DETAILED PROTOCOL
Constraints and Strategies in Speech Production
July 23, 2003
The current proposal is for two fMRI studies that are included in a renewal application
for an NIH-funded project from the Research Laboratory of Electronics, M.I.T.,
“Constraints and Strategies in Speech Production,”, 2 R01 DC01925 – Joseph S. Perkell,
Ph.D., D.M.D., P.I. The studies are to be directed by Prof. Frank Guenther, (Dept. of
Cognitive and Neural Systems, Boston University) as a consultant to the M.I.T. project,
and they also form a logical extension of a project of Dr. Guenther’s that is currently
underway at the MGH NMR Center, “Neural Modeling and Imaging of Speech.” Much
of the following detailed protocol is taken from the Neural Modeling and Imaging
protocol, and differs only in the specifics of the two new studies.
I. BACKGROUND AND SIGNIFICANCE
The speech research literature is at a stage where it is important to formulate models that
address not just a single speech phenomenon, such as motor equivalence or
coarticulation, in isolation, but instead treat these phenomena within a comprehensive
theoretical framework that can account for many aspects of speech. Because the
dynamics of such a model are necessarily complex and its properties typically difficult to
clearly visualize, a means for objective verification of the model’s properties must also be
available. To meet these requirements, it is important to formulate computational models
that are described in sufficient mathematical detail that their properties can be verified
through computer simulation.
The speech research literature currently contains few comprehensive computational
models of this type. Over the past five years, our laboratory at Boston University has
developed, tested, and refined a computational model that extends the current state of the
field in several directions. This framework is one of the first and most comprehensive
computational frameworks that investigates auditory spaces for planning speech
movements (Guenther, Hampson, and Johnson, 1998). The use of self-organization in our
framework allows incorporation of speaker-specific vocal tract models, thus providing a
more accurate and reliable means of interpreting experimental data and generating
predictions for future experiments (Nieto-Castanon and Guenther, 1999). Finally, our
modeling framework is one of the first computational frameworks in which the
development of speech perception and production are addressed. The current proposal
describes several projects designed to further develop this framework (see Specific Aims
section).
2) Models of speech perceptual and motor development.
An understanding of the development of speech skills is important for many reasons.
Potential health benefits include better diagnosis of developmental difficulties in infants
and better therapies and prosthetic devices for overcoming these difficulties. We believe
our modeling framework is the most developed adaptive neural network treatment of
speech perceptual and motor development in the current scientific literature.
As speakers, we are capable of amazingly fast, flexible, and efficient movements.
Competencies such as motor equivalence and coarticulation greatly increase the
efficiency of articulator movements. A model of motor skill acquisition should embody
these competencies, suggesting that we should work toward an understanding of speech
motor skill acquisition within a comprehensive computational model of speech
production. Our modeling framework has been used to address several speech motor
development issues (Guenther, 1995; Callan et al., in press). Our research into motor skill
acquisition has also led to a better understanding of speech production in adults: a convex
region theory of the targets of speech, developed to explain how infants learn languagespecific and phoneme-specific limits on articulatory variability, provides a unified
explanation for such long-studied speech phenomena as contextual variability,
coarticulation, motor equivalence, and speaking rate effects (Guenther, 1995).
As listeners, our brains develop so as to allow very rapid and effortless parsing of a
continuously changing acoustic signal into a discrete set of phonemes, syllables, and
words from our native language. This process appears to be aided by the fact that our
perceptual spaces are warped such that we are more sensitive to between-category
differences than within-category differences, as evidenced by phenomena such as
categorical perception and the perceptual magnet effect. We have developed, tested, and
refined a self-organizing neural network model that addresses this issue (Guenther and
Gjaja, 1996; Guenther et al., 1999b). This model explains the warping of auditory
perceptual space in terms of the development of neural maps in the auditory system. This
work includes an account of the formation of vowel categories through simple exposure
to phonemes from an infant’s native language.
Further studies into developmental aspects of our modeling framework are proposed in
the current research plan, including development of auditory categories and visual
influences on speech perception (see Specific Aims section).
3) fMRI as a tool for studying brain processes.
