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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).

Description

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.