New edition: How do developmental psychologists think?

[This is the new and improved version of an old post, cross-posted from Medium].

Courtesy of Shutterstock.

A developmental psychologist researches how people’s minds change over their lifetime. Most study babies or children, but some focus on adolescence or old age. They could also investigate other life transitions, like parenthood, middle age, or emerging adulthood. Developmental psychologists care about life stages: How do we change as we move from one to the next? How we change within a life stage? Conversely, what about us stays the same as we move from one stage to another?

Developmental psychologists care about processes of continuity and change, not particular things the human mind does. In this respect, they are different from some other sorts of psychologists, who are defined by the functions of the human mind they choose to research (i.e., cognitive psychologists study thought and perception, personality psychologists study personality, and social psychologists study group behavior). Developmental psychology, as a field, is concerned with all these areas of the human mind. Even a developmental psychologist who focuses on cognitive psychology topics, as I do, will know something about personality and social development.

Like people in other fields, developmental psychologists are guided by a set of assumptions, which may or may not be discussed explicitly.

Assumptions Developmental Psychologists Make

1)Gene-environment interactions
While developmental psychologists debate nature vs. nurture just as intensely as other people, they have a unique perspective on it. They argue that you cannot explain human behavior with only genes or only experiences. Instead, they come together in a complex way, with different results than you would get from genes or environment alone. Genes and the environment interact like vinegar and baking soda. Alone, these chemicals are each inert, but they come together to make an explosive reaction. Similarly, genes and the environment come together to create an outcome — like personality traits or intelligence — that neither would have produced alone.

The least controversial interaction is probably height. A large amount of variation in people’s heights is genetically determined: tall people tend to have tall children; short people tend to have short children; and siblings tend to have similar heights. However, nutrition determines whether people will grow as tall as their genes permit them to be. For this reason, my grandparents were taller than my great-grandparents, and my parents were taller than my grandparents. Improvements in nutrition seem to have plateaued, and so has height; my generation (millenials) is the first in some time not to exceed their own parents’ height. Notice that the genetic relationships here (parent to child) are constant across the generations from your great-grandparents to yourself, but differences in environment (nutrition) produce large differences in height.

More complicated and controversial are theories like the Orchid Hypothesis, which posits that different people are differentially reactive to their environments, whether these are good or bad. In other words, some people react a lot to their environments, while others react much less. More reactive people will be the most successful in a good environment, but least successful in a bad environment. As far as I know, this theory is still new and not completely accepted, but it’s based on research on stress and resilience that iswidely accepted. Some children who have suffered abuse and neglect will have worse life outcomes than others, and one contributing factor is differences in specific genes. This is a well-known gene-environment interaction.

2) Developmental trajectories
You don’t have to be a developmental psychologist to notice that different individuals develop at slightly different rates. Some children learn to talk and read early and remain skilled speakers and readers throughout their lives, while others develop language and reading skills more slowly and never achieve the same levels. Some children are taller than their peers from an early age, and remain so over time, while others start out short and stay that way.

More interesting, though, are children who start behind their peers in a skill and come out ahead, or vice versa. For example, Einstein, though a late talker, developed fine speaking, reading, and writing skills by adulthood, and some late-talking children today follow a similar pattern. Meanwhile, some children with precocious academic skills and high IQ scores in preschool, kindergarten, or first grade may perform more like their peers by third grade. (For this reason, experts on gifted children often recommend getting one’s children IQ tested at 6 or 7 years old).

Children’s rate of development of a skill can change — not only relative to peers the same age, but also relative to themselves at earlier ages. When developmental psychologists think about growth, they imagine a line graph, where the steepness of the slope of the line represents the speed of development, and changes in the slope represent changes in the rate of development over time.
In this example of developmental trajectories, each line represents an autistic preschool child's vocabulary. Parents were given a survey four times, which asked how many words their child could both say and understand.

Developmental trajectory is especially interesting in two cases: when comparing typical with atypical development, and when comparing different individual children.

Language development often follows a different trajectory in autism than in typical development. Speech is often delayed. Also, the rate of growth may seem to slow down for a while, stop entirely (what developmental psychologists call a “plateau”), or even reverse (“regression”). On the other hand, autistic people may continue developing language skills longer than neurotypical peers, sometimes improving into adulthood. And of course, since autism embraces people with a wide range of characteristics, you can find autistic people with every imaginable trajectory of language development. Many recent studies have attempted to find subgroups of autistic children with different trajectories, to predict who will have the best language outcomes, and why.

Developmental trajectory is also important when comparing different individuals from the same population. For example, some late talkers eventually catch up with their peers in spoken vocabulary, while others do not. Some developmental psychologists spend a lot of time trying to figure out why these children differ, and what can be done to help the persistently-delayed group catch up.

3) Developmental cascades
While people can and do grow and change throughout their lives, early experiences profoundly shape our abilities and choices later on. The influence of earlier upon later development is called a “developmental cascade,” but I like to think of it as a “developmental avalanche.”

For example, let’s say you’re studying children’s vocabulary size from age 3 to age 5.

