Tongue twisters are not just fun to say; it
turns out that these sound-related slip-ups can also open windows into the
brain's speech-planning processes. A team from the Massachusetts Institute of
Technology (MIT) will report new insights gleaned from a comparison of two
types of tongue twisters at the 166th meeting of the Acoustical Society of
America (ASA), in San Francisco, California.
Stefanie Shattuck-Hufnagel, an MIT
psychologist who will present this work, studies speech errors as a way of
understanding normal brain functions. "When things go wrong, that can tell
you something about how the typical, error-free operation should go," she
For centuries, people have noticed that
when certain combinations of sounds are spoken too quickly, people seem to lose
control of their mouths. Often, one sound seems to replace another:
- "Toy boat" becomes "toy
- "Top cop" becomes "cop
- "The seething sea ceaseth and thus
the seething sea sufficeth us" becomes a mess of misplaced "s's"
Different types of tongue twisters
But when scientists recorded the misspoken
sounds and analysed them, they found that the errors were not always
straightforward sound replacements. At least some of the time, the mistakes
didn't seem to be quite one sound or another, but something in between. And
there were different flavours of in between: in the "top cop" example,
sometimes the "t" and the "c" seemed to arrive almost at
the same time (sort of "tkop") and sometimes there was a delay
between the two, with space for a vowel ("tah-kop"). Linguists refer
to these double sound mistakes as double onsets.
In their recent study, the team from MIT –
along with their colleagues at Haskins Laboratories in New Haven, Connecticut,
Ludwig-Maximilians University in Munich, Wellesley College in Massachusetts,
and the University of Southern California (USC) in Los Angeles – tried to
determine whether they could induce different types of double onset with
different types of tongue twisters.
The researchers recorded volunteers saying
combinations of alternating words that fell into two categories: simple lists
of words, such as the "top cop" example above, and full-sentence
versions of the same sounds with an inversion, such as "the top cop saw a
One particular list of words turned out to
be so difficult that the test subjects couldn't even get through it. The phrase
was "pad kid poured curd pulled cod", and when volunteers tried it,
Shattuck-Hufnagel said, some of them simply stopped talking altogether.
"If anyone can say this [phrase] ten times quickly, they get a
prize," she said.
Overlap between brain processes
After recording their volunteers' efforts,
the researchers analysed the sounds to see what errors people had produced.
They found that in the word list tongue twisters, there was a preponderance of
the "t'kop errors." In contrast, the sentence twisters induced more
of the "tah-kop"-type errors, with the longer delay and the presence
of a short vowel after the consonant.
Though it is too early to say exactly what
is responsible for these differences, Shattuck-Hufnagel said, one possible
factor is the regular rhythm of the word lists compared to the more irregular
timing of the sentences. But the fact that both types of errors occur for
sentences as well as word lists suggests that there is some overlap between the
brain processes used to produce these two types of speech. "You can get
both kinds of errors in both kinds of planning," she said, but the
different proportion of errors indicates key differences as well.
The MIT team, working with colleagues at
Haskins Laboratories, Ludwig-Maximilians University in Munich, and USC, has
already collected data for the next stage of this study, in which tiny
transducers are placed on people's tongues to measure their articulation. The
researchers hope to use this work to find the ghosts of double onsets, in which
the tongue has tried to make both a "t" and "k" but only
one sound is heard. If these double onsets are indeed more likely to be
produced by word list twisters than by sentence twisters, Shattuck-Hufnagel
said, then this work will help scientists understand how the brain plans these
two types of speech.