Auditory perception following hair cell regeneration in European starling (Sturnus vulgaris): frequency and temporal resolution.

Behavioral detection thresholds, auditory filter widths, and temporal modulation transfer functions were obtained from four starlings before, during and after 11 days of subcutaneous injections of kanamycin, an aminoglycoside antibiotic. Birds were operantly conditioned to respond to pure tones and amplitude modulated noises ranging in frequency from 0.25 to 7 kHz using adaptive staircase procedures and were tested daily for 92 days after the first injection of aminoglycoside. All birds had threshold shifts of at least -60 dB at frequencies above 4 kHz. Lower frequencies were affected in some birds, although none of the birds had hearing loss below 3 kHz. All four birds had wider auditory filters at 5 kHz immediately after the aminoglycoside series. Any changes in frequency resolution at frequencies below 5 kHz were slight, transitory, and rarely observed. Two of the four birds had permanently wider auditory filters at 5 kHz. Temporal modulation transfer functions were briefly affected in two birds during the time of greatest threshold shift. Recovery of detection thresholds began soon after the injections ceased and continued for approximately 60 days. Recovery in frequency resolution lagged behind auditory threshold by about 10 days. Normal temporal resolution was observed in the context of impaired intensity and frequency resolution. Changes in auditory threshold and frequency resolution were closely associated for all birds at 5 kHz, but were correlated with statistical significance in only two birds. Scanning electron microscopy was performed on all four birds after 90 days of recovery and confirmed that the extent of initial damage was consistent with the pattern of observed hearing loss.

Infant psychometric functions for detection: mechanisms of immature sensitivity.

Psychometric functions are described for individual 6- to 9-month-old infants and for individual adults for auditory detection of repeated, long- and short-duration tone bursts in quiet and for single, long-duration tone bursts in quiet and in noise. In general, infant psychometric functions have reduced upper asymptotes, shallower slopes, and poorer thresholds than adult psychometric functions. Infant-adult differences in slope and threshold are greater for short-duration tones than for other stimuli. Infant upper asymptotes are around 0.85 correct for all stimuli. One explantation for these findings is that infants are inattentive a certain proportion of time during the detection task. This model cannot account for the very shallow short-duration stimulus slope, nor can it account for infant-adult threshold differences for any stimulus. Other models of immature attention, or listening strategies, may be able to account for the slope and upper asymptote as well as the threshold of infant psychometric functions. Some combination of inattentiveness and primary neural immaturity may also account for the data. Although immaturities exist, some aspects of the detection process appear to be quantitatively similar in infants and adults.

Regenerated hair cells in the European starling: are they more resistant to kanamycin ototoxicity than original hair cells?

Previous work from our laboratory [Marean et al. (1993) Hear. Res. 71, 125-136] has shown that a 10 day dose of 200 mg/kg/day kanamycin produced damage to the basal 34% of the starling basilar papilla. We also observed that repeating the dosing schedule following a 4 month survival period resulted in significantly less damage to the regenerated auditory epithelium. The present study investigated whether or not this apparent resistance was the result of a tendency for regenerated hair cells to be less susceptible to kanamycin ototoxicity, or if other, systemic factors may be involved. Eight European starlings were given subcutaneous injections of 200 mg/kg/day kanamycin for 10 days. Serum levels of kanamycin were measured at the time of sacrifice for all birds, and the basilar papillae of all birds were examined by scanning electron microscopy (SEM). Two of these birds (Group 1) were sacrificed immediately following the dosing period. Two of the birds were allowed to survive for 60 days (Group 2). Two of the birds were redosed with 200 mg/kg/day for 10 days after 60 days survival (Group 3). Finally, two birds were redosed with 250 mg/kg/day until serum levels of kanamycin were the same as Group 1 when sacrificed (> 9 micrograms/ml). The SEM results showed that the regenerated auditory epithelium of the birds dosed a second time sustained less damage compared to previously untreated ears, even though the dosing regimen was the same (Group 3 versus Group 1). The regenerated auditory epithelium of birds dosed a second time sustained the same damage as previously untreated animals when the dosage was increased to attain similar serum levels (Group 4 versus Group 1). These results suggest metabolic changes occur in the starling in response to the initial dose of kanamycin which do not necessarily involve changes in hair cell resistance to ototoxicity.

Hair cell regeneration in the European starling (Sturnus vulgaris): recovery of pure-tone detection thresholds.

Behavioral detection thresholds were obtained from four starlings before, during, and after 11 days of subcutaneous injections of kanamycin. Birds were operantly conditioned to respond to pure-tones ranging in frequency from 0.25 kHz to 7 kHz using the method of constant stimuli and were tested daily for 141 days after the first injection of aminoglycoside. All four birds sustained hearing losses greater than 60 dB at frequencies from 4 kHz to 7 kHz by the end of the 11 day injection schedule. Two birds had a slight shift in threshold at 3 kHz. No change in threshold occurred for any of the birds at lower frequencies. Recovery of detection thresholds began soon after the injections ceased and continued for approximately 50 days. In all four birds there was some degree of permanent hearing loss: 5 dB to 15 dB at frequencies between 4 kHz and 6 kHz, and approximately 25 dB at 7 kHz. Scanning electron microscopy (SEM) was performed at 0 and 5 days post-injection in a separate group of starlings given the same injection schedule. Hair cell loss and damage was observed across the basal 34% to 36% of the basilar papilla. SEM in two behaviorally tested birds sacrificed 142 days after the first injection showed that there was regeneration of hair cells to populate the previously damaged region, but that disorientation of stereocilia bundles in the basal third of the basilar papilla was common. The other two behaviorally tested birds were treated with kanamycin again for 16 days beginning at 142 days after the first injection. Thresholds shifted again, but less than during the first dosing period. SEM of these birds' basilar papillae showed less hair cell loss than observed in the birds given only a single, 11 day dosing of kanamycin. This result suggests that birds may be less susceptible to the ototoxic effects of kanamycin in repeated treatments. In all four birds, the degree and position of damage observed with SEM corresponded with the extent and frequency of hearing loss.

