Identifying a newly discovered HLA-C allele: HLA-C*07:607.

Phased sequencing identified the HLA-C*07:607 allele in an African-American patient and sibling donor.

The role of stimulus complexity, spectral overlap, and pitch for gap-detection thresholds in young and old listeners.

Thresholds for detecting a gap between two complex tones were determined for young listeners with normal hearing and old listeners with mild age-related hearing loss. The leading tonal marker was always a 20-ms, 250-Hz complex tone with energy at 250, 500, 750, and 1000 Hz. The lagging marker, also tonal, could differ from the leading marker with respect to fundamental frequency (f0), the presence versus absence of energy at f0, and the degree to which it overlapped spectrally with the leading marker. All stimuli were presented with steeper (1 ms) and less steep (4 ms) envelope rise and fall times. F0 differences, decreases in the degree of spectral overlap between the markers, and shallower envelope shape all contributed to increases in gap-detection thresholds. Age differences for gap detection of complex sounds were generally small and constant when gap-detection thresholds were measured on a log scale. When comparing the results for complex sounds to thresholds obtained for pure-tones in a previous study by Heinrich and Schneider [(2006). J. Acoust. Soc. Am. 119, 2316-2326], thresholds increased in an orderly fashion from markers with identical (within-channel) pure tones to different (between-channel) pure tones to complex sounds. This pattern of results was true for listeners of both ages although younger listeners had smaller thresholds overall.

How Age Affects Auditory-Cognitive Interactions in Speech Comprehension.

To participate effectively in multi-talker conversations, listeners need to do more than simply recognize and repeat speech. They have to keep track of who said what, extract the meaning of each utterance, store it in memory for future use, integrate the incoming information with what each conversational participant has said in the past, and draw on the listener's own knowledge of the topic under consideration to extract general themes and formulate responses. In other words, to acquire and use the information contained in spoken language requires the smooth and rapid functioning of an integrated system of perceptual and cognitive processes. Here we review evidence indicating that the operation of this integrated system of perceptual and cognitive processes is more easily disrupted in older than in younger adults, especially when there are competing sounds in the auditory scene.

Effects of heifer finishing implants on beef carcass traits and longissimus tenderness.

Effects of finishing implants on heifer carcass characteristics and LM Warner-Bratzler shear force (WBSF) were investigated using commercially fed Continental x British heifers (n = 500). Heifers were blocked by initial BW (block 1, BW > or = 340 kg; block 2, BW < 340 kg) and assigned randomly to 12 treatments that utilized 0, 1, or 2 finishing implants to deliver cumulative dosages of trenbolone acetate (TBA) and estradiol 17-beta (E2) ranging from 0 to 400 mg of TBA and 0 to 40 mg of E2 during the finishing period. Heifers in blocks 1 and 2 were slaughtered after 135 and 149 d on feed, respectively. At these endpoints, the treatment groups did not differ (P > 0.05) in adjusted fat thickness or predicted percentage of empty body fat. Compared with a nonimplanted control, implanting heifers once during finishing increased (P = 0.025) HCW by an average of 7.9 kg without affecting the mean marbling score, the percentage of carcasses grading Choice and Prime, or LM WBSF values. Compared with the use of 1 implant, the use of 2 finishing implants resulted in an additional increase (P = 0.008) in HCW of 6.0 kg. Reimplanting also increased (P < 0.001) LM area, reduced (P = 0.024) the percentage of KPH, and improved (P = 0.004) mean yield grade. However, reimplanted heifers produced a lower (P = 0.044) percentage of carcasses grading Choice and Prime and LM steaks with greater (P < 0.05) WBSF values at all postmortem aging times compared with heifers that were implanted once. Among heifers receiving 2 implants, mean 14-d LM WBSF increased linearly (P < 0.05) as the cumulative, combined dosage of E2 plus TBA increased. Heifers implanted with a combination of E2 plus TBA had larger (P = 0.046) LM areas, lower (P = 0.004) mean marbling scores, and greater LM WBSF values after 3 d (P = 0.001), 7 d (P = 0.001), 14 d (P = 0.003), and 21 d (P = 0.045) of postmortem aging than did heifers implanted with TBA alone. Heifers that received combination implants containing both E2 and TBA also produced fewer (P = 0.005) carcasses with marbling scores of modest or greater compared with heifers that received single-ingredient implants containing TBA alone. Implant treatment effects on LM WBSF gradually diminished as the length of the postmortem aging period increased. Postmortem aging periods of 14 to 28 d were effective for mitigating the detrimental effects of mild or moderately aggressive heifer implant programs on the predicted consumer acceptability of LM steaks.

