We examined the longitudinal development of the cortical auditory evoked potential (CAEP) in 21 c... more We examined the longitudinal development of the cortical auditory evoked potential (CAEP) in 21 children who were Wtted with unilateral cochlear implants and in two children who were Wtted with bilateral cochlear implants either before age 3.5 years or after age 7 years. The age cut-oVs (<3.5 years for early-implanted and >7 years for late-implanted) were based on the sensitive period for central auditory development described in [Ear Hear. 23 (6), 532.] Our results showed a fundamentally diVerent pattern of development of CAEP morphology and P1 cortical response latency for early-and late-implanted children. Early-implanted children and one child who received bilateral implants by age 3.5 years showed rapid development in CAEP waveform morphology and P1 latency. Late-implanted children showed aberrant waveform morphology and signiWcantly slower decreases in P1 latency postimplantation. In the case of a child who received his Wrst implant by age 3.5 years and his second implant after age 7 years, CAEP responses elicited by the second implant were similar to late-implanted children. Our results are consistent with animal models of central auditory development after implantation and conWrm the presence of a relatively brief sensitive period for central auditory development in young children.
Objective: To compare two methods of minimizing cochlear implant artifact in cortical auditory ev... more Objective: To compare two methods of minimizing cochlear implant artifact in cortical auditory evoked potential (CAEP) recordings. Methods: Two experiments were conducted. In the first, we assessed the use of independent component analysis (ICA) as a pre-processing filter. In the second, we explored the use of an optimized differential reference (ODR) for minimizing artifacts. Results: Both ICA and the ODR can minimize the artifact and allow measurement of CAEP responses. Conclusions: When using a large number of recording electrodes ICA can be used to minimize the implant artifact. When using a single electrode montage an optimized differential reference is adequate to minimize the artifact. Significance: The use of an optimized differential reference could allow cortical evoked potentials to be used in routine clinical assessment of auditory pathway development in children and adults fit with cochlear implants.
Journal of The American Academy of Audiology, 2005
We used the latency of the P1 cortical auditory-evoked potential (CAEP) as a bio-marker of the de... more We used the latency of the P1 cortical auditory-evoked potential (CAEP) as a bio-marker of the development of central auditory pathways in three children who received intervention through hearing aids and/or cochlear implants. Our goal was to examine the clinical feasibility of using the latency of the P1 CAEP as an objective tool to evaluate whether acoustic amplification for hearingimpaired children has provided sufficient stimulation for normal development of central auditory pathways. If clinicians have such a marker, then they can more confidently make a decision about whether to provide a child with a cochlear implant following an appropriate hearing-aid trial. Using the same marker, clinicians will also be able to monitor the maturation of central auditory pathways once electrical stimulation is initiated.
AbstractCurrently researchers interested in developing new signal processing algorithms for comm... more AbstractCurrently researchers interested in developing new signal processing algorithms for commercially available cochlear implants must rely on coding these algorithms in low-level assembly language. We propose a Personal Digital Assistant (PDA) based research platform for ...
Journal of The Acoustical Society of America, 2000
... depending on whether that contrast constituted a phonemically relevant change in the ... perc... more ... depending on whether that contrast constituted a phonemically relevant change in the ... perception: Exposure to an experience with a first language, Applied Psycholinguistics ... Electrophysiologicalcorrelates of categorical phoneme perception in adults, NeuroReport 8, 919924 ...
