Cognitive Neuroscience Of Aging Research Articles

Using Dual-Coil TMS-EEG to Probe Bilateral Brain Mechanisms in Healthy Aging and Mild Cognitive Impairment.

A widespread observation in the cognitive neuroscience of aging is that older adults show a more bilateral pattern of task-related brain activation. These observations are based on inherently correlational approaches. The current study represents a targeted assessment of the role of bilaterality using repetitive transcranial magnetic stimulation (rTMS). We used a novel bilateral TMS-stimulation paradigm, applied to a group of healthy older adults (hOA) and older adults with mild cognitive impairment (MCI), with two aims: First, to elucidate the neurophysiological effects of bilateral neuromodulation, and second to provide insight into the neurophysiological basis of bilateral brain interactions. Electroencephalography (EEG) was recorded while participants received six forms of transcranial magnetic stimulation (TMS): unilateral and bilateral rTMS trains at an alpha (8 Hz) and beta (18 Hz) frequency, as well as two sham conditions (unilateral, bilateral) mimicking the sounds of TMS. First, time-frequency analyses of oscillatory power induced by TMS revealed that unilateral beta rTMS elicited rhythmic entrainment of cortical oscillations at the same beta-band frequency. Second, both bilateral alpha and bilateral beta stimulation induced a widespread reduction of alpha power. Lastly, healthy older adults showed greater TMS-related reductions in alpha power in response to bilateral rTMS compared to the MCI cohort. Overall, these results demonstrate frequency-specific responses to bilateral rTMS in the aging brain, and provide support for inhibitory models of hemispheric interaction across multiple frequency bands.

The knowledge domain of cognitive neuroscience of aging: A Scientometric and bibliometric analysis.

Cognitive neuroscience of aging (CNA) is a relatively young field compared with other branches of cognitive aging (CA). From the beginning of this century, scholars in CNA have contributed many valuable research to explain the cognitive ability decline in aging brains in terms of functional changes, neuromechanism, and neurodegenerative diseases. However, very few studies have systematically reviewed the research in the domain of CAN, with regard to its primary research topics, theories, findings, and future development. Therefore, this study used CiteSpace to conduct a bibliometric analysis of 1,462 published articles in CNA from Web of Science (WOS) and investigated the highly influential and potential research topics and theories of CNA, as well as important brain areas involved in CAN during 2000-2021. The results revealed that: (1) the research topics of "memory" and "attention" have been the focus of most studies, progressing into a fMRI-oriented stage; (2) the scaffolding theory and hemispheric asymmetry reduction in older adults model hold a key status in CNA, characterizing aging as a dynamic process and presenting compensatory relationships between different brain areas; and (3) age-related changes always occur in temporal (especially the hippocampus), parietal, and frontal lobes and the cognitive declines establish the compensation relationship between the anterior and posterior regions.

Does Hemispheric Asymmetry Reduction in Older Adults in Motor Cortex Reflect Compensation?

Older adults tend to display greater brain activation in the nondominant hemisphere during even basic sensorimotor responses. It is debated whether this hemispheric asymmetry reduction in older adults (HAROLD) reflects a compensatory mechanism. Across two independent fMRI experiments involving adult life span human samples (N = 586 and N = 81, approximately half female) who performed right-hand finger responses, we distinguished between these hypotheses using behavioral and multivariate Bayes (MVB) decoding approaches. Standard univariate analyses replicated a HAROLD pattern in motor cortex, but in and out of scanner behavioral results both demonstrated evidence against a compensatory relationship in that reaction time measures of task performance in older adults did not relate to ipsilateral motor activity. Likewise, MVB showed that this increased ipsilateral activity in older adults did not carry additional information, and if anything, combining ipsilateral with contralateral activity patterns reduced action decoding in older adults (at least in experiment 1). These results contradict the hypothesis that HAROLD is compensatory and instead suggest that the age-related ipsilateral hyperactivation is nonspecific, consistent with alternative hypotheses about age-related reductions in neural efficiency/differentiation or interhemispheric inhibition.SIGNIFICANCE STATEMENT A key goal in the cognitive neuroscience of aging is to provide a mechanistic explanation of how brain–behavior relationships change with age. One interpretation of the common finding that task-based hemispheric activity becomes more symmetrical in older adults is that this shift reflects a compensatory mechanism, with the nondominant hemisphere needing to help out with computations normally performed by the dominant hemisphere. Contrary to this view, our behavioral and brain data indicate that the additional activity in ipsilateral motor cortex in older adults is not reflective of better task performance nor better neural representations of finger actions.

Reproducibility of the correlative triad among aging, dopamine receptor availability, and cognition.