Binocular detection of masked patterns in young and old observers.

A visual pattern embedded in noise is detected appreciably better when the stimulus complex contains interocular cues (dichoptic condition) than when such cues are absent (binoptic condition). In a recent study (F. Speranza, G. Moraglia, & B. A. Schneider, 1995) the authors showed that the relative difference between binoptic and dichoptic thresholds does not change with age. However, older adults showed higher binoptic and dichoptic thresholds, thus suggesting an age-related difficulty with degraded stimulation. In this article the authors first replicated these findings and proceeded next to investigating whether age-related changes in processing efficiency, additive internal noise, and the spatial frequency bandwidth of the detecting filters could account, separately or concurrently, for the elevated thresholds in noise exhibited by the older adults. Results indicate that this increase is not attributable to age-related changes in filter bandwidth or internal noise. Rather, the findings can be explained in terms of a decrease in processing efficiency with age.

How aging affects the reading of words in noisy backgrounds.

Young and old adults were shown simple sentences masked by visual noise. In half of the sentences, the final word was predictable; in the other half, it was not. The older participants were able to identify the same number of final words as the younger ones only when the intensity of the visual noise was significantly diminished. However, the difference in the number of correct identifications between predictable and unpredictable conditions was higher for the older observers than for the younger observers, indicating that older observers benefit from context more.

The periodicity of forward-masked auditory pip-detection thresholds, predicted from the output power of the auditory filter during ringing.

The plot of detection thresholds vs. time for a forward-masked Gaussian-shaped 2 kHz pip (S.D.=0.5 ms) shows a noisy 'fine structure' that disappears with across-subject averaging. The averaging uncovers a slower threshold periodicity, that can be predicted from the output power of the auditory filter during extended ringing.

Children's perception of speech in multitalker babble.

Children 5, 9, and 11 years of age and young adults attempted to identify the final word of sentences recorded by a female speaker. The sentences were presented in two levels of multitalker babble, and participants responded by selecting one of four pictures. In a low-noise condition, the signal-to-noise ratio (SNR) was adjusted for each age group to yield 85% correct performance. In a high-noise condition, the SNR was set 7 dB lower than the low-noise condition. Although children required more favorable SNRs than adults to achieve comparable performance in low noise, an equivalent decrease in SNR had comparable consequences for all age groups. Thus age-related differences on this task can be attributed primarily to sensory factors.

Listening to discourse in distracting settings: the effects of aging.

Younger and older adults listened to discourse in quiet and in conversational noise, before answering questions concerning the material. Some questions required listeners to recall specific details; others were of a more integrative nature. When the listening situation was adjusted for individual differences in hearing, younger and older adults were equally adept at remembering the gist of the passages in both quiet and in two levels of noise. The two age groups also did not differ with respect to memory for specific details when listening in quiet or in a moderate level of noise, even when required to perform a concurrent task. Only at the loudest noise level did younger adults tend to recall more detail than older adults. However, when no adjustments were made to compensate for the poorer hearing of older adults (all participants tested under identical listening conditions), older adults could not recall as much detail as younger adults, either in quiet or in noise. The results indicate that the speech-comprehension difficulties of older adults primarily reflect declines in hearing rather than in cognitive ability.