Journal of The Acoustical Society of America, 1999
The goal of this study was to examine the neural encoding of voice-onset time distinctions that i... more The goal of this study was to examine the neural encoding of voice-onset time distinctions that indicate the phonetic categories /da/ and /ta/ for human listeners. Cortical Auditory Evoked Potentials ͑CAEP͒ were measured in conjunction with behavioral perception of a /da/-/ta/ continuum. Sixteen subjects participated in identification and discrimination experiments. A sharp category boundary was revealed between /da/ and /ta/ around the same location for all listeners. Subjects' discrimination of a VOT change of equal magnitude was significantly more accurate across the /da/-/ta/ categories than within the /ta/ category. Neurophysiologic correlates of VOT encoding were investigated using the N1 CAEP which reflects sensory encoding of stimulus features and the MMN CAEP which reflects sensory discrimination. The MMN elicited by the across-category pair was larger and more robust than the MMN which occurred in response to the within-category pair. Distinct changes in N1 morphology were related to VOT encoding. For stimuli that were behaviorally identified as /da/, a single negativity ͑N1͒ was apparent; however, for stimuli identified as /ta/, two distinct negativities ͑N1 and N1Ј) were apparent. Thus the enhanced MMN responses and the morphological discontinuity in N1 morphology observed in the region of the /da/-/ta/ phonetic boundary appear to provide neurophysiologic correlates of categorical perception for VOT.
Objective: The aim of the present experiment was to assess the consequences of cochlear implantat... more Objective: The aim of the present experiment was to assess the consequences of cochlear implantation at different ages on the development of the human central auditory system. Design: Our measure of the maturity of central auditory pathways was the latency of the P1 cortical auditory evoked potential. Because P1 latencies vary as a function of chronological age, they can be used to infer the maturational status of auditory pathways in congenitally deafened children who regain hearing after being fit with a cochlear implant. We examined the development of P1 response latencies in 104 congenitally deaf children who had been fit with cochlear implants at ages ranging from 1.3 yr to 17.5 yr and three congenitally deaf adults. The independent variable was the duration of deafness before cochlear implantation. The dependent variable was the latency of the P1 cortical auditory evoked potential.
The subject of this case report is an 18-year-old woman with grossly abnormal auditory brain stem... more The subject of this case report is an 18-year-old woman with grossly abnormal auditory brain stem response (ABR), normal peripheral hearing, and specific behavioral auditory processing deficits. Auditory middle latency responses (MLRs) and cortical potentials N1, P2, and P300 were intact. The mismatch negativity (MMN) was normal in response to certain synthesized speech stimuli and impaired to others--consistent with her behavioral discrimination of these stimuli. Behavioral tests of auditory processing were consistent with auditory brain stem dysfunction. A neuropsychological evaluation revealed normal intellectual and academic performance. The subject was in her first year of college at the time of the evaluation. This case study is important because: (1) Although there have been several reports of absent/abnormal ABR with preserved peripheral hearing and deficits in auditory processing, little is known about the specific nature of the auditory deficits experienced by these individuals. Such information may be valuable to the clinical management of patients with this constellation of findings. (2) Of interest is the information that the mismatch negativity (MMN) cortical event-related potential can bring to the evaluation of patients with auditory processing deficits. The MMN reflects central auditory processing of small acoustic differences and may provide an objective measure of auditory discrimination. (3) From a theorectical standpoint, a patient with neural deficits affecting specific components of the auditory pathway provides insight into the relationship between evoked potentials and physiological mechanisms of auditory processing. How do various components of the auditory pathway contribute to speech discrimination? How might evoked potentials reflect the processes underlying the neural coding of specific features of speech stimuli such as timing and spectral cues?
Journal of The Acoustical Society of America, 2000
Auditory evoked potential ͑AEP͒ correlates of the neural representation of stimuli along a /ga/-/... more Auditory evoked potential ͑AEP͒ correlates of the neural representation of stimuli along a /ga/-/ka/ and a /ba/-/pa/ continuum were examined to determine whether the voice-onset time ͑VOT͒-related change in the N1 onset response from a single to double-peaked component is a reliable indicator of the perception of voiced and voiceless sounds. Behavioral identification results from ten subjects revealed a mean category boundary at a VOT of 46 ms for the /ga/-/ka/ continuum and at a VOT of 27.5 ms for the /ba/-/pa/ continuum. In the same subjects, electrophysiologic recordings revealed that a single N1 component was seen for stimuli with VOTs of 30 ms and less, and two components ͑N1Ј and N1͒ were seen for stimuli with VOTs of 40 ms and more for both continua. That is, the change in N1 morphology ͑from single to double-peaked͒ coincided with the change in perception from voiced to voiceless for stimuli from the /ba/-/pa/ continuum, but not for stimuli from the /ga/-/ka/ continuum. The results of this study show that N1 morphology does not reliably predict phonetic identification of stimuli varying in VOT. These findings also suggest that the previously reported appearance of a ''double-peak'' onset response in aggregate recordings from the auditory cortex does not indicate a cortical correlate of the perception of voicelessness.
