Perceptual Development in Infancy
The union of perceptual and motor information is basic to our nervous systems, and each domain supports development of the other. There are various studies that support this idea, for example: White and Held's study illustrates the close link between perception and action in discovering new skills. To reach for objects, maintain balance or move across various surfaces, infants must continually coordinate their motor behavior with perceptual information. Acting and perceiving are not separate aspects of experience. Instead, motor activity provides infants with vital means for exploring and learning about the new world, and improved perception brings about more effective motor activity.
Researchers have sought answers for the questions what can young infants perceive with their senses, and how does perception change with age for two reasons:
- Studies of infant perception reveal in what ways babies are biologically prepared to perceive the world and how the brain development and experience expand their capacities.
- Infant perception is of interest because it sheds light on other aspects of development.
For example: because touch, vision, and hearing permit us to interact with others, they are basic to emotional and social development. Through learning, language is learned. And because knowledge of the world is first gathered through the senses, perception provides the foundation for cognitive development.
Studying infant perception is especially challenging because babies cannot describe their experiences. Fortunately, investigators can make use of a variety of nonverbal responses that vary with stimulation such as looking, sucking, head turning, facial expression and reaching. Researchers also rely on operant conditioning and habituation to find out whether infants can make certain discriminations.
And psychophysiological measures, such as stimulus induced changes in respiration, heart rate, and EEG brain waves (event related potentials, or ERPs) are sometimes used. Also, the various examples of these methods are as follows as we explore the baby's sensitivity to touch, taste, smell, sound and visual stimulation.
Touch is a fundamental means of interaction between parents and babies. Within the first few days, mothers can recognize their own newborn by stroking the infant's cheek or hand (Kaitz et al., 1993). Touch helps stimulate early physical growth and it is vital for emotional development. Therefore, it is not surprising that sensitivity to touch is well developed at birth. At birth, infants are quite sensitive to pain. Babies often respond to pain with a high-pitched, stressful cry and dramatic rise in heart rate, blood pressure, palm sweating, pupil dilation and muscle tension. Research on infant mammals indicates that physical touch releases endorphins-painkilling chemicals in the brain. Allowing a baby to endure severe pain overwhelms the nervous system with stress hormones, which can disrupt the child's developing capacity to handle common, everyday stressors. The result is heightened pain sensitivity, sleep disturbances, feeding problems and difficulty calming down when upset. Touching that is pleasurable enhances babies' responsiveness to the environment. An adult's soft caresses induce infants to smile and become more attentive to the adult's face. And even newborns use touch to investigate the world. They habituate to an object placed in their palms and recover to a novel object, indicating that they can use touch to distinguish object shapes. Exploratory mouthing peaks in the middle of the first year as hand-mouth contact becomes more accurate. Then, it declines in favor of more elaborate touching with the hand, in which infants turn, poke and feel the surface of things while looking at them intently.
TASTE AND SMELL:
At birth, facial expressions reveal that babies can distinguish several basic tastes. Like adults, they relax their facial muscles in response to sweetness, purse their lips when the taste is sour, and show a distinct archlike mouth opening when it is bitter. These reactions are important for survival. The food that best supports the infant’s early growth is the sweet-tasting milk of the mother’s breast. Not until age 4 months do babies prefer a salty taste to plain water, a change that may prepare them to accept solid foods. As with taste, certain odour preferences are present at birth. For example, the smell of bananas or chocolate causes a relaxed, pleasant facial expression, whereas the odour of rotten eggs makes the infant frown. During pregnancy, the amniotic fluid is rich in tastes and smells that vary with the mother’s diet. These early experiences influence newborns’ preferences.
In a study carried out in the Alsatian region of France, where anise is frequently used to flavor foods, researchers tested newborns for their reaction to the anise odor (Schaal, Marlier,& Soussignan,2000).
Group 1: Infants whose mothers had regularly consumed anise-flavored foods and drinks during the last 2 weeks of pregnancy
Group 2: infants whose mothers had never consumed anise. On the day of birth, the two groups of infants responded similarly to a control odor (paraffin oil). When presented with the anise odor, babies of the anise-consuming mothers spent more time mouthing and turning toward the odor. In contrast, infants of non-anise-consuming mothers were far more likely to turn away and display negative facial expressions.
