Infant development occurs in an orderly and predictable manner that is determined intrinsically. It proceeds from cephalic to caudal and proximal to distal as well as from generalized reactions to stimuli to specific, goal-directed reactions that become increasingly precise. Extrinsic forces can modulate the velocity and quality of developmental progress.
Each developmental domain must be assessed during ongoing developmental surveillance within the context of health supervision.Generalizations about development cannot be based on the assessment of skills in a single developmental domain (ie, one cannot describe infant cognition based on gross motor milestones). However, skills in one developmental domain do influence the acquisition and assessment of skills in other domains.
Speech delays are the most common developmental concern seen by the general pediatrician, yet they often are not well understood or diagnosed expediently. A sound understanding of the distinction between an isolated speech delay (usually environmental and often can be alleviated) and a true language delay (a combined expressive and receptive problem that implies more significant pathology) will help the clinician refer appropriately for precise diagnosis and appropriate management.
It is essential to understand normal development and acceptable variations in normal developmental patterns to recognize early patterns that are pathologic and that may indicate a possible developmental disability.
Assessment of the quality of skills and monitoring the attainment of developmental milestones are essential to early diagnosis of developmental disabilities and expedient referral to early intervention programs.
“Infant” is derived from the Latin word, “ infans,” meaning “unable to speak.” Thus, many define infancy as the period from birth to approximately 2 years of age, when language begins to flourish. It is an exciting period of“ firsts”—first smile, first successful grasp, first evidence of separation anxiety, first word, first step, first sentence. The infant is a dynamic, ever-changing being who undergoes an orderly and predictable sequence of neurodevelopmental and physical growth. This sequence is influenced continuously by intrinsic and extrinsic forces that produce individual variation and make each infant’s developmental path unique. Intrinsic influences include the child’s physical characteristics, state of wellness or illness, temperament, and other genetically determined attributes. Extrinsic influences during infancy originate primarily from the family: the personalities and style of caregiving by parents and siblings, the family’s economic status with its impact on resources of time and money, and the cultural milieu into which the infant is born.
Neurodevelopmental sequences can be viewed broadly in terms of the traditional developmental milestones. Developmental milestones provide a systematic approach by which to observe the progress of the infant over time. Attainment of a particular skill builds on the achievement of earlier skills; only rarely are skills skipped. When this happens, the advanced skill may represent a“ splinter” skill, that is, a deviant developmental pattern. For example, five-word sentences in a 2-year-old child who does not follow simple commands may represent echolalia typical of autism. The sentences are not meaningful and have no communicative intent. Delays in one developmental domain may impair development in another domain. For example, immobility due to neuromuscular disorders prevents exploration of the environment and, in turn, impedes cognitive development arising through manipulation of objects. Last, a deficit in one domain may compromise the assessment of skill levels in another domain, even though development in the second domain is normal. For example, it is difficult to assess problem-solving skills in a child who has cerebral palsy because the child may understand the concept of matching geometric forms, yet be unable to insert them physically into a formboard.
Developmental milestones serve as the basis of most standardized assessment and screening tools. Although these screening tools provide the clinician with a structured method of observing the infant’s progress and help define a developmental delay, many lack sensitivity. Parental concern in the face of normal results in developmental screening should not be disregarded. Focusing narrowly on discrete milestones may fail to reveal atypical organizational processes that are involved in the child’s developmental progress. Thus, it is important to analyze all milestones within the context of the child’s history, growth, and physical examination as part of an ongoing surveillance program. Only then is it possible to formulate an overall impression of the child’s true developmental status and the need for intervention.
Although milestones form the foundation of the discussion, the primary intent of this article is to provide broader insights into infant developmental processes and to help the clinician recognize warning behaviors (“red flags”) indicative of developmental deficits. The milestone ages are not repeated in the text to allow a more fluid discussion of developmental themes within each domain. Milestones have been organized into domains to assist the clinician in recognizing their independence as well as their interrelationships. Tables illustrating all domains at each age can be found in Vaughan (see Suggested Reading). Problem-solving and language milestones facilitate early identification of cognitive deficits. Adaptive skills (ie, skills related to independence in feeding, dressing, toileting) traditionally have been included within the fine motor domain. However, because these milestones are influenced by the social environment, we have included them in a “ psycho-social domain.” Lists for emotional and socialization milestones also are included in this domain. In contrast to motor and cognitive milestones, psychosocial behaviors are influenced more by extrinsic factors, making them less well-defined.
Evolution of Developmental Theory
Developmental theory has been shaped by the persistent debate of whether nature (intrinsic forces) or nurture (extrinsic forces) is the predominant influence. At the turn of the century, developmental theories promoted nature as the major influence. Gesell (early 1900s) was one of the first to study infant development systematically and establish developmental norms. Development was seen as a function of neurologic maturation and growth. Because advancing age and genetic endowment were the chief mechanisms for change, babies were believed to develop at a predetermined biological pace, with parents needing todo little more than provide a good nurturing environment.
By mid-century, theories that stressed the importance of nurture began to prevail. Pavlov (1930s), Watson (1950s), and Skinner (1960s) promoted the opposing view that development was a function of learning. Operant conditioning (positive and negative reinforcements through social interactions or environmental changes) promoted learning and shaped the child’s development. This line of thinking formed the philosophical basis for the Head Start program of the 1960s. Freud (1920s) and Erikson (1950s) promoted developmental progress as a function of the resolution of conflict. The quality of the infant’s relationships with key individuals was considered central to future development.
