The systematic study of the sensory and learning processes of infants is a rather recent science; indeed, infants far surpass what we “knew” about their capacity for learning a few decades ago. Emotion and learning are closely intertwined, because behaviors that elicit positive emotional response are repeated and learned. Understanding these processes can optimize care of newborns by both professionals and parents.
Much like the law of gravity, the laws of learning are always in effect. —Scott Spreat and Susan Rogers Spreat,Learning Principles
Statements of fact are always either true or false, but our knowledge about them always remains to an extent uncertain or incomplete —Charles C. Spiker, 1955, Course teaching notes, University of Iowa1
The study of perceptual and learning processes in humans is of rather recent origin relative to many other scientific endeavors, such as the study of gravity, electricity, and fluid mechanics. Interest in the learning and sensory processes of infants is even more modern. Thus, our knowledge base about the behavioral and psychophysiologic capacities of infants, including motivational processes and emotional characteristics, is still quite inadequate relative to the scientific sophistication and practical wisdom that we would like to have.
Only in the last few years, for example, has the definitive advice of pediatricians been given that infants in the first few months of life are best put in their cribs to sleep on their backs rather than in the prone position, to reduce the risk of sudden infant death. Even so, the debate about this particular child-rearing practice continues, because many pediatricians believe there is a significant risk, in the supine position, that the infant may regurgitate its food.
By the same token, child developmentalists, behavior scientists, and the medical community continue to debate, and individuals among them argue heatedly about, such matters as 1) how soon a mother can return to work after the birth of her infant and still feel secure that the child is not put at developmental or emotional risk; 2) whether circumcision is a traumatic experience for an infant; 3) how early an infant can detect its own mother's voice, and the effect of reading, or simply talking, to an infant from the earliest days and weeks of life; 4) how early infants can remember, and how long those memories last; and 5) whether there is such a phenomenon as recovered memory, whereby an experience of a young child may be forgotten by the child for many years, only later to become a vividly recaptured recollection.
NEW PERSPECTIVES AND OLD MISAPPREHENSIONS
Significant strides have been made by increasing numbers of basic and clinical researchers of infants over the past half century. The “blooming, buzzing confusion” of infancy, as William James characterized the earliest days and weeks of human life, is gone forever. Indeed, it never existed for the healthy, full-term robust infant, and certainly no longer exists in the minds of parents and pediatricians familiar with the fulsome accounts available now of the behavioral and cognitive competencies of infants. Human infants are very orderly in their ways; they actually behave according to laws (even like the rest of us) that can be explored, discovered, confirmed, reconfirmed, and celebrated.
The accessibility of the infant for the systematic observation of developmental regularities, in humans generally and in individuals as well, was recognized in the early writings of Freud, Piaget, and other theorists. They believed, based on empiric study, that early experience is an important determinant of later behavior, along with genetic disposition, and that, as an anonymous New Englander put it, “While people are mostly the same, what little differences there are seem powerful important.”
Today, the sensory and learning capacities of the young infant, even the newborn, far exceed those with which the infant had been credited historically. At least with respect to certain kinds of learning, it is not absurd to suggest that the very young child may never again in its life be as fast at learning as during the newborn period and the succeeding few months.
It is important to look at what we do know through careful clinical observation and laboratory investigation and to note that we have indeed come a long way. In consideration of our interest in new perspectives at this time, it is not a bad idea to reflect on William James and the extant wisdom of his day, as we have done, and to take a quick look at other “ancients” and their perspectives.
GHOSTS IN OUR HISTORY
Time and tradition dictate that we frequently assimilate overly simplified or completely erroneous information from our intellectual forebears. John B. Watson, the noted father of behaviorism in America, is often misrepresented by students, especially those who have just (correctly) learned that Watson is an icon in the field of child development and behavioral psychology, for having said that “all behavior is learned.”
