Recognition of dichotic digits under pre-cued and post-cued response conditions in young and elderly listeners.

Dichotic listening was evaluated in pre-cued and post-cued response conditions using a hierarchical set of one-, two- and three-pair dichotic digit materials. Thirty young adults (mean age 29.1 years) with normal hearing, and 30 older adults in the 60-79-year age range (mean age 68.7 years) with mild-to-moderate sensorineural hearing loss were evaluated. Several patterns of performance were observed. First, recognition performance in the pre-cued condition was better than recognition performance in the post-cued condition for one-, two- and three-pair digits for both age groups. Second, there was a right ear advantage in pre- and post-cued response conditions for both age groups. In the pre-cued condition, the right ear advantage was small owing to ceiling effects associated with ease of the listening task. In the post-cued condition, recognition performance decreased as a function of age, and left ear scores decreased faster than right ear scores, resulting in a larger right ear advantage in the 60-79-year group. Third, as the complexity of the listening task increased from easy (one-pair) to difficult (three-pairs), there was a corresponding decrease in recognition performance for both age groups. The increase in the difference in performance on easy and difficult tasks became larger as a function of age.

Effect of order bias on the recognition of dichotic digits in young and elderly listeners.

Dichotic listening was evaluated in free-recall and directed-recall (pre-cued, post-cued) response conditions using interleaved one-, two-, and three-pair dichotic digit materials. In the free-recall condition, the subjects recalled in any order the digits presented. In the directed-recall condition, a response task was examined where subjects recalled all digits presented to the cued ear (pre- or post-cued) followed by the digits presented to the opposite (non-cued) ear. Thirty 20- to 29-year-old adults with normal hearing and 30 60- to 79-year-old adults with mild-to-moderate sensorineural hearing loss were evaluated. In all conditions, performance by the younger listeners was better than performance by the elderly listeners. As the difficulty of the dichotic digit task increased, recognition performance decreased. The recognition performance of elderly listeners was more affected by increases in the difficulty of the stimulus materials as compared to the younger listeners. In the free-recall condition, there was a right-ear advantage for both age groups. When instructional bias was imposed, the results favored the ear of instructed bias. The differences in recognition performance between young and elderly listeners likely reflect differences in the difficulty of the dichotic digit test conditions and variations in the demand on auditory memory.

Psychometrically equivalent spondaic words spoken by a female speaker.

Several studies demonstrate that thresholds for the individual CID W-1 spondaic words peaked at 0 vu are not equivalent. The purpose of this study was to equate the spondaic word thresholds psychometrically. Two studies were performed on 2 groups of 20 listeners with normal hearing. In Experiment 1, psychometric functions were established for the 36 spondaic words spoken by a male (original recording) and female speaker. Based on the threshold data from Experiment 1, the words spoken by the female speaker were adjusted digitally in level to produce equal thresholds (equal intelligibility). In Experiment 2, psychometric functions then were established for the 36 spondaic words adjusted in level. The mean thresholds for the 2 experiments were the same (0.5 dB HL; ANSI, 1996), but the standard deviations for the word thresholds in Experiment 2 (0.7 dB) were significantly smaller than the standard deviations in Experiment 1 (1.6 dB). Both versions of the spondaic words spoken by the female speaker are included on the Speech Recognition and Identification Materials (Disc 2.0) compact disc.

Recognition of one-, two-, and three-pair dichotic digits under free and directed recall.

A one-, two-, and three-pair dichotic digit test was administered to 180 subjects (20-79 years) with varying degrees of hearing sensitivity. The test was carried out under free- and directed-recall response conditions. The results indicated that recognition performance decreased as a function of increasing age. Statistical analysis using analysis of covariance indicated that differences in performance between age groups were not owing to differences in hearing sensitivity. Thus, with the effects of hearing sensitivity removed, age alone accounted for a significant portion of the variability in the data among age groups. Normative data for the free-recall condition are reported for the two lists of randomly interleaved one-, two-, and three-pair digits included on the Tonal and Speech Materials for Auditory Perceptual Assessment, Disc 2.0 (1998) compact disc. A comparison of performance in free- and directed-recall conditions indicated three patterns of results. First, 58 percent of the subjects had normal recognition performance for one-, two-, and three-pair digits under both recall conditions. Second, 39 percent of the subjects had a deficit in the free-recall condition, with normal performance in the directed-recall condition, which was interpreted as representing primarily a cognitive problem. Third, the remaining 3 percent of the subjects showed a deficit in both free- and directed-recall conditions, which was attributed primarily to an auditory problem.

Stimulus length uncertainty with dichotic digit recognition.