During the second half of the century, the name of Piaget became almost synonymous with child development. Piaget was the first to describe the infant as having intelligence. For centuries, it had been assumed that the infant’s mind was a “blank tablet waiting to be written on.” Because infants could not tell us what they were experiencing, it was believed that they saw and heard little and thought even less, with consciousness as adults knew it not existing. Piaget revealed that infants were, indeed, capable of thinking, analyzing, and assimilating. He viewed development as stage-like cognitive changes. The child actively explores objects in an effort to understand his or her environment. Depending on the developmental stage, a child organizes this information to form new theories about the way the world works.
It was not until the last part of this century that emotional and social development began to receive the same degree of attention as that given to the motor and cognitive domains. Research has revolved around theories regarding infant expression of emotion (Mandler, 1970s), attachment (Bowlby, 1960s; Mahler, 1970s; and Ainsworth, 1980s), and temperament (Thomas and Chess, 1970s). Once it was recognized that newborns could demonstrate distress (pain and hunger), interest, and disgust, these facial expressions have been used to study information processing in infancy prior to the age when thoughts can be verbalized. As the 20th century comes to a close, remarkable advances in behavioral genetics, together with recent discoveries regarding innate infant abilities, have swung the pendulum back in favor of nature as the primary influence on the developmental process.
Developmental Snapshots: The First Two Years of Life
Before dissecting infant development into discrete steps within each developmental domain, it is valuable to view the infant at discrete intervals. These 6-month “snapshots“ are displayed graphically in Figure 1⇓ . This gestalt approach may help the clinician make sense of the interrelatedness of the precise changes within each developmental domain.
These four snapshots illustrate several generalizations about neuro-developmental maturation over time:
Responses to stimuli proceed from generalized reflexes involving the entire body, as seen in the newborn (and fetus), to discrete voluntary actions that are under cortical direction. This specialization allows the child to move from obligatory symmetric reactions when attending to a stimulus (ie, vocalizations, arm waving, and kicking) to voluntary, asymmetric, and precise movements toward a stimulus (ie, grasping with one hand and inspecting with the other).
Development proceeds from cephalic to caudal and proximal to distal. Thus, arm movement comes under cortical direction and visual guidance before leg movement. With this, the child progresses from hand-mouth to foot-mouth play. The upper extremities become increasingly accurate in reaching, grasping, transferring, and manipulating. Distal development is seen when the infant can isolate and use the index finger to poke and explore object parts. When this occurs in concert with thumb opposition, the fine pincer grasp is mastered. Precise release of tiny objects follows, so that fundamental manipulative skills reach adult levels by the end of infancy.
Developmental progression is from dependence to independence. The totally dependent newborn progresses to a toddler who has mobility and manipulative skills that enable him or her to explore most of the environment. Toddlers can move about the house independently, opening doors, maneuvering stairs, and fetching desired objects. They can feed and undress themselves and even may be toilet trained. This new autonomy becomes the foundation for the challenging “ twos.’
Growth milestones are the most predicable, although they must be viewed within the context of each child’s specific genetic and ethnic influences. It is essential to plot the child’s growth on gender- and age-appropriate charts. Charts now are available for some ethnic groups as well as for a few genetic syndromes (eg, Down and Turner syndromes). Fetal weight gain is greatest during the third trimester. During the first few months of life, this rapid growth continues, after which the growth rate decelerates (Table 1⇓ ). Birthweight is regained by 2 weeks of age and doubles by 5 months. Height does not double until between 3 and 4 years of age. Head growth during the first 5 or 6 months is due to continued neuronal cell division. Later, increasing head size is due to neuronal cell growth and supporting tissue proliferation.
RED FLAGS IN PHYSICAL GROWTH
Large and small head size both are relative red flags for developmental problems. Microcephaly is associated with an increased incidence of mental retardation, but there is no straightforward relationship between small head size and depressed intelligence. As a reflection of normal variation, microcephaly is not associated with structural pathology of the nervous system or with low intelligence. Furthermore, microcephaly can be seen with above-average cognitive capability. Micro-cephaly associated with genetic or acquired disorders reflects cerebral pathology and almost always has cognitive implications.
Macrocephaly may be due to hydrocephalus, which is associated with an increased incidence of cognitive deficits, especially learning disabilities. Macrocephaly without hydrocephalus, far from being a predictor of advanced intelligence, also is associated with a higher prevalence of cognitive deficits. It may be due to metabolic or anatomic abnormalities. In about 50% of cases, macrocephaly is familial, and the implications are benign in terms of intellect. When evaluating infants whose macrocephaly is isolated, the finding of a large head size in one or both parents can be reassuring.
Height and Weight
Although the majority of individuals who are of below- or above-average size are otherwise normal, there is an increased prevalence of developmental disabilities in these two subpopulations. Many genetic syndromes are associated with short stature; large stature syndromes are less common. Again, when considering deviation from the norm in the specific child, family characteristics must be reviewed. The concept of mid-parental height is useful in determining whether a given child’s size is appropriate for his or her familial growth pattern.