Watson, however, was in fact a well-trained physiologist, and a believer in the importance of heredity, as was Pavlov. He was a major proponent of the supposition that all behavior is founded in emotion, and that the earliest manifestations of behavior in the human infant are essentially of an emotional nature. In a now classic treatise, he described an array of nonconditioned, congenital, or hereditarily given responses: fear, rage, and love. He elaborated with the following statement:
An emotion is an hereditary “pattern-reaction” involving profound changes of the bodily mechanism as a whole, but particularly of the visceral and glandular systems.2
This celebration of the importance of heredity shows that Watson obviously had great respect for genetic underpinnings of behavior, even as he advocated, foolishly as we now suppose, that fathers should greet their children with handshakes rather than with hugs. Had Watson's scientific career not been interrupted suddenly by an emotional and behavioral (amorous) relationship, we might have found Watson today as much a significant contributor to the literature of and our knowledge about emotional development as of that on the developing learning processes of children.
Misconceptions through the ages continue. Just as Watson continues to be appreciated for some odd reasons, so does Freud become surrounded with inappropriate classic misapprehensions. Freud did not claim, despite suppositions to the contrary, that there is an unconscious element in every aspect of behavior or mental functioning.
Although elaboration of the behaviorism inherent in Freudian theory will carry us too far from our mission here, it should be noted that the widely held presumption that Freud's interest in mentalisms, particularly unconscious processes, precluded interest in overt behavior (or in the science of experimental psychology) is false. An excellent treatise on this aspect of Freudianism by Gustav Bergmann,3 although much ignored, is nonetheless available. What is quite true is that Freud concerned himself very little with direct observations of infants, or even with older children. He wrote about infancy and childhood on the basis of patients' retrospective reports. However, many of his successors, notably Daniel Stern (presented in this supplement toPediatrics), are well-known for their intense involvement in direct observation of the infant and for their systematic substantiation of inferences drawn from those observations. This contemporary innovation lends credibility to aspects of Freudian theory about infantile behavior that it might otherwise not have had. In particular, Freud was very clear that from the earliest days of life, infants have strong proclivities for special cathected objects and events, particularly mother and the stimuli and styles of attachment behavior that she provided. Similarly, infants may object strenuously and unmistakably to noxious events in their environment. The psychological defense behaviors that humans manifest at later ages and that become persistent patterns of behavior for which Freud is noted as the master cataloger, are grounded in infantile experience.
THE PROBLEM WITH EMOTIONS AND BEHAVIOR
Communications about the nature of learning, behavior, emotional expression, and motivation are often hampered by denials that emotional reactions, as mental phenomena, have anything to do with overt behavior. After all, the argument goes, a person can be angry without showing it. And, similarly, a relatively unperturbed person can look quite angry in his or her behavior.
The concepts of emotion and behavior have become so compartmentalized that experts in the study of emotional development hardly give even a tip of the hat to Watson's characterization of the earliest psychological characteristics of the human infant as fear, rage, and love. What could be more emotional than fear, rage, and love? Yet the notion is perpetuated that Watson had little or nothing to do with emotional development, only conditioning—and then only classical conditioning. In fact, Watson used an operant conditioning style of training, which involves quite a different set of procedures from those of classical Pavlovian conditioning.
As for operant conditioning procedures, parents have been doing this kind of training for eons. For example, the child engages in some behavior like that which is desired, perhaps pulling himself almost to a standing position. In anticipation that this is a prelude to walking, parents express their glee to the child with each successive approximation to a standing position. Later, the pleasure of the parents is expressed on the occasion of the first step, then the second, and progressively with each advance in the child's behavior. Much shaping of the child's behavior occurs through the presentation of contingent stimulation like this. That the expressed pleasure of the parents is meaningful to the child, and coaxes him on, is apparent from the way that the child continually refers back with smiles and other measures of satisfaction to the parents. He soon will see that he can't clap for his own performance and pull himself up at the same time. This is not the start of, but is one of many examples of, self-regulatory behavior of the young child.
