Effect of normobaric hypoxia on sound localization

BACKGROUND: Three-dimensional (3D) audio displays have considerable potential for conveying spatial information in the aviation environment. How reliably these displays will function in that environment will depend in part on the extent to which sound localization is affected by hypoxia. Many aircraft systems operators are routinely exposed to mild hypoxia, and all are at risk of exposure to more severe hypoxia. METHODS: We have examined hypoxia's effect on localization by measuring the localization performance of four subjects exposed to simulated altitudes of 0, 1200, 2400 and 3700 m above sea level for about 30 min. Sounds to be localized were presented from a free-field source at locations covering 360 degrees of azimuth and extending from -47.6 to + 80 degrees elevation. RESULTS: Localization performance was statistically indistinguishable across the altitudes tested. Average localization errors ranged from 12.6 degrees +/- 0.7 SE at 2400 m to 14 degrees +/- 0.84 SE at 0 m. CONCLUSION: The finding that hypoxia induced by exposure to simulated altitudes as high as 3700 m has no effect of sound localization is encouraging with respect to the continued development of 3D audio displays for use in the aviation environment.     

Effect of normobaric hypoxia on auditory sensitivity

Previous psychophysical studies of hypoxia's effects on auditory sensitivity have provided mixed results but the weight of evidence supports the conclusion that sensitivity is unaffected by hypoxia. This conclusion is discrepant with that drawn from physiological studies in which hypoxia has been found to affect auditory-evoked response (AER) latency. One possible explanation of this discrepancy concerns the relatively low maximum frequency (8 kHz) for which hypoxia's effects were assessed in the psychophysical studies. We have extended the range of frequencies over which hypoxia's effects have been examined to include frequencies up to 16 kHz. Thresholds for 1-, 8-, 10-, 12-, 14- and 16-kHz tones were measured at levels of hypoxia equivalent to altitudes of 0, 1,200, 2,400 and 3,700 m. Our results indicate that sensitivity for frequencies up to 16 kHz is unaffected by hypoxia. We suggest that AER latency does not provide a valid measure of auditory sensitivity.     

Predictors of hippocampal, cerebral, and cerebellar volume reduction in childhood epilepsy

PURPOSE: We examined the factors related to brain volume reduction in a pediatric sample of patients that included those with nonintractable epilepsy. METHODS: Entry criteria were children less than 18 years old with epilepsy referred for MRI, including a whole brain volumetric sequence. The sample size was 231. Risk factors were ascertained from interviews and reviews of medical records. Factors included age of onset, seizure years, family history, status epilepticus, intellectual disability, and febrile convulsions. MRI data were obtained for 44 normal childhood control subjects. RESULTS: Cerebral and cerebellar volumes were significantly associated with age, gender, moderate-to-severe intellectual disability (p < 0.001), seizure years, and status epilepticus (p < 0.03). Compared with controls, the brain volume of all patients was reduced by 10% (p < 0.001). Hippocampal volume was significantly associated with total brain volume, age (p < 0.001), focal cerebral ischemic injury, and complex febrile convulsions (p < 0.05). CONCLUSIONS: Significant brain volume reduction is present in children with epilepsy. A component of this reduction is due to acquired insults. The reduction is seen even in children with infrequent seizures over a brief time, suggesting an innate structural abnormality. When evaluating possible etiologic factors in the development of hippocampal volume reduction, one must control for total brain volume. We have confirmed the association of complex febrile convulsions with unilateral hippocampal volume reduction.     

Psychophysical sensitivity and physiological response to amplitude modulation in adult dyslexic listeners.

This study reports two experiments conducted to assess the sensitivity of dyslexic listeners to amplitude modulation (AM) of acoustic stimuli. The smallest detectable depth of AM of white noise was measured as a function of modulation frequency. Dyslexic listeners had significantly higher thresholds of AM depth than did matched control listeners. We also recorded the scalp potential evoked by AM of white noise (the amplitude modulation following response, AMFR). Dyslexic listeners had significantly smaller AMFRs than did matched control listeners. The reduced AMFR is consistent with reduced sensitivity to AM, and there was a strong association between these psychophysical and physiological measures. This deficit in AM sensitivity may result in impaired perception of the AM present in speech.     

