Jennifer J. Lister

Central Presbycusis: A Review and Evaluation of the Evidence

BACKGROUND The authors reviewed the evidence regarding the existence of age-related declines in central auditory processes and the consequences of any such declines for everyday communication. PURPOSE This report summarizes the review process and presents its findings. DATA COLLECTION AND ANALYSIS The authors reviewed 165 articles germane to central presbycusis. Of the 165 articles, 132 articles with a focus on human behavioral measures for either speech or nonspeech stimuli were selected for further analysis. RESULTS For 76 smaller-scale studies of speech understanding in older adults reviewed, the following findings emerged: (1) the three most commonly studied behavioral measures were speech in competition, temporally distorted speech, and binaural speech perception (especially dichotic listening); (2) for speech in competition and temporally degraded speech, hearing loss proved to have a significant negative effect on performance in most of the laboratory studies; (3) significant negative effects of age, unconfounded by hearing loss, were observed in most of the studies of speech in competing speech, time-compressed speech, and binaural speech perception; and (4) the influence of cognitive processing on speech understanding has been examined much less frequently, but when included, significant positive associations with speech understanding were observed. For 36 smaller-scale studies of the perception of nonspeech stimuli by older adults reviewed, the following findings emerged: (1) the three most frequently studied behavioral measures were gap detection, temporal discrimination, and temporal-order discrimination or identification; (2) hearing loss was seldom a significant factor; and (3) negative effects of age were almost always observed. For 18 studies reviewed that made use of test batteries and medium-to-large sample sizes, the following findings emerged: (1) all studies included speech-based measures of auditory processing; (2) 4 of the 18 studies included nonspeech stimuli; (3) for the speech-based measures, monaural speech in a competing-speech background, dichotic speech, and monaural time-compressed speech were investigated most frequently; (4) the most frequently used tests were the Synthetic Sentence Identification (SSI) test with Ipsilateral Competing Message (ICM), the Dichotic Sentence Identification (DSI) test, and time-compressed speech; (5) many of these studies using speech-based measures reported significant effects of age, but most of these studies were confounded by declines in hearing, cognition, or both; (6) for nonspeech auditory-processing measures, the focus was on measures of temporal processing in all four studies; (7) effects of cognition on nonspeech measures of auditory processing have been studied less frequently, with mixed results, whereas the effects of hearing loss on performance were minimal due to judicious selection of stimuli; and (8) there is a paucity of observational studies using test batteries and longitudinal designs. CONCLUSIONS Based on this review of the scientific literature, there is insufficient evidence to confirm the existence of central presbycusis as an isolated entity. On the other hand, recent evidence has been accumulating in support of the existence of central presbycusis as a multifactorial condition that involves age- and/or disease-related changes in the auditory system and in the brain. Moreover, there is a clear need for additional research in this area.

Effects of bilingualism, noise, and reverberation on speech perception by listeners with normal hearing

This study compared monosyllabic word recognition in quiet, noise, and noise with reverberation for 15 monolingual American English speakers and 12 Spanish–English bilinguals who had learned English prior to 6 years of age and spoke English without a noticeable foreign accent. Significantly poorer word recognition scores were obtained for the bilingual listeners than for the monolingual listeners under conditions of noise and noise with reverberation, but not in quiet. Although bilinguals with little or no foreign accent in their second language are often assumed by their peers, or their clinicians in the case of hearing loss, to be identical in perceptual abilities to monolinguals, the present data suggest that they may have greater difficulty in recognizing words in noisy or reverberant listening environments.

The aging auditory system: anatomic and physiologic changes and implications for rehabilitation

Over the last century, research in the area of age-related hearing loss has provided a vast amount of knowledge regarding age-related effects on the anatomy and physiology of the auditory system. As we enter the new millennium, researchers are beginning to shift their attention towards developing methods of modulating the effects of age-related hearing loss and the development of efficacious intervention strategies to meet all of an individuals hearing-related rehabilitative needs. The purpose of this review is to provide a framework for considering how the biological aspects of the aging auditory system interact with the most common current therapeutic intervention for age-related hearing loss—the use of amplification—and also how the biological aspects point to other potential intervention strategies.