The young child sorts out, in part because of differential reinforcement administered by the caring persons in its environment, those aspects of the skill that can be, each by itself, performed satisfactorily and followed by pleasure. This reinforcing or rewarding aspect of behavioral development has not been acknowledged sufficiently, historically, largely because of the enormous influence of biological determinists, both on the science of human development and on parents' understandings of what child development is about. Gesell,4 for example, insisted that development essentially is genetically programmed, that successive stages will be arrived at in due time, and that neither facilitative nor interfering stimulation will affect the rate of the child's hereditarily determined mental growth. The profound effects of environmental and experiential influences, in interaction with maturational and congenital factors, have been documented incontrovertibly, and now must be heeded.
Denigration of the importance of experience on children's development and behavior has led to some flagrant devaluations of the influence of the environment on children's welfare and on social programs and policies that might otherwise benefit youngsters growing up in the United States. The national attitude toward maternal leave, child care, enhancements of school budgets, and the implementation of after-school programs generally has been negative, relative to other advanced nations such as the Scandinavian countries, France, and others, to say nothing of the special disregard our society seems to have for the devastating influences, perhaps one of the best-documented facts in the study of child development, that poverty has on the well-being of children.
THE LEGACY OF DEVELOPMENTAL DICHOTOMIES
The historic dichotomization of the many different influences on human growth and development has had a pernicious effect on the way in which we regard lifespan influences. The human organism does not, as it makes its way through development, compartmentalize the genetic and environmental influences on its behavior.
Neither do other psychological dichotomies work in the way that our language often suggests. Dichotomous “manners of speaking,” whether relating to learning and emotion, sensation and perception, or conscious and unconscious ideation, are heuristic fictions created for the benefit of simplified discourse. Developmental psychology is, perhaps more than many other scientific fields, victimized by the entrapments of words.
I come to the point, then, that in our zeal to study conditioning processes of infants, and in our eagerness to understand the origins and changing patterns of emotion in development, we have acted as if there are separate and clearly distinctive processes underlying them. This is, however, patently false. Those who study emotions and emotional development simply cannot avoid the conditioned aspects of emotional reactivity nor the mechanisms and processes that by now have been so carefully documented in the laboratory. I will provide an example below of a “condition of infancy” that is best explicated by drawing on the conjoint effects of both neuromotor capacities of the infant and the experience of the infant to create a neuropsychogenic pattern of behavior. The constellation of behaviors involved in the scenario, in which the infant's response to brief respiratory occlusions is of vital importance, could not appear without contributions from neuromuscular and central nervous system maturation, on the one hand, and experience, on the other.
THE NATURE OF INFANCY
Recent years' advances in the study of infant behavior and development have led to the well-supported conclusion that healthy, full-term humans are capable of perceiving stimulation in all sensory modalities and are able to engage in classical conditioning, operant learning, and the learning of discriminations, even in the first month of life.5,,6
Although most studies conducted in infant laboratories are of “positive” or “approach” responses, such as sucking, rooting, smiling, and tugging at mobiles, a few studies (eg, Watson and Rayner7) and naturalistic evidence indicate clearly that avoidance, aversive, and escape behaviors also are conditionable.
Learned approach and learned avoidance responses are almost invariably mediated by positive and negative hedonic qualities, such as intense pleasure or pain, moderate satisfaction or annoyance, or other “feeling” characteristics. It is practically impossible to speak separately of emotion and learning. Michael Lewis8 has addressed the phenomenon of anger, for example, in connection with the emergence of emotions. At approximately 2 months of age, he says, infants will become angry if a “learned instrumental act is removed” from the possibility of occurrence. His observation lends itself to our supposition that learning and emotion, in this case “anger,” often are conflated in a complex psychological event.
Lewis8 also reports on “surprise” in 6-month-old infants. Under conditions in which “children were taught an instrumental arm-pulling response, the children showed surprise at the point when they discovered that the arm-pull could turn on a [photographic] slide.” The synergistic occurrence of a habit, then, and the manifestation of emotional surprise in one behavioral event or sequence of events advances the present thesis that learning and emotion go hand in hand from the earliest months of life. Lewis adds that, “Surprise can reflect either a violation or a confirmation of expectancy.” Expectancies are, of course, typically based on previous experience, learned models of the way the world is, the way things operate, and the usual consequences of one's own behavior. Infants, even in the first month of life, although not yet superb information processors, use historical information proactively for behavioral and emotional self-regulation.