Functional magnetic resonance imaging (fMRI) was first introduced as a tool for
measuring brain activation by Belliveau et al. (1991). The type of functional magnetic
resonance imaging (fMRI) that we plan to use takes advantage of changes in blood
oxygen levels that result when a particular part of the brain is activated. It has long been
known that neural activation leads to increased local blood flow (Roy and Sherrington,
1890). More recently, this relationship was shown to exist in the absence of a
proportional increase in oxygen consumption (Fox and Raichle, 1986). This results in an
overall higher concentration of blood oxygen in an activated area. The concentration of
deoxyhemoglobin, a paramagnetic substance which can be detected by the magnetic
resonance scanner, varies inversely with blood oxygen level. The oxygenation state of the
blood thus serves as a natural contrast agent in the brain, and the scanner is able to
determine the relative activation of different areas of the brain by measuring the relative
concentrations of deoxyhemoglobin in those areas. This is typically referred to as the
BOLD (blood oxygenation level-dependent) fMRI method (Kwong et al. 1992). This
technique provides a completely non-invasive method for producing maps of brain
activity. These maps can then be used to compare relative activation of different areas of
the brain while a subject is asked to perform a task. Typically this is done by looking at
changes in activation during an experimental task as compared to a carefully chosen
control task.
In recent years, fMRI has provided a wealth of information regarding brain function.
Because it is safe for use with human subjects, this technique is particularly suited to the
study of speech and language. Earlier techniques for studying brain function were
invasive, limiting their use to animal subjects, although a small amount of human data
came from studies of epileptic patients prior to surgery (e.g., Penfield and Roberts, 1959;
Creutzfeldt, Ojemann, and Lettich, 1989). Studies of the effects of brain lesions in
aphasic patients also provided clues (see Goodglass, 1993, for a review), but these data
are difficult to interpret due to the large variability in lesion sites across subjects, small
numbers of subjects, and coarse “grain” of the resulting data. Thus, relatively little was
known about brain function during speech and language tasks until the late 1980’s.
4) Neural models for interpretation of functional brain imaging data.
The relatively recent advent of functional brain imaging techniques that are safe for use
on human subjects has led to an explosion in the amount of data concerning brain activity
during speech and language tasks. Examples include fMRI studies (e.g., Binder et al.,
1997; Calvert et al., 1997; Celsis et al., 1999; Friedman et al., 1998; Neville et al., 1998;
Rueckert et al., 1994; Small et al., 1996; Wildgruber et al., 1996), positron emission
tomography (PET) studies (e.g., Demonet et al., 1992, 1994; Fiez et al., 1995; Friston et
al., 1991; Hirano et al., 1996, 1997; Mazoyer et al., 1993; McGuire et al., 1996; Petersen
et al., 1988, 1989, 1990; Wise et al., 1991, 1999; Zatorre et al., 1992),
electroencephalogram (EEG) studies (e.g., Martin-Loeches, Schweinberger, and Sommer,
1997; Mills, Coffey-Corina, and Neville, 1993; Neville et al., 1993; van Turennout,
Hagoort, and Brown, 1998), and magnetoencephalogram (MEG) studies (e.g., Numminen
and Curio, 1999; Numminen, Salmelin, and Hari, 1999; Salmelin et al., 1999; Sams et al.,
1991; Szymanski, Rowley, and Roberts, 1999). As these data accumulate, it is becoming
increasingly important to have a modeling framework within which to interpret data from
the various studies. Without such a framework, these important data can seem like a
random set of information points rather than a coherent description of the neural
processes underlying speech.
As described above, our laboratory at Boston University has been developing a neural
network modeling framework that explains a wide range of speech perception and
production phenomena, including perceptual warping in the auditory system, contextual
variability in speech production, motor equivalence, speaking rate effects, coarticulation,
and the acquisition of speaking skills. This modeling framework has been used to
interpret data from a range of behavioral studies (Guenther, 1995; Guenther and Gjaja,
1996; Guenther, Hampson and Johnson, 1998), and new experiments have been
performed to test specific model predictions and refine the models when necessary
(Guenther et al., 1999a; Guenther et al., 1999b).
Because our modeling framework is defined using adaptive neural networks, interpreting
the model's components in terms of brain regions and activations is a relatively
straightforward process. We feel that this fact, in combination with the framework's
success in explaining psychophysical and behavioral data concerning speech perception
and production, makes it ideally suited for interpreting the results of current speechrelated imaging studies and guiding future imaging studies. In the current application, we
propose two fMRI experiments that are designed to contribute to this objective.
By refining our neural modeling framework through experimental tests and modeling
projects, we will move closer to an understanding of the neural processes underlying
speech and language that we believe will prove useful for addressing various speechrelated diseases and injuries. Our model has already been used to interpret data from deaf
individuals who have been given cochlear implants (Perkell et al., in press). In the current
proposal, we propose to further this connection to clinical issues in various ways,
including studies of cerebellar involvement in the speech of normal subjects and ataxic
dysarthrics and the effects of lesions in different brain regions.
