Theory of Stuttering – Blog
Theory of Stuttering – Blog
The finding of sports science that an external focus of attention (compared to an internal focus, on the movements themselves) results in more effective performance has recently also influenced stuttering research. Eichorn, Pirutinsky, and Marton (2019) and Eichorn and Pirutinsky (2022) found reduced stuttering under dual task conditions. Bauerly and Mefferd (2023) found reduced lip movement variability when adults who stutter were speaking in a condition with external attentional focus, compared to a condition with an internal focus of attention.
In their new study, Kim Bauerly and Eric Jackson (2024) investigated the effects of an internal versus external attentional focus on the articulatory variability of adults who stutter at the sentence level. Again, the results suggest that an external focus of attention is more beneficial than an internal focus (on articulatory movements). These findings are important, as they call into question therapy methods in which stutterers are taught to focus their attention on the speech movements.
To direct participants’ attention to an external target, Bauerly and Jackson asked them to focus on a ball that moved in random directions on a screen. Likewise, in the other studies mentioned above, external targets were used merely to distract attention from any internal focus. The underlying idea is that speaking works better the more automatic it is, and that attention to speech movements (and their conscious control) may disrupt automaticity. That may be true, but has an external attentional focus really no other function than to distract from internal perception?
Wulf and Lewthwaite (2016) define an external focus of attention as “directing performers’ attention to the (environmental) effects of their movements” (p. 1401). In contrast, the random movement of a ball on a screen is not an effect of the participant’s speech movements but a task-irrelevant, merely distracting stimulus. Wulf and Prinz (2001) have discussed what the optimal focus of external attention is. They write:
“Given a sequence of movement effects that the performer could focus on […]—which of these effects should the performer focus on in order to optimize performance? The first principle is that the effect that the performer focuses on should be as remote as possible. The second principle, which appears to contradict the first principle, is that the effect should be related as closely as possible to the action that produced it. […] it is necessary that the movement effects and the motor commands that produced these effects can be associated” (p. 656)
What follows from this for the optimal attentional focus when speaking? Is attention to a listener’s response (suggested by Bauerly and Jackson) an optimal focus? Probably not, for it is not closely related to the speaker’s articulatory movements; it rather depends on the listener’s opinion, expectation, or interest. By contrast, the auditory feedback of speech is closely related to speech movements—and clearly distinguishable from them.
The sound of the voice and the words, audible for others but also for ourselves, is the task-relevant environmental effect of speaking. It is closely related to speech movements and provides information that the brain needs for speech control (e.g., Tourville, Cai, & Guenther, 2013). Moreover, focusing attention on auditory feedback—listening to one’s voice and one’s words—distracts from internally monitoring and controlling speech movements.
Auditory feedback has not yet been applied as a target for an external focus of attention, probably due to the widespread prejudice that listening to their speech may be harmful to stutterers. This prejudice has several sources: first, the idea that hearing one’s own stutter could exacerbate stuttering; second, the assumption that auditory feedback could be dysfunctional in some way in stutterers; and third, the observation that stuttering often disappears under auditory masking by loud noise.
For instance, the German medicine Sandow (1898) called the disorder “sensory echo stuttering” and suggested: “Either plug your ears with cotton wool, or speak lower! In both cases, the acoustic irritant will become weaker” (p. 67). In the late 1950s, the idea had come up that auditory feedback could be abnormal in stutterers, e.g., due to inter-aural phase disparity or interference between air-conducted and bone-conducted auditory feedback (Stromsta, 1959; 1972; Webster & Lubker, 1968).
Against this background, Van Riper (1973) wrote: “Our position is that some of the stutterer’s difficulties seem to originate in the auditory processing systems. We feel that if we can get him to concentrate upon proprioceptive feedback, we can bypass these difficulties. Accordingly, we use masking noise, DAF, and other methods for facilitating motor control through proprioception. We want the stutterer to stop listening to the gaps and abnormalities in his speech when they occur and when he expects them.” (p. 211)
There actually seems to be a problem with auditory processing in stutterers (see my list of studies). However, it seems to affect auditory gating (Kikuchi et al., 2011; Saltuklaroglu et al., 2017), that is, the suppression of redundant acoustic input and thereby auditory attention. Recently, Lazzari et al. (2024) found in a finger-tapping experiment that normal speakers automatically used auditory feedback to control the rhythm of their tapping even if they were instructed to ignore it and to focus on their movements. In the participants who stuttered, by contrast, the external focus on auditory feedback was not automatic; they had no difficulty ignoring it (see also my comment on the study).
It is thus possible that stutterers ignore auditory feedback also when speaking and instead adopt an internal attentional focus, with the result that auditory information is insufficiently involved in speech control. Fiorin et al. (2021) compared the effects of delayed auditory feedback, masking by noise, and amplified auditory feedback on stuttering. The reduction of stuttering was greatest in the latter condition; the difference was significant for both moderate and severe stutterers (see my comment on the study).
The results of Fiorin et al. (2021) can hardly be explained in another way than by saying that the amplified auditory feedback (through headphones) attracted the participants’ attention, the external focus on auditory feedback improved auditory-motor integration, which reduced stuttering (about the effects of delayed auditory feedback and masking noise on stuttering, see Chapter 3 in the main text). So we have good reasons to assume that auditory feedback is not harmful for stutterers. By contrast, a sufficient amount of attention must be directed on it to supply the brain with information needed for the control of fluent speech.
In the previous studies that aimed to find the best attentional focus for movement control in dart throwing, balancing, or golf, only visual targets for external attentional were tested. However, Wulf and Lewthwaite (2016) write: “Experimental evidence has amassed for the benefits of adopting an external focus on the intended movement effect” (p. 1396; my italics). What is the intended movement effect of speaking? To make one’s thoughts audible, so that others can hear and understand them. There may be further intended effects, e.g., to evoke a listener’s response, but the immediate and movement-dependent intended effect is an audible one. Therefore, this audible effect is also the most natural target for a speaker’s attention.
Lazzari et al. (2024) have shown that normal speakers automatically pay attention to auditory feedback during rhythmic finger-tapping, and we can assume that they do it even more when speaking. Stutterers did not show this automatic attentional behavior in finger-tapping, and we can assume that they tend to ignore their auditory feedback during speech as well. This could be the cause of stuttering. Future research should test this hypothesis and explicitly investigate the effect that attention to auditory feedback has on stuttering.