PubMed Health⌕ Search

Biomedical subjects

David R Moore

Publications and source records attributed to David R Moore.

31 records · Page 2Linked to original sources
PubMed2003

The auditory basis of language impairments: temporal processing versus processing efficiency hypotheses.

Claims have been made that language-impaired children have deficits processing rapidly presented or brief sensory information. These claims, known as the 'temporal processing hypothesis', are supported by demonstrations that language-impaired children have excess backward masking (BM). One explanation for these results is that BM is developmentally delayed in these children. However, little was known about how BM normally develops. Recently, we assessed BM in normally developing 6- and 8-year-old children and adults. Results showed that BM thresholds continue to improve over a comparatively protracted period (>10 years old). We also analysed reported deficits in BM in language-impaired and younger children, in terms of a model of temporal resolution. This analysis suggests that poor processing efficiency, rather than deficits in temporal resolution, can account for these results. This 'processing efficiency hypothesis' was recently tested in our laboratory. This experiment measured BM as a function of delays between the tone and the noise in children and adults. Results supported the processing efficiency hypothesis, and suggested that reduced processing efficiency alone could account for differences between adults and children. These findings provide a new perspective on the mechanisms underlying communication disorders, and imply that remediation strategies should be directed towards improving processing efficiency, not temporal resolution.

Auditory Threshold↗
PubMed2003

Effects of otitis media with effusion (OME) on central auditory function.

Conductive hearing loss attenuates and delays sound passing through the middle ear. This impairs binaural hearing and other central auditory functions dependent on high fidelity sound transmission. Persistent conductive loss leads to central impairments that persist after the peripheral loss has resolved. For example, children who have had multiple episodes of otitis media with effusion (OME) in the first few years of life may have poor detection of sounds in noisy environments, evidenced by reduced binaural unmasking (BU). Recent research shows that a 'threshold' level of OME is required to produce impaired BU. Children who had OME in one or both ears for more than about 50% of the first 5 years had reduced BU. Animal research, using long-term ear plugging, suggests that total OME duration, rather than age at the time of having the disease, determines its effect on BU. Animals reared with bilateral (but not unilateral) ear plugs also have poor auditory temporal resolution, and reduced sensitivity to short tones in the presence of background noise, after plug removal. However, given time (6-24 months) and training, all animals regained normal temporal resolution.

Auditory Diseases, Central↗
PubMed2003

Effects of conductive hearing loss on temporal aspects of sound transmission through the ear.

Effects of conductive hearing loss on level and spectrum are well known. However, little is known about possible additional effects on temporal aspects of sound transmission. This study investigated effects of earplugs and middle ear effusions on amplitude and timing of cochlear microphonic (CM) responses in gerbils. Bilateral CM responses to pure tones (1-16 kHz) were monitored before and after (i). unilateral earplug insertion or (ii). injection of silicone oil, of various viscosities, into one middle ear. Earplugs produced flat hearing losses (mean 13 dB) and delayed CMs more at lower (mean 80 micros, 1-6 kHz) than at higher (20 micros, 8-16 kHz) frequencies. Effusions also produced flat hearing loss. On average, high viscosity effusions produced larger hearing losses (36 dB) than medium (25 dB) or low (20 dB) viscosity effusions. Low and medium viscosity effusions delayed responses to lower (mean 82 and 65 micros respectively, 1-6 kHz) more than to higher (mean 20 and 10 micros respectively, 8-16 kHz) frequencies. High viscosity effusions produced smaller delays across all frequencies (mean 31 micros, 1-16 kHz). In normal animals, CM responses were not delayed over a wide range of stimulus levels. Therefore, in addition to attenuation, conductive loss distorts acoustic temporal cues important for hearing.

Animals↗
PubMed2002

Single-site beta-diiminate zinc catalysts for the ring-opening polymerization of beta-butyrolactone and beta-valerolactone to poly(3-hydroxyalkanoates).

