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CURRENT PROJECTS
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Auditory
Categorization
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Project: Learning
Complex Auditory Categories Through Explicit Feedback (Funded by NSF &
Parmly Research Hearing Institute)
Exciting
new research has promoted a vital sub-field of speech perception research
concerned with describing the function of categories in the development and
maintenance of language-appropriate perception. Recent work has suggested
that at least part of the formation and function of phonetic categories is
a result of general perceptual categorization mechanisms not specific to
speech or language. Thus, there now appears to be opportunity for an
integration of general categorization research with work on first and
second language acquisition. Unfortunately, much of what is known about
perceptual categorization has been derived from examination of categories
that are fundamentally different from phonetic categories. Moreover, it is
difficult to empirically examine influences of categorization using speech
stimuli because it is extraordinarily difficult to determine a detailed
history of experience.
Pilot work by the PIs has suggested the
utility of using complex non-speech sounds in probing the learning
mechanisms that drive auditory categorization. These sounds can be
synthesized to mimic complexities of phonetic categories. Furthermore, the
distributions of stimulus presentation can be theoretically derived to
model aspects of phonetic categories. The experiments described in this
proposal are designed to provide a foundation for understanding the
mechanisms of development and maintenance of complex auditory categories.
Adult listeners will participate in two
different kinds of learning tasks.
In one task, the listener will receive explicit training on
distinguishing two arbitrary categories of sculpted noise. The training sets will be drawn from
carefully controlled distributions.
The listener will be presented the sound and must label the sound by
pressing a labeled button on a response. Feedback about the correct category
will be given. Through collection of accuracy and reaction time measures,
stimulus “goodness” judgments and discrimination data, detailed
descriptions of the response structures will be available along with data
on the development of these structures. In the other learning task,
listeners will be simply exposed to these same distributions of sounds and
subsequent discrimination tasks will determine the extent to which
categorical structure results from this exposure. These data will be
compared to current knowledge about speech sound categories and computational
models of general perceptual categorization.
Several theoretically motivated manipulations
of the training sets will be tested.
In one study, the initial training set will be limited in size and
variance and the full training set will not be presented until some
learning has occurred for the smaller set. This is analogous to an infant
receiving Child-Directed Speech from parents or guardians. In a second study, the training
distributions have a more complex structure that mimics speech input
received from talkers that differ in gender. These manipulations allow one to
provide more detailed tests of models of categorization.
The main goals of this work are
threefold. The first goal is to
provide a detailed database on the formation and structure of complex
auditory categories by humans.
There is a dearth of research in this area and the proposed work
will be useful in developing a taxonomy of auditory learning and testing
extant models of general perceptual categorization based primarily on data
from visual tasks. The second
goal is to compare the resulting structures that arise from these
categorization tasks to structures of speech categories. Determining the role that general
perceptual categorization processes play in first and second language acquisition
is fundamental to the third goal, which is to develop efficient methods of
exposure and training to teach non-native contrasts to second-language
learners. Learning the sound
contrasts for a non-native language is an extremely difficult task. Exposing the mechanisms of complex
category learning could illuminate potential aids to training individuals
to discriminate these complex speech categories. These aids could extend easily to
other complex learning tasks such as musical training, acoustic warning
systems or auditory data displays.
Project: Implicit
Formation of Complex Auditory Categories (Funded by NIH-NIDCD)
The main
goals of this work are threefold. The first goal is to provide a detailed
database of the formation and structure of complex auditory categories.
There is a dearth of research in this area and the proposed work will be
useful in developing a taxonomy of auditory learning and testing extant
models of general perceptual categorization (which have been based
primarily on data from visual tasks). Experiments using explicit and
incidental learning procedures will map the development of categorical
response structures as listeners gain experience with novel stimuli. The
second goal is to compare the resulting structures that arise from these
categorization tasks to structures typical of speech categories such as
categorical perception and the "perceptual magnet" effect. The
third goal is to develop efficient methods of exposure and training to
teach non-native contrasts to second-language learners. Learning the sound
contrasts for a non-native language is an extremely difficult task.
