Theories of early cognitive development fall in and out of fashion. I shall try to weave my way through these explanations. From the preceding section, we recognize that various portions of the brain are becoming more active. I shall attempt to sketch how experiences influence cog-nitive development and aid brain organization.
It may be easiest to conceptualize development of the cognitive bases for language if we divide our discussion into four areas of development: sensation, perception, motor control, and cognition. We’ll explore these areas in light of what we know about information process-ing from Chapter 3 and its four steps of attention, discrimination, organization, and memory.
Then we’ll finish by discussing early learning and the influence of cognition on early language development. Wow, that’s a lot! So let’s get started.
S E N S AT I O N
Sensation is the ability to register sensory information.All senses are functioning at birth and have been for some time. As a newborn, you possessed an impressive array of motor and sensory skills.
Touch is the first sense to develop in utero. From sensitivity in various regions of the body at eight weeks, sensation spreads to the entire body by week 14. Most pregnant women report that by gently stroking their enlarged “tummies” they can calm the fetus within. Pain receptors are formed by the twenty-sixth week.
A fetus is also sensitive to sounds very early and will startle to both sounds and move-ment at eight weeks. The inner ear is formed by 20 weeks postconception, and a fetus’s hearing is functional at this point. While in utero, a fetus is exposed to many auditory stimuli, especially the sound of the mother’s voice (DeCasper & Spence, 1986). For most newborns, mom’s voice is their preferred environmental sound.
The middle and inner ears reach their adult size at 20 weeks of fetal development and are ready to function at birth. The auditory cortex is not mature, however, and the middle ear is
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filled with fluid. The immaturity of the cortex and the lack of internal coordination of the brain’s hemispheres make it difficult for a newborn to integrate sounds. In addition, the middle ear is not as sensitive to sound as it will be within two weeks after birth, when the fluid is absorbed.
We have less information on the other senses, although we do know that fetuses can sense sweet and noxious tastes in their amniotic fluid. Sense of smell must also be activated while in utero because after birth a newborn prefers the scent of her or his mother over other scents and will turn toward its own amniotic fluid. We’re not sure when vision becomes active.
Babies make little change in their sensory abilities with birth. Rather, the change is in the quantity and quality of sensation. Babies seem to love new stimulation. Ever-changing sensory experiences “nourish” their minds.
Newborns or neonates have difficulty controlling attention or concentrating mental activity. Either they cannot direct it willfully or they are captured by sensory stimuli and have difficulty breaking free. This is important because increased or decreased attention to a stimulus corresponds to an increase or decrease in the ease of remembering that stimulus (Adler, Gerhardstein, & Rovee-Collier, 1998).
A neonate is somewhat at the mercy of sensations, although he or she can shut out visual images by closing the eyes or averting gaze. If the level of stimulation is too low, an infant loses interest quickly. Attention is captured more easily by moderate stimulation. At a moderate level of stimulus strength, an infant’s attention is maintained longer and more frequently. As the stimulus strength increases, such as becoming louder, so does attention, until a point is attained at which stimulus strength reaches an infant’s tolerance threshold. A child will then avert his or her face, become restless, or cry for assistance.
Many of an infant’s behavior-state changes reflect internal changes or intrinsic brain ac-tivities. For example, during the first month of life, an infant is frequently asleep or drowsy.
Even so, external stimuli can influence the duration of these states. An infant is most receptive to external stimuli when alert but not overly active. Thus, the ability to attend is influenced by an infant’s internal state. This changes quickly, and, within a few months, the level of external stimulation is a greater determinant of attending than an infant’s state. By that time an infant is capable of maintaining a rather stable internal condition.
By 2 months of age an infant exhibits selective attending skills and can remain unre-sponsive to some background stimulus events. When presented with a stimulus repeatedly, an infant will react less strongly to each successive presentation. Becoming used to a stimulus, called habituation, is the result of patterns formed as stimuli occur repeatedly. An infant begins to expect the stimulus to occur. If the expectation is fulfilled, then the stimulus does not elicit a significant response. Thus, habituation enables an infant to attend to new stimuli without com-petition from older, less novel stimuli. Habituation requires sensory learning and perception.
