Episode Transcript
Interviewer: The Science of Speaking Clearly up next on The Scope.
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Interviewer: I'm talking with Dr. Sarah Hargus Ferguson, associate professor of communication sciences and disorders at the University of Utah. I have a scenario for you to ponder. I have a grandfather-in-law who is getting older and he's definitely having a hard time hearing other people speak. What are your basic suggestions for how we can help people like that understand what we say?
Dr. Ferguson: Audiologists have a number of strategies we offer to family members if they are having trouble communicating with someone who is hard of hearing. We'll have things like make sure they can see your face, make sure you're reducing any noise that is in the background, and another thing that we almost always say is speak slowly and clearly.
Interviewer: What does that mean, slowly and clearly?
Dr. Ferguson: Its sort of one of these things that we sort of assume that talkers know what to do. We say speak slowly and clearly and maybe they'll do something like this, which is just slower. Maybe they'll do something like this. There is a lot of variability in what people do. The earliest research in this, in the mid '80s at MIT, looked at whether or not this clear speech is actually is easier to understand. This clear speech being the speech that people get when you tell them to speak clearly. It showed that yes, it is easier to understand. That's a good thing.
They did some acoustic analysis at that time trying to get at the question of "What makes clear speech clear?" There are lots of things that are different about clear speech acoustically versus conversational speech. We know that it's slower, we know that it's louder, we know that talkers do things like release the final consonants on words. But we don't know actually matters from an understanding standpoint. We don't know which things actually help.
Interviewer: Let's take one part of this like talking about the vowels. What is it that you think is the hard to hear listener can't hear?
Dr. Ferguson: You can think of vowels partly like playing notes together on a piano. There's usually energy. There are two target frequencies for each vowel. These frequencies are called formant frequencies and they have to do with the position of your tongue. When you move your tongue from "e" to "ah" to "ou" you're changing the resident characteristics of your mouth and that moves those formants or these notes around.
So "e" and "ou" the lower of the two notes, the F1, the first formant is the same. The second note of two is quite different. So around 2000 hertz is a very important frequency. And that's about where that second note or formant of these vowels falls. If you can't hear F2 "e" and "u" are going to sound the same.
Interviewer: How would you fix something like that in a speaker?
Dr. Ferguson: We know that if they move their vowels just generally further apart from each other. "E" and "a" are pretty far apart acoustically, "ah" and "ou" are pretty far apart acoustically and there are other vowels in-between that spread out that. We call it a vowel space. If we spread out that vowel space, that tends to make them easier to understand. Telling a talker how to do that is a little challenging.
Interviewer: What about constants? What are some of the tricky ones there?
Dr. Ferguson: For people who have . . . they typical hearing loss we have for people who get older affects the high frequencies. What you're missing mostly there are constants that we call "stops." "Puh", "tuh", "kah", "buh", "duh", "guh" those have high frequency.
Interviewer: There are a lot of them.
Dr. Ferguson: Which is a lot of them and they've got high frequency energy. Then our fricative sounds, "ss", "sh", "ph," those sounds. The complaint that we often hear is the speech is loud enough because if you've got good hearing in the low frequencies, you're hearing vowels, you're hearing people's voices just fine. The loudness of it is just fine. But without your stop and fricative consonants, everything sounds muffled. The Charlie Brown teacher voice, where you're missing that high frequency stuff.
As far as what happens to consonants in clear speech, we know that people put more energy. I mentioned about how they release their final consonants. Instead of saying "bit" they say "bit." They've got this nice "t," that part is called "the burst." First of all, its there, so its not unreleased. But also they tend to put more energy, so the "ss" and "sh" sounds, tend to be higher in intensity and also more distinct from each other acoustically. "Ss" gets a little more higher in pitch and "sh" gets a little more lower in pitch to move them a part from each other.
Interviewer: You've identified some of these vowels and you also know of some of these constants that give people trouble. How do you take it to the next step to figure out how to make those clear to the listener?
Dr. Ferguson: The approach that I have chiefly taken, I refer to as a "talker differences" approach. My dissertation involved recording 41 talkers producing conversational speech and clear speech. There is a huge variability among those 41 talkers in terms of what they do acoustically and in terms of how much clearer their speech sounds, whether its easier to understand. I used statistical techniques to out, okay, I've got this change in how understandable speech is and I've got these acoustic changes. Which of these acoustic changes are actually correlated with the improvements in speech understanding?
Interviewer: So you're taking real people's speech and figuring out, okay, here are my clear talkers. What is it that they're doing to make them understandable. What do you hope to do with this information?
Dr. Ferguson: What I really hope to do is have an intervention that I can apply to the frequent communication partners of people with hearing loss, or patients with hearing loss. It could be their spouse, children, anybody that they talk to a lot and have a quick and dirty test that we can do on that communication partner. Figure out, tell them to speak conversationally, tell them to speak clearly and see are they effective? If I made clear speech clear, I could do an acoustic analysis right on the spot and know if they're an effective clear speaker.
If they're not, there would be an intervention where we could say "Here is how you need to speak for your partner to be able to understand you better." They could practice this, record how it went and this would be part of an overall oral rehabilitation program we would have with a patient with hearing loss. It could involve hearing aids if they were motivated to get them, and clear speech would be just one of the many communication strategies that we would work on.
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