Exposing the mechanisms of complex category learning could illuminate
potential aids to training individuals to discriminate these complex speech
categories. These aids could extend easily to other complex learning tasks
such as musical training, acoustic warning systems or auditory data
displays.
Holt &
Lotto (2003) Lay Language Paper on Statistical Learning of Speech (and
Non-Speech) Categories
Project: Weighting of
Dimensions in Categorization (Nonspeech and Foreign Language Categories)
(Funded by NSF)
One of the challenges facing
someone learning a second language (L2) is to learn a new set of sound
categories. Languages differ in
the acoustic features that define their phonetic categories. In order to become proficient in a
language, the listener must determine the relevant features for the
category contrast and “weight” them properly. For example, the English distinction
between /r/ and /l/ is difficult for native speakers of Japanese, in part,
because it is based on an acoustic feature that is given low weighting by
Japanese listeners. The current
project is a collaboration between several laboratories using multiple
methods to investigate the basic perceptual and cognitive processes that
underlie complex auditory categorization, such as phonetic
categorization.
One
of the goals of the project is to develop efficient and robust L2 training
techniques. In order to
accomplish this, it is important to understand how the general auditory
system deals with variability in the input to create useful categories. With prior NSF support, the PIs have
developed a methodology for training listeners to categorize novel
non-speech sounds that have some of the same complexity as speech
sounds. This approach allows
the researcher to have complete control of the listeners’ experience
and provides a view of category learning as it is happening. In this project, this methodology
will be applied specifically to study the problem of feature determination
and weighting in categorization.
Results from these studies will be analyzed within a Bayesian
statistical decision framework, which provides a means to compute how an
“ideal observer” would perform in the task. Thus, one can determine if a
listener is performing optimally and, if not, discover what biases they may
have in their weighting strategies.
In addition to these non-speech studies, animals (gerbils) will be
trained to learn to identify human speech sound categories by making
appropriate responses. These
animal studies provide an opportunity to use real speech (e.g., productions
of English /l/ and /r/) but to still have complete control over the
listeners’ experience with the sounds. Previous work by the PIs has
demonstrated the usefulness of animal models to elucidate general
perceptual and cognitive processes in speech perception. Based on the results of these
methodologies, training regimens for L2 will be created and tested with
adult participants. Japanese
listeners will be trained on English /l/-/r/ and English listeners will be
trained on a Korean voicing distinction. These techniques may also be useful
for therapy with new users of hearing aids or cochlear implants.
In
addition to the benefits derived from a better understanding of auditory
categorization and improved L2 training techniques, this project also
provides a unique training opportunity for students. The three laboratories involved are
connected to world-class experimental groups with different emphases
(perceptual systems, cognitive neuroscience, audition and communication
disorders). The project will
include substantial interaction in this inter-disciplinary setting for some
excellent young silences. This
includes the support of undergraduates, non-traditional pre-graduate school
students, graduate students and post-docs. These students have many insights
and hypotheses to provide based on their own experiences learning second
languages and the empirical methodologies provide ample opportunity to test
these hypotheses.
Holt & Lotto (2006) Cue
Weighting in Auditory Categorization paper
Project: Tuning Categories
and Speaker Normalization (Funded by NIH-NIDCD)
To respond
adaptively in a variety of situations, organisms form and utilize
perceptual categories or functional equivalence classes. Categories can be
induced from distributions of sensory input experienced across varied but
similar contexts. However, the usefulness of perceptual categories based on
a large corpus of experiences may be limited when the distributional
characteristics of a particular setting differ drastically from the norm.
In these cases, reliance on stable long-term categories may be inefficient
or maladaptive. In order to perform optimally or adaptively, organisms must
dynamically “tune” categories to the regularities of the
current environment. For example, an animal may distinguish friend and foe
by the acoustic patterns of calls. The category distinction may be
established across exposure to the sounds in many listening conditions.
However, if the animal finds itself in an acoustic environment that
deviates from the norm (e.g., a lot of low-frequency noise) then the
categorization decision should be shifted (e.g., increase the low-frequency
energy needed to elicit a response or greater “weighting” of
high-frequency differences).