Effects of age and frequency disparity on gap discrimination

Temporal discrimination was measured using a gap discrimination paradigm for three groups of listeners with normal hearing: (1) ages 18-30, (2) ages 40-52, and (3) ages 62-74 years. Normal hearing was defined as pure-tone thresholds < or = 25 dB HL from 250 to 6000 Hz and < or = 30 dB HL at 8000 Hz. Silent gaps were placed between 1/4-octave bands of noise centered at one of six frequencies. The noise band markers were paired so that the center frequency of the leading marker was fixed at 2000 Hz, and the center frequency of the trailing marker varied randomly across experimental runs. Gap duration discrimination was significantly poorer for older listeners than for young and middle-aged listeners, and the performance of the young and middle-aged listeners did not differ significantly. Age group differences were more apparent for the more frequency-disparate stimuli (2000-Hz leading marker followed by a 500-Hz trailing marker) than for the fixed-frequency stimuli (2000-Hz lead and 2000-Hz trail). The gap duration difference limens of the older listeners increased more rapidly with frequency disparity than those of the other listeners. Because age effects were more apparent for the more frequency-disparate conditions, and gap discrimination was not affected by differences in hearing sensitivity among listeners, it is suggested that gap discrimination depends upon temporal mechanisms that deteriorate with age and stimulus complexity but are unaffected by hearing loss.

Modulation of Presbycusis: Current Status and Future Directions

Literature and ideas are reviewed concerning the modulation of presbycusis – the influence of variables that can alter the severity and/or time course of presbycusis or counteract its negative aspects. Eleven topics are identified: variables related to biological aging; genetics; noise-induced hearing loss; moderately augmented acoustic environment; neural plasticity and the central auditory system; neural plasticity and hearing aids; socioeconomic and cultural barriers to hearing aid use; lifestyle (diet, exercise, etc.); medical variables; pharmaceutical interventions for presbycusis, and cognitive variables. It is concluded that the field of otogerontology will best be served by a comprehensive, integrative interaction among basic researchers and clinical scientists who will continue to learn how the auditory problems associated with presbycusis can be intentionally modulated in beneficial ways.

Preattentive cortical-evoked responses to pure tones, harmonic tones, and speech: influence of music training.

Objective: Cortical auditory evoked potentials, including mismatch negativity (MMN) and P3a to pure tones, harmonic complexes, and speech syllables, were examined across groups of trained musicians and nonmusicians. Because of the extensive formal and informal auditory training received by musicians throughout their lifespan, it was predicted that these electrophysiological indicators of preattentive pitch discrimination and involuntary attention change would distinguish musicians from nonmusicians and provide insight regarding the influence of auditory training and experience on central auditory function. Design: A total of 102 (67 trained musicians, 35 nonmusicians) right-handed young women with normal hearing participated in three auditory stimulus conditions: pure tones (25 musicians/15 nonmusicians), harmonic tones (42 musicians/20 nonmusicians), and speech syllables (26 musicians/15 nonmusicians). Pure tone and harmonic tone stimuli were presented in multideviant oddball paradigms designed to elicit MMN and P3a. Each paradigm included one standard and two infrequently occurring deviants. For the pure tone condition, the standard pure tone was 1000 Hz, and the two deviant tones differed in frequency from the standard by either 1.5% (1015 Hz) or 6% (1060 Hz). The harmonic tone complexes were digitally created and contained a fundamental frequency (F0) and three harmonics. The amplitude of each harmonic was divided by its harmonic number to create a natural amplitude contour in the frequency spectrum. The standard tone was G4 (F0 = 392 Hz), and the two deviant tones differed in fundamental frequency from the standard by 1.5% (F0 = 386 Hz) or 6% (F0 = 370 Hz). The fundamental frequencies of the harmonic tones occur within the average female vocal range. The third condition to elicit MMN and P3a was designed for the presentation of speech syllables (/ba/ and /da/) and was structured as a traditional oddball paradigm (one standard/one infrequent deviant). Each speech stimulus was presented as a standard and a deviant in separate blocks. P1-N1-P2 was elicited before each oddball task by presenting each auditory stimulus alone in single blocks. All cortical auditory evoked potentials were recorded in a passive listening condition. Results: Incidental findings revealed that musicians had longer P1 latencies for pure tones and smaller P1 amplitudes for harmonic tones than nonmusicians. There were no P1 group differences for speech stimuli. Musicians compared with nonmusicians had shorter MMN latencies for all deviances (harmonic tones, pure tones, and speech). Musicians had shorter P3a latencies to harmonic tones and speech but not to pure tones. MMN and P3a amplitude were modulated by deviant frequency but not by group membership. Conclusions: Formally trained musicians compared with nonmusicians showed more efficient neural detection of pure tones and harmonic tones; demonstrated superior auditory sensory-memory traces for acoustic features of pure tones, harmonic tones, and speech; and revealed enhanced sensitivity to acoustic changes of spectrally rich stimuli (i.e., harmonic tones and speech). Findings support a general influence of music training on central auditory function and illustrate experience-facilitated modulation of the auditory neural system.