Although most isolated minor dysmorphic features are inconsequential, the presence of three or more may indicate the presence of developmental dysfunction. Almost 75% of these minor superficial dysmorphisms can be found by examining the face, skin, and hands. The presence of both minor and major abnormalities may indicate a more serious genetic syndrome. In many instances, dysmorphic features will lead to the diagnosis of a clinical syndrome during the neonatal period and predate the recognition of any neurodevelopmental deficits.
To make a meaningful statement about an infant’s motor competence, the pediatrician should organize data gathered from the history, physical examination, and neuro-developmental examination according to the following schema: 1) motor developmental milestones, 2) the classic neurologic examination, and 3) cerebral neuromotor maturational markers (primitive reflexes and postural reactions). Motor milestones are extracted from the developmental history as well as from observations during the neurodevelopmental examination. Reference tables of sequential gross and fine motor milestones are necessary (Table 2⇓ ).
Results of assessment in any domain is summarized best as indicating a developmental age for the child. This approach makes it possible to consider the child in terms of his or her level of functioning compared against chronologic age. For example, the developmental quotient (DQ) is the developmental age divided by chronologic age times 100 (see Example below). This provides a simple expression of deviation from the norm. A quotient above 85 in any domain is considered within normal limits; a quotient below 70 is considered abnormal. A quotient between 70 and 85 represents a gray area that warrants close follow-up. Values in the upper limit of normal do not particularly indicate supernormal abilities. Whether truly gifted athletes can be recognized early by use of this method is thought-provoking but speculative.
GROSS MOTOR DEVELOPMENT
Gross motor development proceeds from a sequence of prone milestones (beginning with head up and ending with rolling), to sitting, and then through a standing/ambulating sequence (Fig. 2⇓ ). Motor milestones do not take into account the quality of a child’s movement. These sequences must be considered in the context of the motor portion of the neurologic examination, including observations of station and gait, where qualitative features can be assessed. However, the neurologic evaluation of tone, strength, deep tendon reflexes, and coordination is difficult in very young infants because of the subjective nature of the assessments and the infant’s limited ability to cooperate. Clinical experience is essential for obtaining accurate and useful information.
Eliciting reflexes requires patience and repeated, yet gentle, trial and error. Muscle tone (passive resistance) and strength (active resistance) are a challenge to distinguish in the contrary infant. The best clues can be obtained from observation, not handling. Spontaneous or prompted motor activities (eg, weight-bearing in sitting or standing) require adequate strength. Thus, weakness may be appreciated best from observing the quality of stationary posture and transition movements. The Gower sign (arising from sitting on the floor to standing, using the hands to “walk up“ one’s legs) is a classic example and indicative of pelvic girdle and quadriceps muscular weakness. Not until 2 to 3 years of age does the neurologic examination become easier and more meaningful as cooperation improves.
Station refers to the posture assumed in sitting or standing and should be viewed from anterior, lateral, and posterior perspectives, looking for body alignment. Gait refers to walking and is examined in progress. Initially, the toddler walks on a wide base, slightly crouched, with the arms abducted and slightly elevated. Forward progression is more staccato than smooth. Movements gradually become more fluid, the base narrows, and arm swing evolves, leading to an adult pattern of walking by 3 years of age.
The motor neuromaturational markers are the primitive reflexes, which develop during gestation and generally disappear between the third and sixth month after birth, and the postural reactions, which are not present at birth but develop sequentially between 3 and 10 months of age (Fig. 3⇓ ). The Moro, tonic labyrinthine, asymmetric tonic neck, and positive support reflexes are the most useful clinically (Fig. 4⇓ ). As with all true reflexes, each requires a specific sensory stimulus to generate the stereotyped motor response. Normal infants demonstrate these postures inconsistently and transiently; those who have central neurologic (ie, cerebral) injuries show stronger and more sustained primitive reflex posturing. Primitive reflexes are somewhat difficult to gauge, even in expert hands. The appearance of postural reactions in sequence beginning after 2 or 3 months of age is easier to elicit clinically and can provide great insight into the neuromotor integrity of young infants. Postural reactions are sought in each of the three major categories: righting, protection, and equilibrium. These movements are much less stereotyped than the primitive reflexes, and they require a complex interplay of cerebral and cerebellar cortical adjustments to a barrage of sensory inputs (proprioceptive, visual, vestibular) (Figs. 5⇓ and 6⇓ ). They are easy to elicit in the normal infant but are markedly slow in appearance in the infant who has central nervous system damage.
FINE MOTOR DEVELOPMENT
In the first year of life, fine motor development is highlighted by the evolution of a pincer grasp. During the second year of life, the infant learns to use objects as tools during functional play. There are many stages in accomplishing these two skills; selected ones are illustrated in Table 2⇑ . In the early months, the upper extremities assist with balance and mobility. As balance in the sitting position improves and the infant assumes biped mobility, the hands become more available for manipulation of objects—their ultimate function. Primitive reflexes are integrated, and the upper extremities come under cortical control. Reaching becomes more accurate, and objects are brought to the mouth for oral exploration. As development progresses from proximal to distal, reaching and manipulative skills are enhanced further, and precise manual exploration replaces oral exploration. During the second year, fine motor skills are assessed by observing the manner in which the hands use objects as tools (eg, blocks to build and crayons to draw). The close association between gross and fine motor skills in the first year of life evolves into a similar relationship between problem-solving and fine motor skills during the second year. One skill enables or promotes the development of the other. If progress in manual dexterity is slow, this may impede cognitive development via manipulation of objects.
