Sensory and Motor Development

Sensory and Motor Development

Most healthy infants are born with the ability to detect visual, auditory, tactile, gustatory (taste), and olfactory (smell) sensations. As they grow and develop, they become more adept at decoding these stimuli, a skill that helps them make sense of the world around them. Many physical, motor, and sensory-perceptual abilities depend upon each other. For instance, the development of vision depends upon physical developments (such as binocular vision (both eyes working together), maturation of rods and cones, and neural connections) as well as perceptual developments (such as interpreting and making sense of colors). Another example is the development of depth perception. Experience in their everyday world contributes to an infant’s understanding of near vs. far. As motor development progresses, infants need time and experience in their new mode of locomotion in order to understand how reapply their understanding of distances and drops (such as off the ledge of the couch or down the stairs). This section will further explore these individual developments as well as how they contribute to each other.

Sensory Development

Newborn infants’ sensory abilities are significant, but their senses are not yet fully developed. Many of a newborn’s innate preferences facilitate interaction with caregivers and other humans. As infants and children grow, their senses play a vital role in encouraging and stimulating the mind and in helping them observe their surroundings. Two terms are important to understand when learning about the senses. The first is sensation, or the interaction of information with the sensory receptors. The second is perception, or the process of interpreting what is sensed. It is possible for someone to sense something without perceiving it. For example, if you turn a fan on, you may notice (percieve) the sound of the fan. But after a while, the sound of the fan will no longer attract your attention. You no longer constantly perceive the sound, even though your ears continue to sense it. Gradually, infants become more adept at perceiving with their senses, making them more aware of their environment and presenting more affordances or opportunities to interact with objects.

Vision

The womb is a dark environment, and consequently, vision is the most poorly developed sense at birth. Prenatally, the fetus has the ability to percieve and process light (e.g., Donovan et al. 2020). Newborns typically cannot see further than 8 to 16 inches away from their faces, have difficulty keeping a moving object within their gaze, and can detect contrast more than color differences. If you have ever seen a newborn struggle to see, you can appreciate the cognitive efforts being made to take in visual stimulation and build those neural pathways between the eye and the brain.

Although vision is their least developed sense, newborns (and perhaps fetuses (Reid et al., 2017)) already show a preference for faces (e.g., Farroni et al., 2005). When you glance at a person, where do you look? Chances are you look into their eyes. If so, why? It is probably because there is more information there than in other parts of the face. Newborns do not scan objects this way; rather, they tend to look at the chin or another less detailed part of the face. However, by 2 or 3 months, they will seek more detail when visually exploring an object and begin showing preferences for unusual images over familiar ones, for patterns over solids, faces over patterns, and three-dimensional objects over flat images. Newborns have difficulty distinguishing between colors, but within a few months are able to discriminate between colors as well as adults. Infants can also sense depth as binocular vision develops at about 2 months of age. By 6 months, the infant can perceive depth perception in pictures as well (Sen et al., 2001).

Hearing

The infant’s sense of hearing is very keen at birth. If you remember from an earlier module, this ability to hear is evidenced as soon as the 5th month of prenatal development. In fact, an infant can distinguish between very similar sounds as early as one month after birth and can distinguish between a familiar and non-familiar voice even earlier. Babies who are just a few days old prefer human voices, they will listen to voices longer than sounds that do not involve speech (Vouloumanos & Werker, 2004), and they seem to prefer their mother’s voice over a stranger’s voice (Mills & Melhuish, 1974). In an interesting experiment, 3-week-old babies were given pacifiers that played a recording of the infant’s mother’s voice if the infant sucked strongly and of a stranger’s voice when the infant sucked more weakly. When the infants heard their mother’s voice, they sucked more strongly on the pacifier (Mills & Melhuish, 1974).

Touch

The sense of touch is acute in infants and is essential to a baby’s growth of physical abilities, language and cognitive skills, and socio-emotional competency. Touch starts developing around week eight of pregnancy, beginning with touch receptors, the neurons that respond to touch. By approximately week thirty, the fetus can feel pain, pressure, and differences in temperature (hot versus cold). This means newborns are sensitive to pain during procedures like blood tests and surgeries (Garcia-Rodriguez et al., 2021).

Touch not only impacts short-term development during infancy and early childhood but also has long-term effects, suggesting the power of positive gentle touch from birth. Through touch, infants learn about their world, bond with their caregiver, and communicate their needs and wants. Research emphasizes the great benefits of touch for premature babies, including increased growth and immunological function, and more quality sleep (Du et al., 2024). When we discuss emotional and social development later, you will also see the important role that touch plays in helping infants feel safe and protected, which builds trust and secure attachments between the child and their caregiver.