Infant auditory temporal acuity: gap detection.

The development of auditory temporal acuity during infancy was examined in 3-, 6-, and 12-month-old infants and in adults using the gap detection paradigm. Listeners detected a series of gaps, or silent intervals, or variable duration in a broadband noise. In order to vary the acoustic frequencies available to the listener, a high-pass noise was used to mask frequencies above specified cutoffs. High-pass maskers with cutoffs of 500, 2,000, and 8,000 Hz were used. The minimum detectable gap was determined using the Observer-based Psychoacoustic Procedure. The thresholds of 3- and 6-month-olds were considerably poorer than those of the adults, although the effect of masker condition was about the same for these 3 groups. The thresholds of 12-month-olds were significantly worse than the adults when the stimulus was unmasked or when the masker cutoff frequency was 2,000 or 8,000 Hz. When the masker cutoff frequency was 500 Hz, 12-month-olds fell into 2 groups: some had gap thresholds that were about the same as 3- and 6-month-olds, while some had gap thresholds that approached those of adults. In a second experiment, a larger group of 12-month-olds were tested with a 500-Hz masker cutoff. Average performance of 12-month-olds was about the same as that of 3- and 6-month-olds in Experiment 1. Some infants attained thresholds close to those of adults. Thus, gap detection thresholds are quite poor in infants, although the similarity of the effect of frequency on performance in infants and adults suggests that the mechanisms governing temporal resolution in infants operate qualitatively like those in adults.

Methods for estimating infant thresholds.

Detection thresholds for 1000-Hz, 16-ms tone bursts were estimated for 3- and 6-month-old infants and for young adults. The test procedure used was the observer-based psychoacoustic procedure. Thresholds were estimated using two different adaptive procedures and the method of constant stimuli. There was little difference among the average thresholds determined by any of these techniques. The least variable thresholds were obtained in the method of constant stimuli. In addition, 10 infants at each age completed two 30-trial blocks of trials in the method of constant stimuli; 22 adults completed 8 blocks of 30 trials. For 3- and 6-month-olds and for adults, there was no significant change in average threshold between blocks. Individual 6-month-olds' thresholds rarely changed by more than 5 dB between blocks, and the correlation between the thresholds obtained in the two blocks was significant. Individual 3-month-olds' thresholds, however, sometimes changed by as much as 10 dB between blocks, and the correlation between first and second block threshold was not significant. The effects of response bias on threshold were assessed by examining receiver operating characteristic plots of hit and false alarm rates at threshold and the correlation between false alarm rate and threshold. Although there was some variability in response bias, infant/observer teams tended to respond in an unbiased fashion. In one of the adaptive procedures only, false alarm rate was significantly correlated with threshold. In all procedures, the exclusion of infants with high false alarm rates changed the average thresholds obtained by less than 5 dB.(ABSTRACT TRUNCATED AT 250 WORDS)

Speech perception in children with histories of recurrent otitis media.

The present study investigated the ability of 5-year-old children to perceive differences in voice onset time (VOT) in naturally produced speech. Three groups of children whose hearing was within normal limits at the time of the experiment were tested on identification and discrimination tasks: (1) group C, in which the children had normal language abilities and no history of severe, recurrent otitis media (OM), (2) group OM, in which the children had histories of severe, recurrent OM but normal language abilities, and (3) group OM/DL, in which the children had histories of severe OM and delays in the acquisition of linguistic competence. Compared to group C, group OM/DL showed marked differences in their ability to identify and discriminate speech patterns. Their perception was less categorical, as well, in that there was less of a peak in the discrimination function at the region of the phoneme boundary. The performance of group OM fell between the other two groups, with deficits being more pronounced in the discrimination task than in the identification task. The results supported the idea that episodes of OM can produce periods of sensory deprivation that alter perceptual abilities. The relation of a history of OM to later language and academic difficulties was also considered.

Acoustic analyses and perceptual data on anticipatory labial coarticulation in adults and children.

The present study investigated anticipatory labial coarticulation in the speech of adults and children. CV syllables, composed of [s], [t], and [d] before [i] and [u], were produced by four adult speakers and eight child speakers aged 3-7 years. Each stimulus was computer edited to include only the aperiodic portion of fricative-vowel and stop-vowel syllables. LPC spectra were then computed for each excised segment. Analyses of the effect of the following vowel on the spectral peak associated with the second formant frequency and on the characteristic spectral prominence for each consonant were performed. Perceptual data were obtained by presenting the aperiodic consonantal segments to subjects who were instructed to identify the following vowel as [i] or [u]. Both the acoustic and the perceptual data show strong coarticulatory effects for the adults and comparable, although less consistent, coarticulation in the speech stimuli of the children. The results are discussed in terms of the articulatory and perceptual aspects of coarticulation in language learning.