RED FLAGS IN MOTOR DEVELOPMENT
It is important to begin the motor evaluation by observing the infant. Pay particular attention to the hands; persistent fisting at 3 months of age often is the earliest indication of neuromotor dysfunction. Spontaneous postures (eg, froglegs and scissoring) provide visual clues to hypotonia/weakness and spastic hypertonus, respectively. Delays in thea ppearance of postural reactions herald future delays in voluntary motor development. An infant will be unable to sit or walk independently without intact protective and equilibrium mechanisms. Abnormal movement patterns may indicate pathology. For example, early rolling (1 to 2 months), pulling directly to a stand at 4 months (instead of to a sit), W-sitting, bunny hopping, and persistent toe walking may indicate spasticity. Hand dominance prior to 18 months of age should prompt the clinician to examine the contralateral upper extremity for weakness associated with a hemiparesis.
Analysis of the information gathered in these areas makes it relatively easy for the practitioner to reassure him- or herself (and the parents) about a child’s motor competence or to identify motor impairment at an early age. Once a motor abnormality has been identified, further assessment of its exact nature and etiology is essential. This almost always warrants referral to an appropriate subspecialist or subspecialty team. Based on clinical examination and history, the astute clinician usually can decide into which category the motor disorder falls: 1) static central nervous system disorders, 2) progressive diseases, 3) spinal cord and peripheral nerve injuries, or 4) structural defects.
Cognitive processing skills are the substrate for intelligence and include a wide range of abilities (Table 3⇓ ).
Intellectual development depends on learning that contains three components: attention, information processing, and memory (which includes both encoding and retrieval of information). Intellectual development is reflected in advancing abilities to comprehend, reason, and make judgments. Standardized intelligence tests generally measure two forms of intelligence in the school-age child: verbal and performance (or nonverbal). Such standardized tests are not available to measure infant intelligence. How then, does one recognize the attributes of verbal and nonverbal intelligence in infants? In the past two decades, the discovery of visual habituation techniques to assess infants’ attention was considered a breakthrough in the study of infant cognition. It is exemplified by one study that describes 4-day-old infants listening to a long series of “ bee-see-lee” sounds. When a novel “da” sound was heard, the infants responded with a change in heart rate and faster, stronger sucking on a pacifier, thereby indicating that very young infants can perceive differences in vowel sounds.
More complex studies using simultaneous auditory and visual stimuli indicate that infants also are capable of organizing perceptions across sensory modalities (cross-modal matching) without the language skills to describe them. For example, 11-month-old infants were presented a sequence of continuous and interrupted pure tones. Two pictures were in the infants’ view throughout the experiment: one contained a continuous line, the other a dashed line. The infants consistently matched the correct visual stimulus to the auditory one, inferring cross-modal matching and some rudimentary understanding of the concept of interruptedness. Using these techniques, it has been demonstrated that infants younger than 1 year old can form a wide range of fairly complex categorical representations, including those for faces, color, geometric shapes, and orientation of lines.
The attempts to measure infant responses precisely, such as those described previously, depend on sophisticated technology, including infrared photography for tracking infant eye gaze and pupillary dilatation, videotaping of facial reactions, and electrophysiologic monitoring of heart rate and evoked potentials. The primary pediatrician can best estimate infant intelligence by evaluating problem-solving and language milestones. Language is the single best indicator of intellectual potential; problem-solving skills are the next best measure. Gross motor skills correlate least with cognitive potential; most infants who are diagnosed later with mental retardation walk on time.
Problem-solving skills consist of manipulating objects to solve a problem (eg, choosing the correct opening for a circular shape in a three-piece form board). The infant’s ability to solve a problem depends on intact vision, fine motor coordination, and cognitive processing. During the early weeks of life, the infant explores the environment visually. Later, these visual experiences reinforce movement. As the upper extremities come under visual guidance, reaching and grasping are enhanced. At first, the infant brings objects to the mouth for oral exploration. Later, the infant visually examines an object held in one hand while manipulating it with the other. Isolation of the index finger promotes more refined manipulation of the various parts of objects, and the infant becomes successful in discovering how they work (eg, fingering the clapper of the bell). Mouthing of objects becomes less appealing. This precise manual-visual manipulation, triggered by a heightened curiosity and facilitated by a longer attention span, heralds true “inspection” of objects. The infant is progressing from “learning to manipulate” to“ manipulating to learn.” Improved macular vision (via myelination of the fovea) and refinement of the pincer grasp promote inspection of progressively smaller objects. As cognitive abilities continue to advance, the infant learns to shift attention between two objects (one in each hand), compare, make choices, and discard or combine objects. This sensory-motor phase of learning is the foundation for ongoing nonverbal intellectual development.
The 1-year-old child recognizes objects and associates them with their functions. Thus, he or she begins to use them functionally as“ tools ” instead of mouthing, banging, and throwing them. This child has left the period of sensory-motor play and entered the stage of functional play. Play serves as a window into the infant’s thoughts and becomes particularly important during the next stage of symbolic play. At this point, the infant uses toys that represent real objects in actions toward him- or herself (putting a toy telephone to the ear and vocalizing) and later in actions toward dolls or teddy bears (putting a toy tea cup to the doll’s mouth). The use of symbols lays the foundation for imaginary play. This next stage of play usually does not appear until 24 to 30 months of age.