In many mammals, the sense of smell plays an important role in protecting the young from predators by helping mothers and babies identify each other. Although smell is less well developed in humans, traces of its survival value remain. Newborn infants’ have a dual attraction to the odors of their mother and of the lactating breast. This helps them locate an appropriate food source and, in the process, begin to distinguish their caregiver from other people.
To take in and make sense of their surroundings, infants must be able to balance the body, adjusting their movements so they remain in a steady position relative to the surface on which they are sitting or standing.
Three sources of sensory information signal a need to adapt body position: (1) proprioceptive stimulation, arising from sensations in the skin, joints, and muscles; (2) vestibular stimulation, arising from the semicircular canals of the inner ear; and (3) optical-flow stimulation, arising from movements in the visual field. Research focuses largely on optical flow—visually detected movements in the surrounding environment because it can be manipulated easily. People sense that they are in motion when the entire visual field moves, and they then make postural adjustments in accord with its direction and speed. Even newborns adapt their head movements to optical flow (Jouen & Lepecq, 1989). As motor control improves, postural adjustments become more precise.
By the end of the first year, infants anticipate loss of balance. Researchers had 10- to 17-month-olds open a cabinet drawer to retrieve toys and then doubled the drawer’s resistance against their pull (Witherington et al., 2002). Between 13 and 16 months, when walking improves, babies increasingly tensed their arm and abdominal muscles prior to opening the drawer, thereby preventing a fall when they let go. Experience with walking may motivate toddlers to make these adjustments. As they repeatedly tumble over, perhaps they realize the need for preventive action.
Newborn infants can hear a wide variety of sounds, although their sensitivity improves greatly over the first few months. At birth, infants prefer complex sounds, such as noises and voices, to pure tones. Babies only a few days old can tell the difference between a few sound patterns—a series of tones arranged in ascending versus descending order; utterances with two versus three syllables; the stress patterns of words; and happy-sounding speech as opposed to speech with negative or neutral emotional qualities.
At the end of the first year, infants recognize the same melody when it is played in different keys. And when the tone sequence is changed only slightly, they can tell that the melody is no longer the same. Responsiveness to sound provides support for the young baby’s exploration of the environment. Infants as young as 3 days old turn their eyes and head in the general direction of a sound. The ability to identify the precise location of a sound improves greatly over the first 6 months and shows further gains into the second year.
Young infants listen longer to human speech than structurally similar nonspeech sounds. Newborns make fine-grained distinctions between many speech sounds—“ba” and “ga,”“ma” and “na,” and the short vowel sounds “a” and “i,” to name just a few.
Adults use a slow, clear, high-pitched, expressive voice with a rising tone at the end of speech segments, and pause before continuing, probably because they notice that infants are more attentive when they do so.
In addition, newborns will suck more on a nipple to hear a recording of their mother’s voice than that of an unfamiliar woman, and to hear their native language as opposed to a foreign language. Over the first year, infants learn much about the organization of sounds in their native language. As they listen to the talk of people around them, they learn to focus on meaningful sound variations.
ERP brain-wave recordings reveal that at around 5 months, they become sensitive to syllable stress patterns in their own language. Between 6 and 8 months, they start to “screen out” sounds not used in their native tongue. Soon after, they focus on larger speech units: They recognize familiar words in spoken passages, listen longer to speech with clear clause and phrase boundaries, and begin to divide the speech stream into wordlike units.
For active exploration of the environment, humans depend on vision more than any other sense. Yet vision is the least mature of the newborn baby’s senses. Visual structures in the eye and the brain continue to develop after birth. Because visual structures are immature, newborn babies cannot focus their eyes well, and their visual acuity, or fineness of discrimination, is limited. Their eye movements are slow and inaccurate.
The visual system develops rapidly over the first few months. Around 2months, infants can focus on objects about as well as adults can. Scanning and tracking improve over the first half-year as infants see more clearly and eye movements come under voluntary control (von Hofsten & Rosander,1998).
Consequently, scanning enhances perception, and perception enhances scanning, in bidirectional fashion. As infants explore the visual field more adeptly, they figure out the characteristics of objects and how they are arranged in space. We can best understand how they do so by examining the development of three aspects of vision: depth, pattern, and object perception.
Depth perception is the ability to judge the distance of objects from one another and from ourselves. It is important for understanding the layout of the environment and for guiding motor activity.
Kinetic depth cues, created by movements of the body or of objects in the environment, are the first to which infants are sensitive. Babies 3 to 4 weeks old blink their eyes defensively when an object moves toward their face as if it is going to hit (Nánez & Yonas, 1994). As they are carried about and as people and things turn and move before their eyes, infants learn more about depth.
