LO5What are reflexes and how do they contribute to motor development?
When her father pressed 3-day-old Christina’s palm with his finger, she responded by tightly winding her small fist around his finger and grasping it. When he moved his finger upward, she held on so tightly that he suspected he could have been able to lift her completely off the crib floor.
The Basic Reflexes. Her father was right: Christina probably could have been lifted in this way. The reason for her resolute grip was activation of one of the dozens of reflexes with which infants are born. Reflexes are unlearned, organized, involuntary responses that occur automatically in the presence of certain stimuli. Newborns enter the world with a repertoire of reflexive behavioral patterns that help them adapt to their new surroundings and serve to protect them.
As we can see from the list of reflexes in Table 5-2, many reflexes clearly represent behavior that has survival value, helping to ensure the well-being of the infant. For instance, the swimming reflex makes a baby who is lying face down in a body of water paddle and kick in a sort of swimming motion. The obvious consequence of such behavior is to help the baby move from danger and survive until a caregiver can come to its rescue. Similarly, the eye blink reflex seems designed to protect the eye from too much direct light, which might damage the retina.
Some Basic Reflexes in Infants
Reflex | Approximate Age of Disappearance | Description | Possible Function |
---|---|---|---|
Rooting reflex | 3 weeks | Neonate’s tendency to turn its head toward things that touch its cheek. | Food intake |
Stepping reflex | 2 months | Movement of legs when held upright with feet touching the floor. | Prepares infants for independent locomotion |
Swimming reflex | 4–6 months | Infant’s tendency to paddle and kick in a sort of swimming motion when lying face down in a body of water. | Avoidance of danger |
Moro reflex | 6 months | Activated when support for the neck and head is suddenly removed.
The arms of the infant are thrustoutward and then appear to grasp onto something. |
Similar to primates’ protection from falling |
Babinski reflex | 8–12 months | An infant fans out its toes in response to a stroke on the outside of its foot. | Unknown |
Startle reflex | Remains in different form | An infant, in response to a sudden noise, flings out its arms, arches its back, and spreads its fingers. | Protection |
Eye-blink reflex | Remains | Rapid shutting and opening of eye on exposure to direct light. | Protection of eye from direct light |
Sucking reflex | Remains | Infant’s tendency to suck at things that touch its lips. | Food intake |
Gag reflex | Remains | An infant’s reflex to clear its throat. | Prevents choking |
Given the protective value of many reflexes, it might seem beneficial for them to remain with us for our entire lives. In fact, some do: the eye blink reflex remains functional throughout the full life span. But quite a few reflexes, such as the swimming reflex, disappear after a few months. Why should this be the case?
Researchers who focus on evolutionary explanations of development attribute the gradual disappearance of reflexes to the increase in voluntary control over behavior that occurs as infants become more able to control their muscles. In addition, it may be that reflexes form the foundation for future, more complex behaviors. As these more intricate behaviors become well learned, they encompass the earlier reflexes (Myklebust & Gottlieb, 1993; Lipsitt, 2003).
It may be that reflexes stimulate parts of the brain responsible for more complex behaviors, helping them develop. For example, some researchers argue that exercise of the stepping reflex helps the brain’s cortex develop the ability to walk. As evidence, developmental psychologist Philip R. Zelazo and his colleagues conducted a study in which they provided 2-week-old infants practice in walking for four sessions of three minutes each over a six-week period. The results showed that the children who had the walking practice actually began to walk unaided several months earlier than those who had had no such practice. Zelazo suggests that the training produced stimulation of the stepping reflex, which in turn led to stimulation of the brain’s cortex, readying the infant earlier for independent locomotion (Zelazo et al., 1993; Zelazo, 1998).
Do these findings suggest that parents should make out-of-the-ordinary efforts to stimulate their infant’s reflexes? Probably not. Although the evidence shows that intensive practice may produce an earlier appearance of certain motor activities, there is no evidence that the activities are performed qualitatively any better in practiced infants than in unpracticed infants. Furthermore, even when early gains are found, they do not seem to produce an adult who is more proficient in motor skills.
In fact, structured exercise may do more harm than good. According to the American Academy of Pediatrics, structured exercise for infants may lead to muscle strain, fractured bones, and dislocated limbs, consequences that far outweigh the unproven benefits that may come from the practice (National Association for Sport and Physical Education, 2006).
Ethnic and Cultural Differences and Similarities in Reflexes. Although reflexes are, by definition, genetically determined and universal throughout all infants, there are actually some cultural variations in the ways they are displayed. For instance, consider the Moro reflex, which is activated when support for the neck and head is suddenly removed. The Moro reflex consists of the infant’s arms thrusting outward and then appearing to seek to grasp onto something. Most scientists feel that the Moro reflex represents a leftover response that we humans have inherited from our nonhuman ancestors. The Moro reflex is an extremely useful behavior for monkey babies, who travel about by clinging to their mothers’ backs. If they lose their grip, they fall down unless they are able to grasp quickly onto their mother’s fur—using a Moro-like reflex (Zafeiriou, 2004).
The Moro reflex is found in all humans, but it appears with significantly different vigor in different children. Some differences reflect cultural and ethnic variations (Freedman, 1979). For instance, Caucasian infants show a pronounced response to situations that produce the Moro reflex. Not only do they fling out their arms, but also they cry and respond in a generally agitated manner. In contrast, Navajo babies react to the same situation much more calmly. Their arms do not flail out as much, and they cry only rarely.
In some cases, reflexes can serve as helpful diagnostic tools for pediatricians. Because reflexes emerge and disappear on a regular timetable, their absence—or presence—at a given point of infancy can provide a clue that something may be amiss in an infant’s development. (Even for adults, physicians include reflexes in their diagnostic bag of tricks, as anyone knows who has had his or her knee tapped with a rubber mallet to see if the lower leg jerks forward.)
Reflexes evolved because at one point in humankind’s history, they had survival value. For example, the sucking reflex automatically helps infants obtain nourishment, and the rooting reflex helps it search for the presence of a nipple. In addition, some reflexes also serve a social function, promoting caregiving and nurturance. For instance, Christina’s father, who found his daughter gripping his finger tightly when he pressed her palm, probably cares little that she is simply responding with an innate reflex. Instead, he will more likely view his daughter’s action as responsiveness to him, a signal perhaps of increasing interest and affection on her part. As we will see in Chapter 6, when we discuss the social and personality development of infants, such apparent responsiveness can help cement the growing social relationship between an infant and its caregivers.