The interdependence of language and problem-solving development becomes stronger as the child begins to label objects and actions. Midway through the second year, this ability to label and categorize allows the child to match objects that are the same (car to a car and spoon to a spoon) and later to match an object to its picture. Nonverbal intelligence is assessed by observing the infant interact with test objects. In the older child, it is assessed through standardized pencil and paper tasks or computerized tests.
One aspect of nonverbal cognitive development deserves extra attention: object permanence, a concept studied extensively by Piaget. Prior to the infant’s mastery of object permanence, a person or object that moves “out of sight“ is“ out of mind”; its disappearance does not evoke a reaction. The ability to maintain an image of a person develops before that of an object. The child will show interest in peek-a-boo play, and separation anxiety will occur when a loved one leaves the room. Shortly thereafter, the child will begin to look for an object that has been dropped. At first, an auditory cue when it hits the floor is necessary to locate it. Later, the child will experience success in finding an object that was dropped from sight and landed silently. Next, the child will progress to finding an object that has been hidden under a cloth or cup. A more complex task is locating an object that has been wrapped inside a cloth. Success requires persistence and memory of the object long enough to complete the three-part unwrapping process. The next skill in this sequence is the ability to locate an object under double layers (eg, a cube is placed under a cup and then the cup is covered with a cloth). This is followed by the ability to locate an object after serial displacements. In this task, an object is hidden under one cover and then changed to another one. The younger infant always will look for it under the first cover, even though the position change was seen. Later, he or she will become successful with this task, as long as each successive displacement still is witnessed. Not until the end of the second year is the child able to deduce the location of an object that is hidden without observing the displacement.
Another important concept dominating this period of development is causality. Initially, the infant accidentally discovers that his or her actions produce a certain effect (eg, kicking the side of the crib activates a mobile overhead). The infant learns to repeat these actions to obtain the same effects. Later, he or she will vary actions to cause a novel effect (pulling a string to obtain the ring). The concept of causality parallels social development in which the infant learns to manipulate the environment by crying or smiling to obtain the desired reaction from caregivers. As the infant approaches 2 years of age, he or she will learn that apparent unrelated actions can be combined to produce an effect (eg, winding a key to make a toy move).
Delays in language development are more common than delays in other developmental domains. Parents and pediatricians generally are less familiar with language milestones. Language is the most difficult domain to assess by observation because infants rarely vocalize spontaneously in the clinician’s office. For this reason, it is essential for the clinician to obtain a thorough and accurate language history. The pediatrician should become familiar with milestone terminology and learn to give examples (eg,“ razzing”). Between 10 and 18 months of age, word counts help in assessing a child’s expressive skills; after 18 months of age, vocabularies increase exponentially, and it is difficult to keep up with counts.
Language includes receptive and expressive skills. Receptive skills reflect the ability to understand language; expressive skills reflect the ability to make thoughts, ideas, and desires known to others. Expression of language can take several forms: speech, gestures, sign language, writing, typing, and“ body language.” Thus, language and speech are not synonymous. Speech is simply the vocal expression of language. A child can have normal language and yet be unable to speak. Examples include children who are deaf and children who have severe cerebral palsy. The child who has a hearing impairment may use manual sign language to communicate. A child who has normal intelligence but cannot speak because of oral-motor dysfunction related to cerebral palsy may use a computer that is activated with a head stick. Conversely, a few children talk but fail to use speech to communicate (eg, children who have autism). Their vocalizations consist of “parrot talk” or echolalia that has no communicative intent and, thus, does not represent language.
Language development during infancy can be divided into three periods: prespeech, naming, and word combination periods.
Prespeech Period (0 to 10 months): Receptive language is characterized by an increasing ability to localize sounds. Sound localization is assessed by using a noisemaker such as a bell (Fig. 7⇓ ). Expressive language consists of musical-like vowel sounds (cooing) that are interrupted by crying when the baby has a need. At about 3 months, the infant will begin vocalizing immediately upon hearing an adult speak. One or two months later the infant is silent and assumes a posture that implies he or she truly is“ listening” to the speaker. These infants make no vocalizations until the speaker is quiet, mimic the speaker, and then quiet again when the adult speaks. They appear to enjoy the “vocal tennis” and repeat this for several cycles. At approximately 6 months of age, the infant adds consonants to the vowel sounds in a repetitive fashion (babbling). Soon the infant appears to initiate conversations. When a random vocalization (eg, “dada”) is interpreted by the parents as a real word, they show pleasure and joy. In so doing, adults give meaning to these first “words” and reinforce their repeated use.
Naming Period (10 to 18 months): This period is characterized by the infant’s realization that people have names and objects have labels. It is an important turning point in language development. The “dada” and “mama” that were vocalized randomly have been reinforced, so the infant now begins to use them appropriately. Infants next recognize and understand their own names and the meaning of “no.” This marks the beginning of exponential growth in receptive language. By 12 months of age, some infants understand as many as 100 words. They also can follow a simple command as long as the speaker uses a gesture. Early in the second year, a gesture no longer is needed to aid in comprehension of the command. Expressive language progresses at a somewhat slower rate. The infant will say at least one “real” word (ie, other than mama, dada, or a proper name) before his or her first birthday. At this time, the infant also will begin to verbalize with sentence-like intonation and rhythm (immature jargoning). As the expressive vocabulary increases, real words are added (mature jargoning). By the end of the naming period, the infant will use approximately 25 words spontaneously.