Binocular depth cues arise because our two eyes have slightly different views of the visual field. In a process called stereopsis, the brain blends these two images, resulting in perception of depth. Results reveal that binocular sensitivity emerges between 2 and 3 months and improves rapidly over the first year (Birch, 1993; Brown& Miracle, 2003).
Last to develop are pictorial depth cues—the ones artists use to make a painting look three-dimensional. Examples include receding lines that create the illusion of perspective, changes in texture (nearby textures are more detailed than faraway ones), and overlapping objects (an object partially hidden by another object is perceived to be more distant).
Why does perception of depth cues emerge in the order just described? Researchers speculate that motor development is involved. For example, control of the head during the early weeks of life may help babies notice motion and binocular cues. And around 5 to 6 months, the ability to turn, poke, and feel the surface of objects may promote perception of pictorial cues as infants pick up information about size, texture, and shape (Bushnell & Boudreau, 1993).
Crawling and Depth Perception: Research suggests that from extensive everyday experience, babies gradually figure out how to use depth cues to detect the danger of falling. As infants discover how to avoid falling in diverse postures and situations, their understanding of depth expands. Crawling experience promotes other aspects of three-dimensional understanding.
For example, seasoned crawlers are better than their inexperienced agemates at remembering object locations and finding hidden objects (Bai & Bertenthal, 1992; Camposet al., 2000). Why does crawling make such a difference? Compare your experience of the environment when you are driven from one place to another as opposed to walking or driving yourself. When you move on your own, you are much more aware of landmarks and routes of travel, and you take more careful note of what things look like from different points of view. The same is true for infants. In fact, crawling promotes a new level of brain organization, as indicated by more organized EEG brain-wave activity in the cerebral cortex. Perhaps crawling strengthens certain neural connections, especially those involved in vision and understanding of space (Bell & Fox, 1996).
Newborns prefer to look at patterned as opposed to plain stimuli—for example, a drawing of the human face or one with scrambled facial features rather than a black-and-white oval. As infants get older, they prefer more complex patterns. For example, 3-week-olds look longest at black-and-white checkerboards with a few large squares, whereas 8- and 14-week-olds prefer those with many squares.
A general principle, called contrast sensitivity, explains early pattern preferences. Contrast refers to the difference in the amount of light between adjacent regions in a pattern. If babies are sensitive to the contrast in two or more patterns, they prefer the one with more contrast.
COMBINING PATTERN ELEMENTS:
In the early weeks of life, infants respond to the separate parts of a pattern. They stare at single, high-contrast features and have difficulty shifting their gaze away toward other interesting stimuli. In exploring drawings of human faces, for example, 1-month-olds often limit themselves to the edges of the stimulus and focus on the hairline or chin. At 2 to 3 months, when contrast sensitivity improves and infants can better control their scanning, they thoroughly explore a pattern’s internal features, pausing briefly to look at each salient.
At the same time, babies’ scanning varies with pattern characteristics. When exposed to dynamic stimuli, such as the mother’s nodding, smiling face, 6-week-olds fixate more on internal features (the mouth and eyes) than on edges. Furthermore, when stimuli are dynamic, development of scanning takes place over a longer period; thorough inspection of the entire stimulus emerges only after 4 months of age. Exploring complex moving patterns seems to be more demanding than exploring stationary patterns—a difference we must keep in mind as we examine research on pattern perception, which is based largely on static stimuli.
Once babies take in all aspects of a pattern, they integrate them into a unified whole. Around 4 months, they are so good at detecting organization in static patterns that they even perceive subjective boundaries that are not really present.
Infant’s tendency to search for structure in a patterned stimulus applies to face perception.
Newborns prefer to look at simple face like stimuli with features arranged naturally(upright) rather than unnaturally(upside down or sideways).
Although newborns respond to a , general, face like structure, they cannot discriminate a complex, static image of the human face from other, equally complex configuration.
Nevertheless, from repeated exposure to their mother’s face ,they quickly learn to prefer her face to that of an unfamiliar woman.
Babies quickly apply their tendency to search for patterns to face perception. Around 2 months, when they can scan an entire stimulus and combine it’s elements into an organized whole, they can recognize and prefer their mother’s facial features.
Around 3 months infants make fine distinctions between the features of different faces. For example, they can tell difference between the photos of two strangers, even when faces are moderately similar.