Hearing of note: an electrophysiologic and psychoacoustic comparison of pitch discrimination between vocal and instrumental musicians.

Cortical auditory evoked potentials of instrumental musicians suggest that music expertise modifies pitch processing, yet less is known about vocal musicians. Mismatch negativity (MMN) to pitch deviances and difference limen for frequency (DLF) were examined among 61 young adult women, including 20 vocalists, 21 instrumentalists, and 20 nonmusicians. Stimuli were harmonic tone complexes from the mid-female vocal range (C4-G4). MMN was elicited by multideviant paradigm. DLF was obtained by an adaptive psychophysical paradigm. Musicians detected pitch changes earlier and DLFs were 50% smaller than nonmusicians. Both vocal and instrumental musicians possess superior sensory-memory representations for acoustic parameters. Vocal musicians with instrumental training appear to have an auditory neural advantage over instrumental or vocal only musicians. An incidental finding reveals P3a as a sensitive index of music expertise.

Cognitive training and selective attention in the aging brain: An electrophysiological study

OBJECTIVE Age-related deficits in selective attention are hypothesized to result from decrements in inhibition of task-irrelevant information. Speed of processing (SOP) training is an adaptive cognitive intervention designed to enhance processing speed for attention tasks. The effectiveness of SOP training to improve cognitive and everyday functional performance is well documented. However, underlying mechanisms of these training benefits are unknown. METHODS Participants completed a visual search task evaluated using event-related potentials (ERPs) before and after 10 weeks of SOP training or no contact. N2pc and P3b components were evaluated to determine SOP training effects on attentional resource allocation and capacity. RESULTS Selective attention to a target was enhanced after SOP training compared to no training. N2pc and P3b amplitudes increased after training, reflecting attentional allocation and capacity enhancement, consistent with previous studies demonstrating behavioral improvements in selective attention following SOP training. CONCLUSIONS Changes in ERPs related to attention allocation and capacity following SOP training support the idea that training leads to cognitive enhancement. Specifically, we provide electrophysiological evidence that SOP training may be successful in counteracting age-related declines in selective attention. SIGNIFICANCE This study provides important evidence of the underlying mechanisms by which SOP training improves cognitive function in older adults.

