during development, there are differential rates in the timing with which new structures and functions appear (i.e., the accelerated development of particular brain areas and behaviors relative to others). While Gesell and McGraw depicted development as essentially heterochronic in nature, they differed in this regard on one important aspect based on the findings of their respective co-twin studies. According to McGraw, but not Gesell, early experiences could affect heterochronicity between functions in the sense of accelerating slower developing components (or what she labelled as ‘ontogenetic skills’ as opposed to ‘phylogenetic skills’).

3. Intra-individual differences: inter-individual differences in intra-individual change, to use a somewhat clumsy formulation, should be the overriding concern in studying ontogenetic development. Only possible to address with a longitudinal design, it tends to be neglected in research on child development. Such was not the case with McGraw and her attention to tracking change within individual infants is considered to have been a key feature of her research (Touwen in Dalton & Bergenn, 1995a, pp. 271-283). Together with her co-workers, she devised a number of analytical techniques for detecting differences in developmental trajectories between infants (McGraw, 1943). Gesell, on the other hand, gave little regard to intra-individual change and at most considered it to be an indication of deviant development (i.e., ‘deviant’ in not complying with the sequential age-related norms in his Development Schedules). Drawing on the distinction between population and typological thinking, McGraw was representative of the former and Gesell of the latter.

4. Chronological age: in keeping with Baldwin and Piaget, McGraw was not particularly concerned with mapping the development of various abilities as a function of chronological age (McGraw in Dalton & Bergenn, 1995a, p. 60). Instead, she was more interested in the ‘how’ and ‘why rather than the ‘when’ of developmental achievements. To say that Gesell did not address all three questions would be to do him a disservice. As Gesell the theoretician, he did so, but as his program of research progressed the questions of’how’ and ‘why’ tended to become subordinated by Gesell the tester to a focus on the modal chronological ages at which particular abilities were attained. Unfortunately, that is what he is chiefly remembered for in the developmental literature despite the fact he distinguished astronomical (i.e., chronological) time from biological (i.e., developmental) time in the following way: “Astronomical time is rigid, neutral, two-way, reversible. Biological time is elastic, cyclical, one-way, irreversible” (Gesell & Amatruda, 1945, p. 16). His observations on preterm infants, never studied by McGraw, reveal an attempt to reconcile these two time scales, and he was one of the first to assert the importance of using corrected age when evaluating their postterm development. In his more popular writings aimed chiefly at parents, Gesell the tester really comes to the fore. Here, parents are confronted with age-encapsulated caricatures of children (e.g., the assentive and conforming three-year-old as against the assertive, lively four-year-old). Such an example of typological thinking was completely absent from McGraw’s publications.

There are many other points of departure that can be discerned when comparing the published work of Gesell and McGraw (e.g., McGraw’s attempts to apply mathematical modeling to her data as outlined in Fig. 4 for one of her studies). However, it should be clear that their approaches to the study of ontogenetic development were so divergent as to leave us wondering why they are still lumped together under the rubric ‘neuromaturational theories.’

Conclusions

If unbridled genetic determinism defines the essence of neuromaturational theories of development and Gesell and McGraw are taken to be their standard-bearers, then we continue to labor under false pretences. Neither of them held to such a reductionistic and monocausal view of development. Their theoretical formulations were much more subtle than this and still bear insights that resonate with current dynamical systems approaches to development. Recognition that development is a self-organizing phenomenon, and intimations that there is a circular causality between perception and action, are readily apparent in both their writings. If the label ‘neuromaturationist’ does in any way seem to be appropriate, then perhaps it is more applicable to Gesell when defending his theory against attacks from the radical behaviorists. Outside this context, both he and McGraw strove to find the middle ground in the maturation versus learning debate of the time.

With the foundation of experimental embryology in the late 19th century by Wilhelm Roux (1850-1924), the bidirectionality of the relationship between structure and function during development became an undisputed maxim (at least among the embryologists). In drawing theoretical inspiration from such a source, both Gesell and McGraw transported this dictum into the realm of postnatal behavioral development. All of this suggests that at least by the end of the 19th century, there was no such thing any more that complied with a radical neuromaturational theory. The irony is that now in fact we have such theoretical radicalism as contained, for example, in theories of innate knowledge and language acquisition as well as those addressing the role of the prefrontal cortex in the development of executive functions. At the same time, Gesell and McGraw continue to be castigated as representatives of an overly simplistic maturational stance on the mechanism of development.

In conclusion, it is long overdue that Gesell and McGraw should no longer be classified as ‘neuromaturationists.’ More germane would be something like ‘developmental psychobiologists,’ while at the same time acknowledging important differences between them in how they endeavored to describe and explain ontogenetic development. The last word is perhaps best given to Myrtle McGraw, the consummate developmentalist:

In the present state of knowledge a more profitable approach lies in the systematic determination of the changing interrelationships between the various aspects of a growing phenomenon. It has been suggested that relative rates of growth may afford a common symbolic means by which the underlying principles of development may be formulated. Once the laws of development have been determined the maturation concept may fade into insignificance.

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