Another example of
the need for category tuning comes from speech perception. Phonetic
identification of a speech sound based on its acoustic properties can be
considered an example of perceptual categorization. Infants and
second-language (L2) learners form phonetic categories from distributions
of experienced speech sounds (Jusczyk, 1997; Kuhl, 1993; Lotto, 2000).
However, the acoustics of speech are notoriously variable across speakers.
Some of this variability is the result of anatomical and physiological
differences in the instrument of speech production, such as the larger (and
differently-proportioned) vocal tracts of male vs. female speakers or
perturbed articulatory patterns resulting from stroke or dysarthria. Other
variability is the result of linguistic experience such as foreign accent
and dialect, or idiosyncratic patterns of speech. The result of all this
variability is that phonetic categories and decision bounds founded on
experience across a variety of talkers may produce mis-categorization in
application to any particular talker. Categories must be tuned dynamically
to the speech of the current talker either by changing the representation
of the individual sounds or influencing the relevant phonetic category
space. Within the field of speech perception, the accommodation of
talker-specific characteristics is referred to as “talker
normalization” (Johnson & Mullennix, 1997).
The problem of
talker-specific acoustics has been a focus of speech perception research
since the beginning of the field (Potter & Steinberg, 1950). Much of
the investigation of talker normalization has been concentrated on
compensating for anatomical differences among speakers, such as gender
differences. Although differences in vocal tracts present a substantial
challenge to pattern-recognition approaches to speech perception, the
variability arising from these differences is relatively constrained. As a
result, some success has been attained by extracting less-variable ratios
of frequency components (Fujisaki & Kawashima, 1968; Syrdal &
Gopal, 1986; Traunmuller, 1981) or re-scaling speech based on vocal-tract
length (Nordstrom & Lindblom, 1975). A more unconstrained source of
variability is that arising from dialectic (speech patterns of a community)
and idiolectic (speech patterns of an individual) differences between
talkers. For example, when producing the same phonetic segments, a
non-native English speaker with an accent may use a different range of
values across an acoustic dimension than a native speaker. Speakers may
even systematically violate correlations among dimensions ordinarily
present in native speech. Despite vast dialectical differences, it is a
commonplace anecdotal experience that non-native speakers become more
intelligible the more experience one has with their speech. How much
tolerance do listeners have for perturbations from established auditory
categories? What mechanisms are responsible for the adaptive tuning of
category responses?
In a previous
NIH-funded project, the PIs investigated the formation of auditory
categories defined by distributions of novel complex sounds. The goals of
that project were to design methods for studying auditory categorization
and to provide insights into categorization of ecologically-valid stimuli
such as speech sounds. One of the conclusions arising from the studies was
that brief exposure to distributions of sounds can radically shift
categorization of subsequent stimuli. Listeners identify stimuli not just
on the basis of the long-term regularities of the training input but also
on the basis of short-term or “local” regularities. We refer to
this as “tuning” the category. Such tuning indicates that
listeners adapt categories dynamically.
The proposed project uses the stimulus sets
and methods developed in the previous project to examine how auditory
categories become tuned to local distributional information. The results of
this investigation will have clear implications for models of talker
normalization. We have designed a multi-level empirical approach, which
relates a clear link between the basic science questions (i.e., How are
auditory categories adaptively tuned?) and applications of the results
(i.e., How is intelligibility of foreign-accent or articulatory
idiosyncrasies altered by experience with the speaker?). The stimulus sets
range from more ecologically-valid but less controlled (natural and altered
speech) to more controlled but ecologically less-valid (shaped bursts of
noise) with some stimulus sets in the middle of the range (hybrid
non-speech/speech). The non-speech and hybrid stimulus sets provide the
control necessary to probe basic perceptual/cognitive processes of category
formation and tuning, whereas the speech stimuli allow a direct test of the
relevance of these basic findings to a “real-world” perceptual
problem. We have used each of these approaches with success in our past
research. The present project is designed to accomplish three specific
aims; first, to determine the extent of phonetic category tuning for talker
differences arising from dialectic and idiolectic differences, second, to
describe the limits of category response tuning as a function of the
spectral-temporal make-up of the local acoustic context, and finally, to describe the limits of category response tuning
based on the distributional statistics of the local context.