Journal of The Acoustical Society of America, 1998
The goals of this study were ͑i͒ to assess the replicability of the ''perceptual magnet effect'' ... more The goals of this study were ͑i͒ to assess the replicability of the ''perceptual magnet effect'' ͓Iverson and Kuhl, J. Acoust. Soc. Am. 97͑1͒, 553-561 ͑1995͔͒ and ͑ii͒ to investigate neurophysiologic processes underlying the perceptual magnet effect by using the mismatch negativity ͑MMN͒ auditory evoked potential. A stimulus continuum from /i/ to /e/ was synthesized by varying F 1 and F 2 in equal mel steps. Ten adult subjects identified and rated the goodness of the stimuli. Results revealed that the prototype was the stimulus with the lowest F 1 and highest F 2 values and the nonprototype stimulus was close to the category boundary. Subjects discriminated stimulus pairs differing in equal mel steps. The results indicated that discrimination accuracy was not significantly different in the prototype and the nonprototype condition. That is, no perceptual magnet effect was observed. The MMN evoked potential ͑a preattentive, neurophysiologic index of auditory discrimination͒ revealed that despite equal mel differences between the stimulus pairs the MMN was largest for the prototype pair ͑i.e., the pair that had the lowest F 1 and highest F 2 values͒. Therefore the MMN appears to be sensitive to within category acoustic differences. Taken together, the behavioral and electrophysiologic results indicate that discrimination of stimulus pairs near a prototype is based on the auditory structure of the stimulus pairs.
The aim of our research was to estimate the time course of development and plasticity of the huma... more The aim of our research was to estimate the time course of development and plasticity of the human central auditory pathways following cochlear implantation. We recorded cortical auditoryevoked potentials in 3-year-old congenitally deaf children after they were ¢tted with cochlear implants. Immediately after implantation cortical response latencies resembled those of normal-hearing newborns. Over the next few months, the cortical evoked responses showed rapid changes in morphology and latency that resulted in age-appropriate latencies by 8 months after implantation. Overall, the development of cortical response latencies for the implanted children was more rapid than for their normalhearing age-matched peers. Our results demonstrate a high degree of central auditory system plasticity during early human development.NeuroReport13:1365^1368
Objective: This study examined morphological changes in the cortical auditory evoked potential (C... more Objective: This study examined morphological changes in the cortical auditory evoked potential (CAEP) waveform as a function of varying stimulation rate. Stimuli were presented in a paradigm which indirectly assesses the refractory properties of the underlying neuronal generators.
The mismatch negativity (MMN) is a passively elicited event-related potential that is extremely s... more The mismatch negativity (MMN) is a passively elicited event-related potential that is extremely sensitive to acoustic stimulus properties. The MMN was characterized in normal adults and school-age children in response to speech stimuli differing minimally in the onset frequency of the second and third formant transitions. The speech-evoked MMN consists of a negative waveform at about 230 msec that occurs in response to the deviant stimulus when it is presented in an oddball paradigm. It is absent in response to that same stimulus when presented alone. The MMN was clearly present in all adults and children tested. Using the procedures developed in this study, this event-related potential was found to be robust enough in individual subjects to be considered a potential clinical measure for assessing central auditory function in school-age children and adults.