PLEASURE AND THE PRECOCITY OF INFANTS
Rather contrary to the usual appreciation of the very young infant, by 2 months of age infants manifest proactive patterns of behavior based on previous experience. Even 6-week-old children have been shown to engage in repetitive behaviors that are instrumental in effecting changes in the environment experienced previously.6
Such self-regulation seems to be based on a primary level of executive function in the form of deliberate approach and avoidance behavior. This is mediated by the pleasantness (hedonic quality) of the response consequences that ensue. As with other humans, infants are responsive from the earliest moments of life to the pleasures and annoyances afforded by the environment, particularly as consequences of their own behavior.
That infants derive pleasure and experience annoyance from their own behavior is the bedrock of learning and emotion in the first year of life. Infants (as well as older individuals) can distinguish between a more pleasurable stimulus and a lesser, and the hedonic properties of an experience are determinants, along with other stimulus features, of whether the behavior will be repeated in the future.
Human infants are capable of preferring. There are some visual stimuli to which they will turn their heads more frequently and concentrate their gaze on. Relatedly, newborns change their sucking and other mouthing behavior, depending on how sweet the fluid is for which they are sucking.9,,10 They suck more times per minute for sweeter fluids, even as they slow down their sucking within bursts of sucking, probably to savor the sweeter fluid. By 1 week of age, infants have been shown to prefer their own mother's odor to the odor of another infant's mother. Examples of this type of differential responding, or preferential behavior, can be found for infants in every sensory modality.
As it happens, such preferential responding, evident in the first days of life and found in increasingly complicated styles as the child matures and assimilates more experience, is the sine qua non of learning. Learning depends on the assimilation of sensory experience and the capability of preference, ie, to like some experiences more than others. The child is capable of learning because, as with his elders, Thorndike's Law of Effect11 is in place: those behaviors that are followed by a “satisfying state of affairs” will tend to be repeated when the occasion arises again, whereas those behaviors that are followed by annoyance or pain will occur less frequently and may result in long-term exclusion from the behavioral repertoire.
The expression “satisfying state of affairs” is, of course, a phrase connoting emotional reactivity. Thorndike is not irrelevant to contemporary analyses of behavioral and emotional interactions between mothers and their infants. When flat affect, resistance to contact with others, and gaze aversion are noted in nonnurtured institutionalized orphans, the terms have a special meaning. They connote suppression or extinction of normal or usual behavioral patterns of infants who have not had the misfortune of being subjected to such abject conditions as have prevailed in Eastern European orphanages in recent years.
Pleasure and annoyance as psychological dispositions are aspects of emotional reactivity. They are revealed in part through indices of autonomic nervous system responsivity, such as the heart rate response or crying. Such emotional reactivity may be accompanied by neuromotor components, as in sucking on a sweet-delivering nipple or pulling the hand away from a hurtful stimulus. The quality of the infant's response, including its approach and avoidance characteristics, signals the pleasure or annoyance inherent in the experience.
An especially striking index of emotional annoyance in the infant is crying behavior, which occurs under conditions of tissue damage or deprivation. Crying is a conditionable behavior. Whereas it might occur under distressing physical stimulation, such as a loud noise, a bump on the head, or a bad taste, it may occur subsequently on the basis of learned anticipation. For example, parents often have noted that their toddler sitting near a refrigerator door that slams may at first jump in response to the sound of the door, but after several such occasions, the child will jump before the door slams, simply at the sight of the door closing.
A similar situation exists with respect to pleasant taste sensations. After a great deal of experience, as occurs in real life, the pleasures associated with taste and the ritualistic feeding regimen may lead to craving. Craving is an appetitional pattern of behavior involving strong approach responses, both neuromotor and emotional, that, when thwarted, may lead to enormous psychological excitement, regret, and anger. Craving is both emotional and conditionable.
