New fluorocarbon iodides.

A general, efficient approach for the synthesis of fluorocarbon iodides and di-iodides bearing hydrocarbon groups is described and the synthetic utility of these new systems is demonstrated in reactions with thiols.

Elemental fluorine. Part 13. Gas-liquid thin film microreactors for selective direct fluorination.

Continuous flow gas-liquid thin film microreactors have been effectively used for the selective fluorination of a range of 1,3-dicarbonyl and aromatic substrates and, additionally, the conversion of aromatic disulfides to the corresponding sulfur pentafluorides. Scale-up was demonstrated by the application of a three channel microreactor device fabricated by replication of a single channel system.

Electrically evoked potentials recorded in adult and pediatric CLARION implant users.

The purpose of this study was to record electrical auditory brain stem responses (EABRs) and electrical middle latency responses (EMLRs) in the clinic from 3 adult CLARION Multi-Strategy Cochlear Implant subjects and to record EABRs in the operating room from 3 pediatric subjects. For 2 of the 3 adult subjects, EABR thresholds were within the subject's behavioral dynamic range, whereas 1 adult subject's EABR thresholds were either absent or, when present, exceeded the upper limit of the dynamic range. For this subject, EMLRs were absent or of poor morphology for the channels tested. Moreover, this subject was not able to understand speech in an open-set, auditory-only format. The EABR thresholds obtained with children were within the behavioral dynamic range for 2 of the 3 subjects, but exceeded comfortable loudness levels for 1 subject. Although the EABR thresholds were measured at stimulus levels that were audible for all subjects, the relationship of the EABR threshold levels to behavioral measures of loudness varied. Evoked potentials that originate more centrally, such as the EMLR, should be investigated further to determine the possible relationship to postimplant performance.

Reliability of threshold estimation in hearing-impaired adults using the AMFR.

The amplitude modulation-following response (AMFR), an auditory evoked potential elicited by continuous amplitude-modulated tones, can be recorded for carrier frequencies across the audiometric range. AMFR thresholds (based on the amplitude spectra of the responses) have been found to closely follow behavioral thresholds in six normal-hearing and four hearing-impaired adults. In the current work, we studied the reliability of the AMFR as an index of behavioral low-frequency (500 and 1000 Hz) thresholds in a larger sample (n = 16) of hearing-impaired adults with mild to moderate hearing loss. The AMFR amplitudes and detection thresholds were strongly correlated across the two recording sessions, and AMFR thresholds obtained in both sessions were strongly correlated to behavioral thresholds. The average absolute difference between the AMFR and behavioral thresholds was 7.3 dB and 6.4 dB for 500 Hz and 1000 Hz, respectively.

Differential age effects for components of the adult auditory middle latency response.

The middle latency components of the auditory evoked response were obtained from a young (20-24 years of age) and an older (51 to 71 years of age) group of normal-hearing, healthy female subjects. Recording procedures and stimulus repetition rates were chosen to promote the resolution of both Pa and Pb. The absolute and peak-to-peak amplitudes of Pa and Pb were significantly larger for the older subjects at all stimulus rates. An amplitude reduction of Pb with increasing stimulus rate was much more pronounced for the young than for the older subjects. This, combined with a shorter latency for Pb in the older subjects, may have contributed to partial and/or complete fusion of Pa and Pb observed in 10 of the 17 older subjects. An apparent positive shift in the response baseline for older subjects also may have contributed to the age-related amplitude effects.

The amplitude modulation-following response as an audiometric tool.

The amplitude modulation-following response (AMFR) is an auditory scalp-recorded potential, evoked using continuous, amplitude-modulated tones. The current study was designed to explore the audiometric utility of the AMFR by demonstrating the frequency specificity of the response and assessing the relation between behaviorally measured pure-tone thresholds and AMFR detection thresholds. Subjects in this study were six normal-hearing and four hearing-impaired adults. High-pass masking results in the normal hearing subjects demonstrated that the AMFR is associated with a narrow range of activation along the cochlea around the carrier frequency. Frequency-specific results from the hearing-impaired subjects confirmed this finding. Thresholds for the AMFR, defined in spectral terms, were consistent with the behavioral estimates in both the normal and the hearing-impaired subjects.

Effects of age on the adult auditory middle latency response.