Electroencephalography and Clinical Neurophysiology/evoked Potentials Section, 1997
Normal maturation and functioning of the central auditory system affects the development of speec... more Normal maturation and functioning of the central auditory system affects the development of speech perception and oral language capabilities. This study examined maturation of central auditory pathways as reflected by age-related changes in the P1/N1 components of the auditory evoked potential (AEP). A synthesized consonant-vowel syllable (ba) was used to elicit cortical AEPs in 86 normal children ranging in age from 6 to 15 years and ten normal adults. Distinct age-related changes were observed in the morphology of the AEP waveform. The adult response consists of a prominent negativity (N1) at about 100 ms, preceded by a smaller P1 component at about 50 ms. In contrast, the child response is characterized by a large P1 response at about 100 ms. This wave decreases significantly in latency and amplitude up to about 20 years of age. In children, P1 is followed by a broad negativity at about 200 ms which we term N1b. Many subjects (especially older children) also show an earlier negativity (N1a). Both N1a and N1b latencies decrease significantly with age. Amplitudes of N1a and N1b do not show significant age-related changes. All children have the N1b; however, the frequency of occurrence of N1a increases with age. Data indicate that the child P1 develops systematically into the adult response; however, the relationship of N1a and N1b to the adult N1 is unclear. These results indicate that maturational changes in the central auditory system are complex and extend well into the second decade of life.
The mismatch negativity (MMN) is an automatic cortical evoked potential that signifies the brain&... more The mismatch negativity (MMN) is an automatic cortical evoked potential that signifies the brain&#39;s detection of acoustic change. In other words, the MMN reflects the neurophysiologic processes that underlie auditory discrimination. As such, the MMN provides an objective tool for evaluating central auditory mechanisms involved in speech perception. We are using the MMN to study the central auditory processes that encode acoustic changes important for speech perception in 1) normal-hearing adults and children, 2) individuals with impaired auditory systems (including persons with learning disabilities, attention deficit disorders, cochlear implants), and 3) an animal model. Specifically, we have demonstrated that the MMN provides information about the central processing of fine acoustic differences, the neuroanatomic pathways that encode acoustic change, central auditory processing in the presence of peripheral hearing deficits, and central auditory system plasticity. In addition, we have considered methodological challenges associated with measuring the MMN in individual subjects. Several methodological issues--including appropriate stimuli, stimulus presentation variables, the recording protocol and environment, and validation of the MMN in individuals--are discussed.
Journal of Urban Health-bulletin of The New York Academy of Medicine, 2002
This article presents information on pregnant women with incident blood lead levels (BLLs) of 20 ... more This article presents information on pregnant women with incident blood lead levels (BLLs) of 20 μg per deciliter or greater as reported to the New York City Department of Health between September 1996 and June 1999 (n=33). Almost half of the women were diagnosed during their third trimester of pregnancy, often at their first prenatal visit. The median BLLs at incidence and at last report among women who were retested were 25 and 15 γ/dL, respectively, a 40% decline. The median incident BLL among newborns (n=25) was 12 μg/dL. The BLLs were inversely associated with maternal age and length of time in the United States and directly associated with gestational age and pica behavior. Cases were more than twice as likely to be foreign-born women than all women who gave birth in New York City. Prenatal care facilities employing a policy of universal blood lead testing of all pregnant women at the time of their first visit reported disproportionate numbers of cases, accounting for 77% of cases yet only 11% of all births citywide. The findings suggest that (1) the promulgation of recent rules and guidelines for lead risk assessment and screening among pregnant women appears to have been effective in identifying cases that might not have otherwise come to light; (2) case management and environmental interventions were initiated promptly; (3) cases experienced, on average, significant BLL reductions over time; and (4) there is a need for additional public health interventions for pregnant women in urban, multicultural centers. While the data suggest that universal screening may increase case finding among high-risk, immigrant populations, further studies and surveillance are needed to determine systematically the most effective approach.