During this period, pointing becomes important to both receptive and expressive language skills. Pointing already has become a method of exploration within the problem-solving domain. The infant beginning to look in the general vicinity where the adult is pointing is a receptive language skill. This ability is facilitated by the infantrsquo;s new realization that objects have labels. Later, the infant begins to take part in pointing games. He or she will point first to family members, then objects, body parts, articles of clothing, and pictures upon request. These all reflect receptive language skills.
Pointing also is used for language expression. First, the infant points at an object and uses the adult as a tool to retrieve the object, referred to by linguists as protoimperative pointing. The infant first points to the object (eg, a cookie) and then looks back and forth between the adult and the object expectantly. At a later stage, he or she directs attention to the adult and alternately points at the adult and the desired object while vocalizing (eg, “uh...uh”). Next, the infant uses the object as a tool to obtain the parent’s attention (protodeclarative pointing). Protodeclarative pointing is a social act; the parent is an active and important partner in a shared world. Rather than acquisition of the object, the infant’s goal becomes the parent’s acknowledgment of the interesting object. For example, when an infant hears an airplane overhead, he or she points to it and vocalizes to get the parent to look at it. If the parent does not comply with these initial efforts, the infant may approach the parent and turn his or her face toward the plane in a more determined effort to obtain what is sometimes called “joint attention.” Finally, the infant will point at an object and vocalize (“uh?”) in an effort to obtain the proper label or name for that object from the listener. This is called “pointing for naming.”
Word Combination Period (18 to 24 months): Typically, children begin to combine words approximately 6 to 8 months after they say their first word. If word combinations appear much earlier, they are likely “giant words.” Giant words are two- or three-word combinations that the infant hears frequently, such as “Thank you,” “Stop it,” or “Let’s go.” When the infant says one of these, he or she really is treating the phrase as a polysyllabic single word. At this stage of development the infant does not use either word separately or in novel combinations with other words.“ Holophrases” also are beginning to appear at this time. For example, an infant may point to a mother’s keys and say “mommy” instead of saying “keys.” In this context, the single word,“ mommy,” has a sentence-like meaning, such as “These keys belong to mommy.” Single words take on multiple meanings and no longer simply label an object. The infant usually does not combine words into true phrases or sentences until he or she has acquired an expressive vocabulary of approximately 50 words. Early word combinations are“ telegraphic” in that they do not contain function words (prepositions, pronouns, and articles). They do, however, convey the same meaning as the more mature sentence. For example,“ Go out,” in the context of the situation, conveys the same meaning as “I want to go outside.” Telegraphic speech is the first stage in the child’s ability to“ grammaticize” speech, that is, to form sentences with proper morphology and syntax. At this point in development, a stranger should be able to understand at least 50% of the infant’s speech (intelligibility). Language blossoms after 2 years of age.
RED FLAGS IN COGNITIVE DEVELOPMENT
Language development provides the clinician with an estimate of verbal intelligence; skill development in the problem-solving domain provides an estimate of nonverbal intelligence. If deficiencies are global (ie, skills are delayed in both domains) and significant (ie, >2 standard deviations below the mean), there is a possibility of mental retardation. Mental retardation refers to significant sub-average general intellectual functioning as measured by standardized tests. By current definition, these deficits must be associated with significant deficits in adaptive functioning. About 3% of the population is mentally retarded. If the deficiencies are very mild (ie, in the low range of normal), the child is considered to be of borderline intelligence or a “slow learner.”
When a discrepancy exists between problem-solving and language abilities, with only language being deficient, one must consider the possibility of a hearing impairment or a communication disorder. If either language or problem-solving skills is deficient, the child is at high risk for manifesting a learning disability later. A learning disability refers to academic achievement that is substantially below what would be expected from a person’s general intellectual potential. Approximately 5% to 7% of school-aged children have learning disabilities. A learning disability cannot be diagnosed formally until the child reaches school age and demonstrates an inability to keep up in one or more academic areas. Thus, a reading disability cannot be diagnosed until at least age 6 or 7 years when children normally are expected to read. A delay in language development is a “red flag” and should prompt careful monitoring and further evaluation if the child later demonstrates reading difficulties in school. The neurologic substrate for specific learning disabilities involves patchy dysfunction in cortical information processing that results in specific difficulties with academic tasks.
Unless the deficiencies are severe during infancy, a child rarely presents with a parental concern of“ cognitive delay.” Concerns usually present as speech delays, but such complaints are infrequent before 24 months of age. The average age at which mental retardation is diagnosed is 3 to 4 years. Usually, the more severe the degree of impairment, the earlier the diagnosis is made. Because the majority of children who are mentally retarded are in the mild category, most children are diagnosed well after infancy. Some are not diagnosed until they enter school. The child who is born with dysmorphic features and has a recognizable syndrome known to be associated with mental retardation will be diagnosed earlier regardless of the degree of impairment. Additionally, abnormal findings on magnetic resonance imaging (performed because of atypical head growth or because of a known cerebral insult) indicate that the child is at risk for intellectual deficits.