The fine structure of the recovering auditory detection threshold.

Detection thresholds were gathered for a 2 kHz Gaussian-shaped probe (standard deviation = 0.5 ms), centered at intervals of as little as half a millisecond over 0-30 ms following a 200 ms, 97 dB SPL, 2 kHz tone. Surprisingly, there were small, sudden rises and falls superimposed on each subject's generally smooth recovery. Even more obvious were nonmonotonicities in the standard deviation of the cumulative normal fitted to each threshold's psychometric function.

Gap detection thresholds as a function of tonal duration for younger and older listeners.

Twenty normal hearing younger and twenty older adults in the early stages of presbycusis, but with relatively normal hearing at 2 kHz, were asked to discriminate between the presence versus absence of a gap between two equal-duration tonal markers. The duration of each marker was constant within a block of trials but varied between 0.83 and 500 ms across blocks. Notched-noise, centered at 2 kHz, was used to mask on- and off-transients. Gap detection thresholds of older adults were markedly higher than those of younger adults for marker durations of less than 250 ms but converged on those of younger adults at 500 ms. For both age groups, gap detection thresholds were independent of audiometric thresholds. These results indicate that older adults have more difficulty detecting a gap than younger adults when short marker durations (i.e., durations characteristic of speech sounds) are employed. It is shown that these results cannot be explained by linear models of temporal processing but are consistent with differential adaptation effects in younger and older adults.

Binocular vision enhances phase discrimination by filtering the background.

Previous studies have shown that the detectability of a noise-masked target can be enhanced under stereoscopic viewing when the target's interocular disparity differs from that of the noise. This enhanced detectability can be accounted for by a model postulating that the binocular system linearly sums the left-eye and right-eye views of a visual scene. This model also predicts enhanced phase discrimination under specifiable interocular disparities of target and noise. Two experiments were conducted in which subjects were asked to discriminate between two luminance patterns (target and foil) that differed only in phase. The target patterns were constructed by summating two vertical sinusoidal gratings in which the phase difference between the higher and the lower spatial frequency gratings was 45 degrees. The foils contained the same two component frequencies, with a phase difference of -45 degrees. Thus, targets and foils were mirror images of one another. The ability of subjects to discriminate between these stereoscopically viewed mirror-image patterns was investigated under two sets of interocular disparities: those that, according to our model, would unmask one or both spatial frequency components, and those that would leave both components masked by the noise. Phase discrimination was enhanced only when both component frequencies of the target and foil were unmasked. The implications of these findings for template-matching and phase-discrimination models of pattern discrimination are considered.

Masking-level differences in older adults: the effect of the level of the masking noise.

In Experiment 1, masking-level differences (MLDs) for a 500-Hz tone at five masker levels were obtained from younger and older adults. For both age groups, there were no reliable increases in MLD once the spectrum level of the masker exceeded 27 dB SPL. MLDs were larger for younger than for older adults over the range of masker levels tested. In Experiment 2, the levels of both the signal and the masker in one ear were attenuated by either 15 or 30 dB relative to their level in the other ear, which was fixed at a spectrum level of 47 dB SPL. MLDs for both age groups declined with increasing IAA and age-related differences were observed in all conditions. The findings of these experiments indicate that (1) age-related differences in MLDs exist even when the level of the masker is sufficiently high that older adults achieve their plateau performance, and (2) older listeners are not disadvantaged more than younger listeners by interaural differences in the level of the input.

Binaural additivity of loudness in children and adults.