We examined the longitudinal development of the cortical auditory evoked potential (CAEP) in 21 c... more We examined the longitudinal development of the cortical auditory evoked potential (CAEP) in 21 children who were Wtted with unilateral cochlear implants and in two children who were Wtted with bilateral cochlear implants either before age 3.5 years or after age 7 years. The age cut-oVs (<3.5 years for early-implanted and >7 years for late-implanted) were based on the sensitive period for central auditory development described in [Ear Hear. 23 (6), 532.] Our results showed a fundamentally diVerent pattern of development of CAEP morphology and P1 cortical response latency for early-and late-implanted children. Early-implanted children and one child who received bilateral implants by age 3.5 years showed rapid development in CAEP waveform morphology and P1 latency. Late-implanted children showed aberrant waveform morphology and signiWcantly slower decreases in P1 latency postimplantation. In the case of a child who received his Wrst implant by age 3.5 years and his second implant after age 7 years, CAEP responses elicited by the second implant were similar to late-implanted children. Our results are consistent with animal models of central auditory development after implantation and conWrm the presence of a relatively brief sensitive period for central auditory development in young children.
Objective: To compare two methods of minimizing cochlear implant artifact in cortical auditory ev... more Objective: To compare two methods of minimizing cochlear implant artifact in cortical auditory evoked potential (CAEP) recordings. Methods: Two experiments were conducted. In the first, we assessed the use of independent component analysis (ICA) as a pre-processing filter. In the second, we explored the use of an optimized differential reference (ODR) for minimizing artifacts. Results: Both ICA and the ODR can minimize the artifact and allow measurement of CAEP responses. Conclusions: When using a large number of recording electrodes ICA can be used to minimize the implant artifact. When using a single electrode montage an optimized differential reference is adequate to minimize the artifact. Significance: The use of an optimized differential reference could allow cortical evoked potentials to be used in routine clinical assessment of auditory pathway development in children and adults fit with cochlear implants.
Journal of The American Academy of Audiology, 2005
We used the latency of the P1 cortical auditory-evoked potential (CAEP) as a bio-marker of the de... more We used the latency of the P1 cortical auditory-evoked potential (CAEP) as a bio-marker of the development of central auditory pathways in three children who received intervention through hearing aids and/or cochlear implants. Our goal was to examine the clinical feasibility of using the latency of the P1 CAEP as an objective tool to evaluate whether acoustic amplification for hearingimpaired children has provided sufficient stimulation for normal development of central auditory pathways. If clinicians have such a marker, then they can more confidently make a decision about whether to provide a child with a cochlear implant following an appropriate hearing-aid trial. Using the same marker, clinicians will also be able to monitor the maturation of central auditory pathways once electrical stimulation is initiated.
AbstractCurrently researchers interested in developing new signal processing algorithms for comm... more AbstractCurrently researchers interested in developing new signal processing algorithms for commercially available cochlear implants must rely on coding these algorithms in low-level assembly language. We propose a Personal Digital Assistant (PDA) based research platform for ...
Journal of The Acoustical Society of America, 2000
... depending on whether that contrast constituted a phonemically relevant change in the ... perc... more ... depending on whether that contrast constituted a phonemically relevant change in the ... perception: Exposure to an experience with a first language, Applied Psycholinguistics ... Electrophysiologicalcorrelates of categorical phoneme perception in adults, NeuroReport 8, 919924 ...
