development?
3 How might safety concerns be addressed? ●
Brain development is a multifaceted process that is not a result of maturational or environmental input alone. Brains do not develop normally in the absence of a basic genetic code or in the absence of essential environmental input. At all points in development, intrinsic and environmental factors interact to support the increasingly complex and elaborate structures and functions of the brain.
Thinking in Context 4.2
1 Consider the role of contextual factors in brain development. What role does experience play in brain development and how might the different contexts in which children live influence their development?
2 Marta hopes to promote her baby’s brain development. Explain the processes that influence infants’ brain development and provide advice to help Marta promote her infant’s development.
Early Learning Capacities
Can newborns learn? If we define learning as changing behavior in response to experience, certainly: Animals and even insects learn. Yet infants were once believed to be born incapable of sensing and understanding the physical world around them. Most new parents will quickly tell you that this is far from the truth. At birth, and even before, neonates can perceive their physical world and have powerful capacities for learning about it.
Habituation
Less than 1 day old, cradled next to his mother in the hospital maternity center, Tommy is already displaying the earliest form of learning. He no longer cries each time he hears the loud beep made by the machine that reads his mother’s blood pressure. This type of learning is called habituation; it occurs when repeated exposure to a stimulus results in the gradual decline in the intensity, frequency, or duration of a response (see Figure 4.10). All animals and humans are programmed to learn. Even before birth, humans demonstrate habituation, as early as 22 to 24 weeks’ gestation (Hepper, 2015). For example, 27- to 36-week-old fetuses demonstrate habituation to vibration as well as auditory stimuli, such as the sound of a tone. Initially, the fetus moves in response to the vibration, suggesting interest in a novel stimulus. After repeated stimulation, the fetus no longer responds to the stimulus, indicating that it has habituated to it (McCorry & Hepper, 2007; Muenssinger et al., 2013). Not only can the fetus habituate to stimuli but it can recall a stimulus for at least 24 hours (van Heteren, Boekkooi, Jongsma, & Nijhuis, 2000).
Habituation improves with development. For example, the performance of fetuses on habituation tasks improves with gestational age (James, 2010). After birth, habituation is often measured by changes in an infant’s heart rate and in attention or looking at a stimulus (Domsch, Thomas, & Lohaus, 2010). Younger infants require more time to habituate than older infants (Kavšek & Bornstein, 2010). Five- to 12-month-old babies habituate quickly—even after just a few seconds of sustained attention—and in some cases, they can recall the stimulus for weeks, such as recalling faces that they have encountered for brief periods of time (Richards, 1997).
Figure 4.10 Habituation
Looking time declines with each trial as the infant habituates to the pattern. Dishabituation, renewed interest, signifies that the infant detects a change in stimulus pattern.
Source: Visual development by Marcela Salamanca and Donald Kline, University of Calgary (http://psych.ucalgary.ca/PACE/VA-Lab/). Reprinted by permission of the authors.
Neural development, specifically development of the prefrontal cortex, is thought to underlie age-related gains in habituation skill (Nakano, Watanabe, Homae, & Taga, 2009). As the brain matures, infants process information more quickly and learn more about stimuli in fewer exposures. Younger infants and those with low birthweight require more time to habituate than do older and more fully developed infants (Kavšek & Bornstein, 2010; Krafchuk, Tronick, & Clifton, 1983; Rovee-Collier, 1987). Fetuses with more mature nervous systems require fewer trials to habituate than do those with less well-developed nervous systems, even at the same gestational age (Morokuma et al., 2004). Fetal habituation predicts measures of information processing ability at 6 months of age (Gaultney & Gingras, 2005).
There are also individual differences in habituation among healthy, developmentally normal infants. Some habituate quickly and recall what they have learned for a long time. Other infants require many more exposures to habituate and quickly forget what they have learned. The speed at which infants habituate is associated with cognitive development when they grow older. Infants who habituate quickly during the first 6 to 8 months of life tend to show more advanced capacities to learn and use language during the second year of life (Tamis-LeMonda & Bornstein, 1989). Rapid habituation is also associated with higher scores on intelligence tests in childhood (Kavšek, 2004). The problem-solving skills measured by intelligence tests tap information processing skills such as attention, processing speed, and memory—all of which influence the rate of habituation (McCall, 1994).
Innate learning capacities permit young infants to adapt quickly to the world, a skill essential for survival. Researchers use these capacities to study infant perception and cognition (Aslin, 2014). For example, to examine whether an infant can discriminate between two stimuli, a researcher presents one until the infant habituates to it. Then a second stimulus is presented. If dishabituation, or the recovery of attention, occurs, it indicates that the infant detects that the second stimulus is different from the first. If the infant does not react to the new stimulus by showing dishabituation, it is assumed that the infant does not perceive the difference between the two stimuli. The habituation method is very useful in studying infant perception and cognition and underlies many of the findings discussed later in this chapter.
Classical Conditioning
In addition to their capacity to learn by habituation, infants are born with a second powerful tool for learning. They can learn through association. Classical conditioning entails making an association between a neutral stimulus and an unconditioned stimulus that triggers an innate reaction. Eventually, the neutral stimulus (now conditioned stimulus) produces the same response as the unconditioned stimulus.
Newborns demonstrate classical conditioning. For example, when stroking the forehead was paired with tasting sugar water, 2-hour-old infants were conditioned to suck in response to having their heads stroked (Blass, Ganchrow, & Steiner, 1984). Let’s look at this example more closely. Sugar water is an unconditioned stimulus, as it naturally evokes the unconditioned response of sucking in infants. Touching or stroking the forehead yielded no response from the 2-hour-old infants; it was a neutral stimulus. When the researcher paired the neutral stimulus (stroke) with the unconditioned stimulus (sugar water), infants soon showed the conditioned response. That is, they associated the stroking with sugar water and thereby responded to the stroke with sucking movements.
Similarly, Lipsitt and Kaye (1964) paired a tone with the presentation of a nipple to 2- and 3-day-old infants. Soon, the infants began to make sucking movements at the sound of the tone. Sleeping neonates can be conditioned to respond to a puff of air to the eye (Tarullo et al., 2016). Even premature infants can demonstrate associative learning, although at slower rates than full-term infants (Herbert, Eckerman, Goldstein, & Stanton, 2004). Research with chimpanzee fetuses has shown that they display classical conditioning before birth (Kawai, 2010). It is likely that the human fetus can as well. Although classical conditioning is innate, neurological damage can hinder infants’ abilities to learn by association. Infants with fetal alcohol syndrome (FAS) require much more time than other infants to associate eye blinking with external stimuli, such as sounds (Cheng et al., 2016).
Newborns tend to require repeated exposures to conditioning stimuli because they process information slowly (Little, Lipsitt, & Rovee-Collier,