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Abstract–Speech understanding in noise declines with age, even in older subjects with normal hearing (ONH). Key words: aging, audiometry, auditory cortex, consonant, hearing loss, learning, nonsense syllables, speech comprehension, threshold, vowel.
Although it is well established that aging impairs speech comprehension in noise in older subjects [1–4], the relative contribution of peripheral and central changes to presbycusic deterioration remains an area of active investigation. A number of studies have suggested that phonological processing in noise is impaired by advancing age [12–14]. In experiment 1, we used the California Syllable Test (CaST) [16–17] to compare consonant identification in younger subjects with normal hearing (YNH) and ONH subjects. Previous studies have found age-related decrements in consonant identification when consonants are presented in nonsense syllables [8,12,15,18]. In experiment 2, we evaluated higher-level semantic processing using two SeRT measures: the Quick Speech in Noise Test (QuickSIN) [20] and Hearing in Noise Test (HINT) [21]. During each test session, 720 CVC tokens were pseudorandomly selected from the syllable corpus of 9,600 tokens such that each leading consonant and coda was presented 36 times. Signal-to-noise levels used for presentation of leading and coda consonants in experiment 1. Slideshare uses cookies to improve functionality and performance, and to provide you with relevant advertising. Development Timing? Week 3 - otic placode, otic vesicle? Week 5 - cochlear part of otic vesicle elongates (humans 2.5 turns)? Week 9 - Mesenchyme surrounding membranous labrynth (otic capsule) chondrifies? Week 12-16 - Capsule adjacent to membranous labrynth undegoes vacuolization to form a cavity (perilymphatic space) around membranous labrynth and fills with perilymph? Week 16-24 - Centres of ossification appear in remaining cartilage of otic capsule form petrous portion of temporal bone. Cochlear Implant? Bionic ear? Hearing is the only special sense which is conquered? Electronic device when implanted provides sense of sound? The cochlear implant is the most significant technical advance in the treatment of hearing impairment since the development of the hearing aid around the turn of the century.
These age-related declines could reflect reductions in phonological processing ability or impairments in semantic and lexical processing required for sentence understanding.
Some researchers hypothesize that age-related changes in speech comprehension primarily reflect deterioration in cochlear function [5], whereas others ascribe an important role to deficits in central auditory processing [6–7].
The appropriate target for OHI subjects is to restore their speech comprehension to age-normal performance levels observed in older subjects with normal hearing (ONH).
The CaST measures the signal-to-noise ratio (SNR) required to identify consonants in consonant-vowel-consonant (CVC) syllables presented in speech spectrum noise.

Greater age-related decrement in SeRTs than in CaST thresholds would suggest age-related impairments in higher-level semantic processing. We obtained individual noise spectra from each talker, and 100 different 1,200 ms noise segments were generated and randomly sampled during test sessions to mask spoken CVCs.
The interior walls were covered by 2.5-cm acoustic foam, reducing ambient third-octave noise levels to less than 20 dB sound pressure level (SPL) from 250 to 4,000 Hz. We controlled stimulus delivery, dynamic masking-noise-level adjustment, response recording, and d' calculations using Presentation?? B SNRs for each leading and coda consonant had been previously adjusted so as to equate the identifiability of different consonants, producing a mean of approximately 2.20 (~65% correct) in the control YNH subjects [17]. In experiment 1, we used the California Syllable Test (CaST) to examine age-related changes in the ability of subjects to identify consonants in ??consonant-vowel-consonant syllables in noise. Central deficits may reflect impaired phonological processing [8] or higher-level lexical and semantic impairments that are most clearly revealed in sentence testing [9].
Hence, the careful measurement of speech comprehension in noise in ONH subjects is necessary to provide a reliable benchmark against which the success of audiological rehabilitation can be measured. It uses the signal detection measure to quantify the SNRs necessary to identify each of 20 leading and 20 trailing consonants. In contrast, greater decrements in CaST thresholds than in SeRTs would suggest that ONH subjects were able to compensate for age-related declines in consonant processing through enhanced reliance on alternative vowel and semantic cues. We obtained low-frequency pure-tone average (LPTA) thresholds by averaging thresholds at 250, 500, 1,000, 1,500, and 2,000 Hz. After 1.0 s, twoindependent 1,200 ms noise bursts were presented through leftand right loudspeakers. Additional small adjustments had been incorporated to equate the identifiability of tokens spoken by different talkers and containing different vowels.
ONH subjects showed impaired performance in comparison with younger subjects with normal hearing, particularly for hard-to-identify consonants, but otherwise showed similar influences of consonant position, lexicality, and vowel nuclei. In previous studies, we demonstrated that consonants differ substantially in the SNRs required for their identification [16].
Because the CaST contains both words and nonsense syllables, it permits a comparison of the effects of lexicality on consonant identification in ONH and YNH subjects.

We obtained high-frequency pure-tone average (HPTA) thresholds by averaging thresholds at 3,000, 4,000, 6,000, and 8,000 Hz.
Consonant-vowel-consonants (CVCs)were presented simultaneously through both loudspeakers atrandom intervals after noise burst onset. Regression analyses showed that CaST performance was independently affected by both age and audiometric thresholds.
The differences persisted after factoring out individual pure-tone thresholds in the 250 to 4,000 Hz range but were correlated with thresholds at 8,000 Hz, suggesting that subtle changes in hearing acuity contributed to consonant identification deficits, even in older adults with virtually normal thresholds. Not surprisingly, although still within the range of normal hearing up to 4,000 Hz, the ONH subjects had somewhat poorer audiometric thresholds than the YNH subjects, particularly at higher frequencies (Figure 1). Two recordings of each syllable were obtained from four phonetically trained talkers, creating a corpus of 9,600 CVCs. The CVC was then presented through both loudspeakers after a random noise-to-CVC delay. Noise amplitudes werelinearly adjusted over 100 ms interval during midvowel segmentof CVC to provide appropriate masking levels for different leading and coda consonants.Click Image to Enlarge. Lincoln authorizes the National Deaf-Mutes College to grant degrees; the institution later becomes Gallaudet University.
In experiment 2, we examined sentence reception thresholds (SeRTs) using the Quick Speech in Noise Test and Hearing in Noise Test.
An investigator transcribed responses and queried the subject via intercom when responses could not be scored.
SeRT preservation in ONH subjects appeared to reflect the age-resistant ability to identify easy consonants in noise as well as intact top-down contextual and lexical processing. These results establish benchmark values that can be used to evaluate the success of audiological rehabilitation in older subjects with hearing impairment.

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