THE PERTURBABLE INFANT
Even the well-nurtured, wanted infant of parents who have fallen in love with him or her, will be perturbed on occasion by environmental events under the best of circumstances. Some such experiences can quickly become major family crises as, for example, when a 3-year-old child has a temper tantrum during his older sister's piano recital. Such occasions are behavioral and emotional and often are the consequence of some learning process that is not easy to follow as to its origins and are even more difficult to address as to their “curability.”
There are some conditions of early infancy that have that same kind of stress-evoking durability, and for which, as with the condition called colic, we tend to find ourselves devoid of antidotes! Perhaps we do not look often enough to the specific behaviors involved or have the necessary confidence in an environmental and behavioral analysis to look at the instigating circumstances that promoted the behavior in the first place and the reinforcing events that perpetuate it.
Fortunately, we have a test instance taught to us by a wise pediatrician who adopted a behavioral approach to the understanding of, and eventual treatment of, breastfeeding problems. Mavis Gunther reported her initial observations in a Lancetarticle,12 then expanded on her theory in a volume on theDeterminants of Infant Behavior.13
Aversive behavior sometimes occurs in the human newborn when biological threat exists. In its milder forms, such behavior is manifested in withdrawal responses of the infant to intense stimulation such as bright lights, painful touch, unpleasant odorants, loud noises, and so on. The amount of active response to such threats is proportional to the intensity of the aversive stimulation. When the annoying stimulation persists, the infant often becomes agitated and cries.14
Gunther described such a situation in newborns and explained the anger that can be evoked in infants under rather specific conditions. A particularly striking pattern of behavior may be seen in newborns when they experience the threat of respiratory occlusion. This can happen when they press their faces fleetingly against a mattress or when their respiratory passages are blocked with mucous or regurgitated fluids.
Stimulation that supports or threatens such “smothering” tends, Gunther said, to elicit a response sequence consisting of five components. She described this behavior as a “fixed action pattern,” using an ethologic term of biologists studying stereotypic species-specific response sequences. The five-stage response sequence, she said, often is found in the natural course of breastfeeding of the infant. The infant will have the nipple in its mouth, with a tight pressure seal around it, preventing any respiration through the mouth. The nostrils are the only source of oxygen. The infant objects to, and defends itself against, additional respiratory occlusion with an adaptive sequence of responses, going to the next increasingly vigorous behavioral defense on the list if the earlier coping tactic does not free the respiratory passages for breathing:
side-to-side head waving,
head withdrawal, with backward jerks and grimacing,
arm jabbing, and
In fact, Gunther reported that she observed “one-trial learning” in which, after an episode of the type just described, infants would, when put to the same breast again, turn their head in the opposite direction.
This continuum of responses is, from all appearances, a build-up of angry behavior. It abates when the threatening or noxious stimulation is removed or reduced. From Gunther's poignant descriptions of the phenomenon, one realizes that once the infant is successful through its progressively aggressive pursuit of air, there occurs an enormous sigh of relief that can only be described as rewarding.
Especially striking are Gunther's observations of the breastfeeding infant in the arms of its mother, particularly a new mother who had had little experience with infants. Some mothers, either because they have not observed other women breastfeeding an infant, or because of some awkwardness of build or posture, would inadvertently smother their infants for brief times. These episodes of respiratory occlusion at the breast elicited the fixed action pattern of behavior to the point that some infants went through the entire sequence of defensive behaviors, culminating in the relief associated with crying and thrusting the nipple from their mouths. Mothers who avoided this “crisis” were those who deftly used their fingers to hold the breast away from the infant's nostrils.
The fixed action pattern of the infant has the effect of freeing the respiratory passages, by displacing the offending object or by impelling the mother to adjust her feeding position. The freeing from occlusion is a reinforcement condition that may increase the probability of the fixed action pattern's occurrence again under this and similar conditions. From what we know of the shaping of behavior through reinforcement, it is not unthinkable that the angry response may occur subsequently in a shorter period of time or even anticipatorily to less intense stimulating conditions.