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Auditory Contrasts
& Phonetic Context Effects
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Project:
Psychophysics and Neural Basis of Contrast
Spectral Contrast
Summary
Project: A General
Auditory Explanation for Lexical (i.e., TRACE model) Context Effects
In
1988, Elman and McClelland (1988) presented data suggesting that context
effects can be triggered by “illusory phonemes.” In their study, listeners were asked
to participate in a phoneme identification task whereby context words
(e.g., “foolish” and “Christmas”) were followed by
a target sound (an ambiguous /t/-/k/ or /d/-/g/). Manipulations were made to the final
sound of the context word to create an intermediate
“sh”/”s” sound. The TRACE model was then used to
accurately predict listeners’ phoneme identification shifts, through
the use of top-down lexical influences. We, however, believe there is a
simpler explanation to these findings, one that relies on general auditory
contrast effects like those obtained by Lotto and Kluender (1998). This study will attempt to explain
Elman and McClelland’s classic findings in terms of spectral
contrast, based on the acoustics of the context word and target sound.
Elman &
McClelland (1988) paper
Project: Phonetic
Context Effects in Listeners with Cochlear Implants (with Dr. Radhika
Aravamudhan)
Perception of phonemes change as a function
of the characteristics of preceding or following phonemes. These changes in
percept are referred to as phonetic
context effects. Experimentally, this effect is measured in terms of
a shift in phoneme identification (ID) boundary or a change in the
percentage of phoneme ID that occurs when the same target stimuli are presented with
different context
sounds. Previous research (e.g.,
Lotto & Kluender, 1998) has demonstrated that many of these context
effects are the result of interactions between the spectral patterns of the
context and target sounds. It
is likely that if the spectral representations of speech sounds are changed
(as happens with cochlear implants), phonetic context effects will be
affected.
Two
types of contexts are used in this study; spectral based and temporal based
context. In the Spectral-based
context effects experiments, listeners identify a consonant or vowel
that is preceded by phonemes that differ in their spectral pattern. NH listeners show a shift in
responses that is predicted by the spectral relations of target and context
(contrastive). In the temporal
based context effect experiments, listeners identify a target
consonant distinction that is temporal (e.g., /b/ vs. /w/) that is followed
by a context vowel that varies in duration. NH listeners show a contrastive
shift in target identification based on vowel duration.
As
predicted, CI listeners showed normal temporal context effects but not
spectral context effects. This is
probably because of the substantial deviation of spectral patterns but
preserved duration patterns in CI input. The lack of normal spectral
context effects may have practical implications for situations in which
there is substantial coarticulation (e.g., non-laboratory speech) or talker
variability (e.g., switching between multiple speakers). Thus, in order to
understand how these poor spectral representations in cochlear implants can
affect the percept of speech sounds, further simulations experiments are
being conducted with normal hearing listeners. Simulations are done using
both Shannon Speech and CI-Simulation programs.
Parts
of this work have been presented at The Acoustical Society of America
(2004, San Diego), the Symposium on Cochlear
Implants in Children (2005, Dallas), and
most recently, at the Conference on Implantable Auditory Prosthesis (2005, Asilomar, CA).
Aravamudhan
& Lotto poster on Phonetic Context Effects for CI Users
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Hearing Disorders
& Speech
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Project: Effects of
Communication Mode and Inflection on CI-user Speech (Funded by NIH-NIDCD)
The
goal of this study was to determine if the acoustics of speech produced by
cochlear implant (CI) children could be affected by variables of the
elicitation task. Two variables
were examined: communication mode and inflection of a sign model. Based on previous findings with NH
adults (Schiavetti,
Whitehead, Metz, & Moore, 1999; Schiavetti, Whitehead, Metz, Whitehead,
& Mignerey, 1996; Whitehead, Schiavetti, Metz, & Farrell, 1999;
Whitehead, Schiavetti, Whitehead, & Metz, 1995), we predicted that
spoken word, vowel and VOT duration would be lengthened during simultaneous
communication (SC) compared to speech alone (SA) and that these
perturbations would be greatest for children with limited speech
skills. These predictions were
not supported by the data.
