PREPARED LEARNING

physical world. We follow this with sections on young children’s quantitative- mathematical and spatial abilities. We then devote substantial space to various evolutionary-friendly views of language acquisition and conclude the chapter

by

examining the role of immaturity in cognitive development.

The classic demonstration of prepared learning is conditioned taste aversion, termed the Garcia effect after its discoverer psychologist John Garcia (Garcia, Ervin, & Keolling, 1966; Garcia & Keolling, 1966). In a series of experiments, Garcia and his colleagues gave rats novel foods and, several hours later, exposed them to radiation, which made them sick.

Despite the fact that the nausea occurred several hours after they ate the food, the rats later avoided the food they had eaten shortly before getting sick. It was not as easy to condition the rats to avoid nonfood stimuli (flashing lights and sounds) that the researchers paired with the nausea; it was the association of sickness and food (especially novel food, as later research showed) that was conditioned, despite the long delay between consumption and illness. Garcia argued that, counter to the conventional wisdom of the day, animals are prepared to make associations between nausea and food and that the rules of learning are not independent of the stimuli used.

148 THE ORlClNS OF HUMAN NATURE

For humans, the argument for prepared learning of fears extends back more than

30

years (Marks, 1969; Seligman,

1971).

According to Seligman

(1971),

fear responses are more easily made and are more difficult to extin- guish for biologically relevant stimuli-stimuli that may have represented danger to our ancestors-than for biologically irrelevant stimuli. Learning is still necessary (e.g., there is not an innate fear of snakes or spiders), but emotional responses are more easily conditioned to objects and situations that would have represented threats to our ancestors than to other stimuli. In support of this, clinical phobias are more likely to be found for evolutionarily- significant stimuli, such as spiders, snakes, heights, and closed spaces, than for other contemporary objects and events that reflect greater danger for modern humans, such as automobiles, knives, or guns (Nesse,

1990).

More- over, in laboratory work, adults conditioned with fear-relevant stimuli display greater resistance to extinction than adults conditioned with fear-irrelevant stimuli (Cook, Hodes, & Lang, 1986; Ohman,

1986;

but see McNally,

1987,

for exceptions).

Research with monkeys suggests that such “prepared fears” are not limited to humans. Psychologists Michael Cook, Susan Mineka, and their colleagues performed a series of studies examining rhesus monkeys’ acquisition of fears to biologically relevant stimuli versus biologically irrelevant ones

(M.

Cook & Mineka,

1989, 1990; M.

Cook, Mineka, Wolkenstein,

6r

Laitsch,

1985;

Mineka,

1992;

Mineka, Davidson, Cook, & Keir,

1984).

In their studies, laboratory-raised monkeys showed no initial fear of snakes (realistic toy snakes were always used as stimuli). Wild-raised monkeys, however, do display fear of real snakes. Cook and Mineka showed laboratory monkeys videos of other monkeys displaying fear reactions to snakes versus fear reactions to “neutral” stimuli such as flowers and rabbits.

(A

“fear of flowers” video clip was created

by

combining shots of a monkey’s fear response-actually to a snake-with shots of a flower.) The observer monkeys later showed fear of snakes but not of the neutral stimuli. These and related data suggest that the animals were prepared to make fear associations with snakes, which would have been adaptive when living in an environment in which snakes were a major danger. Note that the fear response was not just to “animate objects.” Fear reactions were not acquired from watching videos of monkeys reacting fearfully to rabbits.

Although fear responses are proposed to be acquired in infancy and childhood, there has been no published research on humans, to our knowledge, that has looked at the acquisition of children’s fear responses as a function of the evolutionary significance of the stimuli.’ Rather, develop-

’

We are aware of one unpublished conference presentation in which infants displayed fear responses to toy snakes and artificial stimuli that had lifelike qualities when their mothers also responded fearfully (Walden & Passaretti, 1998). The authors interpreted their findings as consistent with

mental psychologists have looked at perceptual and cognitive biases of infants and young children, examining the extent to which (and how) children are prepared to acquire certain classes of ecologically important information (see Gelman & Williams,

1998;

Gopnik & Meltzoff,

1997;

Mandler,

1998;

Spelke & Newport,

1998),

and it is to some of this research that we now turn.

What Infants Know Without Being

Told

(Much)

Cognitive anthropologist Pascul Boyer (

1998)

proposed that the human mind is equipped with an intuitive ontology, which is a set of expectations about the kinds of things that are to be found in the world (see also Geary,

1998, 2001).