Although a cognitive deficit is the most common reason for language delay, all children who have delayed language development should receive audiologic testing to rule out hearing loss. The child who has a hearing loss will demonstrate normal expressive language skills through the babbling stage (6 months). He or she will begin to babble on time, but lack of auditory reinforcement for these vocalizations results in their disappearance and a general decline in verbal expression. Receptive language abilities continue to progress normally for a few more months. A 1-year-old who is deaf will follow a command with a gesture (relying solely on the gestural cue) and may seem to hear. This ability to use environmental cues can fool parents and professionals and is one of the chief reasons that the average age of diagnosis of a severe hearing loss is 2 years. Children who have a mild hearing loss will present even later with articulation errors, inability to localize sounds, or “attentional problems.” An infant who is deaf will attempt to communicate by using gestures. If a child has delayed speech and fails to demonstrate a desire to communicate, a more pervasive problem, such as autism, should be considered. Although children who have autism may demonstrate protoimperative pointing (eg, pointing to obtain food or drink), they rarely point to the object for the purpose of having the adult join in the pleasure of admiring an interesting object (protodeclarative pointing) or point to obtain the name of an object. Prodeclarative pointing is a social action, and one of the cardinal features of autism is the lack of social relatedness. Another red flag is the finding that a child’s expressive skills are advanced compared with his or her receptive skills. A child who speaks in five-word sentences but does not understand simple commands is at risk of having a pervasive developmental disorder. The advanced speech may not be functional or have communicative intent. Finally, some parents will excuse their child’s lack of speech because of an “Uncle Albert” who didn’t speak until he was 4 years old but grew up to be a rocket scientist. In reality, this is very rare. Normal receptive language skills in a child who has speech delay would be reassuring and typically are easy to demonstrate.
Other problems may masquerade as cognitive delay or impair the assessment of cognitive abilities. Problem-solving tasks require intact fine motor skills. Having poor fine motor skills puts the child at a disadvantage with certain manipulative tasks used to assess nonverbal cognition. Due to cerebral palsy, a child may not be able to place a square form in a form board; however, he or she might be able to indicate the correct position by pointing or by eye gaze. Thus, the child actually could “pass” the form board item in the problem-solving assessment. Similarly, visual impairment can interfere with a child’s ability to perform many problem-solving tasks successfully.
Emotional, social, and adaptive milestones have been assimilated from multiple sources (Table 4⇓ ). These milestones are more variable than those in motor and cognitive domains because of the greater influence of environmental factors (nurture). An infant inherits a set of emotional-social characteristics and a style of interacting, but these are modified by parenting style,“ goodness of fit,” and the social environment. Emotions include the infant’s feelings as well as the expression of these feelings. Social milestones include the steps necessary to form interpersonal relationships. Temperament influences social relationships and generally reflects a consistent pattern (or style) in “how” a child reacts. It is different from the“ why” (motivation) and the “what” (content) of social interactions. The inclusion of adaptive skills (ie, skills required for independence in feeding, dressing, toileting, and other activities of daily living) is unique to the discussion of psychosocial development and reflects the concept that these skills influence, and are influenced by, social factors.
Emotions are present in infancy and motivate expression (pain elicits crying). Emotion has three elements: neural processes, mental processes (feelings), and motor expression (facial, verbal) and actions. Emotions are mediated through the limbic system, which is responsible for receiving, interpreting, and processing emotion-producing stimuli and then initiating and modulating emotional responses. There is evidence that an infant can express emotion without direct cognitive mediation. An infant who has anencephaly or hydranencephaly may show disgust at sour flavors and interest in sweet flavors in ways very similar to a normal infant. Later, in the normal infant, these instinct-like reactions are modified by cognition. Although emotional feelings are constant over the life span, their causes change and become more abstract. The infant may show disgust for a bitter taste; the older child may show disgust for a revolting idea. Other emotions have a definite cognitive foundation. To experience fear, the 7- to 9-month-old child must be able to shift attention, compare, and recognize “familiar” from“ unfamiliar” in the development of stranger anxiety. As the child develops, the interrelationship between emotion and cognition becomes increasingly complex. When the child begins to associate language symbols with emotions and memory, he or she can remember prior emotional experiences. A verbal reminder of the event then can evoke feelings identical to those experienced previously. Thus, language and cognition add flexibility and complexity to emotional behavior.
The expression of emotions also evolves with age and developmental advancement. Consider this example of an emotional reaction (fear) to a stranger, based on skill level: In addition to developmental progress, the feedback loop between care providers and child modifies emotional expression. Social forces and cultural factors also modulate emotional expression to produce more restrictive and controlled facial signals. An older child may learn to modulate the expression of pain (a facial grimace only) and appear quite stoic. Furthermore, children can learn to mask emotions such as smiling at a disappointing gift. At early stages, however, the true emotion typically leaks out from under the mask.
The infant is surrounded by a social network. Sensory processing is influenced by the infant’s social needs. The infant has greater discrimination ability for social voices) than for nonsocial (environmental noise) stimuli. There are two primary theories: the Epigenetic Model and the Social Network Model. In the Epigenetic Model, the mother-child relationship is considered to be all important. If this relationship is negative, then other relationships will be poor. If it is positive, then future relationships will be good. The Social Network Model recognizes the relative importance of the mother-child relationship, but also recognizes the ability of other relationships to compensate for absent or poor mother-child interactions. The devastating effect of a poor relationship can be overcome by adequate substitutes and a supportive environment. The latter reflects the popular concept of childhood resiliency.