Communication mode did not significantly impact any of these
temporal measures and there was no interaction with PBK grouping of the
children. We also proposed that
temporal disturbances would be more substantial for signs with multiple
movements (Whitehead,
Schiavetti, Whitehead, & Metz, 1997), but this was also
not borne out in the data.
McCleary,
Ide Helvie, Lotto, Carney & Higgins (2007) paper
Project: Strategies
used to Increase Speech Clarity by Normal-Hearing Children (Funded by
NIH-NIDCD)
It
is common among clinicians to ask children to produce their “best
speech” during intervention.
However, it is unclear that children know how to make their speech
clearer. The strategies used by
children with and without hearing loss have implications for maximizing
intelligibility and for understanding the development of communication
competency. As a first step
toward this understanding, children (7 to 12 years of age) with normal
hearing were asked to read ten simple sentences. They were told that they testing a
new computer program designed to recognize speech. There was, in fact, no recognition
program and each child received the same “output”
feedback. After providing
“normal” speech to allow the program to “get used to
their voices”, they subsequently produced their “best”
and then “very best, very clearest” speech in order to see how
accurate the recognition program could be. Acoustic analyses (intensity,
fundamental and first two formant frequencies for all vowels, as well as
sentence, vowel, and VOT durations) were performed on recorded waveforms
from each repetition in order to determine what the children were varying
to comply with “best speech” instructions. The results demonstrate large
individual differences in strategies and persistent gender differences.
148th
ASA San Diego Clarity poster
Project: Creating an
Auditory Skills Therapy CD-ROM for Children with Auditory Processing
Disorder (with Dr. Gail Chermak, Washington
State University
& Dr. Frank Musiek, University
of Connecticut)
Recent
studies indicate that auditory training is a useful intervention tool,
particularly for those with language impairments and auditory processing
disorder (APD). Because of this
clinical need, I have been working with Dr. Gail Chermak (Washington State
University) and Dr. Frank Musiek (University of Connecticut) to develop a CD-ROM
that will be targeted towards these special populations. The training CD will contain a
number of basic auditory exercises such as intensity training tasks,
frequency training tasks, and temporal training tasks, etc. The CD is being designed to be
implemented in both clinical and home settings in a kid-friendly format
(every task is embedded into a game format).
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Experimental
Phonetics
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Project: Auditory
Enhancement in Female Speech (Funded by NIH-NIDCD)
One
of the more notable differences between male and female speech is that
females have a higher fundamental frequency (f0) than males (this is because
female vocal tracts are, on average, 15% shorter than male vocal
tracts). Signals with higher
f0s are represented by fewer harmonics and therefore, should result in
intelligibility problems. That
is, vowels produced by females (with their high f0) are under-sampled
relative to vowels produced by males.
Basic acoustic manipulations demonstrate this idea; as you raise a
vowel in f0, identification scores drop. It turns out; however, that female
speech is actually more
intelligible than male speech.
This means that females must do something to compensate for their
high f0’s.
A
basic observation of English-speaking females is that they use breathy
phonation more often then males.
A popular theory explains this as “If a woman can manage to
sound as though she is sexually aroused, she may be regarded as more
desirable or with greater approbation by a male interlocutor than if she
speaks with an ordinary modal voice” (Bladon & Henton,
1985). This explanation is
clearly flawed; however, in that it can’t explain why prepubescent
boys also use breathy speech (certainly they aren’t trying to sound
sexually excited!). Acoustical
analysis of breathy voice reveals an increase in the fundamental component,
an increase in spectral tilt, and an increase in noise at higher
frequencies. It seems plausible
that the noise from breathiness is filtered by the vocal tract, which would
result in a clearer spectral envelope, leading to better intelligibility. I propose that females use breathy
phonation contrastively in order to make vowels more distinctive (i.e.,
ideally, females should make high tense vowels breathy but not the lax
counterparts). Simply put, I
believe that breathiness is utilized to compensate for the challenges of
high f0 and not a result of social pressure.