Thirty-six different binaural noises were formed by crossing six right-ear intensities of a broadband noise with the same six intensities in the left ear in a 6 X 6 factorial design. Children (6-7 years of age) and adults were presented with 2 of these 36 binaural noises on a trial and asked to indicate which noise was louder. In Experiment 1, the left- and right-ear noises were in phase and differed only in intensity. In Experiment 2, the left- and right-ear noises were in opposite phase. For both the children and adults in Experiments 1 and 2, the paired comparison judgments of binaural loudness were shown to satisfy the testable axioms of conjoint measurement (transitivity and double cancellation), permitting the determination of interval scales of loudness for the left ear, right ear, and the sum of the two ears. Power functions provided a good description of the relation between loudness and sound pressure for the left and right ears of both children and adults. For both adults and children, an examination of the pattern of differences in judgments between Experiments 1 and 2 indicated that, when the noises were in phase, the contribution of the right ear to fused loudness was greater than when the noises were presented in counterphase.

Noise-limited detection in young and old observers.

11 young (M age = 24.3 yr.) and 11 old (M age = 67.4 yr.) observers attempted to detect signals of limited bandwidth in visual noise. The older observers did not perform as well as the young ones. We considered whether, as suggested by a current hypothesis, these differences could be attributed to higher internal additive noise in the elderly observers. The results suggested that internal noise did not differ across the two age groups and that the lower performance of the older observers stemmed instead from reduced processing efficiency.

Gap detection in infants, children, and adults.

Listeners who were 6.5 months, 12 months, 5 years, and 21 years of age were required to discriminate a pair of 500-Hz, Gaussian-enveloped tone pips from a short 500-Hz tone of the same duration and total energy. Groups of 6.5-month-old infants were tested on a single gap duration: 8, 12, 16, 20, 28, or 40 ms. Groups of 12-month-olds were also tested on a single gap duration: 8, 12, 16, or 20 ms. The 5-year-old children and adults were tested on gap durations of 8, 12, and 16 ms. The mean performance of 6.5-month-olds significantly exceeded chance levels on all gap durations except 8 ms, and that of 12-month-olds was above chance levels on all gap durations. For 5-year-old children and adults, mean performance also exceeded chance levels for all gap durations tested. Adults performed significantly better than 5-year-old children on gap durations of 12 and 16 ms. Gap-detection thresholds, defined by a performance criterion of d' = 0.5, were estimated at 11, 5.6, and 5.2 ms for infants, children, and adults, respectively. It is likely that smaller adult-infant differences in the present study compared to those reported in previous research stem from our use of Gaussian-enveloped tone pips and the consequent minimization of adaptation effects.

Age-related changes in binocular vision: detection of noise-masked targets in young and old observers.

This study investigated the effects of age on binocular unmasking. This term denotes the fact that a visual signal embedded in noise is detected appreciably better when the stimulus complex contains interocular cues (dichoptic condition) than when such cues are absent (binoptic condition). Detection thresholds for two Gabor signals differing in spatial frequency were determined in young and old adults with no identifiable ocular pathologies. The signals were embedded, in both conditions, in two-dimensional Gaussian noise. Binocular Masking Level Differences, defined as the difference between the binoptic thresholds and the dichoptic thresholds, did not change with age; however, the older adults showed higher binoptic thresholds with both signals and higher dichoptic thresholds with only the lower-spatial-frequency signal. For both groups, binoptic and dichoptic thresholds increased with spatial frequency. The implications of these results are discussed.

How young and old adults listen to and remember speech in noise.