Journal of The Acoustical Society of America, 1999
The goal of this study was to examine the neural encoding of voice-onset time distinctions that i... more The goal of this study was to examine the neural encoding of voice-onset time distinctions that indicate the phonetic categories /da/ and /ta/ for human listeners. Cortical Auditory Evoked Potentials ͑CAEP͒ were measured in conjunction with behavioral perception of a /da/-/ta/ continuum. Sixteen subjects participated in identification and discrimination experiments. A sharp category boundary was revealed between /da/ and /ta/ around the same location for all listeners. Subjects' discrimination of a VOT change of equal magnitude was significantly more accurate across the /da/-/ta/ categories than within the /ta/ category. Neurophysiologic correlates of VOT encoding were investigated using the N1 CAEP which reflects sensory encoding of stimulus features and the MMN CAEP which reflects sensory discrimination. The MMN elicited by the across-category pair was larger and more robust than the MMN which occurred in response to the within-category pair. Distinct changes in N1 morphology were related to VOT encoding. For stimuli that were behaviorally identified as /da/, a single negativity ͑N1͒ was apparent; however, for stimuli identified as /ta/, two distinct negativities ͑N1 and N1Ј) were apparent. Thus the enhanced MMN responses and the morphological discontinuity in N1 morphology observed in the region of the /da/-/ta/ phonetic boundary appear to provide neurophysiologic correlates of categorical perception for VOT.
Objective: The aim of the present experiment was to assess the consequences of cochlear implantat... more Objective: The aim of the present experiment was to assess the consequences of cochlear implantation at different ages on the development of the human central auditory system. Design: Our measure of the maturity of central auditory pathways was the latency of the P1 cortical auditory evoked potential. Because P1 latencies vary as a function of chronological age, they can be used to infer the maturational status of auditory pathways in congenitally deafened children who regain hearing after being fit with a cochlear implant. We examined the development of P1 response latencies in 104 congenitally deaf children who had been fit with cochlear implants at ages ranging from 1.3 yr to 17.5 yr and three congenitally deaf adults. The independent variable was the duration of deafness before cochlear implantation. The dependent variable was the latency of the P1 cortical auditory evoked potential.
The subject of this case report is an 18-year-old woman with grossly abnormal auditory brain stem... more The subject of this case report is an 18-year-old woman with grossly abnormal auditory brain stem response (ABR), normal peripheral hearing, and specific behavioral auditory processing deficits. Auditory middle latency responses (MLRs) and cortical potentials N1, P2, and P300 were intact. The mismatch negativity (MMN) was normal in response to certain synthesized speech stimuli and impaired to others--consistent with her behavioral discrimination of these stimuli. Behavioral tests of auditory processing were consistent with auditory brain stem dysfunction. A neuropsychological evaluation revealed normal intellectual and academic performance. The subject was in her first year of college at the time of the evaluation. This case study is important because: (1) Although there have been several reports of absent/abnormal ABR with preserved peripheral hearing and deficits in auditory processing, little is known about the specific nature of the auditory deficits experienced by these individuals. Such information may be valuable to the clinical management of patients with this constellation of findings. (2) Of interest is the information that the mismatch negativity (MMN) cortical event-related potential can bring to the evaluation of patients with auditory processing deficits. The MMN reflects central auditory processing of small acoustic differences and may provide an objective measure of auditory discrimination. (3) From a theorectical standpoint, a patient with neural deficits affecting specific components of the auditory pathway provides insight into the relationship between evoked potentials and physiological mechanisms of auditory processing. How do various components of the auditory pathway contribute to speech discrimination? How might evoked potentials reflect the processes underlying the neural coding of specific features of speech stimuli such as timing and spectral cues?
Journal of The Acoustical Society of America, 2000
Auditory evoked potential ͑AEP͒ correlates of the neural representation of stimuli along a /ga/-/... more Auditory evoked potential ͑AEP͒ correlates of the neural representation of stimuli along a /ga/-/ka/ and a /ba/-/pa/ continuum were examined to determine whether the voice-onset time ͑VOT͒-related change in the N1 onset response from a single to double-peaked component is a reliable indicator of the perception of voiced and voiceless sounds. Behavioral identification results from ten subjects revealed a mean category boundary at a VOT of 46 ms for the /ga/-/ka/ continuum and at a VOT of 27.5 ms for the /ba/-/pa/ continuum. In the same subjects, electrophysiologic recordings revealed that a single N1 component was seen for stimuli with VOTs of 30 ms and less, and two components ͑N1Ј and N1͒ were seen for stimuli with VOTs of 40 ms and more for both continua. That is, the change in N1 morphology ͑from single to double-peaked͒ coincided with the change in perception from voiced to voiceless for stimuli from the /ba/-/pa/ continuum, but not for stimuli from the /ga/-/ka/ continuum. The results of this study show that N1 morphology does not reliably predict phonetic identification of stimuli varying in VOT. These findings also suggest that the previously reported appearance of a ''double-peak'' onset response in aggregate recordings from the auditory cortex does not indicate a cortical correlate of the perception of voicelessness.