Project: Korean
Phonetics (with Mi-Ran Cho Kim)
In
the past, Dr. Kim and I have investigated the acoustic characteristics of
Korean stops produced by non-heritage learners as well as the manner
contrast in inter-vocalic Korean stops. One of our more recent studies
investigated the acoustic characteristics of the Korean approximates [l,
flap, w, j]. Even though both
Korean and English contain all four approximant sounds in their phonetic
inventory, the difference of the phonemic realization of each sound and the
different phonetic context of each sound in the two languages may cause
difficulties for second language learners (Ingram & Park, 1998). For Korean speakers, for example, it
is very difficult to produce the light lateral [l] in word-initial
position. It is also difficult
for Korean speakers to produce [w] before [υ],
as in ‘wolf, wood’.
For English speakers, it is difficult to produce the flap
word-initially and the light lateral [l] word-finally. This study provided more precise
acoustic phonetic descriptions of the Korean approximants in different
phonetic contexts. For the
glides, we limited our attention to the syllables [wi] and [ju] in order to
make the findings compatible to the previous measures, which are mostly
from English. The close
comparisons of Korean and English were expected to provide (1) better
understanding of the language learners’ difficulty and (2) more
efficient teaching techniques in language teaching situation. Recent detailed acoustic comparisons
of English liquids with Japanese phonemes have yielded insights into the
task of the second language learner (Lotto, Sato & Diehl, 2004). This project is part of an effort to
extend this methodology to the teaching of Korean and English.
Kim & Lotto (2004) Acoustic Measurements of
Korean Approximates paper
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Other Collaborations
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Project: Neurocognitive
Processes Underlying Perception of Spoken Language: An Event-Related
Desynchronization Brain Mapping Study (with Dr. John Caviness at Mayo
Clinic and Dr. Julie Liss at Arizona
State University,
Funded by Mayo Clinic Scottsdale)
Whereas there has been progress in describing
the representation of the speech signal in the auditory periphery and in
delineating the cortical regions associated with semantic processing of
comprehended speech, there is little known about the processes involved in
the mapping of the auditory signal to word or semantic representations.
This gap in our knowledge has at least two sources. The first is the
artificial boundaries of scientific inquiry. The study of the
representation of sounds at the auditory periphery and midbrain
traditionally has been the realm of audiology and the psychology of
perception, while language comprehension has been the purview of
psycholinguistics and speech-language pathology. That is to say, those who
work at the auditory “periphery” and those concerned with
“central” or “cognitive” issues rarely intersect in
their research pursuits. As a result, it is virtually unknown how the
peripheral representation of the speech signal eventually becomes
recognized as words. These “intermediate” steps have direct
bearing on disorders associated with the neural processes involved in
transforming the auditory representation into meaningful representations,
including autism, aphasia, central auditory processing disorders, and
persons with cochlear implants. We also need to understand these steps to
define how healthy listeners come to perceive speech that is different from
their own, either from dialect or from disease/disorder.
A second reason for
the gap in our understanding of the neurocognitive underpinnings of spoken
language perception is because of the limitations in brain imaging
technology. A recent
flurry of studies has used functional neuroimaging to delineate the
sound-to-meaning pathways in the auditory association areas of the temporal
lobes (e.g., Hickok & Poeppel, 2004; Praghakaran et al., 2006). Despite
the abundance of detailed anatomical data, the temporal sequence of
activation of these cortical structures remains to be established. The main
reason for the lack of temporal data is that the most powerful functional
imaging technologies (i.e., fMRI and PET) have poor temporal resolution. In
fact, these imaging techniques yield rather gestalt snapshots of brain activation patterns associated with some
given speech stimulus. This means that the pictures portray all activation
associated with the perception, rather than just the processes particularly
associated with the mapping from auditory representation to semantic
representation. Scott and colleagues (2006) examined PET data from listeners
presented with intelligible or unintelligible speech. Unfortunately for
interpretation, when listeners hear intelligible speech, brain activation
is present not only in the regions involved in spoken language perception,
but also the regions involved in auditory representation and in the
conceptual representation of the meaning of the speech. What we are
interested in are those processes that MAKE the speech intelligible,
especially if it is degraded in some form. That is, we need to be able to
see which regions are active immediately prior to the comprehension of the
speech (spoken language perception) and segregate those from regions that
are active subsequent to perception (e.g., activation related to conceptual
processing). This difference has special relevance to clinical issues as it
addresses what cortical processes cause and what ones simply result from
disordered communication. In order to accomplish this goal, we need
temporal resolution capabilities that are beyond PET and fMRI techniques
alone.
