The Preventing Alzheimer's with Cognitive Training (PACT) randomized clinical trial.

BACKGROUND: To address the rising prevalence of Alzheimer's disease and related dementias, effective interventions that can be widely disseminated are warranted. The Preventing Alzheimer's with Cognitive Training study (PACT) investigates a commercially available computerized cognitive training program targeting improved Useful Field of View Training (UFOVT) performance. The primary goal is to test the effectiveness of UFOVT to reduce incidence of clinically defined mild cognitive impairment (MCI) or dementia with a secondary objective to examine if effects are moderated by plasma ß-amyloid level or apolipoprotein E e4 (APOE e4) allele status. METHODS/DESIGN: This multisite study utilizes a randomized, controlled experimental design with blinded assessors and investigators. Individuals who are 65 years of age and older are recruited from the community. Eligible participants who demonstrate intact cognitive status (Montreal Cognitive Assessment score > 25) are randomized and asked to complete 45 sessions of either a commercially available computerized-cognitive training program (UFOVT) or computerized games across 2.5 years. After three years, participants are screened for cognitive decline. For those demonstrating decline or who are part of a random subsample, a comprehensive neuropsychological assessment is completed. Those who perform below a pre-specified level are asked to complete a clinical evaluation, including an MRI, to ascertain clinical diagnosis of normal cognition, MCI, or dementia. Participants are asked to provide blood samples for analyses of Alzheimer's disease related biomarkers. DISCUSSION: The PACT study addresses the rapidly increasing prevalence of dementia. Computerized cognitive training may provide a non-pharmaceutical option for reducing incidence of MCI or dementia to improve public health. REGISTRATION: The PACT study is registered at http://Clinicaltrials.govNCT03848312.

Are auditory processing and cognitive performance assessments overlapping or distinct? Parsing the auditory behaviour of older adults.

OBJECTIVE: Auditory processing predicts cognitive decline, including dementia, in older adults. Auditory processing involves the understanding, interpretation, and communication of auditory information. Cognition is linked to auditory processing; however, it is disputed whether auditory processing is a separate construct distinct from cognition. The purpose of this study was to determine if auditory processing is distinct from cognition in older adults. DESIGN: Participants completed 14 cognitive and auditory processing assessments. Assessments were subjected to exploratory factor analysis with principal components extraction and varimax rotation with Kaiser normalisation. Study sample: 213 community-dwelling older adults (M = 71.39 years, 57% female, 93% Caucasian, M = 16 years education) with and without mild cognitive impairment (MCI) participated. RESULTS: Four factors were identified, explaining 66.3% of the total variance: (1) executive functions, visual processing speed, and dichotic auditory processing, (2) auditory processing of degraded speech, (3) memory, and (4) auditory temporal processing of nonspeech. CONCLUSIONS: Two domains of auditory processing (processing degraded speech and temporal processing) account for unique variance to which cognitive measures are not sensitive, while measures of auditory dichotic processing appear to be tapping similar abilities as measures of cognition. Older adults who perform poorly on dichotic measures should be screened for cognitive impairment.

Cortical auditory evoked potentials in mild cognitive impairment: Evidence from a temporal-spatial principal component analysis.

Mild cognitive impairment (MCI) is considered an intermediate transitional stage for the development of dementia, especially Alzheimer's disease. The identification of neurophysiological biomarkers for MCI will allow improvement in detecting and tracking the progression of cognitive impairment. The primary objective of this study was to compare cortical auditory evoked potentials between older adults with and without probable MCI to identify potential neurophysiological indicators of cognitive impairment. We applied a temporal-spatial principal component analysis to the evoked potentials achieved during the processing of pure tones and speech sounds, to facilitate the separation of the components of the P1-N1-P2 complex. The probable MCI group showed a significant amplitude increase in a factor modeling N1b for speech sounds (Cohen's d = .84) and a decrease in a factor around the P2 time interval, especially for pure tones (Cohen's d = 1.17). Moreover, both factors showed a fair discrimination value between groups (area under the curve [AUC] = .698 for N1b in speech condition; AUC = .746 for P2 in tone condition), with high sensitivity to detect MCI cases (86% and 91%, respectively). The results for N1b suggest that MCI participants may suffer from a deficit to inhibit irrelevant speech information, and the decrease of P2 amplitude could be a signal of cholinergic hypoactivation. Therefore, both components could be proposed as early biomarkers of cognitive impairment.

Keys to staying sharp: A randomized clinical trial of piano training among older adults with and without mild cognitive impairment.