At 5 months and strengthening over the second half of the first year- infants perceive emotional expressions as meaningful wholes. They treat positive faces as different from negative ones, even when, even when expressions are demonstrated in varying ways by different models. Extensive face to face interaction between infants and the caregivers undoubtedly contributes to the refinement of face perception.
Perception of an object’s size as stable, despite changes in the size of its retinal image— evident in the first week of life.
Perception of an object’s shape as stable, despite changes in the shape projected on the retina – also evident in the first week of life.
PERCEPTION OF OBJECT IDENTITY:
As adults, we distinguish an object from its surroundings by looking for a regular shape and uniform texture and color. When two objects are touching and either move in unison or stand still, babies younger than 4 months cannot distinguish between then.
As infants become familiar with many objects and can integrate each object’s diverse features into a unified whole, they rely more on shape, color, and texture and less on motion (Cohen & Cashon, 2001). Babies as young as 4 and 1⁄2 months can discriminate two touching objects on the basis of their features in simple, easy-to-process situations. And prior exposure to one of the test objects enhances 4 and 1⁄2-month-olds’ ability to discern the boundary between two touching objects—a finding that highlights the role of Experience.
In everyday life, objects frequently move in and out of sight. In addition to discerning objects by their features, infants must keep track of their disappearance and reappearance to perceive their identity.
INTERMODAL - involving two or more different modes of transport in conveying goods.
INTERMODAL PERCEPTION - Intermodal perception refers to perception of information from objects or events available to multiple senses simultaneously. Because most objects and events can be seen, heard, and touched, everyday perception is primarily intermodal. In intermodal perception, we make sense of these running streams of light, sound, tactile, odor, and taste information by perceiving unitary objects and events.
Research reveals that babies perceive input from different sensory systems in a unified way by detecting amodal sensory properties, information that is not specific to a single modality but that overlaps two or more sensory systems, such as rate rhythm, duration, intensity, and (for vision and hearing) temporal synchrony.
Human newborns are highly sensitive to amodal properties in audiovisual stimulation. Within the first half-year, infants master a remarkable range of intermodal relationships. For example, they match the motions of a wide array of objects with their appropriate sounds.
With experience, perceptual capacities become more flexible. In the second half of the first year, infants can discriminate amodal properties in both intermodal and unimodal (sights or sounds alone) stimulation. But early on, when much input is unfamiliar and confusing, intermodal stimulation helps babies selectively attend to and make sense of their surroundings.
In addition to easing infants’ perception of the physical world, intermodal stimulation facilitates social and language processing, as infant’s gaze at an adult’s face, they initially require both vocal and visual input to distinguish positive from negative emotional expressions. Furthermore, in their earliest efforts to make sense of language, infants profit from temporal synchrony between a speech sound and the motion of an object.
In sum, intermodal perception is a fundamental ability that fosters all aspects of psychological development. In animals, the intermodal stimulation arising out of early social interaction—for example, the mother’s simultaneous touch, smell, vocalizations, and gestures—is vital for normal development of both intermodal and unimodal perceptual responsiveness (Lickliter & Bahrick, 2000).
UNDERSTANDING PERCEPTUAL DEVELOPMENT.
Perceptual development progresses from infancy throughout early childhood. In order to put all these perceptual capacities together Eleanor and James Gibson have given Differentiation Theory.
According to the Gibsons, infants actively search for Invariant features of the environment Invariant features refer to those features that remain stable in a constantly changing environment.
The word differentiation is used in the theory because the baby detects finer and finer invariant features among stimuli. Differentiation applies to depth and object perception also. According to the differentiation theory perception is guided by AFFORDANCES I.e. action possibilities a situation offers an organism with certain motor capabilities. AFFORDANCES make our actions future oriented and largely successful rather than reactive and blundering. For example- When babies crawl, and again when they walk, they gradually realize that a steeply sloping surface affords the possibility of falling. With added weeks of practicing each skill, they hesitate to crawl or walk down a risky incline.
Some researchers however believe that babies do more than make sense of experience by searching for invariant features and discovering affordances. They also impose meaning on what they perceive, constructing categories of objects and events in the surrounding environment. For example, older babies interpret a familiar face as asource of pleasure and affection and a pattern of blinking lights as a moving human being. Therefore one way of understanding Perceptual Development is to think of it as a built-in tendency to search for order and stability in the surrounding world a capacity that becomes fine-tuned with age.