Biomedical subjects

L R Mancl

Publications and source records attributed to L R Mancl.

4 recordsLinked to original sources

PubMed2001

Human auditory brainstem response to temporal gaps in noise.

Gap detection is a commonly used measure of temporal resolution, although the mechanisms underlying gap detection are not well understood. To the extent that gap detection depends on processes within, or peripheral to, the auditory brainstem, one would predict that a measure of gap threshold based on the auditory brainstem response (ABR) would be similar to the psychophysical gap detection threshold. Three experiments were performed to examine the relationship between ABR gap threshold and gap detection. Thresholds for gaps in a broadband noise were measured in young adults with normal hearing, using both psychophysical techniques and electrophysiological techniques that use the ABR. The mean gap thresholds obtained with the two methods were very similar, although ABR gap thresholds tended to be lower than psychophysical gap thresholds. There was a modest correlation between psychophysical and ABR gap thresholds across participants. ABR and psychophysical thresholds for noise masked by temporally continuous, high-pass, or spectrally notched noise were measured in adults with normal hearing. Restricting the frequency range with masking led to poorer gap thresholds on both measures. High-pass maskers affected the ABR and psychophysical gap thresholds similarly. Notched-noise-masked ABR and psychophysical gap thresholds were very similar except that low-frequency, notched-noise-masked ABR gap threshold was much poorer at low levels. The ABR gap threshold was more sensitive to changes in signal-to-masker ratio than was the psychophysical gap detection threshold. ABR and psychophysical thresholds for gaps in broadband noise were measured in listeners with sensorineural hearing loss and in infants. On average, both ABR gap thresholds and psychophysical gap detection thresholds of listeners with hearing loss were worse than those of listeners with normal hearing, although individual differences were observed. Psychophysical gap detection thresholds of 3- and 6-month-old infants were an order of magnitude worse than those of adults with normal hearing, as previously reported; however, ABR gap thresholds of 3-month-old infants were no different from those of adults with normal hearing. These results suggest that ABR gap thresholds and psychophysical gap detection depend on at least some of the same mechanisms within the auditory system.

Adolescent↗

PubMed1996

Preliminary observations on the development of auditory sensitivity in infants with Down syndrome.

OBJECTIVE: Hearing loss commonly is associated with Down syndrome, but little is known about the development of auditory sensitivity in individuals with Down syndrome. This study had two objectives: 1) to determine whether an observer-based procedure can be used to assess the behavioral sensitivity of infants with Down syndrome, and 2) to provide preliminary information about the early course of hearing development among infants with Down syndrome. DESIGN: Behavioral measures of sensitivity were made in 16 infants with Down syndrome using an observer-based procedure. Ten of the infants were followed longitudinally between 2 and 12 mo of age. All infants passed a screening auditory brain stem response at 20 dB nHL during the study and completed screening tympanometry at each test session. The infants detected a 4000 Hz tone at levels ranging from 25 to 50 dB SPL; psychometric functions and thresholds for the tone were obtained. RESULTS: Infants with Down syndrome completed 80% of the test sessions they began, a rate similar to that seen in normally developing infants in the same type of study. Performance improved with increasing stimulus level, as one would expect, and thresholds were obtained from 15 of 16 infants for at least one age. The performance of infants with Down syndrome generally improved with age. The sensitivity of 2- to 3-mo-olds was poorer than that of older infants, but little if any improvement in sensitivity occurred between 4 and 12 mo. This pattern is similar to that seen in normally developing infants. Thresholds of infants with Down syndrome were 10 to 25 dB higher than those reported for normally developing infants. The psychometric functions of infants with Down syndrome were shallower than the psychometric functions of normally developing infants, and the slope of the psychometric functions did not change with age. Infants with Down syndrome achieved only 75 to 80% correct at any of the levels tested, 5 to 10% poorer than reported for other infants. These characteristics of the psychometric functions of the infants with Down syndrome suggest that they are inattentive during testing more often than are normally developing infants. CONCLUSIONS: An observer-based procedure can be used to obtain reasonable thresholds from infants with Down syndrome who are as young as 2 mo of age. Both sensory and nonsensory factors could contribute to the threshold elevation seen in infants with Down syndrome. At least on preliminary examination, the course of auditory sensitivity development of infants with Down syndrome is qualitatively similar to that seen in normally developing infants.

Acoustic Impedance Tests↗

PubMed1994

The relationship between auditory brainstem response latencies and behavioral thresholds in normal hearing infants and adults.

The relationship between behavioral thresholds and auditory brainstem response (ABR) latencies for 4 and 8 kHz tone pips were examined in normal-hearing 3-month-olds, 6-month-olds and adults. The latencies of waves I and V and the I-V interval of the ABR were analyzed. A linear latency-intensity function was also fit to each subject's latencies for each wave at several levels. The y-intercept of the latency-intensity function was used as a summary measure of latency to examine behavior-ABR correlations. The pattern of age-related change in behavioral threshold was not closely matched by age-related latency reduction for Wave I, Wave V or the I-V interval. However, 3-month-olds with higher behavioral thresholds had longer Wave V latencies and longer I-V intervals than 3-month-olds with lower behavioral thresholds. There was no significant difference in latency between 6-month-olds or adults with higher thresholds and 6-month-olds or adults with lower thresholds. There was also a significant correlation between the Wave V-Wave I latency-intensity intercept difference and behavioral threshold at both 4 and 8 kHz among 3-month-olds. The correlation was not significant among 6-month-olds or adults. These findings suggest that one of the factors responsible for immature behavioral thresholds at 3 months is related to transmission through the auditory brainstem. Because variability in hearing threshold among normal-hearing adults is low, it is not surprising that behavioral threshold is unrelated to ABR latency in this group. However, the lack of such a relationship among 6-month-olds implies that structures central to the auditory brainstem, either sensory or nonsensory, or both, must be responsible for immature behavioral thresholds after 6 months of age.

Acoustic Stimulation↗

PubMed1993

The relationship between auditory brainstem response and behavioral thresholds in normal hearing infants and adults.

The nature of age-related improvements in auditory sensitivity was explored by comparing behavioral and auditory brainstem response (ABR) thresholds in 3- and 6-month-old infants and in adults. Thresholds were estimated for tone pips at 1, 4, and 8 kHz, presented at a rate of 13.3/s. The time course of development of the two response measures was compared, and the correlation between thresholds for individual subjects was examined. Infant ABR threshold was adultlike at all frequencies, even among 3-month-olds. Infant behavioral thresholds were elevated relative to adult thresholds. Between 3 and 6 months, significant improvement occurred in the 8-kHz behavioral threshold, but no improvement occurred at other frequencies. This difference between ABR and behavioral measures in developmental time course suggests that peripheral sensitivity is not a major determinant of behavioral threshold elevation during infancy. The correlation between behavioral and ABR thresholds was significant at 4 kHz for 3-month-olds and at 8 kHz for adults. This suggests that variability in sensory function at these frequencies contributes to both behavioral and ABR thresholds, although other factors are likely to be involved as well.

Acoustic Stimulation↗