BACKGROUND: The prevalence of dementia, the most expensive medical condition (Kirschstein, 2000 and Hurd et al., 2013 [1,2]), and its precursor, mild cognitive impairment (MCI) are increasing [3]. Finding effective intervention strategies to prevent or delay dementia is imperative to public health. Prior research provides compelling evidence that central auditory processing (CAP) deficits are a risk factor for dementia [4-6]. Grounded in the information degradation theory [7, 8], we hypothesize that improving brain function at early perceptual levels (i.e., CAP) may be optimal to attenuate cognitive and functional decline and potentially curb dementia prevalence. Piano training is one avenue to enhance cognition [9-13] by facilitating CAP at initial perceptual stages [14-18]. OBJECTIVES: The Keys To Staying Sharp study is a two arm, randomized clinical trial examining the efficacy of piano training relative to music listening instruction to improve CAP, cognition, and everyday function among older adults. In addition, the moderating effects of MCI status on piano training efficacy will be examined and potential mediators of intervention effects will be explored. HYPOTHESES: We hypothesize that piano training will improve CAP and cognitive performance, leading to functional improvements. We expect that enhanced CAP will mediate cognitive gains. We further hypothesize that cognitive gains will mediate functional improvements. METHOD: We plan to enroll 360 adults aged 60 years and older who will be randomized to piano training or an active control condition of music listening instruction and complete pre- and immediate post- assessments of CAP, cognition, and everyday function.

Can Cognitive Speed of Processing Training Improve Everyday Functioning Among Older Adults With Psychometrically Defined Mild Cognitive Impairment?

OBJECTIVE: The aim of these secondary analyses was to examine cognitive speed of processing training (SPT) gains in cognitive and everyday functioning among older adults with psychometrically defined mild cognitive impairment (MCI). METHOD: A subgroup of participants from the Staying Keen in Later Life (SKILL) study with psychometrically defined MCI ( N = 49) were randomized to either the SPT intervention or an active control group of cognitive stimulation. Outcome measures included the Useful Field of View (UFOV), Road Sign Test, and Timed Instrumental Activities of Daily Living (IADL) Test. A 2 × 2 repeated-measures MANOVA revealed an overall effect of training, indicated by a significant group (SPT vs. control) by time (baseline vs. posttest) interaction. RESULTS: Effect sizes were large for improved UFOV, small for the Road Sign test, and medium for Timed IADL. DISCUSSION: Results indicate that further investigation of cognitive intervention strategies to improve everyday functioning in patients with MCI is warranted.

Comparison of Subjective and Objective Measures of Hearing, Auditory Processing, and Cognition Among Older Adults With and Without Mild Cognitive Impairment.

Purpose: The aims of the study were to compare the Cognitive Self-Report Questionnaire (CSRQ; Spina, Ruff, & Mahncke, 2006) Hearing and Cognitive subscale ratings among older adults with and without probable mild cognitive impairment (MCI) and to examine whether self-report, as measured by the CSRQ, is associated with objective measures of hearing, auditory processing, and cognition. Method: Data analyses included 97 older adults of ages 61-91 years. Participants completed the CSRQ self-report measure as well as a battery of objective measures, including pure-tone audiometry, degraded speech understanding, temporal processing, and memory. Results: Older adults with probable MCI rated their cognitive abilities more poorly than those without MCI (p = .002), but ratings of hearing and auditory abilities did not differ between the two groups (p = .912). Age and CSRQ Hearing subscale ratings explained a significant proportion of variance in objective measures of hearing and degraded speech understanding (R2 = .39, p < .001). Age, sex, mental status, and CSRQ Cognition subscale ratings explained a significant proportion of variance in objective memory performance (R2 = .55, p < .001). Conclusions: Taken together, these results suggest that the CSRQ is an appropriate self-report measure of hearing, cognition, and some aspects of auditory processing for older adults with and without probable MCI.

Cognitive Training Enhances Auditory Attention Efficiency in Older Adults.

Auditory cognitive training (ACT) improves attention in older adults; however, the underlying neurophysiological mechanisms are still unknown. The present study examined the effects of ACT on the P3b event-related potential reflecting attention allocation (amplitude) and speed of processing (latency) during stimulus categorization and the P1-N1-P2 complex reflecting perceptual processing (amplitude and latency). Participants completed an auditory oddball task before and after 10 weeks of ACT (n = 9) or a no contact control period (n = 15). Parietal P3b amplitudes to oddball stimuli decreased at post-test in the trained group as compared to those in the control group, and frontal P3b amplitudes show a similar trend, potentially reflecting more efficient attentional allocation after ACT. No advantages for the ACT group were evident for auditory perceptual processing or speed of processing in this small sample. Our results provide preliminary evidence that ACT may enhance the efficiency of attention allocation, which may account for the positive impact of ACT on the everyday functioning of older adults.

