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Explaining the feedback effect in stuttering: A new thesis
Manish K. Rami, Ph.D.
Department of Communication Sciences and Disorders
University of North Dakota
Contact Information:
Manish K. Rami
Communication Sciences and Disorders
University of North Dakota
Grand Forks, ND 58202-8040
701 777 3724
manish.rami@und.edu
Suggested citation:
Rami, M. K. (2003). Explaining the feedback effect in stuttering: A new thesis. Unpublished
manuscript. University of North Dakota.
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Abstract
Conditions such as choral reading, delayed or frequency altered auditory feedback and masking
with noise decrease the frequency of stuttering in people who stutter people. This effect is
known as the feedback effect. This paper proposes that the speech module mediates these
effects. When speech stimuli -as feedback, actively engages the speech module in perceptual
processes while the module is in the act of producing speech, the speech module enhances
fluency in people who stutter. The characteristics of modules and their implications are
considered and some suggestions for investigations are made.
Keywords: Stuttering, Feedback Effect, Speech Perception-Production Link
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This paper introduces a new thesis to explain the feedback effect in stuttering. The
feedback effect is elicited in people who stutter (PWS) when they listen to one or more of the
various types of speech stimuli and simultaneously read or talk. Under these conditions, PWS
show a remarkable decrease in the frequency of stuttering. The important reason for examining
this effect is to understand the mechanisms that aid PWS in producing fluent speech. A clear
knowledge of the way in which fluent speech may be elicited could help us develop an efficient
and long-term treatment of stuttering. In addition, empirical follow up of this thesis would bear
upon the revised motor theory of speech perception and the construct of the speech module
(Liberman & Mattingly, 1985).
Several conditions produce the feedback effect in PWS. These conditions include the
choral reading (Barber, 1939), and the shadowing (Cherry & Sayers, 1956) during which the
PWS listen to and read or speak along with a normal speaker. Under these conditions, the
speech of another normal speaker becomes the stimuli that appears to precipitate decreases
the frequency of stuttering, producing the feedback effect. Other conditions that have been
successful in producing fluency in PWS include reading or speaking with any one of these
stimuli: stuttered speech (Kalinowski, Dayalu, Stuart, Rastatter, & Rami, 2000), filtered speech
(Rami, Kalinowski, Rastatter, Holbert, & Allen, 2005), reversed speech (Rami & Diederich, 2005),
vowel and consonant trains (Kalinowski et al, 2000), delayed auditory feedback (DAF) (Lee,
1950, 1951) and frequency altered feedback (FAF) (Howell, El-Yaniv, & Powell, 1987). Under
these conditions, PWS listen to either an electronically modified speech of another speaker or
their own speech that is electronically modified. In the case of DAF, the speech of PWS lag in
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the time domain, and in FAF, their pitch is shifted either up or down a fraction of an octave and
thus either lags or leads in the frequency domain. One study has documented fluency
producing effects of visual choral speech (Kalinowski, Stuart, Rastatter, Snyder, & Dayalu,
2000). In this case, the PWS do not hear any speech stimuli but they saw another person
silently making the speech movements while they were producing speech. All of these
conditions are known as feedback conditions and they use either normal or modified speech as
stimuli. Two other conditions that do not use speech as stimuli but also decrease the frequency
of stuttering in PWS include noise (Shane, 1955) and a tone (Cherry, Sayers, & Marland, 1955).
Under these conditions, the PWS listened to a noise or a tone while reading or speaking and
may be affected by a change in the intensity domain. All of the above conditions -except the
noise and the tone conditions appear to involve the acts of speech perception and production
simultaneously.
Some theories attempting to explain the feedback phenomenon include the correct
feedback explanation (Lee, 1950), the distraction hypothesis (Barber, 1939, Bloodstein, 1995),
external pace setting hypothesis (Pattie & Knight, 1944), and emphasized phonation and
continuity of phonation (Wingate, 1969). However, none of these theories address the issue (1)
of the instancy of the feedback effect, that the feedback effect is elicited instantaneous; (2) of
the rate of speech of PWS, which is independent of the stimuli once the feedback effect is
elicited; (3) the variety of stimuli that elicits the feedback effect, (4) the wide range of
conditions under which the feedback effect exists, and finally, (5) the suggestions that not all
PWS show feedback effect. Considering that the above speculations explaining the feedback
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effect in a variety of conditions have found either no empirical support or inadequate support,
further understanding of the feedback effect has remained elusive.
A New Thesis
Noting that speech stimuli are usually involved in the listening conditions with changes
in either the frequency, intensity or the time domain, a new thesis is suggested. It is proposed
that speech and speech-like stimuli, when used as feedback, engage the speech module in
perceptual processes while the module is either engaged in producing speech or is about to
produce speech. It is suggested that this dual activation of the speech module lead to a
decrease in the frequency of stuttering in PWS. When the feedback is discontinued, the speech
module disengages from the perceptual process, losing its state of dual activation and resulting
in stuttering.
Background
The concept of a “speech module” was proposed to explain the processes of speech
perception and production (Liberman & Mattingly, 1985). The speech module is conceived to
be independent of the general auditory perception, free from cognitive bias, and is defined as
“a piece of neural architecture that performs the special computations required to provide
central cognitive processes with representations of objects or events belonging to a natural
class that is ecologically significant for the organism.” (p. 27). The speech module has privileged
access to speech or speech-like events in the environment. Further, this module is adapted for
the reciprocal processes of speech perception and speech production.
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Specialized modules such as the speech module above are attributed to have a set of
characteristics (Fodor, 1983). These characteristics with reference to the speech module and
their relevance to the proposed thesis may be considered as follows.