Journal of The Acoustical Society of America, 1998
The goals of this study were ͑i͒ to assess the replicability of the ''perceptual magnet effect'' ... more The goals of this study were ͑i͒ to assess the replicability of the ''perceptual magnet effect'' ͓Iverson and Kuhl, J. Acoust. Soc. Am. 97͑1͒, 553-561 ͑1995͔͒ and ͑ii͒ to investigate neurophysiologic processes underlying the perceptual magnet effect by using the mismatch negativity ͑MMN͒ auditory evoked potential. A stimulus continuum from /i/ to /e/ was synthesized by varying F 1 and F 2 in equal mel steps. Ten adult subjects identified and rated the goodness of the stimuli. Results revealed that the prototype was the stimulus with the lowest F 1 and highest F 2 values and the nonprototype stimulus was close to the category boundary. Subjects discriminated stimulus pairs differing in equal mel steps. The results indicated that discrimination accuracy was not significantly different in the prototype and the nonprototype condition. That is, no perceptual magnet effect was observed. The MMN evoked potential ͑a preattentive, neurophysiologic index of auditory discrimination͒ revealed that despite equal mel differences between the stimulus pairs the MMN was largest for the prototype pair ͑i.e., the pair that had the lowest F 1 and highest F 2 values͒. Therefore the MMN appears to be sensitive to within category acoustic differences. Taken together, the behavioral and electrophysiologic results indicate that discrimination of stimulus pairs near a prototype is based on the auditory structure of the stimulus pairs.
The aim of our research was to estimate the time course of development and plasticity of the huma... more The aim of our research was to estimate the time course of development and plasticity of the human central auditory pathways following cochlear implantation. We recorded cortical auditoryevoked potentials in 3-year-old congenitally deaf children after they were ¢tted with cochlear implants. Immediately after implantation cortical response latencies resembled those of normal-hearing newborns. Over the next few months, the cortical evoked responses showed rapid changes in morphology and latency that resulted in age-appropriate latencies by 8 months after implantation. Overall, the development of cortical response latencies for the implanted children was more rapid than for their normalhearing age-matched peers. Our results demonstrate a high degree of central auditory system plasticity during early human development.NeuroReport13:1365^1368
Objective: This study examined morphological changes in the cortical auditory evoked potential (C... more Objective: This study examined morphological changes in the cortical auditory evoked potential (CAEP) waveform as a function of varying stimulation rate. Stimuli were presented in a paradigm which indirectly assesses the refractory properties of the underlying neuronal generators.
The mismatch negativity (MMN) is a passively elicited event-related potential that is extremely s... more The mismatch negativity (MMN) is a passively elicited event-related potential that is extremely sensitive to acoustic stimulus properties. The MMN was characterized in normal adults and school-age children in response to speech stimuli differing minimally in the onset frequency of the second and third formant transitions. The speech-evoked MMN consists of a negative waveform at about 230 msec that occurs in response to the deviant stimulus when it is presented in an oddball paradigm. It is absent in response to that same stimulus when presented alone. The MMN was clearly present in all adults and children tested. Using the procedures developed in this study, this event-related potential was found to be robust enough in individual subjects to be considered a potential clinical measure for assessing central auditory function in school-age children and adults.