Boyer proposed that there are five intuitive ontological categories: person, animal, plant, artifact (manufactured objects), and natural object (non-manufactured and nonliving objects, such as mountains and rivers). In addition to these ontological categories, Boyer proposed that humans come into the world with (or develop very early) three classes of intuitive expectations: those related to physical objects, to biological entities, and theory of mind.

We examine two of these classes of intuitive expectations in this book, infants’ expectations related to physical objects in this section and theory of mind in the next chapter. Space limitations prevent us from discussing infants’ and children’s understanding of biological entities (see Wellman &

Gelman,

1998).

First, we look at the perceptual biases of infants and how they might have played a function in the environment of evolutionary adapt- edness.

Perceptual Preferences in Infancy

Not long ago well-informed people believed that infants enter the world unable to perceive sights and sounds. When

I (DB)

was teaching my first child development class as a graduate student in the early

1970s, 1

mentioned that newborn infants can “see,” meaning that they can tell the difference between two visual displays. A middle-age woman informed me that

I

was wrong; infants cannot see. She had had four children, and her obstetrician and pediatrician had both told her that her babies were functionally blind at birth and that they “learned” to see over their first month of life. We know now that infants can see (and hear, smell, taste, and “feel”) at birth, that there are some stimuli that they prefer to attend to, and that perceptual learning associated with ecologically relevant stimuli

biological preparedness, but the absence of a truly neutral stimulus requires that these findings he interpreted cautiously.

150 THE ORIGINS OF H U M A N N A T U R E

occurs early in life. Although working sensory systems are adaptive for all organisms, an evolutionary developmental psychological approach holds that certain aspects of children’s developing sensory systems should be both well suited to their current environment and helpful to them in gaining information that

will

be useful to them in the near future. We briefly examine evidence from several developing sensory systems consistent with this argument.

Audition

At birth, infants can discriminate sound, and they display certain preferences. For example, they tend to prefer the voices of women, particularly their mother’s voice, to those of men (DeCasper & Fifer,

1980;

Spence

& Freeman, 1996). They also prefer to listen to speech spoken in their

mother tongue than in a foreign language (Mehler et al., 1988). The apparent reason for these biases can be found in prenatal auditory experience. Hearing develops before birth, and the voice a fetus is most likely to hear is that of its mother. In a classic study

by

developmental psychologists Anthony DeCasper and Melanie Spence

(1986),

mothers read one of two stories to their unborn

child

during the last six weeks of pregnancy. At birth, infants were fitted with headphones and a pacifier and could control what they heard (the story their mother had read to them in utero or another story) by altering their sucking rate. Neonates varied their sucking rate to hear the stories their mothers had read to them, reflecting prenatal learning but also the establishment of a bias (to attend to what was heard before birth) that may promote attachment and thus survival. Other aspects of infants’

auditory abilities that, on the surface, appear to be specifically related to language acquisition are discussed later in the chapter.2

Olfaction

Newborns can discriminate among a wide variety of odors (Steiner, 1979), and they develop preferences for certain odors within the first week.

For example, in one experiment (Macfarlane,

1975),

babies were placed between two breast pads-one from the baby’s mother and one from another woman. Infants showed no preference in terms of head turning at

2

days of age, but

by

Day

6

they turned to their own mother’s pad more often than to the pad of another woman. Other research has shown that by

4

‘Infants have also been found to show a preference for well-formed, as opposed to poorly formed, music (Krumhansl & Jusczyk, 1990) and to be able to discriminate out-of-tune versus in-tune sequences of music from different musical traditions (Lynch, Eilers, Oller, & Urbano, 1990). It is interesting to speculate on the evolutionary and biological roots of music (Gardner, 1983) and to propose that human infants are predisposed to acquire musical systems, just as they are seemingly predisposed to acquire language. However, such speculation is beyond the scope of this book.

days of age, infants develop a preference for the odor of milk versus the odor of amniotic

fluid

(which they had been living in for

9

months; Marlier, Schaal, & Soussignan,

1998),

and that bottle-fed, 2-week-old infants prefer the breast odor of a lactating female to that of a nonlactating female (Makin

& Porter,

1989).

These findings suggest that infants are particularly sensitive

to the odor of breast milk and develop a preference for it (and particularly for the odor of their mother’s milk) within the first days of life.

