Psychophysical data on hearing sensitivity and various measures of supra-threshold auditory temporal processing are presented for large groups of young (18–35 y), middle-aged (40–55 y) and older (60–89 y) adults. Hearing thresholds were measured at 500, 1414 and 4000 Hz. Measures of temporal processing included gap-detection thresholds for bands of noise centered at 1000 and 3500 Hz, stimulus onset asynchronies for monaural and dichotic temporal-order identification for brief vowels, and stimulus onset/offset asynchronies for the monaural temporal masking of vowel identification. For all temporal-processing measures, the impact of high-frequency hearing loss in older adults was minimized by a combination of low-pass filtering the stimuli and use of high presentation levels. The performance of the older adults was worse than that of the young adults on all measures except gap-detection threshold at 1000 Hz. Middle-aged adults performed significantly worse than the young adults on measures of threshold sensitivity and three of the four measures of temporal-order identification, but not for any of the measures of temporal masking. Individual differences are also examined among a group of 124 older adults. Cognition and age were found to be significant predictors, although only 10–27% of the variance could be accounted for by these predictors.

Although research has focused on the perceptual contribution of consonants to spoken syllable or word intelligibility, in sentences vowels have a distinct perceptual advantage over consonants in determining intelligibility [Kewley-Port et al., J. Acoust. Soc. Am. 122, 2365-2375 (2007)]. The current study used a noise replacement paradigm to investigate how perceptual contributions of consonants and vowels are mediated by transitional information at segmental boundaries. The speech signal preserved between replacements is defined as a glimpse window. In the first experiment, glimpse windows contained proportional amounts of transitional boundary information that was either added to consonants or deleted from vowels. Results replicated a two-to-one vowel advantage for intelligibility at the traditional consonant-vowel boundary and suggest that vowel contributions remain robust against proportional deletions of the signal. The second experiment examined the combined effect of random glimpse windows not locked to segments and the distributions of durations measured from the consonant versus vowel glimpses observed in Experiment 1. Results demonstrated that, for random glimpses, the cumulative sentence duration glimpsed was an excellent predictor of performance. Comparisons across experiments confirmed that higher proportions of vowel information within glimpses yielded the highest sentence intelligibility.

This project focused on the individual differences underlying observed variability in temporal processing among older listeners. Four measures of vowel temporal-order identification were completed by young ͑N = 35; 18-31 years͒ and older ͑N = 151; 60-88 years͒ listeners. Experiments used forced-choice, constant-stimuli methods to determine the smallest stimulus onset asynchrony ͑SOA͒ between brief ͑40 or 70 ms͒ vowels that enabled identification of a stimulus sequence. Four words ͑pit, pet, pot, and put͒ spoken by a male talker were processed to serve as vowel stimuli. All listeners identified the vowels in isolation with better than 90% accuracy. Vowel temporal-order tasks included the following: ͑1͒ monaural two-item identification, ͑2͒ monaural four-item identification, ͑3͒ dichotic two-item vowel identification, and ͑4͒ dichotic two-item ear identification. Results indicated that older listeners had more variability and performed poorer than young listeners on vowel-identification tasks, although a large overlap in distributions was observed. Both age groups performed similarly on the dichotic ear-identification task. For both groups, the monaural four-item and dichotic two-item tasks were significantly harder than the monaural two-item task. Older listeners' SOA thresholds improved with additional stimulus exposure and shorter dichotic stimulus durations. Individual differences of temporal-order performance among the older listeners demonstrated the influence of cognitive measures, but not audibility or age.

This study investigated the relative contributions of consonants and vowels to the perceptual intelligibility of monosyllabic consonant-vowel-consonant ͑CVC͒ words. A noise replacement paradigm presented CVCs with only consonants or only vowels preserved. Results demonstrated no difference between overall word accuracy in these conditions; however, different error patterns were observed. A significant effect of lexical difficulty was demonstrated for both types of replacement, whereas the noise level used during replacement did not influence results. The contribution of consonant and vowel transitional information present at the consonant-vowel boundary was also explored. The proportion of speech presented, regardless of the segmental condition, overwhelmingly predicted performance. Comparisons were made with previous segment replacement results using sentences ͓Fogerty, and Kewley-Port ͑2009͒. J. Acoust. Soc. Am. 126, 847-857͔. Results demonstrated that consonants contribute to intelligibility equally in both isolated CVC words and sentences. However, vowel contributions were mediated by context, with greater contributions to intelligibility in sentence contexts. Therefore, it appears that vowels in sentences carry unique speech cues that greatly facilitate intelligibility which are not informative and/or present during isolated word contexts. Consonants appear to provide speech cues that are equally available and informative during sentence and isolated word presentations.

The speech signal may be divided into frequency bands, each containing temporal properties of the envelope and fine structure. For maximal speech understanding, listeners must allocate their perceptual resources to the most informative acoustic properties. Understanding this perceptual weighting is essential for the design of assistive listening devices that need to preserve these important speech cues. This study measured the perceptual weighting of young normal-hearing listeners for the envelope and fine structure in each of three frequency bands for sentence materials. Perceptual weights were obtained under two listening contexts: (1) when each acoustic property was presented individually and (2) when multiple acoustic properties were available concurrently. The processing method was designed to vary the availability of each acoustic property independently by adding noise at different levels. Perceptual weights were determined by correlating a listener's performance with the availability of each acoustic property on a trial-by-trial basis. Results demonstrated that weights were (1) equal when acoustic properties were presented individually and (2) biased toward envelope and mid-frequency information when multiple properties were available. Results suggest a complex interaction between the available acoustic properties and the listening context in determining how best to allocate perceptual resources when listening to speech in noise.