One of the amazing things about learning language is that children rarely hear language sounds in ideal acoustic environments. Maybe other people are talking in the background, or the dishwasher is running, or the TV is on. Yet somehow children they learn words just the same. By the time we’re adults, we’ve become experts at filtering out irrelevant sounds and patching together meaning out of the cacophony of everyday life.
As one example, listen to this short clip of me saying the word “dinosaur” three times.
I edited the “s” sound out of the first “dinosaur,” so you can clearly hear me saying “dino_aur.” The last “dinosaur” is obviously complete. But what about the middle “dinosaur,” where I edited in a cough/sneeze right over where the “s” sound is supposed to be? Can you still hear the “s” in the background? Let’s make this a poll:
Most adults believe they hear the “s” sound in cases like this, even if the sound has been edited out: the perceptual system adds in a sound where it doesn’t exist. (Did I edit the sound out here? I’ll keep that a mystery for now.) The effect, known as perceptual restoration, has been observed in children as young as five years old.
But what about younger children — kids who are just beginning to learn language? Do they also exhibit perceptual restoration? It’s a difficult question to study, since children who only know a few words aren’t able to tell us what they hear with the precision needed (they can’t read, so how can they tell us whether they heard an “s” sound?).
But Rochelle Newman did figure out an innovative way to study the phenomenon in very young children. At 24 months of age, toddlers understand a lot of words, but they still don’t typically produce much. Even a three-word sentence is a rarity in children this young. Newman had parents of 24-month-olds sit with their children in their laps in front of two video monitors. One played a movie of a dog, while the other played a cat movie. Both animals basically stayed in place or groomed themselves for the duration of the experiment.
While the videos played, a voice repeated either “Kitty! Kitty! Kitty!” or “Doggie! Doggie! Doggie!” eight times. The video played for 10.7 seconds, then blanked out until the next repetition of the words. The words were either complete and intact, edited to include silence instead of the central consonant sounds, or edited to include a noise instead of the central consonant sounds (tt in kitty and gg in doggie). All toddlers heard all three types of words — clear, silent, or noise. The time they spent watching each video was compared to the time they spent watching each of the videos when there was no sound. Here are the results:
So when they heard the complete, intact words, the toddlers looked at the matching videos significantly longer than they looked at the non-matching video (e.g. when “doggie” was spoken, they looked at the dog video longer than the cat video, and vice versa). When the central consonants were replaced with silence, they still looked longer at the matching videos, but for significantly less time than with the complete words. When noise was added in, there was actually no significant difference in looking time at the cat or the dog.
This is the opposite of what you’d expect if the toddlers were experiencing perceptual restoration! It suggests that they understand the words with silent gaps better than the words with noise added in. Remember, adults believe they hear the entire word when noise is added in, but not when a silent gap is edited into a recording.
Newman repeated the study with several variations: complete sentences instead of single words; more complex words and older (30-month-old) children; even carefully using dummy words like “dobby” and “kippy” as the basis for the edited-down versions to ensure that subtle hints of the edited letters weren’t present in the sounds played for the children. In each case, the results were the same: Toddlers respond as if they do not experience the perceptual restoration effect.
There are many possible reasons why the effect isn’t observed. Toddlers may not know the words as well as adults and older kids; the effect might require a very good knowledge of the words. They might simply be more open to new words, and thus treat the words with noise as if they are new words. They might be slower to process the words with noises. Or they might know the words just as well as older people, but not focus as much on this knowledge.
Whatever the explanation, this study suggests that perceptual restoration is acquired sometime between the second and fifth year of life. It may be a later add-on as kids get better with language, not one of the fundamental building blocks of language learning.
So, did I edit out that “s” sound in the middle word of my demo? Why don’t you let me know what you think in the discussion? I’ll let you know what I actually did after I hear a few of your guesses.
Newman, R.S. (2006). Perceptual restoration in toddlers. Perception & Psychophysics, 68(4), 625-642.