Auditory Processing of Older Adults With Probable Mild Cognitive Impairment.

Purpose: Studies suggest that deficits in auditory processing predict cognitive decline and dementia, but those studies included limited measures of auditory processing. The purpose of this study was to compare older adults with and without probable mild cognitive impairment (MCI) across two domains of auditory processing (auditory performance in competing acoustic signals and temporal aspects of audition). Method: The Montreal Cognitive Assessment (Nasreddine et al., 2005) was used to classify participants as with or without probable MCI. In this cross-sectional study, participants (n = 79) completed 4 measures of auditory processing: Synthetic Sentence Identification with Ipsilateral Competing Message (Gates, Beiser, Rees, D'Agostino, & Wolf, 2002), Dichotic Sentence Identification (Fifer, Jerger, Berlin, Tobey, & Campbell, 1983), Adaptive Tests of Temporal Resolution (ATTR; Lister & Roberts, 2006; across-channel and within-channel subtests), and time-compressed speech (Wilson, 1993; Wilson, Preece, Salamon, Sperry, & Bornstein, 1994). Audiometry was also conducted. Results: Those with probable MCI had significantly poorer performance than those without MCI on Synthetic Sentence Identification with Ipsilateral Competing Message, Dichotic Sentence Identification, and the ATTR within-channel subtest. No group differences were found for time-compressed speech, ATTR across-channel, or audiometric measures. Conclusions: Older adults with cognitive impairment not only have difficulty with competing acoustic signals but may also show poor temporal processing. The profile of auditory processing deficits among older adults with cognitive impairment may include multiple domains.

Association of Hearing Impairment and Subsequent Driving Mobility in Older Adults.

Purpose of the Study: Hearing impairment (HI) is associated with driving safety (e.g., increased crashes and poor on-road driving performance). However, little is known about HI and driving mobility. This study examined the longitudinal association of audiometric hearing with older adults' driving mobility over 3 years. Design and Methods: Secondary data analyses were conducted of 500 individuals (63-90 years of age) from the Staying Keen in Later Life (SKILL) study. Hearing (pure tone average of 0.5, 1, and 2kHz) was assessed in the better hearing ear and categorized into normal hearing ≤25 dB hearing level (HL); mild HI 26-40 dB HL; or moderate and greater HI ≥41 dB HL. The Useful Field of View Test (UFOV) was used to estimate the risk for adverse driving events. Multivariate analysis of covariance compared driving mobility between HI levels across time, adjusting for age, sex, race, hypertension, and stroke. Adjusting for these same covariates, Cox regression analyses examined incidence of driving cessation by HI across 3 years. Results: Individuals with moderate or greater HI performed poorly on the UFOV, indicating increased risk for adverse driving events (p < .001). No significant differences were found among older adults with varying levels of HI for driving mobility (p values > .05), including driving cessation rates (p = .38), across time. Implications: Although prior research indicates older adults with HI may be at higher risk for crashes, they may not modify driving over time. Further exploration of this issue is required to optimize efforts to improve driving safety and mobility among older adults.

Attention demands of language production in adults who stutter.

OBJECTIVE: We investigated whether language production is atypically resource-demanding in adults who stutter (AWS) versus typically-fluent adults (TFA). METHODS: Fifteen TFA and 15 AWS named pictures overlaid with printed Semantic, Phonological or Unrelated Distractor words while monitoring frequent low tones versus rare high tones. Tones were presented at a short or long Stimulus Onset Asynchrony (SOA) relative to picture onset. Group, Tone Type, Tone SOA and Distractor Type effects on P3 amplitudes were the main focus. P3 amplitude was also investigated separately in a simple tone oddball task. RESULTS: P3 morphology was similar between groups in the simple task. In the dual task, a P3 effect was detected in TFA in all three distractor conditions at each Tone SOA. In AWS, a P3 effect was attenuated or undetectable at the Short Tone SOA depending on Distractor Type. CONCLUSIONS: In TFA, attentional resources were available for P3-indexed processes in tone perception and categorization in all distractor conditions at both Tone SOAs. For AWS, availability of attentional resources for secondary task processing was reduced as competition in word retrieval was resolved. SIGNIFICANCE: Results suggest that language production can be atypically resource-demanding in AWS. Theoretical and clinical implications of the findings are discussed.

Cortical auditory evoked responses of older adults with and without probable mild cognitive impairment.