To carry the learning prospects still further, it is possible that the behavior executed previously directly to stimulus instigators might be adopted as a coping pattern in other situations in which arousal has reached panic proportions. We may be describing the origins of aggressive behavior here, mediated by anger that had been generated initially from circumstances different from those in which the behavior was first learned.
That such defensive behaviors are necessary for survival and that the learned consequences of experiences like these may be of considerable importance in understanding the ontogeny of aggression and other learned patterns of behavior may go without saying.15Perhaps a modicum of such experience is necessary for infants to learn lifelong coping skills or useful defensive patterns of behavior. An excess of such experience might, on the other hand, conduce to a pattern of reactivity characterized by anger and aggression. Of special interest is the possibility that the inability of an infant to defend itself against episodes of respiratory occlusion may forecast a hazardous first year of life, particularly during that window of time—2 to 5 months of age—when behavior shifts gradually from a reflexive basis to become increasingly under the control of learned responses.
WHEN THE TORCH IS PASSED
The behavior of human infants, like that of other mammals, is mediated by subcortical brain structures in the earliest days of life. Over the course of the next 2 or 3 months, there is a gradual shift of executive function to cortical structures. Mediation by these eventually acquired responses is based largely on experience, especially those that facilitate learning. The early reflexes appear in many instances to be preludes of and preparations for the to-be-acquired responses. For example, healthy, full-term infants born under conditions of minimal perinatal stress have strong, obligatory grasp reflexes; they engage in stepping reflexes, and they exhibit stereotypic swimming reflexes when placed in water.
McGraw16 has shown that these and other reflexes are transformed over the first weeks of life from obligatory behaviors to slower, more deliberative voluntary patterns of behavior. Based on the neurophysiologic evidence available to McGraw at the time of her writing, she concluded that the neuromuscular maturation of the infant, and particularly the rapid maturation of cortical structures in the first few months after birth, enabled the transition of the infant's behavioral repertoire from largely reflexive functioning to a repertoire of largely learned functioning.
This transition from reflexive to learned function may operate in the following way. A reflexive response usually is elicited by a stimulus condition that is fairly obvious. The grasp reflex is stimulated by pressure on the palms of the infant. The stepping reflex is stimulated by pressure against the soles of both feet. The rooting reflex is produced by a touch to the face by the side of the mouth. The respiratory occlusion reflex occurs in response to diminished availability of air or the threat of such occlusion produced by an object blocking the nose and mouth. In the normal course of events, these reflexes are exercised, in some infants more strongly than in others. The practice of reflexes that have a rewarding effect, such as relief from smothering, will tend to provide learning trials, such that in later stages of development when the intense reflex has waned, a learned anticipation of reward for engaging in that pattern of behavior will be manifested. This learned consequence of reflex functioning probably is at the root of much self-regulatory behavior of the infant and young child and may well be responsible for most infants “knowing what to do” when threatened with respiratory occlusion after the primary control of behavior has shifted from subcortically mediated reflexive functioning to what McGraw called voluntary or learned functioning mediated by cortical structures.
It is quite possible that crib death eventually will be understood partly in terms of failure of that transition to occur effectively. Epidemiologic statistics indicate that ∼90% to 95% of all crib deaths occur in that critical 2- to 5-month period when the infant makes the transition from the early mode of behavior to the later. Before 2 months of age, the infant essentially is free of critical occlusion because of the presence of a safety reflex; after 4 to 5 months of age, the learned “voluntary” aspects of behavior provide the safety net.
SUMMARY AND REFLECTIONS
Most human infants come into the world with all sensory systems functioning, and they are capable of learning. Their perceptual processes and learning capabilities have been rather well-studied by now, although much remains to be discovered, particularly about the wondrous ways in which nature and nurture, heredity and environment, congenital dispositions and experience work synchronously and symbiotically to shape the developmental destinies of individuals.