P E R C E P T I O N
Perception is using both sensory information and previous knowledge to make sense of in-coming stimuli. The ability to discriminate differences in inin-coming information is a portion of perception, a process of gaining awareness of what is happening around us.
Of most interest for our study of language and speech development are auditory per-ceptual skills. In order for an infant’s perper-ceptual skills in these areas to grow and change, he or she must be exposed to stimulation from the environment. A child must hear speech over and over again. From birth, an infant is an active stimulus seeker who will even work to attain cer-tain types of stimulation.
A newborn is capable of many types of auditory discrimination. For example, a newborn can discriminate between different sound durations and loudness levels, and different
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phonemes and consonants in short syllables (Bertoncini, Bijeljac-Babic, Blumstein, & Mehler, 1987; Davis & DeCasper, 1989; Moon, Bever, & Fifer, 1992). The ability to discriminate between phonemes evolves quickly. Newborns are also capable of discriminating different pitches or frequencies, especially in the human speech range. In fact, neonates respond to the human voice more often and with more vigor than to other environmental sounds. By 2 months, an infant is also able to discriminate frequency changes, such as high to low. Because intonational patterns are closely related to frequency shifts, we would expect to see this type of discrimina-tion shortly thereafter, and this occurs by 7 months. At about the same time, infants are able to discriminate different words.
Visually, infants are able to perceive the somewhat blurry human face at birth and learn to direct their attention at faces very quickly. Within a few days, they can discriminate between dif-ferent facial expressions. By 2 months, infants prefer an “average” face, probably because it matches an internalized concept of a face. When I had a beard—anything but “average”—infants often gave me very quizzical looks. By 3 months, infants can perceive facial differences. Between 5 and 8 months, children begin to perceive their own face, although they probably don’t yet understand exactly who that vision in the mirror is (Legerstee, Anderson, & Schaffer, 1998).
Similarly, recognition of different facial expressions does not imply that an infant under-stands emotion. In any case, between 4 and 6 months, children respond more positively to a smile.
Some faces are more important than others. Within a few days of birth, infants can recognize their mother’s face (Pascalis, deSchonen, Morton, Deruelle, & Fabre-Grener, 1995;
Walton, Bower, & Bower, 1992). Although a stranger’s face receives a longer study by an infant at 1 month, mom’s face receives a more emotional response.
With increasing memory, a child moves from recognition of familiar faces, objects, and sounds to evocation of these. After repeated exposures, stimuli will elicit signs of recognition from a child. For example, the sight of the bottle might elicit sucking. With increased memory, a child is able to recall a stored image with only minimal stimulation. Thus, mother’s footsteps may elicit her image for an infant. Within a child’s memory, different aspects of a concept be-come linked, such as sight, sound, smell, feel, and a related sound sequence or word. Accessing one aspect of the concept opens all. Hearing the word dog triggers the concept. At some time around a child’s first birthday, any stimulus may open the concept and elicit the symbol or name for a child. For example, seeing the dog or hearing a bark may enable a child to extract
“Doggie!” By about 18 months, a toddler is able to evoke the word with no external stimulus.
How that word forms requires some specific perception.
The Formation of Auditory Patterns
During the first year, a child lays down a perceptual framework for learning first words. An in-fant actively encodes the sound patterns of his or her native language, organizing these patterns into types and sequences. Although it was initially thought that these abilities were specific to humans, later research indicated that the ability to discriminate the sounds of human language is found in other mammals (Kuhl & Miller, 1978).
Since this discovery, the focus of study has shifted to the process by which children tune their perception to fit their native language. Learning about speech signals may begin as soon as the auditory system is functional. Thus, it’s likely that an infant is learning something about the rhythms of its native language even while in utero. For example, French newborns seem to prefer listening to French, Japanese infants to Japanese, and so on.
Neonates prefer human speech to other nonlinguistic auditory stimuli.Although as neonates they are especially sensitive to intonation, by 3 months of age they seem to be more attentive to words (Ferry, Hespos, & Waxman, 2010).
