Next month, I'll be giving a talk called "Explaining Intelligibility: What matters most in L2 Speech?" at Second Language Research Forum 2017 in Columbus, Ohio. That talk will examine features of L2 Korean speech that caused intelligibility issues, based on data from 30 Korean native speaking listeners. This post is a preview, where I'll show some of my initial summary data.
In second language speech, a handful of constructs are widely studied and considered important: intelligibility, comprehensibility, accentedness, and fluency. Arguably, intelligibility is the most important, as you can't really have successful communication without it. When we think about intelligibility, we might think of it holistically to describe a person's general ability or a person's performance in some speaking context. Language tests are a good example of this- the word "intelligibility" pops up in rubrics that are used to assess someone's speaking performance on a test task. Visually, we might think of people having different degrees of intelligibility looking like this:
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| Fig 1. Average proportion of eojeols (words) in a picture description task correctly transcribed by 30 Korean listeners. |
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In Fig. 1, we do see some variation- around 80% or so of Speaker B's words (actually 어절,
eojeol, a word + bound morphemes, the preferred unit of analysis in Korean linguistics) were intelligible to Korean listeners, on average, while speaker F clocked in at around 50%. But it isn't necessarily the case that Speaker B is always 30% more intelligible than Speaker F- everybody stumbles sometimes, right? What if we look at each utterance (sentence) that the speakers produced?
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| Fig 2. Average proportion of eojeols correctly transcribed in each utterance. |
We can see here that Speaker F, while generally having troubles with intelligibility, really dropped the ball on his/her first sentence, which was almost completely unintelligible to the listeners in the study. Speaker B is relatively intelligible throughout, but his/her first sentence was a little harder to grasp compared to the following two. Speaker A shows one of the starkest contrasts, with his/her first sentence around 50% and the rest being 80% or so. It's worth noting that the person and sentence level is about as fine-grained as a lot of L2 intelligibility research using naturalistic or contextualized speech has gone. Some studies focused on single-word intelligibility (i.e., a learner reads single words, or names single objects) do get to the word level, but I am curious about what leads to intelligibility issues in more realistic contexts. After all, these utterances aren't uniformly 50% intelligible- each word is either intelligible, or not. So we can dial in here and look at things this way:
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| Fig 3. Proportions of correct transcriptions for each eojeol. |
To me, this is where things get really interesting. For one, we can see much more variation- there's more red and orange in this plot compared to the utterance-level depiction in Fig 2. Some words were almost completely unintelligible to listeners. Those who read Korean might notice that many of these words are names! This is interesting, and was intentional in the task design for the speakers- a name that involves a nasal assimilation at the meeting of its two syllables was chosen. But other words, often involving times and days of the week, were also quite difficult for listeners to understand. What I'm more interested in, though, is the speech features that might cause these words to be unintelligible- is it phoneme substitutions? Deletions? Pauses or repetitions in the utterance? Lexical errors? Grammatical errors? And that's my next task- building models to examine the relative impacts of these (and other) features on intelligibility.
Stay tuned!
P.S. - It's also worth pointing out that the 30 listeners were not monolithic in their overall ability to understand and correctly transcribe words. I'll be looking at listener factors in another analysis at a later time, but here's a little preview of that:
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| Fig 4. Proportion of eojeols correctly transcribed by each listener. |
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