Out of sight but not out of mind

Love, quantum mechanics, yesterday’s weather — humans readily discuss these and many other things they cannot see. Infants start to develop this ability early, new research suggests. Even 15-month-olds can guess the meanings of nouns without seeing their corresponding objects, according to work performed by Elena Luchkina, a research scientist in Elizabeth Spelke’s lab at the Harvard Department of Psychology, and Sandra Waxman, a professor of psychology and director of the Infant and Child Development Center at Northwestern University.

In this edited conversation with the Gazette, Luchkina discusses how she infers what infants are thinking, why her work could help treat learning difficulties, and whether the ability to discuss the unseen sets us apart in the animal kingdom.

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Are humans the only animals that talk about things they can’t see?

That’s debatable, and the answer depends on who you ask. There’s evidence that great apes can communicate about things that aren’t around, but in a limited way. For example, if you show an ape an object and then rapidly hide it, they may point to the place where they’ve just seen it. Or they can request food that is not currently around them. But this is not the same as how we, humans, can communicate about absent or invisible things via language.

For example, if I describe my favorite mug, I can give you all kinds of details that aren’t obvious from its appearance, like that my sister gave it to me and that she bought it at the corner store. Scientists haven’t observed nonhuman animals communicating about hidden objects or abstract concepts in such depth.

“The capacity to represent an unseen object and learn its name might be a building block for communication about more sophisticated abstract concepts.”

But we’re not born with this ability. By their first birthdays, most kids can do what apes do — point to the former locations of things they’ve seen recently, like a ball that their parent has just hidden. This is a big leap forward. Yet, being able to refer to recently seen things is different from being able to refer to unseen or abstract things. Kids usually develop this ability by age 2, and then they start talking about things like absent caregivers and what’s going to happen tomorrow. I hope to understand how and when this capacity emerges.

How did you figure out the age at which infants can learn the meanings of new words without seeing their corresponding objects?

We’re working with children who are too young to say more than the odd word here and there, so we tracked their eye movements to infer what they know and think.

During the training portion of the experiment, we showed infants a video of an actress who looked over her shoulder and named objects that popped up on a screen behind her. For example, if an apple appeared, she’d say, “Look, it’s an apple!” She did that three times, naming three objects from a particular category, like fruits. The fourth time, the object popped up behind her body where the infant couldn’t see it. Instead of using the real name of the fruit, she used a nonsense word, like, “Look, it’s a blicket!”

Finally, during the test, a screen popped up with two objects — one was a fruit that we thought would be unfamiliar to most infants in our study, such as a dragon fruit. The other was an unrelated item such as an ottoman or a car. Then we said to the infant, “Find the blicket!,” and we tracked how long the infant looked at each object. If an infant looked at the fruit longer than the unrelated item, we inferred that they understood a blicket to be a type of fruit, even without seeing it, because the other three items were fruits.

We repeated the procedure a few times with different categories of objects, and control conditions helped us gain confidence in the results.

And what did you learn?

What was really interesting was that 15-month-olds were able to find the blicket, but not 12-month-olds. That could be because 12-month-olds don’t have the attention span or memory capacity to complete the task yet. Or 12-month-olds may not have developed the ability to form a mental image of an object without ever having seen it, whereas 15-month-olds are mature enough to do it.

When scientists tried to answer this question in the past, their research suggested that infants had to be 19-24 months old before they could attach a word to an unseen object. So we’ve found that infants have this ability at a younger age than was previously thought.

In the paper, you compare an infant’s ability to spot the blicket to an adult’s ability to discuss some pretty sophisticated concepts, like justice or the square root of negative one. What’s the connection?

It’s true — the infants won’t be discussing imaginary numbers anytime soon. But the capacity to represent an unseen object and learn its name might be a building block for communication about more sophisticated abstract concepts. Similar to adults, infants in our study are creating mental representations of things they can’t currently see and holding such representations in mind while mapping words to them.

What’s next for this research?

We’d like to know whether the infants who are best at finding the blicket at 15 months are also most able to learn from language alone at 24 months. If that’s the case, it could mean that an early ability to learn about unseen objects gives infants an important foundation for learning from language later in life.

What kind of applications might this work have?

If infants who perform better on our task at 15 months also are better at learning from language at 24 months — and that’s truly because of the ability to learn from language and not other factors like memory or attention — then the find-the-blicket task might be useful as a diagnostic tool for difficulties with learning from language. Diagnosing these problems early could give us the opportunity to design interventions that would smooth out those difficulties before they lead to trouble in school.

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The research described in this story received funding from the National Institutes of Health.