OBJECTIVE: Hearing loss has been well-documented as a risk factor for cognitive impairment, but the simple presence of hearing loss is not a sufficient predictor of cognitive decline. Although auditory behavioral research has not revealed an effective indicator of early cognitive impairment, a limited number of studies using cortical auditory evoked potentials (CAEPs) have shown promising evidence of an auditory neurophysiological indicator of early-stage cognitive impairment. The purpose of this study was to examine the P1-N1-P2 complex for indicators of cognitive impairment. METHODS: The latency and amplitude of the P1-N1-P2 complex was measured for two stimuli (pure tone, speech) in two groups: cognitively normal older adults (CNOAs) and older adults with probable mild cognitive impairment (MCI), based on the Montreal Cognitive Assessment. RESULTS: Significantly smaller P2 amplitudes were found for those with probable MCI compared to CNOA across stimulus conditions. Stimulus effects were found for P1 and P2 latency. CONCLUSION: P2 amplitude may be a useful indicator of early-stage cognitive impairment. SIGNIFICANCE: As effective treatments become available, early identification of cognitive impairment can facilitate the prescription of treatment at the earliest juncture. CAEPs have the potential to serve as efficient, non-invasive, cost-effective indicators of future cognitive decline and impairment.

Interaction of Musicianship and Aging: A Comparison of Cortical Auditory Evoked Potentials.

OBJECTIVE: The goal of this study was to begin to explore whether the beneficial auditory neural effects of early music training persist throughout life and influence age-related changes in neurophysiological processing of sound. DESIGN: Cortical auditory evoked potentials (CAEPs) elicited by harmonic tone complexes were examined, including P1-N1-P2, mismatch negativity (MMN), and P3a. STUDY SAMPLE: Data from older adult musicians (n = 8) and nonmusicians (n = 8) (ages 55-70 years) were compared to previous data from young adult musicians (n = 40) and nonmusicians (n = 20) (ages 18-33 years). RESULTS: P1-N1-P2 amplitudes and latencies did not differ between older adult musicians and nonmusicians; however, MMN and P3a latencies for harmonic tone deviances were earlier for older musicians than older nonmusicians. Comparisons of P1-N1-P2, MMN, and P3a components between older and young adult musicians and nonmusicians suggest that P1 and P2 latencies are significantly affected by age, but not musicianship, while MMN and P3a appear to be more sensitive to effects of musicianship than aging. CONCLUSIONS: Findings support beneficial influences of musicianship on central auditory function and suggest a positive interaction between aging and musicianship on the auditory neural system.

Perceptual and cognitive neural correlates of the useful field of view test in older adults.

The Useful Field of View Test (UFOV) is often used as a behavioral assessment of age-related decline in visual perception and cognition. Poor performance may reflect slowed processing speed, difficulty dividing attention, and difficulty ignoring irrelevant information. However, the underlying neural correlates of UFOV performance have not been identified. The relationship between older adults' UFOV performance and event-related potential (ERP) components reflecting visual processing was examined. P1 amplitude increased with better UFOV performance involving object identification (subtest 1), suggesting that this task is associated with stimulus processing at an early perceptual level. Better performance in all UFOV subtests was associated with faster speed of processing, as reflected by decreases in P3b latency. Current evidence supports the hypothesis that the UFOV recruits both early perceptual and later cognitive processing involved in attentional control. The implications of these results are discussed.

Peripheral Hearing and Cognition: Evidence From the Staying Keen in Later Life (SKILL) Study.

OBJECTIVES: Research has increasingly suggested a consistent relationship between peripheral hearing and selected measures of cognition in older adults. However, other studies yield conflicting findings. The primary purpose of the present study was to further elucidate the relationship between peripheral hearing and three domains of cognition and one measure of global cognitive status. It was hypothesized that peripheral hearing loss would be significantly associated with poorer performance across measures of cognition, even after adjusting for documented risk factors. No study to date has examined the relationship between peripheral hearing and such an extensive array of cognitive measures. DESIGN: Eight hundred ninety-four older adult participants from the Staying Keen in Later Life study cohort were eligible, agreed to participate, and completed the baseline evaluation. Inclusion criteria were minimal to include a sample of older adults with a wide range of sensory and cognitive abilities. Multiple linear regression analyses were conducted to evaluate the extent to which peripheral hearing predicted performance on a global measure of cognitive status, as well as multiple cognitive measures in the domains of speed of processing (Digit Symbol Substitution and Copy, Trail Making Test Part A, Letter and Pattern Comparison, and Useful Field of View), executive function (Trail Making Test Part B and Stroop Color-Word Interference Task), and memory (Digit Span, Spatial Span, and Hopkins Verbal Learning Test). RESULTS: Peripheral hearing, measured as the three-frequency pure-tone average (PTA) in the better ear, accounted for a significant, but minimal, amount of the variance in measures of speed of processing, executive function, and memory, as well as global cognitive status. Alternative measures of hearing (i.e., three-frequency PTAs in the right and left ears and a bilateral, six-frequency PTA [three frequencies per ear]) yielded similar findings across measures of cognition and did not alter the study outcomes in any meaningful way. CONCLUSIONS: Consistent with literature suggesting a significant relationship between peripheral hearing and cognition, and in agreement with our hypothesis, peripheral hearing was significantly related to 10 of 11 measures of cognition that assessed processing speed, executive function, or memory, as well as global cognitive status. Although evidence, including the present results, suggests a relationship between peripheral hearing and cognition, little is known about the underlying mechanisms. Examination of these mechanisms is a critical need to direct appropriate treatment.