The project described in this proposal is
designed to overcome these two barriers to understanding spoken language
processing by 1) bringing together researchers from both sides of the
“divide” who have successful R01-funded programs that examine
complementary aspects of spoken language perception and by 2) utilizing
novel high-density EEG capabilities that will provide the spatial and
temporal resolution necessary to segregate and examine the processes
involved in spoken language perception. In addition, we propose to 3)
develop a larger collaborative environment across Arizona to foster discussion that can
ameliorate the artificial boundaries that plague auditory/speech
neuroscience. The overarching goal of these efforts is to create a
sustainable federally-funded research program that melds the work of
researchers at ASU, U of A and Mayo.
Project: Tiger
Vocalization (with Drs. Ed Walsh and JoAnn McGee, Boys Town
National Research
Hospital)
While
at Boys Town National
Research Hospital,
I collaborated with Dr. Edward Walsh and Dr. Joann McGee on a study aimed
to describe the hearing capabilities of tigers and the acoustic properties
of their calls. Audiograms indicate that the tiger’s auditory
system is highly sensitive to low frequency sounds and possibly infrasonic
sounds. We are in the process of analyzing the acoustic properties of
tiger vocalizations to determine whether production data are consistent
with the perceptual findings. Low frequency sounds travel farther and
would be adaptive to the solitary tiger who wished to maintain hunting
territories and communicate with possible mates. Through this
research, it may be possibly to identify individual tigers based on their
unique vocalizations. Tiger identification through acoustic measures
would be useful in the monitoring of tigers in their natural habitat.
Walsh et. al
(2003) ASA Lay Language paper
NewScientist.com
Tiger article
Project: Effects of
Hearing Aid Characteristics on Child Language Development (with Dr. Pat
Stelmachowicz, Boys
Town National
Research Hospital,
Funded by NIH-NIDCD)
The overall goal of this
project is to explore ways in which to enhance auditory access and auditory
perceptual abilities in young children with hearing loss. In the previous cycle of this grant,
the PIs focused on the optimization of amplification characteristics in
these children. The results of
these studies suggest that, in order to optimize speech and language
development, hearing-impaired infants and children require different
amplification characteristics (e.g., broader bandwidths, greater
audibility) than adults with similar hearing losses. In addition, recent studies have
shown that early amplification alone is not sufficient to ensure normal
speech and language development (Mayne et al., 2000a, 2000b; Moeller, 2000,
Stelmachowicz et al., in press; Lederberg & Spencer, 2001). In the current proposal, the
PIs take the position that
these persistent delays are the result of reduced auditory access and
limited auditory experiences, despite early amplification and
intervention. Auditory access
to speech is limited by the hearing loss (e.g., reduced audibility, poor
frequency and/or temporal resolution) and an inability to adequately
compensate for the consequences of hearing loss with amplification. Likewise, the number and quality of
auditory experiences is influenced by many factors (e.g., distance, noise,
reverberation, and inability to use linguistic context. Two potential solutions to this
problem are being investigated.
First, we are exploring the influence of selected forms of advanced
signal processing on speech perception, speech production, novel-word
learning, and ease of listening in older with hearing loss. Second, we are examining whether the
quality and quantity of auditory experiences can be enhanced in order to
accelerate auditory skill development and adaptation to new
signal-processing algorithms.
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