Dichotic digit listening was made more difficult by interleaving one-, two-, three-, and four-pair digits within a test list in which the subjects did not know a priori the number of digit pairs presented on a given trial, thereby introducing listener uncertainty. Twenty right-handed (mean age = 26.8 years) and 20 left-handed adults (mean age = 24.0) with normal hearing and 40 right-handed adults in the 60- to 75-years age range (mean age = 67.2) with mild-to-moderate sensorineural hearing loss were evaluated. Compared to traditional paradigms, the uncertainty of stimulus length (one, two, three, or four pairs) reduced overall recognition performance on stimuli presented to both ears of all groups, but the reduction was more pronounced for the left ear than for the right ear. The recognition performance of the right-handed subjects was more homogeneous than the performance of the left-handed subjects. In comparison to the young subjects, the 60- to 75-year-old group had substantially reduced recognition performance.

Temporal processing in the aging auditory system.

Measures of monaural temporal processing and binaural sensitivity were obtained from 12 young (mean age = 26.1 years) and 12 elderly (mean age = 70.9 years) adults with clinically normal hearing (pure-tone thresholds < or = 20 dB HL from 250 to 6000 Hz). Monaural temporal processing was measured by gap detection thresholds. Binaural sensitivity was measured by interaural time difference (ITD) thresholds. Gap and ITD thresholds were obtained at three sound levels (4, 8, or 16 dB above individual threshold). Subjects were also tested on two measures of speech perception, a masking level difference (MLD) task, and a syllable identification/discrimination task that included phonemes varying in voice onset time (VOT). Elderly listeners displayed poorer monaural temporal analysis (higher gap detection thresholds) and poorer binaural processing (higher ITD thresholds) at all sound levels. There were significant interactions between age and sound level, indicating that the age difference was larger at lower stimulus levels. Gap detection performance was found to correlate significantly with performance on the ITD task for young, but not elderly adult listeners. Elderly listeners also performed more poorly than younger listeners on both speech measures; however, there was no significant correlation between psychoacoustic and speech measures of temporal processing. Findings suggest that age-related factors other than peripheral hearing loss contribute to temporal processing deficits of elderly listeners.

Evidence against the influence of aging on distortion-product otoacoustic emissions.

Previous research has reported reduced otoacoustic emission amplitude as a function of age. In each study, however, interpretation of findings was confounded by age-related hearing loss. The present study was designed to re-evaluate the contribution of age and peripheral hearing loss on the prevalence and amplitude of distortion-product otoacoustic emissions (DPOAEs) by controlling for degree of peripheral hearing loss. Twenty subjects were divided into four age ranges. All subjects in each group had 15 dB HL or better thresholds from 0.25 through 8 kHz and normal immittance findings. DPOAE audiograms recorded at three intensity levels and input/output functions recorded at six discrete frequencies showed no significant differences in amplitude or noise level between age groups. Findings indicate that when the degree of peripheral hearing loss is adequately controlled, there is no direct effect of advanced age on DPOAE measures. Clinical implications are discussed.

Central auditory processing in Alzheimer's disease.

OBJECTIVE: This investigation was designed to determine whether people in the early to middle phases of Alzheimer's disease (AD) show impaired central auditory processing as compared with nondemented elderly. DESIGN: A peripheral and central auditory test battery was administered to 10 subjects diagnosed with mild-to-moderate AD based on a neuropsychological test battery and radiographic techniques, and a control group of 10 subjects with no evidence of dementia, matched for age, gender, and average degree of hearing loss. Immittance audiometry, pure-tone and speech audiometry, and otoacoustic emissions were recorded in all subjects. Central auditory assessment included the synthetic sentence identification with ipsilateral competing message, dichotic digits, dichotic sentence identification, pitch patterns, and duration patterns. RESULTS: Peripheral auditory status was statistically similar between subject groups. Neither average high frequency hearing sensitivity nor mean speech recognition ability was significantly different. However, a significant difference was noted between groups for average low frequency hearing sensitivity in the left ear (p < 0.05). Subjects with AD showed slightly poorer low frequency thresholds versus matched controls. Based on analysis of performance on each measure of the central auditory test battery, the AD group scored significantly lower than the matched control group on four of the five measures utilized. Differences for right versus left ear performance were found among AD subjects. CONCLUSIONS: Overall patterns in findings cannot be easily explained as artifacts of cognitive decline. Results support screening for central auditory dysfunction in the AD population, since impaired processing could influence psychiatric assessment of cognitive deficit as well as audiologic management of peripheral hearing loss in this population.

Test-retest reliability of a dichotic digits test for assessing central auditory function in Alzheimer's disease.

Test-retest reliability for the dichotic digits test was measured in 10 subjects diagnosed with mild-to-moderate Alzheimer's disease and a control group of 10 subjects with no evidence of dementia, matched for age, gender and average degree of hearing loss. Although initial scores among the Alzheimer group were more variable, test-retest reliability over a month period was reasonably high for both subject groups. Results are in agreement with previous reports on dichotic digits showing good sensitivity, ease in administration and time efficiency. Use of the dichotic digits test for screening of central auditory function in the Alzheimer population is supported.