Vision

More research has been performed on infant vision than on any other sense. Vision is relatively poor at birth but develops rapidly over the first

6

months (Kellman & Banks,

1998).

The lens is not very flexible, so that focusing is difficult. Stimuli that are most likely to be “in focus’’ for a newborn will be about

20 (8

in.) from its eyes (Haynes, White, & Held,

1965),

about the distance between the faces of an infant and its mother during nursing. Much (but not all) of an infant’s looking behavior during the first two months is controlled by subcortical areas of the brain, reflecting

“automatic” as opposed to “purposeful” processes

(M.

H. Johnson,

1998).

3

months of age, infants show greater control of their looking behavior, and they display decided preferences for what they like to look at. Among the preferences for physical stimulus features include movement (Haith,

1966),

vertical symmetry (i.e., stimuli that are similar on their right- and left-hand sides; Bornstein, Ferdinandsen, & Gross, 198l), and curvilinearity (Ruff & Birch,

1974).

These are all characteristics of the human face, and early research showed that infants generally prefer facelike to nonfacelike stimuli (Fantz,

1961).

One somewhat surprising visual preference found in young infants is that for attractive faces (Langlois et al., 1987). Langlois and her colleagues presented pairs of photographs of attractive and less attractive female faces, as judged

by

groups of college students, to groups of infants ranging between

2-6

months of age. Infants of all ages spent more time looking at the more attractive than at the less attractive faces. This preference was unrelated to how attractive an infant’s mother was judged to be. More recent research has shown that this preference extends across sex, race, and age of the modeled face; 6-month-olds consistently showed a preference for attractive faces of both men and women, Black and White adult females, and 3-month-old infants, despite the fact that the infants had little or no experience with some of these classes of faces (Langlois, Ritter, Roggman,

& Vaughn,

1991).

One possible explanation for these and related findings is that attractive faces might have more of the physical stimulus characteristics that attract

152

THE ORIGINS OF HUMAN NATURE

infant attention than do unattractive faces. For example, symmetry is a sign of physical (Gangestad & Thornhill,

1997)

and psychological (Shackelford

& Larsen,

1997)

health and, among adults, facial symmetry is perhaps the

most potent factor in determining attractiveness (Gangestad, Thornhill, &

Yeo, 1994). An alternative possibility is that infants are born with a schema of a human face, and that attractive faces match that schema better than unattractive ones. Evidence indicating that preference for attractive faces involves more than simply symmetry comes from work with newborns, who displayed a preference for (i.e., looked longer at) attractive faces positioned upright (versus less attractive faces) but not for the same faces presented upside down (Slater, Quinn, Hayes, & Brown,

2000).

Such a finding suggests that if infants are born with a schema, or prototype, for a human face, it includes information about its orientation.

Some evidence indicates that attractive faces are those that reflect the

“average” of a range of facial features (e.g., average distance between the eyes, average nose length; Langlois & Roggman,

1990;

Rhodes & Tremewan, 1996).

This

would make sense from an evolutionary perspective.

If

attention to faces is important in forming social relations in early infancy, and thus aids survival, the best bet would be to have an attentional bias toward average features (even if the combination of these average features results in an attractive, and thus “above-average,” face). More recent research has found a relationship between attractiveness and averageness not only for human faces, but for dogs, birds, and wristwatches (Halberstadt & Rhodes,

2000). This

suggests the possibility that the preference for average faces is built, in part, on a mechanism for averageness in general rather than on a domain-specific mechanism exclusively for faces.

The work of Langlois and her colleagues suggests that by at least age

2

months, infants are influenced

by

individual differences in the features of human faces. This work also implies that young infants know something about faces, with little in the way of experience necessary for them to express this knowledge. Such knowledge, however, is implicit, and does not imply self-awareness. In retrospect, such findings should not be surprising, for there is likely no single visual stimulus that is of greater significance to a human infant than that of the face of another member of its own species.

Research has demonstrated that infants show a preference for facelike as opposed to nonfacelike stimuli from the first weeks of life. Working with

1

-month-old infants, Johnson and his colleagues showed infants different head-shaped stimuli, moving each stimulus across the babies’ line of vision (Johnson, Dziurawiec, Ellis, & Morton, 1991; Johnson & Morton, 1991; Morton & Johnson,

1991).

