non-invasive imaging method

Natureから非常に興味深い実験の報告が届きました。なぜ早口言葉は難しいのか、がわかってきました。記事に出てくる表現は、そこまで面白いものはないものの、研究内容が面白かったのでシェアします。ここで使用されるnon-invasive imaging methodとは、「被験者の身体に器具や医療道具などを入れないで、身体の中の様子をX線などで観察する方法」を指します。医学や脳科学の言葉ですが、invasive(侵入するような、侵入する、侵略的な)という形容詞にnonが付いていて、尚且つ脳のことなのですから、想像できます。もっと解明されて、いつか教育に役立つ日が来ることを期待しています。(Othello)

Why tongue twisters are hard to say

http://www.nature.com/news/why-tongue-twisters-are-hard-to-say-1.12471

Say the word 'rutabaga', and you have just performed a complex dance with many body parts — lips, tongue, jaw and larynx — in a flash of time. Yet little is known about how the brain coordinates these vocal-tract movements to keep even the clumsiest of us from constantly tripping over our own tongues.

A study of unprecedented detail now provides a glimpse into the neural codes that control the production of smooth speech. The results help to clarify how the brain uses muscles to organize sounds and hint at why tongue twisters are so tricky. The work is published today in Nature.

Most neural information about the vocal tract has come from watching people with brain damage or from non-invasive imaging methods, neither of which provide detailed data in time or space

(中略)

The lips, the teeth, the tip of the tongue

The different patterns might help to explain why slips of the tongue occur in predictable ways: we often interchange two consonants in so-called spoonerisms ('boat tag' instead of 'tote bag') or confuse two vowels ('wheel' for 'whale'), but rarely swap consonants for vowels4.

The team also found that the brain seems to coordinate articulation not by what the resultant phonemes sound like, as has been hypothesized, but by how muscles need to move. Data revealed three categories of consonant: front-of-the-tongue sounds (such as 'sa'), back-of-the-tongue sounds ('ga') and lip sounds ('ma'). Vowels split into two groups: those that require rounded lips or not ('oo' versus 'aa').

“This implies that tongue twisters are hard because the representations in the brain greatly overlap,” Chang says. 'Sss' and 'Shh' are both stored in the brain as front-of-the-tongue sounds, for example, so the brain probably confuses these more often than sounds that are made by different parts of the tongue. ‘Sally sells seashells’ is tricky. ‘Mally sells sea-smells’ is not.