Theory of Stuttering – Blog
Theory of Stuttering – Blog
When I started pondering on the cause of stuttering in 2011, I soon realized that the disorder can hardly be explained in the framework of the standard model of speech production and self-monitoring (see here in the main text). Thus I developed a simple alternative model without pre-articulatory monitoring in spontaneous speech, but with an important role of auditory feedback. (Section 1.3 in the main text).
In November last year, I found the paper by Andreas Lind and colleagues (2014) in the web, and I was happy when I read it. The study provides evidence for an important part of my model: the assumption that (i) auditory feedback is crucial for the self-monitoring of speech, and (ii) that the idea of a pre-articulatory monitoring in spontaneous speech is superfluous.
The paper has a long titled: “Auditory feedback is used for self-comprehension: When we hear ourselves saying something other than what we said, we believe we said what we hear.” The authors covertly manipulated their (normal fluent) participants’ auditory feedback in real time so that they said one thing but heard themselves saying something else. In 85% of all cases in which the exchange went undetected, the inserted words were experienced as self-produced.
So the authors demonstrate how much normal fluent speakers rely on auditory feedback. The results suggest: When we are speaking, we indeed have an idea of the message we are going to tell, but it is the auditory feedback which informs us about what we actually have exactly said.
The authors write that their real-time speech-exchange method could be used to study cases in which aberrant feedback processing has been implicated, such as in stuttering. So the question arises: Can their method be useful to test my theory of stuttering?
The core idea of my theory is that invalid error signals occur in the monitoring system because auditory feedback (in some cases also the proprioception of breathing) is insufficiently processed by the brain. The cause of the insufficient processing is a misallocation of attention during speech, that is, a misallocation of perceptual and processing capacity.
Of course, it would be great to test whether stuttering-like disfluencies, or at least involuntary interruptions of speech flow, can be caused in normal fluent speakers by transient disruption of auditory feedback. For example, the end of a word, or a short unstressed function word (best preceding the main content word of an utterance) could be distorted or replaced by noise. Importantly, participants’ attention should be distracted from auditory feedback such that they not become aware of the manipulation.
However, I’m skeptical if stuttering would be elicited in such an experiment. There is a difference between a distortion outside and inside the brain. In the experiment, the participants would hear their own speech with disruptions. In the mechanism of stuttering assumed in my theory, the speaker hears his or her own speech without disruption – disruptions occur in the brain, on the way from the inner ear to the network responsible for the self-monitoring of speech. That’s a difference. In the experiment, the participants’ attention would drawn to the auditory channel just because of the manipulation, that is, because their own speech sounds anyway odd to them...