The middle latency components of the auditory evoked response were obtained from a group of normal-hearing, healthy female subjects from 22 to 68 years of age. Recordings were made at several intensity levels to assess the level-dependence of any age-related effects. Cross-sectional analyses revealed that the amplitude of component Pa grows linearly with age, becoming significantly larger in older (50-68 years of age) compared to younger (22-37 years) subjects. The amplitude-intensity function is steeper in the older subjects by a factor of two. Correlational analyses suggested that at higher intensity levels age accounts for about 20% of the variance in the amplitude of Pa. A positive shift in response baseline was observed in the older subjects, and could contribute to the age-related increase in the absolute amplitude of Pa. However, a similar increase in the peak-to-peak and area measures of Pa suggests that some of the increase in the magnitude of Pa is independent of baseline shift. A confounding of age and hearing sensitivity in this study makes it difficult to interpret the age-related effects as strictly central in nature.

Statistical dependence among the wave latencies of the auditory brain stem response.

If the interpeak intervals in the auditory brain stem response (ABR) are assumed to be statistically independent variables that represent the neural transmission time between loci, then the absolute latency of an ABR wave is the sum of the transmission times between successive loci. Consequently, the correlations between the absolute latencies of the ABR waves would be part-whole correlations whose expected values are appreciably different from r = 0. We derived the expected values of the correlations between the latencies of the ABR waves on the assumption that their latencies are the sum of independent elements (transmission times) and found them to be 0.707, 0.577, and 0.816 for I.III, I.V, and III.V, respectively. In addition, the expected values of the correlations between the latencies of the ABR waves assuming that the absolute wave latencies themselves are independent variables (e.g., rI.III = 0) were derived. Several of the correlations among interpeak and between the interpeak and absolute latencies were demonstrated to be appreciably different from r = 0. It would appear that it is more reasonable to assume that the elements (transmission times) rather than the component latencies are the variables of choice for statistical analysis of ABR data.

Correlations between various measures of head size and auditory brainstem response latencies.

The literature is mixed concerning the degree to which between-subject variance in the latencies of the auditory brainstem response (ABR) relates to differences in the length of the auditory pathway. Most investigations have used one of several measures of head size to indirectly index brain size and neural pathway length. While some studies have found a positive correlation between head size and the latencies of the ABR, others have reported little or no relationship. We hypothesized that the differences between studies result from differences in the head dimensions measured, the precision of measurement technique, and issues of sampling. We therefore decided to use the International 10-20 system of electrode placement to provide reproducible skull benchmarks on which to base head size measures, to obtain measures of head size via two procedures, and to control external variables that might influence the ABR. The results show that head size has a moderate positive influence on the latencies of the ABR given precise head size measures.

Auditory brain-stem responses in children with previous otitis media.

The auditory brain-stem responses (ABRs) of 18 children who received tympanostomy tubes due to well-documented history of otitis media with effusion (OME) were compared with a matched control group with little or no history of effusion. The subjects in the OME group had significantly longer ABR latencies for waves III and V, with the most compelling delay for wave III and the III-I interwave interval. Although wave I prolongation in the OME group was not significant, the possible contribution of a peripheral effect on the latencies of waves III and V was investigated. The typical gender effect for the ABR latencies was unaltered in the OME group, and there was no group by gender interaction. We suggest that although the data support increased ABR latencies for children with a history of OME, they do not establish a causal relationship.

The relation between the human frequency-following response and the low pitch of complex tones.

The relation between the auditory brain stem potential called the frequency-following response (FFR) and the low pitch of complex tones was investigated. Eleven complex stimuli were synthesized such that frequency content varied but waveform envelope periodicity was constant. This was accomplished by repeatedly shifting the components of a harmonic complex tone upward in frequency by delta f of 20 Hz, producing a series of six-component inharmonic complex tones with constant intercomponent spacing of 200 Hz. Pitch-shift functions were derived from pitch matches for these stimuli to a comparison pure tone for each of four normal hearing adults with extensive musical training. The FFRs were recorded for the complex stimuli that were judged most divergent in pitch by each subject and for pure-tone signals that were judged equal in pitch to these complex stimuli. Spectral analyses suggested that the spectral content of the FFRs elicited by the complex stimuli did not vary consistently with component frequency or the first effect of pitch shift. Furthermore, complex and pure-tone signals judged equal in pitch did not elicit FFRs of similar spectral content.