The evidence that dopamine function mediates the association between aging and cognition is one of the most cited findings in the cognitive neuroscience of aging. However, few and relatively small studies have directly examined these associations. Here we examined correlations among adult age, dopamine D2-like receptor (D2R) availability, and cognition in two cross-sectional studies of healthy human adults. Participants completed a short cognitive test battery and, on a separate day, a PET scan with either the high-affinity D2R tracer [18F]Fallypride (Study 1) or [11C]FLB457 (Study 2). Digit span, a measure of short-term memory maintenance and working memory, was the only cognitive test for which dopamine D2R availability partially mediated the age effect on cognition. In Study 1, age was negatively correlated with digit span. Striatal D2R availability was positively correlated with digit span controlling for age. The age effect on digit span was smaller when controlling for striatal D2R availability. Although other cognitive measures used here have individually been associated with age and D2R availability in prior studies, we found no consistent evidence for significant associations between low D2R availability and low cognitive performance on these measures. These results at best only partially supported the correlative triad of age, dopamine D2R availability, and cognition. While a wealth of other research in human and nonhuman animals demonstrates that dopamine makes critical contributions to cognition, the present studies suggest caution in interpreting PET findings as evidence that dopamine D2R loss is a primary cause of broad age-related declines in fluid cognition. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Cognitive Neuroscience of Aging.

Cognitive Neuroscience of Aging.

Between-network Functional Connectivity Is Modified by Age and Cognitive Task Domain.

Research on the cognitive neuroscience of aging has identified myriad neurocognitive processes that are affected by the aging process, with a focus on identifying neural correlates of cognitive function in aging. This study aimed to test whether internetwork connectivity among six cognitive networks is sensitive to age-related changes in neural efficiency and cognitive functioning. A factor analytic connectivity approach was used to model network interactions during 11 cognitive tasks grouped into four primary cognitive domains: vocabulary, perceptual speed, fluid reasoning, and episodic memory. Results showed that both age and task domain were related to internetwork connectivity and that some of the connections among the networks were associated with performance on the in-scanner tasks. These findings demonstrate that internetwork connectivity among several cognitive networks is not only affected by aging and task demands but also shows a relationship with task performance. As such, future studies examining internetwork connectivity in aging should consider multiple networks and multiple task conditions to better measure dynamic patterns of network flexibility over the course of cognitive aging.

Neurociencia cognitiva del envejecimiento. Aportaciones y retos

The cognitive neuroscience of aging is a young discipline that has emerged as a result of the combination of: A) the theoretical and explanatory frameworks proposed by the cognitive psychology perspective throughout the second half of the twentieth century; B) the designs and methodological procedures arising from experimental psychology and the need to test the hypotheses proposed from the cognitive psychology perspective; C) the contributions of the computer sciences to the explanation of brain functions; and D) the development and use of neuroimaging techniques that have enabled the recording of brain activity in humans while tasks that test some cognitive process or function are performed. An analysis on the impact of research conducted from this perspective over the last 3decades has been carried out, including its shortcomings, as well as the potential directions and usefulness that will advantageously continue to drive this discipline in its description and explanation of the process es of cerebral and cognitive aging.

Neuropsychology of aging, past, present and future: Contributions of Morris Moscovitch

In this review we provide a broad overview of major trends in the cognitive neuroscience of aging and illustrate their roots in the pioneering ideas and discoveries of Morris Moscovitch and his close collaborators, especially Gordon Winocur. These trends include an on-going focus on the specific and dissociable contributions of medial temporal and frontal lobe processes to cognitive aging, especially in the memory domain, the role of individual variability stemming from different patterns of underlying neural decline, the possibility of compensatory neural and cognitive influences that alter the expression of neurobiological aging, and the investigation of lifestyle and psychosocial factors that affect plasticity and may contribute to the rate and level of neurocognitive decline. These prescient ideas, evident in the early work of Moscovitch and Winocur, continue to drive on-going research efforts in the cognitive neuroscience of aging.

Noninvasive Brain Stimulation for the Study of Memory Enhancement in Aging

Abstract. Noninvasive brain stimulation (NIBS) techniques have recently attracted interest due to their potential for transiently improving cognition. This may prove particularly valuable in aging, given the known impact of age-related cognitive dysfunction on quality of life. The present review summarizes the currently available evidence of working and episodic memory enhancements achieved using NIBS in healthy elderly people. The evidence reviewed indicates that research is still at an early stage and that there is a need to define the best procedures for operating and performing multicentre characterization of protocols. However, a limited number of sham-controlled studies have reported improvements in both cognitive domains. Furthermore, evidences of long-term beneficial effects opens up the possibility of using NIBS as an adjuvant therapeutic strategy. However, the relevance of certain variables involved and approaches used remains to be elucidated, including the potential benefits of single versus multiple NIBS sessions, the putative synergistic effects of using NIBS in combination with cognitive training, and the importance of individual differences. Overall, NIBS techniques represent a promising opportunity for psychologists seeking strategies to improve memory functions in the elderly. Nevertheless, their use requires appropriate technical knowledge coupled with a clear understanding of the neurophysiology and cognitive neuroscience of aging.