II. SPECIFIC AIMS
The primary goal of this research project is the continued development, testing, and
refinement of a comprehensive computational modeling framework addressing the neural
processes underlying speech perception and production. This framework is defined using
adaptive neural networks, allowing comparisons with data from imaging studies of brain
function. The aims of the current two studies is to investigate mechanisms of feedback
and feedforward control of speech movements through the use of fMRI in combination
with perturbations of somatosensory and auditory feedback. We expect these
experiments to provide valuable data regarding the neural processes underlying speech
production and perception. This data will be used to refine our neural model.
III. SUBJECT SELECTION
Inclusion criteria: healthy right-handed male and female adults between the ages of 18
and 50 will be recrutied for this study.
Exclusion criteria: left handedness, native language other than American English, history
of serious head injury (with loss of conciousness), history or current diagnosis of
neurological disorder, current injury to hands or arms that would impede task
performance, pregnancy, MR incompatibility (see attached MR screening sheet); subjects
with a history of epilepsy or other seizure disorder will be exluded from studies involving
visual stimuli.
Subjects will be recruited via advertisements posted at the MGH and the M.I.T. and
Boston University campuses, via electronic mails, advertisements in student newspapers,
and via word of mouth.
IV. SUBJECT ENROLLMENT
We will enroll 34 subjects in a total of two fMRI experiments -- 17 subjects per
experiment. Subjects will be screened over the telephone or in person to ensure that they
meet the basic inclusion-exclusion criteria for the study. On the day of the study, just
prior to scanning, subjects will read and sign the informed consent document detailing the
general purposes and procedures of the experiment, and any questions the subject has will
be answered.
Informed consent will be obtained prior to each experimental session by the Principal
Investigator, Dr. Frank Guenther, or a study co-investigator. The informed consent
clearly states that the subject may choose to terminate the experiment at any time.
V. STUDY PROCEDURES
Subjects will undergo telephone screening to ensure that they meet the basic
inclusion/exclusion criteria for the study. On the day of the study, subjects will give
informed consent, and will be screened again for MR compatibility. This will be
followed immediately by the fMRI scanning session. Some subjects will be asked to
perform psychophysical tests immediately prior to MRI scanning. These tests will
consist of word stem completion tasks that will require subjects to complete a word
presented on a computer monitor, either verbally, or by typing on a keyboard. The tests
are expected to take approximately 1 hour to complete. Each scanning session starts with
the subject lying on the table of the MRI scanner. Blankets and pillows are used to help
insure the comfort of the subject, which is very important for preventing unwanted
movements during the 2-hour scanning session. The subject’s head is immobilized using
foam pads inserted between the subject’s head and the head carriage of the scanner. The
table is then slid into a large magnet with a bore of approximately 1 meter. During the
first fifteen minutes or so of scanning, a conventional high-resolution anatomical scan is
obtained to allow localization of brain structures. After these localizing images are
obtained, functional images are obtained using the high-speed function of the MRI
scanner, which is capable of measuring changes in blood flow that correlate with brain
function. High-speed images are collected during 5 to 10 experimental runs, each lasting
approximately 4 to 6 minutes. During these runs, subjects will be asked to attend to
auditory stimuli, attend to visual stimuli, produce speech, and/or lie silently in the
scanner. Auditory stimuli will be presented via insert headphones (see below) at a volume
deemed comfortable by the subject. If no auditory stimuli are used in an experiment,
earplugs are inserted to protect the subject from the sounds created by the scanner during
imaging. Visual stimuli are projected onto a screen that the subject views through a
mirror. The flashing pattern displayed by the video projector does not present any health
hazards to normal volunteers. Subjects with a history of epilepsy or other seizure disorder
will be excluded from studies involving visual stimuli. Subjects with corrected-to-normal
vision who participate in experiments with visual stimuli will be provided with nonmagnetic corrective glasses, available at the MGH MRI facility. After the high-speed
imaging runs are completed, a few additional conventional images are collected to help
with registering the functional data with the anatomical data. The entire imaging session
lasts approximately 2 hours in addition to any psychophysical testing.