Taste and Smell

Taste and smell help us identify flavors and thus directly influence the foods we choose and thereby our nutrition. Taste is the sensation of flavor—sweet, salty, bitter, sour, or savory—that we receive from receptors in the mouth and on the tongue. Smell is our perception of odors via the nose; it’s a function of the olfactory system (nose and mouth). Both taste and smell begin developing prenatally.

Infants prefer the familiar scents of their biological mothers. For example, six-day-old infants turn more often toward a breast milk pad scented with their biological mother’s milk than one scented by a donor (Loos et al., 2019; Porter et al., 1992). As early as one day after birth, infants are also soothed by the smell of their mother (André et al., 2020; Rattaz et al., 2005; Sullivan et al., 2011).

As a first taste experience, the fetus starts swallowing amniotic fluid by around week twelve and can perceive distinct flavors based on the biological mother’s diet. A newborn will show signs of recognizing those flavors (Mennella, 2014), and many will exhibit a preference for flavors and scents to which they were exposed via amniotic fluid (Lipchock et al., 2011). For example, the newborns of biological mothers who consumed more garlicky food in pregnancy were more accepting of garlic odors, as indicated by mouthing and head orientation (Forestell, 2020, 2024; Hepper, 1988). This finding held true for anise, carrot, mint, vanilla, blue cheese, fruits, and vegetables (Bakalar, 2012; Gabriel & Mennella, 2023).

Newborns enter the world able to distinguish between sweet, sour, bitter, and salty flavors, and within hours of being born, they show different facial expressions for different flavors. For bitter, they might wrinkle their nose or frown; for sweet or savory, they make rhythmic tongue protrusions, elevate the corners of the mouth, or smack their lips (Lipchock et al., 2011). Infants continue to acquire taste preferences through flavors in human milk or formula. The flavor of human milk changes based on the mother’ diet. Infants and young children who are fed human milk as infants are more accepting of new foods that were a part of their mother’s diet (Dunn & Lessen, 2017). Formula-fed infants have also been shown to prefer the flavor of the formula they consume, but because there is no variation in the flavor, they are often less accepting of new foods at first than infants fed human milk (Forestell, 2017).

Multimodal Perception

If you eat an ice cream sundae, you simultaneously see the dripping hot fudge, feel the cold sensation of the first spoonful, and taste the sweetness of the chocolate flavor. An awareness of the world gained through multiple senses at the same time is known as multimodal perception (sometimes also called cross-modal perception or intermodal perception).

The integration of auditory and visual sensory information is one of the first intermodal pairings we make. For example, one study showed that four-month-olds can connect the sound of a ball to the height of its bounce (Lewkowitz, 1999). Infants as young as two months can connect phonetic information from the lips and from the voice. In other words, they can tell whether spoken words match the movement of the lips (Choi et al., 2021; Edgar et al., 2022). Motor skills can help facilitate infants’ ability to integrate intermodal perception. For example, the ability to turn the head and reach for a toy allows the infant to see, touch, and process information about the toy at the same time. Similarly, parental lip smacking during mealtime also serves as an important signal for the infant about the process of eating and can encourage infants to start feeding (Wiggins & Keevallik, 2021). Thus, intermodal connections allow infants to link perceptual experiences and information in their environment, an important task in cognitive development (Streri & de Havia, 2023).

We have seen that newborns can use all their senses to gain information about their world. These sensory and perceptual abilities are still immature but quickly develop over the first year of life to adult levels (Johnson & Hannon, 2015). Understanding the sensory abilities of infants along with their perceptual preferences allows us to interact with them in more effective ways and to use the appropriate stimuli to support their development.

Motor Development

From Reflexes to Voluntary Movements

Every basic motor skill (any movement ability) develops over the first two years of life. The sequence of motor skills first begins with reflexes. Infants are equipped with a number of reflexes, or involuntary movements in response to stimulation, and some are necessary for survival. These include the breathing reflex, or the need to maintain an oxygen supply (this includes hiccups, sneezing, and thrashing reflexes), reflexes that maintain body temperature (crying, shivering, tucking the legs close, and pushing away blankets), the sucking reflex, or automatically sucking on objects that touch their lips, and the rooting reflex, which involves turning toward any object that touches the cheek (which manages feeding, including the search for a nipple). Other reflexes are not necessary for survival, but signify the state of brain and body functions. Some of these include: the babinski reflex (toes fan upward when feet are stroked), the stepping reflex (babies move their legs as if to walk when feet touch a flat surface), the palmar grasp (the infant will tightly grasp any object placed in its palm), and the moro reflex (babies will fling arms out and then bring to chest if they hear a loud noise). These movements occur automatically and are signals that the infant is functioning well neurologically. Within the first several weeks of life, these reflexes are replaced with voluntary movements or motor skills.