Electroencephalography and Clinical Neurophysiology/evoked Potentials Section, 1997
Normal maturation and functioning of the central auditory system affects the development of speec... more Normal maturation and functioning of the central auditory system affects the development of speech perception and oral language capabilities. This study examined maturation of central auditory pathways as reflected by age-related changes in the P1/N1 components of the auditory evoked potential (AEP). A synthesized consonant-vowel syllable (ba) was used to elicit cortical AEPs in 86 normal children ranging in age from 6 to 15 years and ten normal adults. Distinct age-related changes were observed in the morphology of the AEP waveform. The adult response consists of a prominent negativity (N1) at about 100 ms, preceded by a smaller P1 component at about 50 ms. In contrast, the child response is characterized by a large P1 response at about 100 ms. This wave decreases significantly in latency and amplitude up to about 20 years of age. In children, P1 is followed by a broad negativity at about 200 ms which we term N1b. Many subjects (especially older children) also show an earlier negativity (N1a). Both N1a and N1b latencies decrease significantly with age. Amplitudes of N1a and N1b do not show significant age-related changes. All children have the N1b; however, the frequency of occurrence of N1a increases with age. Data indicate that the child P1 develops systematically into the adult response; however, the relationship of N1a and N1b to the adult N1 is unclear. These results indicate that maturational changes in the central auditory system are complex and extend well into the second decade of life.
The mismatch negativity (MMN) is an automatic cortical evoked potential that signifies the brain&... more The mismatch negativity (MMN) is an automatic cortical evoked potential that signifies the brain&#39;s detection of acoustic change. In other words, the MMN reflects the neurophysiologic processes that underlie auditory discrimination. As such, the MMN provides an objective tool for evaluating central auditory mechanisms involved in speech perception. We are using the MMN to study the central auditory processes that encode acoustic changes important for speech perception in 1) normal-hearing adults and children, 2) individuals with impaired auditory systems (including persons with learning disabilities, attention deficit disorders, cochlear implants), and 3) an animal model. Specifically, we have demonstrated that the MMN provides information about the central processing of fine acoustic differences, the neuroanatomic pathways that encode acoustic change, central auditory processing in the presence of peripheral hearing deficits, and central auditory system plasticity. In addition, we have considered methodological challenges associated with measuring the MMN in individual subjects. Several methodological issues--including appropriate stimuli, stimulus presentation variables, the recording protocol and environment, and validation of the MMN in individuals--are discussed.
Journal of Urban Health-bulletin of The New York Academy of Medicine, 2002
This article presents information on pregnant women with incident blood lead levels (BLLs) of 20 ... more This article presents information on pregnant women with incident blood lead levels (BLLs) of 20 μg per deciliter or greater as reported to the New York City Department of Health between September 1996 and June 1999 (n=33). Almost half of the women were diagnosed during their third trimester of pregnancy, often at their first prenatal visit. The median BLLs at incidence and at last report among women who were retested were 25 and 15 γ/dL, respectively, a 40% decline. The median incident BLL among newborns (n=25) was 12 μg/dL. The BLLs were inversely associated with maternal age and length of time in the United States and directly associated with gestational age and pica behavior. Cases were more than twice as likely to be foreign-born women than all women who gave birth in New York City. Prenatal care facilities employing a policy of universal blood lead testing of all pregnant women at the time of their first visit reported disproportionate numbers of cases, accounting for 77% of cases yet only 11% of all births citywide. The findings suggest that (1) the promulgation of recent rules and guidelines for lead risk assessment and screening among pregnant women appears to have been effective in identifying cases that might not have otherwise come to light; (2) case management and environmental interventions were initiated promptly; (3) cases experienced, on average, significant BLL reductions over time; and (4) there is a need for additional public health interventions for pregnant women in urban, multicultural centers. While the data suggest that universal screening may increase case finding among high-risk, immigrant populations, further studies and surveillance are needed to determine systematically the most effective approach.
Uploads
Papers by Anu Sharma