Spectral hyperacuity in the cat: neural response to frequency modulated tone pairs

When two tones are presented to the ear, distortion products are generated which are lower in frequency than the presented (primary) tones. We studied the responses of neurons from the inferior colliculus of the cat to small frequency modulations (FM) of primary tone combinations which gave rise to distortion products within the neuron's response area. Neural discharges were modulated in response to the FM of the distortion product in a similar manner to modulation of discharges by FM of a pure tone to which these neurons were sensitive. However, very shallow, neurally-insignificant FM of high-frequency primaries could be transposed into significant FM of lower frequency distortion products. Because the sensitivity of a low-frequency neuron to a transposed FM exceeds that of neurons sensitive to a single tone with the same FM, the effect is termed hyperacuity.     

Visual and Auditory Processing Impairments in Subtypes of Developmental Dyslexia: A Discussion

There has been a large body of research exploring sensory processing deficits in dyslexia, in both the visual and the auditory domains. Recently, there has also been evidence to suggest that dyslexia may be a heterogeneous disorder, with different patterns of dyslexia being identifiable. In this paper, we examine the relationship between these two bodies of research. First, we briefly review the evidence for sensory processing impairments in dyslexia, in both the visual and the auditory domains. Second, we consider how such deficits might affect the development of different component processes in reading and, therefore, be associated with different subtypes of dyslexia. Finally, we present some illustrative data, which points to the importance of considering different component processes of reading when investigating sensory processing deficits in dyslexia.     

Preconception Health of Reproductive Aged Women of the Mississippi River Delta

Optimal preconception health (PCH) may improve maternal and infant outcomes, priority issues in Mississippi (MS). Our study objective was to compare the PCH of women in the MS Delta to other regions. We analyzed Behavioral Risk Factor Surveillance System data from 2005, 2007, and 2009, and limited analyses to 171,612 non-pregnant black and white women 18–44 years of age. Region was defined as 14 MS Delta counties (MS Delta), remainder of MS (MS non-Delta), Delta states (LA, AR, TN), and non-Delta US states. We calculated adjusted prevalence ratios (aPR) to assess associations between region and 16 indicators of optimal PCH, controlling for demographic characteristics. Healthy PCH factors such as consuming ≥5 fruits and vegetables daily and normal body mass index (18.5 kg/m² to <25 kg/m²), respectively, were more prevalent in the MS non-Delta (aPR = 1.3; 95 % CI: 1.0,1.7 and aPR = 1.2; 95 % CI: 1.0,1.4), non-MS Delta (aPR = 1.5; 95 % CI: 1.2,2.0 and aPR = 1.3; 95 % CI: 1.1,1.5) and non-Delta states (aPR = 1.7; 95 % CI: 1.3,2.2 and aPR = 1.4; 95 % CI: 1.2,1.6) compared to the MS Delta. Physical activity levels were higher among non-Delta US states compared to the MS Delta (aPR = 1.3; 95 % CI: 1.1,1.4). Household income and race confounded the associations between region and PCH. Reproductive aged women in the MS Delta had poorer PCH, particularly for physical activity and nutrition, than women in other regions. MS Delta service providers and public health practitioners should consider implementing or enhancing lifestyle, nutrition, and physical activity interventions, with a special focus on reducing income-based and racial disparities.     

Antimicrobial comparison of a new multi-purpose disinfecting solution to a 3% hydrogen peroxide system.

PURPOSE: We compared the antimicrobial activity of a new multi-purpose disinfection solution (OPTI-FREE EXPRESS with ALDOX) to a 3% hydrogen peroxide disinfecting system. The antimicrobial ingredients in the new solution are polyquaternium-1 and myristamidopropyl dimethylamine. METHODS: The solutions were tested for antimicrobial activity against Staphylococcus sp.., Pseudomonas aeruginosa, Serratia marcescens, Candida albicans, Fusarium solani, and two Acanthamoeba species and were evaluated according to the primary criteria of the FDA and ISO contact lens disinfection procedures. RESULTS AND CONCLUSIONS: OPTI-FREE EXPRESS with ALDOX (EXPRESS MPDS) Multi-Purpose Disinfecting Solution provided a multiple spectrum of antimicrobial activity and met the FDA and ISO primary Stand Alone Test criteria for disinfection of contact lenses. EXPRESS MPDS showed disinfection activity in the range of a 3% hydrogen peroxide system. Unlike the 3% hydrogen peroxide system, it retarded contamination during storage.