Polymerization of beta-butyrolactone (BBL) and beta-valerolactone (BVL) using the zinc alkoxide initiator (BDI-1)ZnO(i)()Pr [(BDI-1) = 2-((2,6-diisopropylphenyl)amido)-4-((2,6-diisopropylphenyl)imino)-2-pentene] proceeds very rapidly under mild conditions to produce poly(3-hydroxybutyrate) (PHB) and poly(3-hydroxyvalerate) (PHV), respectively. For the monomer-to-initiator ratio 200:1, PHB number-average molecular weights (M(n)) are proportional to conversion throughout the reaction and polydispersity indices (PDIs) are narrow, consistent with a living polymerization. Higher monomer-to-initiator ratios can be used to achieve high molecular weight PHB (M(n) > 100 000). End-group analysis verifies that the polymerization of BBL follows a coordination-insertion mechanism, where complexes of the form (BDI-1)ZnOCH(Me)CH(2)CO(2)R are the active species. Variable temperature NMR experiments show that (BDI-1)ZnO(i)()Pr is monomeric in benzene-d(6) solution. In contrast, (BDI-2)ZnO(i)()Pr [(BDI-2) = 2-((2,6-diethylphenyl)amido)-4-((2,6-diethylphenyl)imino)-2-pentene] is a poor initiator at room temperature because it prefers to form a bis-mu-isopropoxide dimer in solution. According to kinetic studies, propagation by (BDI-1)ZnO(i)()Pr is first order in both monomer as well as (BDI-1)ZnO(i)()Pr concentration. These results lead us to propose a monometallic active species. Several results suggest that elimination side reactions are slowly catalyzed by zinc alkoxides, leading to degradation of the polymer.

4-Butyrolactone↗
PubMed2002

High-activity, single-site catalysts for the alternating copolymerization of CO2 and propylene oxide.

Despite recent advances regarding catalysts for CO2/epoxide copolymerization, the development of high-activity catalysts for alternating polymerization of CO2 and commodity epoxides, such as propylene oxide, remains a challenge. A new class of unsymmetrically substituted beta-diiminate zinc complexes is reported that exhibits unprecedented activity for CO2/propylene oxide copolymerization. The polymers formed are of high molecular weight (Mn approximately 35 kg/mol) and have narrow polydispersities (PDI approximately 1.1), consistent with a living polymerization.

Journal Article↗
PubMed2002

Ultrastructural transynaptic effects of unilateral cochlear ablation in the gerbil medial superior olive.

This study investigated the long-term effects of unilateral hearing loss on the structure of synapses within the gerbil medial superior olivary (MSO) nuclei. Five animals had complete (surgical) left cochlear ablation at postnatal day 18. Previous studies have shown this to produce, within 3 days, significant transneuronal atrophy in the left dendritic field of both MSOs. Electron micrographs from sagittal ultrathin sections through the MSOs of the cochlear-ablated animals were compared to those from unoperated normals. Qualitatively, the ultrastructural features were similar. Most of the axodendritic terminals were R-type (round-type vesicles, putative excitatory) whereas, in the central part of the nucleus, predominated by neuron soma profiles, terminals of P- and F-type (pleomorphic- and flattened-type vesicles, putative inhibitory) were present in equal numbers with R-type terminals. F-type terminals were infrequent and occurred most around lateral parts of the MSO somata. These three types of terminals seen around the somata and proximal dendrites all had extended profiles with multiple, discontinuous appositions. Quantitative analysis revealed that R-type axodendritic terminals became smaller and less densely populated with vesicles where they synapsed onto the remaining dendrites arrayed towards the ablated side of both MSOs, and axosomatic P-type afferent terminals were smaller in the contralateral nuclei. A significant reduction in the number of terminals and synapses occurred in the central, somatic, region of the ipsilateral MSO. However, the terminal vesicle concentration in the remaining terminals increased. The results indicate that cochlear ablation can induce transynaptic reduction in the size of afferent axon terminals within the MSO, and alter their vesicle concentration. These changes are likely to affect the probability of transmitter release and thus influence their signaling power within the nucleus.