They then measured the extent to

which

the infants followed each moving stimulus (a) with their eyes and

(b)

by turning their heads. They found significantly greater eye and head movement

to facelike than to nonfacelike stimuli for infants ranging in age from several minutes to

5

weeks. These data suggest that infants are born with some idea of “faceness” and will visually track face-like stimuli more than nonfacelike stimuli. More recent research has found visual preferences for face-like stimuli for newborns (Mondloch et al.,

1999).

Morton and Johnson

(1991)

developed a two-process model to explain infant face preference. An initial process involves primarily subcortical neural pathways.

This

system is responsible for human newborns’ preference for the human face, but because of limited sensory capabilities, infants are not able to learn about specific features of faces until about

2

months of age. Beginning about this time, the second process, which is under the control of cortical brain areas, begins to take over. The functioning of this system depends on cortical maturation and experience with faces during the first two months of life, as infants begin to build a representation that enables them “to discriminate the human face from other stimuli and especially from faces of other species” (p.

178).

Recent research has shown, consistent with the model, that

3-

and 4-month-old infants are able to use cues from the faces of animals (e.g., dogs and cats) to identify not only specific individuals, but also an animal’s species (Quinn & Eimas, 1996).

That is, they are able to acquire a category for “dogs” versus “cats” based on facial features.

Other research has found that newborns look longer at the faces of their mothers than those of other women, suggesting an ability to discriminate among faces at birth (Bushnell, Sai, & Mullin, 1989).3 In other research,

12-

to 36-hour-old infants varied their rate of sucking more to see a picture of their mother’s face than they

did

to see a picture of another woman’s face (Walton, Bower, & Bower, 1992). These data suggest not only that newborns can tell the difference between faces and nonfaces, but also that they learn a preference for their mothers’ faces within the first day of life (see also Walton & Bower, 1993).

Although the research findings are not

100%

consistent, they agree that even newborns are predisposed to be attentive to human faces and that learning about faces develops early. This makes sense from an evolutionary perspective; it is also consistent with the speculation of pioneering infant researcher Robert Fantz (1961), who wrote more than

40

years ago that

’When using infant looking time to determine whether infants can discriminate between two stimuli, it IS sufficient to demonstrate that they consistently look more at one stimulus than another.

Most research using visual preferences with infants has found that looking time is greater for a novel versus a familiar stimulus. This is not always the case, however, especially for young infants and for infants learning about new classes of stimuli. Although there is debate about what various patterns of looking behavior indicate (Bahrick h ^Perkins,^1995;Bogartz & Shinskey, 1998), to demonstrate that infants can tell the difference between two stimuli, it does not matter whether they prefer the novel or the familiar.

154

THE ORIGINS OF HUMAN NATURE

infants’ preferences for facelike patterns may “play an important role in the development of behavior

by

focusing attention to stimuli that will later have adaptive significance’’ (p.

72).

Physical Objects

As

adults, we take many things for granted about physical objects:

Only one can occupy a space at a time; unsupported objects will fall; one object cannot pass through another; objects continue to exist even when they are out of our immediate perception.

Do

infants enter the world with such knowledge, or must they discover it through experience?

If

the latter, are these early developing abilities, or ones that take time before being mastered? Neonativists argue the former, proposing that infants have innate knowledge about objects, or are biased to acquire such knowledge very early in life.

Core Knowledge

Writing about young infants’ knowledge of continuity and solidity, developmental psychologist and neonativist Elizabeth Spelke (

199

1 ) proposed that such knowledge

may derive from universal, early-developing capacities to represent and reason about the physical world. These capacities may emerge in all infants whose early growth and experience fall within some normal range. They may enable children to infer how any material body will move in any situation. (pp. 160-161)

Spelke (

1994;

Spelke, Breinlinger, Macomber, & Jacobson, 1992) proposed that there are three core principles of innate knowledge about objects that infants possess: continuity, the idea that an object moves from one location to another in a continuous path and cannot be in the same place as another object; cohesion, the idea that objects have boundaries and that their compo- nents stay connected to one another; and contact, the idea that one object must contact another object to make it move. Infants’ understanding of these three principles develops with experience, but, according to Spelke, babies possess core knowledge (representational innateness) about these domains from birth.

The first of these three domains to be investigated in infants was that of continuity. Figure

6.1

shows a solid rectangle with two bars extending from its top and bottom. Adults infer that the rectangle is occluding a solid bar, although no solid bar is actually seen. What do infants think?

Researchers use changes in infants’ visual attention as an indication of what they know. For instance, if a baby is repeatedly shown a stimulus, his

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