  • Age 3 vocabulary size has an effect on age 4 vocabulary size.
  •  Age 4 vocabulary size has an effect on age 5 vocabulary size.
  •  Age 3 vocabulary has an additional effect on age 5 vocabulary size.

Initial vocabulary has both direct and indirect influences, via vocabulary at intermediate ages. It’s like a small snowball that hits more snow and becomes a bigger snowball, which hits more snow and becomes an even bigger snowball, and so on. Eventually, small differences between people early in life can lead to big differences.

4) Two-way interaction between child and environment
Children aren’t just shaped by their environment. Their behavior also shapes the input they get from their environment. For example, a child who is shy from infancy will be treated differently than a more outgoing child. The shy child might be reproached, shamed, pushed hard, or gently encouraged to interact, depending on the parents’ parenting style and values. These actions in turn will shape how the child behaves around other people, and whether he becomes a painfully shy or quietly confident adult. A child who has been told she is smart from an early age will probably think of herself differently, and take different levels of risk in the classroom, than one who has been told that she is average, or even dumb. I’m sure you can think of many more examples.

While the role of children in shaping their environment seems obvious when pointed out, it looks different than the description of children in many parenting books*. Too often, the paradigm seems to be “push the right button, receive the desired behavior,” with little focus on children’s reasons for their behavior (good or bad), or on how the children might be triggering parents’own insecurities about parenting. Not surprisingly, many of these books aren’t written by developmental psychologists.

These four assumptions lead developmental psychologists to ask a special set of questions.

1) Are some capabilities innate? If so, which ones?
William James pointed out that at any given moment, there are so many shapes, colors, sounds, textures, smells, temperatures, and more that without any inborn means to sort them out, a newborn’s world would seem like a “blooming, buzzing confusion.” I think most developmental psychologists accept that at the least, babies are born with some basic learning abilities, and an inclination to observe and learn about the world. But psychologists differ on how much “software” babies come with. Some people think we’re born with implicit knowledge of all the grammatical rules of human language; a basic understanding of how objects move (e.g., that they fall), and concepts about other people (e.g., that they have minds and intentions). Others think we develop these concepts early in life, but aren’t born with them. This debate has inspired interesting research on what babies understand about people, things, numbers, and more. The debate will likely continue for decades.

2) Are there developmental stages, and if so, how do people transition between them?
Does development have discrete steps, like a staircase, or is it continuous, like a ramp?

Piaget thought at certain ages, children transition from one way of thinking to a qualitatively different one. Everyone progresses through the same stages in the same order at a similar age. Also, if children have reached a developmental stage in, say, math, then they must have reached it in all other areas of knowledge. (That is, if you are at the “concrete operational stage” in thinking about the movement of objects, then you must also be at the concrete operational stage in thinking about other people’s behavior). Piaget had an extreme stage theory.

His successors, the Neo-Piagetians, were a little more flexible, particularly about different areas of knowledge and individual differences. However, they still thought that development has steps.

Whether development looks continuous or stage-like depends on how closely you zoom in. If you observe a child two times a month apart, you will observe more abrupt changes than if you observed the child every day for a month.
Courtesy of Getty Images. Grandma is much more likely to say "My, how you've grown!" than Mom, because Mom has seen all the gradual changes in between.

If you ask parents to rate the child’s behavior using a continuous scale, it will look less stage-like than if they use a Likert scale, with discrete numbers on it. It’s hard to tell how much our findings merely reflect our measurement tools, and how much they reflect how children really develop.

3) How do individuals differ in their development?

I think this is pretty self-explanatory.

4) How do changes in the brain contribute to development?
This question is easy to understand, but hard to answer. It’s even harder to study the brain in children than adults.

5) What develops, and how does change occur?
Last year, Anna didn’t understand the principle of “conservation of matter,” but this year she does, and she passed Piaget’s conservation of matter task. How exactly is she thinking differently now than she did last year? How did she get from the understanding she had last year to the one she had this year? This difficult, abstract question is the central question of developmental psychology, and probably the hardest to answer.

6) How does the social world contribute to development?
We are constantly observing, imitating, and being taught by other people. We grow up in cultures that provide us with tools for thinking, such as language, writing, the abacus, or the internet. Our cultures also determine how we spend our time, and who we spend it with, at different ages (for example, do children spend more time with age peers, or adults?)

People interact with various institutions either directly or indirectly, including schools, churches, and governments. We are assigned to categories of age, gender, ethnicity, religion, and more, all of which come with messages about how a person in our category should and should not behave. We also generally have innate desires to learn from and connect emotionally with other people, and make them like us. All these things shape both what we experience and how we choose to behave.

So next time you talk to a developmental psychologist or read about a new study, know that development is all about change — and change is a complicated mass of factors that changes over time and differs between individuals. Their goal is to sort out that complex system.

*This generalization is based on parenting books read between 1995 to 2008, so it may not apply to books published since then, or to books I might have missed. There are also some brilliant exceptions, such as The Heart of Parenting, which explains how to help children recognize and verbalize their emotions.

[This post was inspired by a developmental psychology seminar I took with Dr. Bennett Bertenthal at Indiana University].