Social milestones begin with bonding, which reflects the feeling of the caregiver for the child. Attachment takes place within a few months and represents the feeling of the infant for the caregiver. These social relationships are manifested by the evolution of the smile, in which the level of stimulus required to elicit reciprocity decreases. At first, high-pitched vocalizations and a smile from the adult are needed; later, a smile alone is successful. When recognition of and attachment to a familiar caregiver develops, the simple sight of this person (smiling or nonsmiling) will elicit a smile. The infant also becomes more discriminating in producing a smile as he or she begins to differentiate between familiar and unfamiliar faces. As the infant acquires the concept of causality, he or she begins to use smiling to manipulate the environment and satisfy personal needs.
Later in infancy, other social relationships are established. Several behaviors are necessary for the development of these relationships. First, the infant must have a concept of self versus others. Next, he or she must be able to put self in the place of another, that is, to show empathy. The infant must perceive a separate identity with a different set of needs. He or she must realize the consequences of his or her interactions on others. Empathy is critical to forming a relationship. Next the child must be able to share, which is critical to maintaining a relationship. There are four basic types of relationships: with acquaintances, strangers, friends, and loves. Whereas relationships with acquaintances and strangers simply require a concept of self, friendship and love require all three (a concept of self, empathy, and sharing). About the same time that the child can label emotions (via language), he or she begins to think about social interactions. A child will demonstrate recursive social thoughts, that is, show early signs of thinking about how others behave toward him or her and how he or she behaves toward others.
Temperament, or the infant’s overall style of reacting, can affect social relationships. The precise definition of temperament is controversial, but it generally is believed to represent the characteristic style of a child’s emotional and behavioral response in a variety of situations. It is determined by genetic factors but is modified by environmental forces. Temperament shows considerable stability over time. Thomas and Chess describe nine traits that determine whether a child will have an “easy,”“ difficult,” or “slow-to-warm-up” temperament:
Activity level—proportions of periods of activity to inactivity
Adaptability to change
Positive or negative mood
Intensity of emotional responses
Rhythmicity of biologic functions
Persistence in the face of environmental counterforces
Distractibility or ease of soothing
Approach versus withdrawal tendencies in new situations
Threshold of stimulation necessary to produce a response
The Carey Infant Temperament Questionnaire often is used to evaluate these traits formally. Approximately one third of infants will be characterized as difficult or slow-to-warm up. The other two thirds will be classified as easy infants. The easy infants fall into three subcategories: 1) gentle, tender, sensitive, affectionate; 2) changeable, variable, adaptable; and 3) social, playful, happy, attention-seeking. A child’s temperament can influence developmental testing. The child who is difficult or slow to warm up may refuse to cooperate with test items, thereby receiving lower scores that do not reflect his or her true abilities.
ADAPTIVE SKILL DEVELOPMENT
Adaptive skill development is influenced by the infant’s social environment, as well as by motor and cognitive skill attainment. A child who has quadriparesis may not be able to feed him- or herself, even with normal intelligence and a supportive social environment.
In contrast, acquisition of self-help skills by an able-bodied infant may be delayed in the face of mental retardation and the lack of motivation to become independent. In spite of normal motor and cognitive skills, an infant may demonstrate delays in adaptive skills when social support and encouragement are lacking. This is exemplified by delays in self-feeding skills when the caregiver is overly concerned about messy spillage or feels the need to rush mealtime. Additionally, parents may persist in dressing the older child in an effort to rush to child care. The decision to initiate toilet training often is influenced by both family and culture.
RED FLAGS IN PSYCHOSOCIAL DEVELOPMENT
Decreased rhythmicity (eg, colic) may be an early indication of a“ difficult child.” Delay in the appearance of a reciprocal smile may indicate an attachment problem, which may be associated with maternal depression. In severe cases, child neglect or abuse may be suspected. However, a delay in smiling also may be associated with visual or cognitive impairment. The lack of social relationships plays a key role in the diagnosis of autism when it is accompanied by delayed or deviant language development and stereotypic behaviors. History and observation of an infant’s behavior at play may alert the clinician to abnormal social relationships. The emotional status of the parents and parenting styles may affect the infant’s development of adaptive skills. A controlling, rejecting parenting style may be revealed in an oppositional child who refuses to cooperate with self-care. Delays in adaptive skills also may indicate overprotective parents or an excessive emphasis on cleanliness.
The journey through infancy truly is fascinating—a time of incomparably rapid changes in physical growth and motor development. By the end of this period, the child is mobile and explores his or her environment independently. The child’s pincer grasp and release rival that of the adult. Cognitive and social changes are equally prodigious. The baby has progressed from simple methods of expression (crying and grimacing) to a “little person” who has a complex array of emotional expressions that are becoming “socialized.” He or she has learned to use these emotions to manipulate the environment and obtain the attention and the objects that he or she desires. Additionally, the child can think about emotions and feel empathy for the emotions of others. He or she has strong love and friendship relationships with family members and a few significant others. The next few years are characterized by exponential language development, which will reveal the complex thoughts, feelings, and humor owned by this amazing creature destined to become an adult.
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