Two experiments using the materials of the Revised Speech Perception in Noise (SPIN-R) Test [Bilger et al., J. Speech Hear. Res. 27, 32-48 (1984)] were conducted to investigate age-related differences in the identification and the recall of sentence-final words heard in a babble background. In experiment 1, the level of the babble was varied to determine psychometric functions (percent correct word identification as a function of S/N ratio) for presbycusics, old adults with near-normal hearing, and young normal-hearing adults, when the sentence-final words were either predictable (high context) or unpredictable (low context). Differences between the psychometric functions for high- and low-context conditions were used to show that both groups of old listeners derived more benefit from supportive context than did young listeners. In experiment 2, a working memory task [Daneman and Carpenter, J. Verb. Learn. Verb. Behav. 19, 450-466 (1980)] was added to the SPIN task for young and old adults. Specifically, after listening to and identifying the sentence-final words for a block of n sentences, the subjects were asked to recall the last n words that they had identified. Old subjects recalled fewer of the items they had perceived than did young subjects in all S/N conditions, even though there was no difference in the recall ability of the two age groups when sentences were read. Furthermore, the number of items recalled by both age groups was reduced in adverse S/N conditions. The resutls were interpreted as supporting a processing model in which reallocable processing resources are used to support auditory processing when listening becomes difficult either because of noise, or because of age-related deterioration in the auditory system. Because of this reallocation, these resources are unavailable to more central cognitive processes such as the storage and retrieval functions of working memory, so that "upstream" processing of auditory information is adversely affected.

Gap detection and the precedence effect in young and old adults.

Thresholds for detecting a gap between two Gaussian-enveloped (standard deviation = 0.5 ms), 2-kHz tones were determined in young and old listeners. The gap-detection thresholds of old adults were more variable and about twice as large as those obtained from young adults. Moreover, gap-detection thresholds were not correlated with audiometric thresholds in either group. Estimates of the width of the temporal window of young subjects, based on the detection of a gap between two tone pips, were smaller than those typically obtained when a relatively long duration pure tone is interrupted [Moore et al., J. Acoust. Soc. Am. 85, 1266-1275 (1989)]. Because the amount of time it takes to recover from an adapting stimulus is likely to affect gap detection thresholds [Glasberg et al., J. Acoust. Soc. Am. 81, 1546-1556 (1987)], smaller estimates of temporal window size would be expected in this paradigm if the amount of adaptation produced by the first tone pip was negligible. The larger gap-detection thresholds of old subjects indicate that they may have larger temporal windows than young subjects. The lack of correlation between audiometric and gap-detection thresholds indicates that this loss of temporal acuity is not related to the degree of sensorineural hearing loss. In a second experiment on the precedence effect using the same subjects, a Gaussian-enveloped tone was presented over earphones to the left ear followed by the same tone pip presented to the right ear. To more realistically approximate a sound field situation, the tone pip presented to each ear was followed 0.6 ms later by an attenuated version presented to the contralateral ear. The delay between the left- and right-ear tone-pips was varied and the transition point between hearing a single tone on the left, and hearing two such sounds in close succession (one coming from the left and the other from the right) was determined. The transition point in this experiment did not differ between young and old subjects nor were these transition points correlated with gap-detection thresholds. These results indicate that monaural temporal acuity and binaural echo suppression may be based on different processes.

The effect of interaural delay of the masker on masking-level differences in young and old adults.

Diotic (SoNo) thresholds and dichotic (S pi N pi tau) thresholds were measured for young and old adults using a 500-Hz pure-tone signal and broadband burst masking noise at 37 dB SPL/Hz. In the dichotic condition both the signal and the masker were phase reversed and the masker was presented with an interaural delay of 0.25, 0.5, 0.75, 1, 1.25, 1.5, 1.75, 2, 3, or 5 ms. Masking-level differences (MLDs) were determined by subtracting dichotic thresholds from diotic thresholds. The SoNo thresholds for the old subjects did not differ significantly from those for the young subjects; however, when MLDs were plotted as a function of delay, the pattern of results differed significantly between young and old subjects. This difference in pattern was completely accounted for in terms of a delay-line version of Durlach's equalization and cancellation (EC) model [N. I. Durlach, in Foundations of Modern Auditory Theory, edited by J. V. Tobias (Academic, New York, 1972); B. A. Schneider and P. M. Zurek, J. Acoust. Soc. Am. 86, 1756-1763 (1989)] by assuming that temporal jitter increases with internal delay in young subjects but that it does not vary with the amount of internal delay in old subjects.