Animals↗
PubMed2002

Auditory development and the role of experience.

The human ear is functionally mature shortly after birth, but the central auditory system continues to develop for at least the first decade of life. Current interest focuses on the relation between the very late developing aspects of hearing and other aspects of cognition and behaviour. While active neural input to the brain is essential during the very early stages of development, auditory experience is now thought to be a powerful influence on central function throughout an individual's lifespan. Studies of sound localization and hearing with two ears have shown the capacity of the auditory system to adapt to altered environmental cues, even into adulthood. This environmental influence may either be harmful, as during conductive deafness, or beneficial, as evidenced by the positive outcomes of auditory training.

Adaptation, Physiological↗
PubMed2002

Auditory processing efficiency deficits in children with developmental language impairments.

The "temporal processing hypothesis" suggests that individuals with specific language impairments (SLIs) and dyslexia have severe deficits in processing rapidly presented or brief sensory information, both within the auditory and visual domains. This hypothesis has been supported through evidence that language-impaired individuals have excess auditory backward masking. This paper presents an analysis of masking results from several studies in terms of a model of temporal resolution. Results from this modeling suggest that the masking results can be better explained by an "auditory efficiency" hypothesis. If impaired or immature listeners have a normal temporal window, but require a higher signal-to-noise level (poor processing efficiency), this hypothesis predicts the observed small deficits in the simultaneous masking task, and the much larger deficits in backward and forward masking tasks amongst those listeners. The difference in performance on these masking tasks is predictable from the compressive nonlinearity of the basilar membrane. The model also correctly predicts that backward masking (i) is more prone to training effects, (ii) has greater inter- and intrasubject variability, and (iii) increases less with masker level than do other masking tasks. These findings provide a new perspective on the mechanisms underlying communication disorders and auditory masking.

Adult↗
PubMed2002

Optical imaging of intrinsic signals in ferret auditory cortex: responses to narrowband sound stimuli.

This paper describes optical imaging of the auditory cortex in the anesthetized ferret, particularly addressing optimization of narrowband stimuli. The types of sound stimuli used were tone-pip trains and sinusoidal frequency and amplitude modulated (SFM and SAM) tones. By employing short illumination wavelengths (546 nm), we have successfully characterized the tonotopic arrangement, in agreement with the well-established electrophysiological tonotopic maps of the ferret auditory primary field (AI). The magnitude of the optical signal increased with sound level, was maximal for a modulation frequency (MF) of 2-4 Hz, and was larger for tone-pip trains and SFM sounds than for SAM sounds. Accordingly, an optimal narrowband stimulus was defined. Thus optical imaging can be used successfully to obtain frequency maps in auditory cortex by an appropriate choice of stimulus parameters. In addition, background noise consisting of 0.1-Hz oscillations could be reduced by introduction of blood pressure enhancing drugs. The optical maps were largely independent of 1) the type of narrowband stimulus, 2) the sound level, and 3) the MF. This stability of the optical maps was not predicted from the electrophysiological literature.

Acoustic Stimulation↗
PubMedDate not supplied

North Carolina high-risk insurance pools.

Imagine this: You are a 58-year-old man. You have worked all your life, paid taxes, and helped support your family. Two years ago you had a mild heart attack. Your wife has diabetes and high blood pressure. Luckily, you had health insurance through your job that helped you pay for the hospitalization, doctor's visits, and necessary medications for you and your wife. With a new diet, exercise, and the medications, you both are doing well managing your health problems. A little over a year ago, you lost your insurance when your company downsized. You found another job, but your current employer doesn't offer insurance. Your wife also works, but she works for a small employer that does not offer coverage. So, you pay approximately dollar 600/month for continuation coverage (COBRA) for your wife and yourself through your former employer. Last month, you found out your COBRA coverage is about to end. You want to continue to buy insurance coverage, but you were told that purchasing a comprehensive policy with a dollar 1,000 deductible (70% coinsurance) that covers your needed medications would cost more than dollar 4,000/month for your wife and yourself.

Fees and Charges↗