Effects of Age, Age-Related Hearing Loss, and Contralateral Cafeteria Noise on the Discrimination of Small Frequency Changes: Psychoacoustic and Electrophysiological Measures

Abstract

The aim of the study was to examine central auditory processes compromised by age, age-related hearing loss, and the presentation of a distracting cafeteria noise using auditory event-related potentials (ERPs). In addition, the relation of ERPs to behavioral measures of discrimination was investigated. Three groups of subjects participated: young normal hearing, elderly subjects with normal hearing for their age, and elderly hearing-impaired subjects. Psychoacoustic frequency discrimination thresholds for a 1000-Hz pure tone were determined in quiet and in the presence of a contralateral cafeteria noise. To elicit ERPs, small frequency contrasts were presented with and without noise under unattended and attended conditions. In the attended condition, behavioral measures of dS detectability and reaction times were also obtained. Noise affected all measures of behavioral frequency discrimination significantly. Except N1, all ERP components in the standard and difference waveforms decreased significantly in amplitude and increased in latency to the same degree in all three subject groups, arguing against a specific age-related sensitivity to the effects of contralateral background noise. For N1 amplitude, the effect of noise was different in the three subject groups, with a complex interaction of age, hearing loss, and attention. Behavioral frequency discrimination was not affected by age but deteriorated significantly in the elderly subjects with hearing loss. In the electrophysiological test, age-related changes occurred at various levels. The most prominent finding in the response to the standard stimuli was a sustained negativity (N2) following P2 in the young subjects that was absent in the elderly, possibly indicating a deficit in the inhibition of irrelevant information processing. In the attended difference waveform, significantly larger N2b and smaller P3b amplitudes and longer N2b and P3b latencies were observed in the elderly indicating different processing strategies. The pronounced agerelated changes in the later cognitive components suggest that the discrimination of difficult contrasts, although behaviorally maintained, becomes more effortful in the elderly.

Age-related differences in sensitivity to small changes in frequency assessed with cortical evoked potentials

“…Similarly, Harkrider et al (2005) observed that P2 latencies were delayed in older subjects in response to changes in the spectral cues of speech stimuli and suggested that prolonged latencies in older listeners may be due to reduced neural synchrony in response to changes in spectral cues. Bertoli et al (2005) observed similar increases in P2 latencies in older normal-hearing and hearing-impaired adults as compared to younger adults.…”

“…Limited data are available regarding the effects of age on P1-N1-P2 thresholds when elicited by small changes in frequency. However, Bertoli et al (2005) examined the MMN in older and younger subjects in response to frequency contrasts at 1000 Hz and reported that larger frequency contrasts were required to elicit the MMN in older subjects than younger subjects.…”

“…Although, differences in the P1-N1-P2 suggest age-related changes in auditory processing, changes in attention and cognition can not be ruled out. Bertoli et al (2005) examined agerelated changes in behavioral measures of frequency discrimination thresholds for a 1000 Hz tone as well as several electrophysiologic responses elicited by small frequency contrasts (presented as two separate tones in an odd-ball paradigm) including the P1-N1-P2 (elicited by the onset of the standard stimuli, not to a change in frequency), the MMN and the P300. In contrast to He et al (1998) and others Konig, 1957), no significant differences in behavioral discrimination thresholds were reported.…”

“…However, larger frequency contrasts were required to elicit the MMN in older subjects and significant effects of aging were reported for P1, N1, and P2 responses as well as the N2b and P3b (elicited in response to the frequency contrast stimulus when the difference was consciously perceived). Bertoli et al (2005) hypothesized that age-related changes in the electrophysiologic potentials reflect a decrease in inhibitory control, decreased sensitivity in preattentive stimulus discrimination, and a more effortful delayed stimulus evaluation.…”

“…The effect of aging on auditory physiologic processes associated with frequency discrimination has been measured using endogenous cortical potentials including the mismatch negativity (MMN), an early preattentive potential, and the P300, a later cognitive attention-related potential (Bertoli et al, 2005). Despite similar frequency discrimination performance on behavioral measures, pronounced effects of age were observed in the physiologic responses, such that older adults were less sensitive to the smallest frequency change, as indicated by an absent MMN to the smallest deviant stimuli.…”