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Development of speech perception proceeds through the first year of life. Newborns are capable of detecting virtually every phoneme contrast used in human languages, something most adults can no longer perceive. The accuracy of a child’s perceptual ability declines during the first year, as infants learn to lump together sounds that their language treats as equivalent, such as the /b/ and /v/ in Spanish (Polka & Werker, 1994). In other words, children spend much of the first year losing their ability to perceive contrasts that are not used in the speech around them. Thus, Japanese adults and older children find it very difficult to perceive the difference between “ra” and “la,” although Japanese infants have no trouble at all.
As they are exposed to their native language, even newborns begin to recognize regulari-ties, patterns that occur, some frequently, some less. This is part of the way in which our mind functions; it looks for patterns then forms concepts based on these patterns. The ability to detect patterns and to make generalizations is extremely important for later symbol and language rule learning (Marcus, 2001). Significant correlations exist between speech perception at 6 months of age and later word understanding, word production, and phrase understanding, thus indicating the importance of early phonetic perception in language acquisition (Tsao, Liu, & Kuhl, 2004).
Extracting and learning individual speech sounds from the speech stream is difficult, even though newborns are capable of discriminating individual phonemes. It is extremely problematic for a child to discern individual words and sounds in the ongoing, multiword utterances of adult speech. Yet by 5 months, most children respond to their own name and, within another month, respond to either mommy or daddy (Mandel, Jusczyk, & Pisoni, 1995; Tincoff & Jusczyk, 1999).
These are frequently occurring words in a child’s world. By 8 months, children begin to store the sound patterns for words, although meaning is not attached yet (Jusczyk & Hohne, 1997).
Between birth and 6 months of age, infants begin to show a preference for vowel sounds in their native language. Language-specific preference for consonants seems to occur later. An infant’s perceptual ability is usually restricted to its native language’s speech sounds by 8 to 10 months of age, about the time that most infants start to comprehend words. It’s possible that tuning in to its own language sounds in order to comprehend requires an infant to tune out phonemes not used in that language (Bates, 1997).
Infants’ decreasing ability to discriminate most sounds outside their native language re-sults from experience (Best, 1995; Tsushima et al., 1994; Werker & Tees, 1994). As an aside, you can now appreciate why it is important for second-language learning to occur very early.
The period of 8 to 10 months is marked by changes in both perception and production.
Timing may be related to brain developments that occur around the same time, including synaptogenesis or a burst in synaptic growth, changes in activity levels in the frontal lobes, and an increase in frontal control over other brain functions (Elman et al., 1996). In fact, the 8- to 10-month period includes dramatic changes in several cognitive and social domains, as noted in imitation of others and intentional communication, discussed later. In other words, speech and language development may to be linked to changes in other nonlinguistic factors.
Babies learn the prosodic patterns, syllable structure, and phonotactic organization of their native language and at this age use these skills to help break up and analyze the relative unbroken speech stream of mature speakers into recognizable words. Prosody is the flow of language. The prosodic pattern in English is characterized as stress-time, meaning that differ-ent syllables receive more stress and are held for a longer time while others receive less of both.
Not all languages are so organized. For example, Japanese has short syllables with nearly equal stress and time. In English, 80% of words in conversation have stress on the initial syllable.
Young infants are sensitive to stress and to rising and falling intonational patterns. Even newborns are capable of discriminating different prosodic patterns and can recognize utterances in their native language from those in languages with different prosodic patterns (Mehler et al., 1988; Nazzi, Bertoncini, & Mehler, 1998). Stress patterns are one tool used by infants to determine
88 CHAPTER 4 ■ Cognitive, Perceptual, and Motor Bases of Early Language and Speech
word boundaries (Echols, Crowhurst, & Childers, 1997; Jusczyk, Houston, & Newsome, 1999;
Morgan, 1994; Morgan & Saffran, 1995).
As noted, soon after birth, infants prefer their native languages to other languages (Moon, Cooper, & Fifer, 1993). Most likely, these preferences emerge from the infant’s ability to detect language-specific prosodic or rhythm patterns. From early on, infants seem to be sen-sitive to the intonation of the language they hear. Even 2-month-olds tend to remember words better when presented with normal sentence intonation, than when they are presented with flat prosody (Mandel, Jusczyk, & Kemler Nelson, 1994). Stress or emphasis may also be important.
Children tend to perceive and remember stressed syllables more readily than unstressed ones (Mandel, Jusczyk, & Pisoni, 1995).
