Human Frequency Following Responses to Filtered Speech.

OBJECTIVES: There is increasing interest in using the frequency following response (FFR) to describe the effects of varying different aspects of hearing aid signal processing on brainstem neural representation of speech. To this end, recent studies have examined the effects of filtering on brainstem neural representation of the speech fundamental frequency (f0) in listeners with normal hearing sensitivity by measuring FFRs to low- and high-pass filtered signals. However, the stimuli used in these studies do not reflect the entire range of typical cutoff frequencies used in frequency-specific gain adjustments during hearing aid fitting. Further, there has been limited discussion on the effect of filtering on brainstem neural representation of formant-related harmonics. Here, the effects of filtering on brainstem neural representation of speech fundamental frequency (f0) and harmonics related to first formant frequency (F1) were assessed by recording envelope and spectral FFRs to a vowel low-, high-, and band-pass filtered at cutoff frequencies ranging from 0.125 to 8 kHz. DESIGN: FFRs were measured to a synthetically generated vowel stimulus /u/ presented in a full bandwidth and low-pass (experiment 1), high-pass (experiment 2), and band-pass (experiment 3) filtered conditions. In experiment 1, FFRs were measured to a synthetically generated vowel stimulus /u/ presented in a full bandwidth condition as well as 11 low-pass filtered conditions (low-pass cutoff frequencies: 0.125, 0.25, 0.5, 0.75, 1, 1.5, 2, 3, 4, 6, and 8 kHz) in 19 adult listeners with normal hearing sensitivity. In experiment 2, FFRs were measured to the same synthetically generated vowel stimulus /u/ presented in a full bandwidth condition as well as 10 high-pass filtered conditions (high-pass cutoff frequencies: 0.125, 0.25, 0.5, 0.75, 1, 1.5, 2, 3, 4, and 6 kHz) in 7 adult listeners with normal hearing sensitivity. In experiment 3, in addition to the full bandwidth condition, FFRs were measured to vowel /u/ low-pass filtered at 2 kHz, band-pass filtered between 2-4 kHz and 4-6 kHz in 10 adult listeners with normal hearing sensitivity. A Fast Fourier Transform analysis was conducted to measure the strength of f0 and the F1-related harmonic relative to the noise floor in the brainstem neural responses obtained to the full bandwidth and filtered stimulus conditions. RESULTS: Brainstem neural representation of f0 was reduced when the low-pass filter cutoff frequency was between 0.25 and 0.5 kHz; no differences in f0 strength were noted between conditions when the low-pass filter cutoff condition was at or greater than 0.75 kHz. While envelope FFR f0 strength was reduced when the stimulus was high-pass filtered at 6 kHz, there was no effect of high-pass filtering on brainstem neural representation of f0 when the high-pass filter cutoff frequency ranged from 0.125 to 4 kHz. There was a weakly significant global effect of band-pass filtering on brainstem neural phase-locking to f0. A trends analysis indicated that mean f0 magnitude in the brainstem neural response was greater when the stimulus was band-pass filtered between 2 and 4 kHz as compared to when the stimulus was band-pass filtered between 4 and 6 kHz, low-pass filtered at 2 kHz or presented in the full bandwidth condition. Last, neural phase-locking to f0 was reduced or absent in envelope FFRs measured to filtered stimuli that lacked spectral energy above 0.125 kHz or below 6 kHz. Similarly, little to no energy was seen at F1 in spectral FFRs obtained to low-, high-, or band-pass filtered stimuli that did not contain energy in the F1 region. For stimulus conditions that contained energy at F1, the strength of the peak at F1 in the spectral FFR varied little with low-, high-, or band-pass filtering. CONCLUSIONS: Energy at f0 in envelope FFRs may arise due to neural phase-locking to low-, mid-, or high-frequency stimulus components, provided the stimulus envelope is modulated by at least two interacting harmonics. Stronger neural responses at f0 are measured when filtering results in stimulus bandwidths that preserve stimulus energy at F1 and F2. In addition, results suggest that unresolved harmonics may favorably influence f0 strength in the neural response. Lastly, brainstem neural representation of the F1-related harmonic measured in spectral FFRs obtained to filtered stimuli is related to the presence or absence of stimulus energy at F1. These findings add to the existing literature exploring the viability of the FFR as an objective technique to evaluate hearing aid fitting where stimulus bandwidth is altered by design due to frequency-specific gain applied by amplification algorithms.

Health Disparities in Pediatric Asthma: Comprehensive Tertiary Care Center Experience.

LOCATION: Study conducted at Nemours /Alfred I. duPont Hospital for Children, Wilmington, DE 19803 BACKGROUND: Although the treatment and management of asthma hasimproved over time, incidence and prevalence among children continues to rise in the United States. Asthma prevalence, health services utilization, and mortality rate demonstrate remarkable disparities. The underlying causes of these disparities are not fully understood. We aimed to examine racial/ethnic variances in pediatric asthma prevalence/admission. PATIENTS AND METHODS: We retrospectively reviewed data on 1070 patients and applied a cross-sectional design to assess asthma admission between 2010 and 2011. Information was available on race/ethnicity, sex, insurance status, severity of illness (SOI), and length of stay/hospitalization (LOS).Chi-square statistic was used for the association between race and other variables in an attempt to explain the racial/ethnic variance. RESULTS: The proportionate morbidity of asthma was highest amongCaucasians (40.92%) and African Americans (40.54%), intermediate among others (16.57%), and lowest among Asian (0.56%), American Indian/Alaska Native (0.28%), and Hawaiian Native/Pacific Islander (0.28%). Overall there were disparities by sex, with more boys (61.80%) diagnosed with asthma than girls (38.20%), χ2(7)=20.1, p=0.005. Insurance status, and SOI varied by race/ethnicity, but not LOS. Caucasian children were more likely to have private insurance, while African Americans and Hispanics were more likely to have public insurance (p<0.005). Asthma was more severe among non-Hispanic children, χ2(14)=154.6, p<0.001. While the overall readmission proportion was 2.8%, readmission significantly varied by race/ethnicity. CONCLUSION: Racial/ethnic disparities in asthma admission exist among children in the Delaware Valley. There were racial/ethnic disparities in insurance status, asthma severity, and sex differed by race/ethnicity, but not in length of hospitalization.