Video 6.10 Neonatal Reflexes reviews many of the primitive and survival reflexes present at birth.

Major Motor Milestones

Motor development occurs in an orderly sequence as infants move from reflexive reactions (e.g., sucking and rooting) to more advanced motor functioning. Children experience two growth patterns during infancy. The cephalocaudal pattern of growth is growth from the head down. Children often appear “top-heavy” with their heads proportionally larger than their bodies. The proximodistal pattern of growth starts at the center of the body and moves toward the extremities.  Infants have control of the trunk of their body, then their arms, then their hands and fingers. 

As motor skills develop, there are certain developmental milestones that caregivers and pediatricians typically watch for. For each milestone, there is an average age, as well as a range of ages in which the milestone is typically reached. An example of a developmental milestone is a baby holding up their head. Babies, on average, are able to hold up their heads at 6 weeks old, and 90% of babies achieve this between 3 weeks and 4 months old. If a baby is not holding up his head by 4 months old, he is showing a delay. On average, most babies sit alone at 7 months old. Sitting involves both coordination and muscle strength, and 90% of babies achieve this milestone between 5 and 9 months old. If the child is displaying delays on several milestones, this may indicate to a parent or caregiver that they should discuss this with the child’s pediatrician. Some developmental delays can be identified and addressed through early intervention.

Video 6.11. Major Motor Milestones identifies some of the major motor developments in the first few years of life.

Gross Motor Skills

Gross motor skills are 

voluntary movements that involve the use of large muscle groups and are typically large movements of the arms, legs, head, and torso. These skills begin to develop first. Examples include moving to bring the chin up when lying on the stomach, moving the chest up, rocking back and forth on hands and knees. But it also includes exploring an object with one’s feet as many babies do, as early as 8 weeks of age, if seated in a carrier or other device that frees the hips. This may be easier than reaching for an object with the hands, which requires much more practice. And sometimes an infant will try to move toward an object while crawling and surprisingly move backward because of the greater amount of strength in the arms than in the legs!

Fine Motor Skills

Fine motor skills are more exact movements of the hands and fingers and include the ability to reach and grasp an object. These skills focus on the muscles in the fingers, toes, and eyes, and enable coordination of small actions (e.g., grasping a toy, writing with a pencil, and using a spoon). Newborns cannot grasp objects voluntarily but do wave their arms toward objects of interest. At about 4 months of age, the infant is able to reach for an object, first with both arms and within a few weeks, with only one arm. At this age, grasping an object involves the use of the fingers and palm, but no thumbs. Stop reading for a moment and try to grasp an object using the fingers and the palm. How does that feel? How much control do you have over the object? If it is a pen or pencil, are you able to write with it? Can you draw a picture? The answer is, probably not. Use of the thumb comes at about 9 months of age when the infant is able to grasp an object using the forefinger and thumb (the pincer grasp). This greatly enhances the ability to control and manipulate an object, and infants take great delight in this newfound ability. They may spend hours picking up small objects from the floor and placing them in containers. By 9 months, an infant can also watch a moving object, reach for it as it approaches, and grab it. This is quite a complicated set of actions if we remember how difficult this would have been just a few months earlier.

Table 6.2

Timeline of Developmental Milestones.

Motor Skill Development

Remember that gross motor skills are voluntary movements involving the use of large muscle groups while fine motor skills are more exact movements of the hands and fingers and include the ability to reach and grasp an object. Early childhood is a time of development of both gross and fine motor skills.

Early childhood is a time when children are especially attracted to motion and song. Days are filled with moving, jumping, running, swinging and clapping, and every place becomes a playground. Even the booth at a restaurant affords the opportunity to slide around in the seat or disappear underneath and imagine being a sea creature in a cave! Of course, this can be frustrating to a caregiver, but it’s the business of early childhood. Children may frequently ask their caregivers to “look at me” while they hop or roll down a hill. Children’s songs are often accompanied by arm and leg movements or cues to turn around or move from left to right. Running, jumping, dancing movements, etc. all afford children the ability to improve their gross motor skills.

Fine motor skills are also being refined in activities such as pouring water into a container, drawing, coloring, and using scissors. Some children’s songs promote fine motor skills as well (have you ever heard of the song “itsy, bitsy, spider”?). Mastering the fine art of cutting one’s own fingernails or tying their shoes will take a lot of practice and maturation. Fine motor skills continue to develop in middle childhood, but for preschoolers, the type of play that deliberately involves these skills is emphasized.