On Birds and Speech Therapy

This past winter Kevin Munhall and colleagues at Queens University made a big splash when they concluded that toddlers do not monitor their own speech; for some reason this made the headlines in quite a few news venues starting with Science Daily (http://bit.ly/O45LDH). In their study they used one of the most fascinating procedures for studying feedback control of speech – a procedure that was pioneered by John Houde (http://bit.ly/Opqtnn) who, as an aside, recently published a superb article called “Speech Production as a State of Feedback Control” (http://1.usa.gov/Nf3k2v). As another aside I believe that the first published speech adaptation study with kids was actually done in my lab by Doug Shiller (http://bit.ly/PSlmXk) (http://bit.ly/xCdRsQ). In Munhall’s study, toddlers, children, and adults were asked to say the word ‘bed’ repeatedly while an apparatus shifted the first two formants of their speech closer together so that they would hear themselves saying ‘bad’. As expected, the children and adults compensated by changing their articulation of the word to move their formants even further apart. The toddlers did not compensate which is what prompted the authors to conclude that the toddlers were not monitoring their own speech. I think there are quite a few dodgy things about this study but I’ll get to them later because the most interesting part of the paper is the discussion in which the authors suggest that one explanation for the toddler’s failure to compensate can be found in the literature in vocal learning on birds. I was reminded of this study as I observed the birds at the feeder outside my window at the cabin where I am working. It was from the Munhall paper that I learned that there is fascinating bird research going on at McGill (strange I hadn’t heard of it before).

Vocal learning in song birds and humans share many similar processes but the processes are easier to pull apart and more amenable to laboratory investigation in the songbird (http://bit.ly/NjNAeJ) . Parts of the vocal learning process that seem all jumbled up in the human infant are more clearly separable in the bird because they occur in more specific times and places. First the young male bird, in a listening stage, learns the target song from his father. Later during the subsong phase the bird practices the individual elements of the song in a manner similar to the human babbling stage. This is followed by practice of the sequenced elements in a stage called plastic song. Finally crystalized song emerges and the bird uses this to attract females. Sakata and Brainard (http://biology.mcgill.ca/faculty/sakata/articles/Sakata_Brainard2009.pdf) from McGill explain that even adult finches practice their song when they are alone however (undirected song) and that this practice song is somewhat less structured than the song produced during actual courtship performance (female directed song). Now, the cool part is that Sakata and Brainard tested the influence of auditory feedback on the finches’ vocal motor control using a procedure rather similar to the one Houde designed for humans. And it turns out that manipulations of feedback of the birds’ songs influenced their singing during practice (undirected song condition) but not during performance (female directed song condition).

This reminds me of the way that toddlers will wake the whole house up happily yapping away to themselves early in the morning but later in the day when a cookie is desired, resort to whining and pointing.  For toddlers and for birds, vocalizing for practice and communicating to meet a functional goal are two very different contexts.  Feedback control of speech may be strongest under practice conditions. When the toddler wants a cookie, he or she may ask for one if a well-practiced motor plan for an approximation to the word is available but otherwise nonverbal communication will have to do. It is generally accepted that, once learned, sensory feedback is not essential to speaking. Once the toddler learns to say ‘cookie’ the motor plan for the word can be implemented with feedforward control. Sensory feedback is absolutely essential to the process of learning to talk however. If access to this feedback is attenuated in functional contexts, what are the implications for speech therapy?

Many approaches to speech therapy involve working with the child in functional, communicative contexts. Francoise and I describe these in Chapters 9 and 11 of our book. These approaches have the purpose of strengthening the children’s acoustic-phonetic representations for speech targets or helping the child experience the functional consequences of using the appropriate phonological forms in communicative contexts. When the child’s fundamental underlying problem is with processing or organizing phonological input these approaches are known to be effective and lead to rapid carry-over of learning to non-clinic settings. Throughout our book and in previous blogs I have stressed functional contexts as a motivator for speech practice and I have talked about authentic practice contexts as being essential for carryover. Is it possible that some aspects of speech motor learning are best learned in non-communicative contexts however?

During my 20 years of clinical practice, prior to switching to full-time academic work, I specialized in the treatment of childhood apraxia of speech. With these children I used a different approach designed to foster the development of speech motor control. Described as a sensory-motor approach in Chapter 10 of the book, this approach focuses on intense practice of nonsense syllable drills. Theoretically these children have a problem that is specifically with the development of motor plans for speech and thus access to sensory feedback during speech practice will be very important for the success of any therapeutic intervention. Possibly working with non-meaningful speech material is one way to help the child use critical sensory feedback for speech motor learning during speech therapy sessions. Neither birds nor humans practice in social isolation however and social cues are known to shape the quality of the bird’s song. Currently there is very little research to help us choose the right mix of drill versus play and nonsense versus meaningful practice material. There are two research programs we can keep an eye on though. Patricia McCabe and colleagues have registered a randomized control trial to compare their Rapid Syllable Transition Treatment (ReST) with the Nuffield Approach (http://bit.ly/Pbsxy7). One of the features of ReST is practice with multisyllable pseudowords in quite structured contexts employing principles of motor learning. I am very excited about the trial and look forward to seeing the outcome. I also plan to keep watching the birdsong literature because I think that there is a lot more to learn about the social, behavioral and neurophysiological conditions that promote vocal learning and I have a feeling that more useful discoveries will be coming our way from the bird laboratories in the near future.

Although I enjoyed Sakata and Brainard’s paper and think that it may provide some support for sensory-motor approaches to the treatment of CAS, I can’t see how their findings explain the toddlers’ failure to compensate in Munhall’s study however. The children and the toddlers produced the word ‘bed’ repeatedly in the context of a sort of video game in which saying the word bed caused an animated robot to move across the video monitor. I am trying to imagine why feedback control would become more rather than less active in that context as children become older and more practiced at speech. To be honest I am not convinced that the results have anything to do with the toddlers’ access to or use of auditory feedback. The paper lacks any perceptual evidence that the acoustic manipulation of the toddlers’ speech resulted in changes that were equally perceptible (compared to the manipulation of the adult’s speech). There are plenty of reasons to think that these manipulations would not be perceptible to the toddlers involving both the acoustic characteristics of the toddlers’ speech and known biases in toddler perceptual abilities. Secondly and more importantly the standard deviations of the toddlers’ formant frequency values during baseline was 100Hz and the expected shift in formant frequencies was 100 Hz! How did they expect to see a 100 Hz compensatory shift against a background of 100 Hz noise? I wouldn’t conclude that toddlers don’t monitor their own speech just yet. None-the-less, I enjoyed finding out about the birdsong research and the idea that access to feedback might be context specific is something to keep in mind.

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3 Comments

  1. Great post!I am interested to see the results of the ReST study.

    Reply
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  1. Feedback Control and Speech Therapy Revisited | Developmental Phonological Disorders

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