In realistic listening environments, speech perception requires grouping together audible fragments of speech, filling in missing information, and segregating the glimpsed target from the background. The purpose of this study was to determine the extent to which age-related difficulties with these tasks can be explained by declines in glimpsing, phonemic restoration, and/or speech segregation. Younger and older adults with normal hearing listened to sentences interrupted with silence or envelope-modulated noise, presented either in quiet or with a competing talker. Older adults were poorer than younger adults at recognizing keywords based on short glimpses but benefited more when envelope-modulated noise filled silent intervals. Recognition declined with a competing talker but this effect did not interact with age. Results of cognitive tasks indicated that faster processing speed and better visual-linguistic closure were predictive of better speech understanding. Taken together, these results suggest that age-related declines in speech recognition may be partially explained by difficulty grouping short glimpses of speech into a coherent message.

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The spectral (frequency) and amplitude cues in speech change rapidly over time. Study of the neural encoding of these dynamic features may help to improve diagnosis and treatment of speechperception difficulties. This study uses tone glides as a simple approximation of dynamic speech sounds to better our understanding of the underlying neural representation of speech. The frequency following response (FFR) was recorded from 10 young normal-hearing adults using six signals varying in glide direction (rising and falling) and extent of frequency change ( 1 3 , 2 3 , and 1 octave). In addition, the FFR was simultaneously recorded using two different electrode montages (vertical and horizontal). These factors were analyzed across three time windows using a measure of response strength (signal-to-noise ratio) and a measure of temporal coherence (stimulus-toresponse correlation coefficient). Results demonstrated effects of extent, montage, and a montageby-window interaction. SNR and stimulus-to-response correlation measures differed in their sensitivity to these factors. These results suggest that the FFR reflects dynamic acoustic characteristics of simple tonal stimuli very well. Additional research is needed to determine how neural encoding may differ for more natural dynamic speech signals and populations with impaired auditory processing.

This study investigated how single-talker modulated noise impacts consonant and vowel cues to sentence intelligibility. Younger normal-hearing, older normal-hearing, and older hearing-impaired listeners completed speech recognition tests. All listeners received spectrally shaped speech matched to their individual audiometric thresholds to ensure sufficient audibility with the exception of a second younger listener group who received spectral shaping that matched the mean audiogram of the hearing-impaired listeners. Results demonstrated minimal declines in intelligibility for older listeners with normal hearing and more evident declines for older hearing-impaired listeners, possibly related to impaired temporal processing. A correlational analysis suggests a common underlying ability to process information during vowels that is predictive of speech-in-modulated noise abilities. Whereas, the ability to use consonant cues appears specific to the particular characteristics of the noise and interruption. Performance declines for older listeners were mostly confined to consonant conditions. Spectral shaping accounted for the primary contributions of audibility. However, comparison with the young spectral controls who received identical spectral shaping suggests that this procedure may reduce wideband temporal modulation cues due to frequency-specific amplification that affected high-frequency consonants more than low-frequency vowels. These spectral changes may impact speech intelligibility in certain modulation masking conditions.

Fluctuating noise, common in everyday environments, has the potential to mask acoustic cues important for speech recognition. This study examined the extent to which acoustic cues for perception of vowels and stop consonants differ in their susceptibility to simultaneous and forward masking. Younger normal-hearing, older normal-hearing, and older hearing-impaired adults identified initial and final consonants or vowels in noise-masked syllables that had been spectrally shaped. The amount of shaping was determined by subjects' audiometric thresholds. A second group of younger adults with normal hearing was tested with spectral shaping determined by the mean audiogram of the hearing-impaired group. Stimulus timing ensured that the final 10, 40, or 100 ms of the syllable occurred after the masker offset. Results demonstrated that participants benefited from short temporal delays between the noise and speech for vowel identification, but required longer delays for stop consonant identification. Older adults with normal and impaired hearing, with sufficient audibility, required longer delays to obtain performance equivalent to that of the younger adults. Overall, these results demonstrate that in forward masking conditions, younger listeners can successfully identify vowels during short temporal intervals (i.e., one unmasked pitch period), with longer durations required for consonants and for older adults.

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Nonsimultaneous amplitude modulations from a competing talker significantly interacted with the preserved speech segment, and additional listener factors were observed for age and hearing loss. Importantly, listeners may obtain benefit from nonsimultaneous competing modulations when they match the preserved modulations of the sentence.

Perceived listening effort was assessed for a monaural irregular-rhythm detection task while competing signals were presented to the contralateral ear. When speech was the competing signal, listeners reported greater listening effort compared to either contralateral steady-state noise or no competing signal. Behavioral thresholds for irregular-rhythm detection were unaffected by competing speech, indicating that listeners compensated for this competing signal with effortful listening. These results suggest that perceived listening effort may be associated with suppression of task-irrelevant information, even for conditions where informational masking and competition for linguistic processing resources would not be expected.