By 5 months, infants can discriminate their own language from others with the same prosodic patterns (Bosch & Sebastián-Gallés, 1997; Nazzi, Jusczyk, & Johnson, 2000). Pre-sumably, children use phonemes, frequent phoneme combinations, and syllable structure to reach this decision. For example, when 8-month-old children listen to long sound sequences such as “dabigogatanagotidabigo,” they tend to pull out repeated sequences such as “dabigo”
and to listen to these familiar sequences more than to other sequences (Saffran, Aslin, &
Newport, 1996). By 9 months, children are using both the prosodic and these phonotactic clues to discern individual speech sounds within connected speech. Within two months, they are able to recognize allophones and to use these to aid in word boundary identification (Jusczyk, Houston, & Newsome, 1999).
Phonotactic organization consists of syllable structure and sound combinations. For example, /pt/ can appear at the end of both a syllable and a word in English but not at the beginning. In contrast, /fh/ and /vt/ are likely to occur across word boundaries, as in calf hide and glove touches respectively. Armed with this information, it’s easier for a child to deter-mine word boundaries.
Identifying word boundaries in continuous speech is relatively easy for adult listeners.
For infants, however, this task can be very challenging because words are not consistently sep-arated by pauses. Luckily, there are other types of information embedded in speech that mark word boundaries. These include phonotactic regularities and prosodic or flow patterns (Jusczyk et al., 1999; Mattys & Jusczyk, 2001). In fact, 8-month-old infants have been found to be sensitive to regularities in infant-directed speech (IDS) and can learn them quickly even in another language (Pelucchi, Hay, & Saffran, 2009).
Young language learners are especially sensitive to frequently occurring patterns in the language of their environment (Werker & Curtin, 2005). These patterns can be thought of as phonotactic probabilities or the likelihood that certain sounds, sound sequences, and syllable types will occur. For example, the likelihood of a word in English ending in /h/—not the letter but the sound—is zero. Nine-month-old infants have a listening preference for non-words com-posed of high phonotactic probabilities versus those with low phonotactic probabilities (Jusczyk, Luce, & Charles-Luce, 1994). In production, infants are better at saying frequent sequences (e.g., /kt/) than infrequent sequences (e.g., /gd/) (Edwards, Beckman, & Munson, 2004).
Phonotactic representations are also correlated with vocabulary growth. Children with smaller vocabularies have less robust phonological representations, making it more difficult for them to parse or divide words into their sounds and sound sequences. More specifically, vo-cabulary size seems to be related to young children’s (26–32 months) ability to repeat phoneme combinations, especially in the initial position in non-words (Zamuner, 2009).
Of course, this doesn’t explain how infants figure out these patterns in the first place.
First, we need to recognize that an infant would not need complete knowledge of sound regu-larities. Instead, an infant would only need some word-like units with which to figure out reg-ularities. For example, some words are heard as single words or in frequent word combinations
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that would help a child identify those words (Bortfeld, Morgan, Golinkoff, & Rathbun, 2005;
Brent & Siskind, 2001).
In short, infants are little statisticians, figuring out the probabilities of certain sound combinations in certain locations in words. Then they apply these probabilities to speech to figure out where word boundaries occur. One regularity available to infants is the probability between syllable sequences or the probability of one syllable type following another. Studies have demonstrated that infants are also sensitive to the probabilities of sound co-occurrences in speech (Aslin, Saffran, & Newport, 1998; Saffran, Aslin, & Newport, 1996).
In summary, infants and other mammals seem to start with an innate ability to hear speech sounds used in all human languages. Throughout the first year an infant tunes out irrelevant speech sounds and tunes into the phonological characteristics of his or her native language, but the infant will need oral motor control before he or she can talk.
M OTO R CO N T R O L
Motor control is muscle movement and the sensory feedback that informs the brain of the ex-tent of that movement. Just discernable movement begins at seven weeks postconception with isolated limb movement evident two weeks later. Hand-to-face contact and body rotation are
Motor control is muscle movement and the sensory feedback that informs the brain of the ex-tent of that movement. Just discernable movement begins at seven weeks postconception with isolated limb movement evident two weeks later. Hand-to-face contact and body rotation are