Domain Specificity
This characteristic specifies the domain in which the module operates. The domain of
the speech module is speech, regardless of whether speech is presented auditorily or visually.
The speech module is engaged only in the cases when the incoming stimuli are speech. If the
stimulus is non-speech, the speech module does not come in to play (Liberman, Cooper,
Shankweiler, Studdert-Kennedy, 1967). This characteristic could explain the feedback effect
seen in PWS with delayed auditory stimuli (Lee, 1950, 1951), frequency altered stimuli (Howell,
El-Yaniv, & Powell, 1987), and other speech stimuli such as filtered speech (Rami et al, 2005)
and reversed speech (Rami & Diederich, 2005). Further, this specialty of dealing with speech
regardless of the mode of presentation of the stimuli, could explain the effects of visual choral
speech (Kalinowski, Stuart, et al, 2000). It is suggested that because all of these stimuli consist
of speech, the speech module should be dually engaged. That is, the speech module is engaged
in perceiving these speech stimuli at the same time when it is engaged in the process of speech
production, a condition that is suggested to lead to fluent speech in PWS.
Mandatory Operation
This characteristic specifies that the modules are operational at all times. This implies
that the speech module is operational at all times. However, it must be noted that it is actively
engaged in processing the incoming stimuli only if the incoming stimuli are speech.
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Consequently, if the incoming stimuli are not speech, the speech module though operational is
not actively engaged in processing the incoming stimuli. This characteristic could explain the
instancy with which the feedback effect appears in PWS. As soon as the speech stimuli are
received, the speech module is actively engaged and the feedback effect may be elicited in PWS
while they speak.
The only way to disengage the speech module while it is receiving speech stimuli is to
not attend to the incoming speech stimuli and attend to some other stimuli. This characteristic
could explain the suggestions that the feedback effect though present in many PWS, is not
found to decrease the frequency of stuttering in everyone who stutters (Ingham, Moglia, Frank,
Ingham, & Cordes, 1997). It is suggested that for the feedback effect to happen the PWS must
attend to the incoming speech stimuli. In the absence of attention, the effect may either be
inconsistent or absent (Fodor, 1983)
Speed
The specialized modules, since they are mandatorily operational and automatic, are fast.
The automatic operation saves time. Such a characteristic in the speech module would support
the fact that the feedback effect is instantaneous. As soon as the incoming stimuli are detected
to be speech, the speech module is actively engaged. This characteristic could also explain the
immediate recurrence of stuttering in PWS while they are speaking, once the feedback is
paused.
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Information Encapsulation
The specialized modules are assumed to deal with a specific task on its own. The module
does not have an access to any additional information even if that information may have some
bearing on the task in which the module specializes. The speech module is assumed to deal only
with incoming speech stimuli and does not have access to any other information that might be
present. This property allows the speech module to operate fast, almost instantly. This property
could explain the fact that it is only speech stimuli that elicits the feedback effect and that this
effect is not colored by any knowledge in the PWS about the feedback effect itself or that they
are under the feedback effect or that they are under an experimental condition under which
they usually have increased instances of stuttering such as talking in front of an audience
(Kalinowski, Stuart, Wamsley, & Rastatter, 1999). Such knowledge has no bearing on the
presence of the feedback effect.
Breakdown Patterns
The speech module is assumed to have a specific breakdown pattern that may not be
easily explained by global capacities like memory, and attention. This property supports the
suggestions that the disorder of stuttering develops in phases. Various accounts of a pattern of
development of the characteristics of stuttering are available (Bloodstein, 1960, Van Riper,
1992).
Issues Explained
Several known aspects of the phenomenon of stuttering and the feedback effect may be
accounted for with the new thesis. Among them are: the instancy of the feedback effect, the
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variety of auditory and a visual speech stimuli that elicit the feedback effect, the breadth of
conditions under which the feedback effect exists, and the differences among PWS in their
individual responses to the various speech stimuli.
In addition to the above, the present thesis also accommodates and explains the effect
of noise, or the masking effect, in decreasing the frequency of stuttering in PWS. It has been
suggested, while explaining the various properties of input modules such as the speech module,
that since these modules are operating fast and informationally encapsulated they are
“prepared to trade false positives for speed” (Fodor, 1983 p. 71). It may then be inferred that
the speech module perhaps adopts a heightened state of alert and activates itself as it has
difficulty separating any speech information that may be present in the noise or a tone and
hence performs better (D. H. Whalen, personal communication, February 10, 2003). However, a
possibility that a different mechanism might be responsible for the masking effect cannot be
ruled out.
Producing Empirical Evidence
From the proposed thesis, it may be predicted that speech and speech-like stimuli, as
feedback, would elicit the feedback effect in PWS. Non-speech stimuli, it may be predicted, will
not engage the speech module in the perceptual process and hence they would not be as
efficient in eliciting the feedback effect in PWS. Further, it may predict that there should be a
continuum, from speech, to speech-like, to non-speech, of these stimuli in their ability to elicit
the feedback effect in PWS. For prospective studies, it is suggested that various types of speech
stimuli such as non-native languages and non-native vowel and consonant trains, speech like
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stimuli such as sine wave speech or glides, and non-speech stimuli such as frequency
modulated tones, and clicks should be used.
Additionally, and importantly, the data produced by pursuing the experiments
suggested may speak to the revised motor theory of speech perception and the presence of a
single speech module (Liberman & Mattingly, 1985). Such a line of investigation could lead to
new areas of research with a significant impact on the discipline of stuttering as well as speech
perception and production.
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Acknowledgement
The thanks Dr. Doug Whalen for his comments on an earlier draft of this paper.
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