One of the two fMRI experiments involves the use of a pneumatically operated device
that we have developed for perturbing mandibular closing movements. The device
consists of a small, tubular-shaped inelastic balloon that is held in place between the
molar teeth on one side. The balloon is connected via stiff plastic tubing to a small air
cylinder driven by a powerful solenoid. Activation of the solenoid causes inflation of the
balloon to a diameter of about 1 cm at a pressure of 4-5 psi within 100 ms. Under control
of the computer that displays stimuli to the subject and records acoustic and movement
signals, the solenoid can be activated for selected utterances at a predetermined delay
from the onset of the subject's voicing. To avoid giving the subject auditory cues about
the perturbation, the solenoid and air cylinder are located in the MRI control room. The
other fMRI experiment involves the use of a sensorimotor adaptation apparatus that we
have developed to modify the acoustic structure of speech sounds that are fed back to the
subject (with a very short delay) as he or she pronounces simple utterances. Insert
earphones are used, along with a slightly amplified feedback signal to effectively prevent
the subject from hearing his own air-conducted vowel formant structure. Both of these
perturbation devices have been tested and used successfully and safely in the speech
physiology laboratory in the Speech Communication Group, R.L.E., M.I.T. The
possibility of these types of perturbation is addressed in the fMRI consent form.
If, during a scanning session, an abnormality is suspected, an immediate consultation by
the radiologist on duty at Bay 1 (the clinical magnet) will be requested while the subject
is still in the magnet. Additional images will be acquired if deemed necessary by the
radiologist. If clinical follow-up is recommended, the radiologist, not the co-investigator
conducting the research, will convey this to the subject. If no radiologist is available for
immediate consultation, films will be printed of the brain area in question. If the potential
abnormality is detected on the T1-weighted image, an additional T2-weighted scan will
also be acquired. At the earliest opportunity following the research study, a consultation
with Greg Sorensen, MD, or another available radiologist. Under no circumstances will
the potential abnormality be discussed with the subject before a radiologist has been
consulted and the situation has been explained to the subject by a medical professional.
Subjects will be informed that if an abnormality is suspected, a radiologist will be
consulted
VI. BIOSTATISTICAL ANALYSIS
The primary data variables we will analyze are voxel activation values. A control
condition, such as lying quietly or passively observing a blank screen, is employed to
serve as an activation baseline. T-tests are then used to determine which voxels have a
significantly different level of activation in experimental conditions as compared to the
control condition. Regions of interest (ROIs) will be identified using anatomical scans
collected at the beginning of each scanning session. Multivariate analysis of variance
(ANOVA) will be used to determine differences in the percentage of active voxels within
an ROI across conditions, as well as to investigate laterality effects and differences
between ROIs.
From past experience, we believe that approximately 15-17 subjects will be needed to
reach statistical significance in the above-mentioned comparisons for each experiment.
Keeping in mind that scanner data collection problems occur fairly frequently, we believe
that good data from 15-17 subjects can be achieved with 15 scanning sessions per
experiment.
The study will begin on 12/1/2003, and it will end after data collected from all subjects
has been analyzed (by 11/30/2007).
VII. RISKS AND DISCOMFORTS
There are no known or foreseeable risks or side effects associated with conventional MRI
procedures except for those individuals who have electrically, magnetically, or
mechanically activated implants (such as cardiac pacemakers or cochlear implants) or
those who have intracerebral vascular clips. There are no known additional risks
associated with high-speed MRI. Both the conventional and high-speed MRI systems
have been approved by the FDA and will be operated within the operating parameters
reviewed and accepted by the FDA. There are no known risks or discomforts associated
with either of the perturbation devices.
As described above, careful screening for contra-indicators is conducted before a subject
is enrolled in the study. Just prior to entering the scanning suite, subjects will be orally
interviewed again to ensure that they are metal free. Periodically throughout the duration
of the MRI exam, the examiner will confirm with the subject that they are still
comfortable and wish to continue. This "participant status check" will occur after each
series of images is acquired, and any adjustments required to facilitate subject comfort
will be made. All subjects will be provided with mandatory hearing protection in the
form of earplugs, or headphones, for experiments involving auditory stimuli, which will
prevent discomfort due to scanner noise.
VIII. POTENTIAL BENEFITS
Subjects derive no benefit from the procedures except payment. However, risk is
negligible and their participation will contribute very useful information concerning the
mechanisms of speech perception and production. Thus the risk/benefit ratio is
negligible. Subjects will be paid $100 for an experimental session lasting approximately
2 hours plus $10/hour for any testing done immediately prior to scanning..
IX. MONITORING AND QUALITY ASSURANCE
The technical staff of the MGH NMR Center will continually monitor the nature and
quality of the data collection on the 3T magnet system. Modifications to enhance data
quality and statistical power will be performed when appropriate.
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