Mechanisms of the Hearing-Cognition Relationship.

This review provides a description of age-related changes in hearing and cognition, the relationship between hearing and cognition, and several potential mechanisms that underlie the relationship. Several studies have shown a significant relationship between peripheral hearing loss and cognitive impairment/decline but other studies have not. Furthermore, poor performance on measures of central auditory processing has been significantly associated with cognitive impairment. Important to understanding these relationships are the nature of the underlying mechanisms. Possible mechanisms are overdiagnosis, widespread neural degeneration, sensory degradation/deprivation, cognitive resource allocation/depletion, and social isolation/depression. Overdiagnosis occurs when hearing loss impacts tests of cognitive function or vice versa. Widespread neural degeneration can impact hearing, cognition, or both. Sensory degradation/deprivation due to hearing loss can result in neural degradation and reduced cognitive function. Increased demands due to hearing loss can result in changes in neural resource allocation, reducing available resources for cognitive function. Finally, hearing difficulties can cause social isolation and even depression, increasing the risk for cognitive decline. Data from our laboratory provide support for cognitive resource allocation/depletion. Understanding all five of these mechanisms will advance the development of effective interventions and treatments, thereby enhancing the quality of life of older adults.

The Efficacy of InSight Cognitive Training to Improve Useful Field of View Performance: A Brief Report.

OBJECTIVE: It is well established that cognitive speed of processing training (SOPT) improves Useful Field of View (UFOV) performance and transfers to enhanced performance of instrumental activities of daily living, including driving. InSight is a recently developed version of SOPT formatted for self-administration by older adults with exercises translated into a gaming format. The goal was to examine whether InSight training improves UFOV performance. METHOD: Participants ranged in age between 59-95 years and were randomized to InSight cognitive training or a control condition. Cognitive performance and self-perceptions were measured pre- and post-training, or for controls, after an equivalent delay. Participants completed training twice a week over a 12-week period with the goal of completing 20 sessions. RESULTS: Participants randomized to InSight training experienced greater improvements in their UFOV performance relative to the control condition, F(1, 58) = 4.26, p = .043, but no changes in cognitive self-perceptions were found. CONCLUSIONS: The InSight program is a viable tool for enhancing older adults' UFOV performance. Future research should examine if training gains from the program endure and transfer to improved everyday function.

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.

An examination of mediators of the transfer of cognitive speed of processing training to everyday functional performance.

The purpose of these analyses was to examine mediators of the transfer of cognitive speed of processing training to improved everyday functional performance (J. D. Edwards, V. G. Wadley,, D. E. Vance, D. L. Roenker, & K. K. Ball, 2005, The impact of speed of processing training on cognitive and everyday performance. Aging & Mental Health, 9, 262-271). Cognitive speed of processing and visual attention (as measured by the Useful Field of View Test; UFOV) were examined as mediators of training transfer. Secondary data analyses were conducted from the Staying Keen in Later Life (SKILL) study, a randomized cohort study including 126 community dwelling adults 63 to 87 years of age. In the SKILL study, participants were randomized to an active control group or cognitive speed of processing training (SOPT), a nonverbal, computerized intervention involving perceptual practice of visual tasks. Prior analyses found significant effects of training as measured by the UFOV and Timed Instrumental Activities of Daily Living (TIADL) Tests. Results from the present analyses indicate that speed of processing for a divided attention task significantly mediated the effect of SOPT on everyday performance (e.g., TIADL) in a multiple mediation model accounting for 91% of the variance. These findings suggest that everyday functional improvements found from SOPT are directly attributable to improved UFOV performance, speed of processing for divided attention in particular. Targeting divided attention in cognitive interventions may be important to positively affect everyday functioning among older adults.

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.

Auditory evoked response to gaps in noise: older adults.

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 (Lister et al., 2007) 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.