Auditory evoked response to gaps in noise: Older adults

Abstract Objective: The objective of this study was to describe the auditory evoked response to silent gaps for a group of older adults using stimulus conditions identical to those used in psychophysical studies of gap detection. Design: The P1-N1-P2 response to the onsets of stimuli (markers) defining a silent gap for within-channel (spectrally identical markers) and across-channel (spectrally different markers) conditions was examined using four perceptually-equated gap durations. Study Sample: A group of 24 older adults (mean age = 63 years) with normal hearing or minimal hearing loss participated. Results: Older adults exhibited neural activation patterns that were qualitatively different and more frontally oriented than those observed in a previous study (20) of younger listeners. Older adults showed longer P2 latencies and larger P1 amplitudes than younger adults, suggesting relatively slower neural travel time and altered auditory inhibition/arousal by irrelevant stimuli. Conclusion: Older adults appeared to recruit later-occurring T-complex-like generators for gap processing, compared to earlier-occurring T-complex-like generators by the younger group. Early and continued processing of channel cues with later processing of gap cues may represent the inefficiency of the aging auditory system and may contribute to poor speech understanding in noisy, real-world listening environments. Sumario Objetivo: El objetivo de este estudio fue describir las respuestas evocadas auditivas ante brechas de silencio para un grupo de adultos mayores utilizando condiciones de estimulación idénticas a aquellas usadas en estudios psico-fisiológicos de detección de brechas. Diseño: Se examinaron las respuestas P1-N1-P2 ante los inicios de estímulos (marcadores) que definen una brecha de silencio en condiciones dentro del canal (marcadores espectralmente idénticos) y entre canales (marcadores espectralmente diferentes), usando cuatro brechas de duración perceptualmente ecualizada. Muestra del Estudio: Participó un grupo de 24 adultos mayores (edad media = 63 años) con audición normal o con una pérdida auditiva mínima. Resultados: Los adultos mayores exhibieron patrones de activación neural que fueron cuantitativamente diferentes y más frontalmente orientados que aquellos observados en un estudio previo (20) con oyentes más jóvenes. Los adultos más viejos mostraron latencias más prolongadas de P2 y amplitudes mayores de P1 que los adultos jóvenes, sugiriendo un tiempo de tránsito en el nervio relativamente más lento y una alteración de la inhibición-estimulación auditiva para estímulos no relevantes. Conclusion: Los adultos mayores parecen reclutar generadores tipo complejo T de aparición tardía para procesamiento de brechas, comparado con los generadores tipo complejo T de aparición más temprana de los adultos jóvenes. Es posible que el procesamiento temprano y complejo de claves por canal, con el procesamiento tardío de claves de brecha, pueda representar la ineficiencia del sistema auditivo que envejece y que contribuye a una pobre comprensión del lenguaje en ambientes de escucha ruidosos del mundo real.

Cortical evoked response to gaps in noise : Within-channel and across-channel conditions

Objectives: The objective of this study was to describe the cortical evoked response to silent gaps in a group of young adults with normal hearing using stimulus conditions identical to those used in psychophysical studies of gap detection. Specifically, we sought to examine the P1-N1-P2 auditory evoked response to the onsets of stimuli (markers) defining a silent gap for within-channel (spectrally identical markers) and across-channel (spectrally different markers) conditions using four perceptually-equated gap durations. It was hypothesized that (1) P1, N1, and P2 would be present and consistent for 1st marker (before the gap) onsets; (2) for within-channel markers, P1, N1, and P2 would be present for 2nd marker (after the gap) onsets only when the gap was of a duration equal to or larger than the behaviorally measured gap detection threshold; and (3) for the across-channel conditions, P1, N1, and P2 would be present for 2nd marker onsets regardless of gap duration. This is expected due to the additional cue of frequency change following the gap. Design: Twelve young adults (mean age 26 years) with normal hearing participated. Within-channel and across-channel gap detection thresholds were determined using an adaptive psychophysical procedure. Next, cortical auditory evoked potentials (P1-N1-P2) were recorded with a 32-channel Neuroscan™ electroencephalogram system using within-channel and across-channel markers identical to those used for the psychophysical task and four perceptually weighted gap durations: (1) individual listeners gap detection threshold; (2) above gap detection threshold; (3) below gap detection threshold; and (4) a 1-ms gap identical to the gap in the standard interval of the psychophysical task. P1-N1-P2 peak latencies and amplitudes were analyzed using repeated-measures analyses of variance. A temporal-spatial principal component analysis was also conducted. Results: The latency of P2 and the amplitude of P1, N1, and P2 were significantly affected by the acoustic characteristics of the 2nd marker as well as the duration of the gap. Larger amplitudes and shorter latencies were generally found for the conditions in which the acoustic cues were most salient (e.g., across-channel markers, 1st markers, large gap durations). Interestingly, the temporal-spatial principal component analysis revealed activity elicited by gap durations equal to gap detection threshold in the latency regions of 167 and 183 ms for temporal-parietal and right-frontal spatial locations. Conclusions: The cortical response to a silent gap is unique to specific marker characteristics and gap durations among young adults with normal hearing. Specifically, when the onset of the 2nd marker is perceptually salient, the amplitude of the P1-N1-P2 response is relatively larger and the P2 latency is relatively shorter than for nonsalient 2nd marker onsets, providing noninvasive, nonbehavioral indicators of the neural coding of this important temporal cue in the thalamic-cortical region of the central auditory system. Gap duration appears to be most clearly indicated by P1 and T-complex amplitude.