Child development professionals are not satisfied entirely with their expertise in predicting lifespan destinies from early behavioral characteristics, social indices, family attributes, or schooling, but the study of specific processes and mechanisms of early development and behavior has yielded some helpful hints as to what may be possible to know in the future. At the very least, they are confident that early life experiences are of inestimable importance in that severe deprivation of sensory and learning opportunities, as well as the chance to become attached to a loving, trusted other person, usually results in developmental retardation, intellectual incompetency, and insufficient capacity for engaging in close, caring relationships with others.
Fortunately, most children, even those reared under handicapping conditions, are resilient in at least some areas of psychological functioning, especially fortuitous insults that are not long-lasting. Later experience, it seems, can help deleteriously affected children to overcome the assaults of abuse, poverty, emotional deprivation, and early cognitive deficits. Just how these compensatory mechanisms can be implemented best, and for whom, is a matter of social policy as well as of scientific exploration and documentation.
Some adverse developmental destinies that are reached early and with either tragic finality or lifespan consequences require much more scientific attention by child development researchers than they have been afforded thus far. Among these are the so-called sudden infant death syndrome and the failure-to-thrive phenomenon. Some advances have been made in understanding crib death as in part attributable to the environmental conditions of the sleeping infant and the experience of respiratory occlusion. Similarly, failure to thrive in young children has yielded to alterations in the environment in which the child lives.
Behavioral problems of infancy must be researched by experts in behavior analysis and should be addressed therapeutically and preventatively by applied developmental scientists, among others.
- ↵Spiker CS. Research Methods in Child Psychology. Iowa City, IA: University of Iowa; 1955. Lecture notes
- ↵Watson JB. Psychology From the Standpoint of a Behaviorist. 2nd ed. Philadelphia, PA: Lippincott; 1924
- ↵Bergmann G. Psychoanalysis and experimental psychology. In: Marx MH, ed. Psychological Theory. New York, NY: Macmillan; 1951
- ↵Gesell A. Maturation and the patterning of behavior. In: Murchison C, ed. A Handbook of Child Psychology. Worcester, MA: Clark University Press; 1933
- ↵Lipsitt LP. Learning in the first year of life. In: Lipsitt LP, Spiker CC, eds. Advances in Child Development and Behavior. Vol 1. New York, NY: Academic Press; 1963
- ↵Rovee-Collier C, Lipsitt LP. Learning, adaptation, and memory in the newborn. In: Stratton P, ed. Psychobiology of the Human Newborn. New York, NY: John Wiley & Sons; 1982
- ↵Lewis M. The emergence of human emotions. In: Lewis M, Haviland JM, eds. Handbook of Emotions. New York, NY: Guilford Press; 1993
- ↵Lipsitt LP. Developmental psychobiology comes of age. In: Lipsitt LP, ed. Developmental Psychobiology: The Significance of Infancy. Hillsdale, NJ: Lawrence Erlbaum Associates; 1976:109–127
- ↵Lipsitt LP. Toward understanding the hedonic nature of infancy. In: Lipsitt LP, Cantor JH, eds. Experimental Child Psychologist: Essays and Experiments in Honor of Charles C. Spiker. Hillsdale, NJ: Lawrence Erlbaum Associates; 1986:97–109
- ↵Thorndike EL. Animal Intelligence. New York, NY: Macmillan; 1911
- Gunther M
- ↵Gunther M. Infant behavior at the breast. In: Foss B, ed. Determinants of Infant Behavior. London, UK: Methuen; 1961:37–44
- ↵Lipsitt LP. Infant anger: toward an understanding of the ontogenesis of human aggression. Presented at the Department of Psychiatry, The Center for the Health Sciences, University of California at Los Angeles, March 4, 1971; Los Angeles, CA
- ↵McGraw M. Maturation and behavior. In: Carmichael L, ed. Manual of Child Psychology. New York, NY: Wiley; 1946
- Copyright © 1998 American Academy of Pediatrics