Age-related changes to oscillatory dynamics in hippocampal and neocortical networks

Recent models of hippocampal function have emphasized its role in relational binding – the ability to form lasting representations regarding the relations among distinct elements or items which can support memory performance, even over brief delays (e.g., several seconds). The present study examined the extent to which aging is associated with changes in the recruitment of oscillatory activity within hippocampal and neocortical regions to support relational binding performance on a short delay visuospatial memory task. Structural magnetic resonance imaging and MEG were used to characterize potential age-related changes in hippocampal volume, oscillatory activity, and subsequent memory performance, and the relationships among them. Participants were required to bind the relative visuospatial positions of objects that were presented singly across time. Subsequently, the objects were re-presented simultaneously, and participants were required to indicate whether the relative spatial positions among the objects had been maintained. Older and younger adults demonstrated similar task accuracy, and older adults had preserved hippocampal volumes relative to younger adults. Age-group differences were found in pre-stimulus theta (∼5Hz) and beta (∼20Hz) oscillations, and this pre-stimulus activity was related to hippocampal volumes in younger adults. Age-group differences were also found in the recruitment of oscillatory activity from the pre-stimulus period to the task. Only younger adults showed a task-related change in theta power that was predictive of memory performance. In contrast, older adults demonstrated task-related alpha (∼10Hz) oscillatory power changes that were not observed in younger adults. These findings provide novel evidence for the role of the hippocampus and functionally connected regions in relational binding that is disrupted in aging. The present findings are discussed in the context of current models regarding the cognitive neuroscience of aging.

Neuroplasticity in middle age: an ecologically valid approach

A commentary on The effect of leisure activity golf practice on motor imagery: an fMRI study in middle adulthood by Bezzola, L., Merillat, S., and Jancke, L. (2012). Front. Hum. Neurosci. 6:67. doi: 10.3389/fnhum.2012.00067 “You know you're middle aged when caution is the only thing you care to exercise.” In “The effect of leisure activity golf practice on motor imagery: an fMRI study in middle adulthood,” Bezzola et al. (2012) demonstrate changes in the neural representations of imagined movement following 40 h of golf training. An experimental (golf novice) and control group were scanned using functional MRI during kinetic motor imagery of their golf swing both prior to and following the golf training (with the control group matched for average pre- to post-test duration). The authors found reductions in bilateral dorsal premotor cortex activity during motor imagery following the training period only in the experimental group and not the control group, suggesting more efficient neural representations following training. This study is unique among the large number of papers that have been published in recent years on experience-dependent sensorimotor neuroplasticity. One defining feature of this work is that the characteristics of the training program were not regulated. The experimental group simply participated in golf training for a total of 40 h. This ecologically valid approach makes the findings generalizable to what individuals may choose to do for their own leisure and exercise on any given day. This indicates that precisely regimented training programs are not de rigueur for behavioral and brain plasticity to occur. Secondly, the participants ranged in age from 40 to 60 years. Research on the cognitive neuroscience of aging has begun to yield insights into age differences in motor control and learning at both the behavioral and brain levels (cf. Seidler et al., 2010). However, work with individuals in the middle aged range of the lifespan is scant. It is important to investigate both behavioral and neural plasticity within this age range, however, because these individuals make up a large portion of the workforce. Moreover, such an approach will be critical for identifying trajectories of decline. The few studies that have investigated behavioral and brain function of participants in this age range have yielded the sobering finding that many changes evident in older adults are already manifest at this point. For example, individuals aged 40–60-years old exhibit evidence of declines in sensorimotor adaptation in comparison to those in their twenties (Heuer and Hegele, 2011). Interestingly, retention of the ability to transfer learning to new conditions is preserved (Heuer and Hegele, 2011), similar to what has also been reported in older individuals (Seidler, 2007; Langan and Seidler, 2011). Likewise, numerous studies have shown that older adults tend to under-recruit task relevant brain regions while over-activating additional areas in comparison to young adults (Langan et al., 2010; Seidler et al., 2010). Different theories exist regarding the function of this over-activation (cf. Lindenberger et al., 2012), including the compensation viewpoint and the nonselective recruitment or dedifferentiation view. The compensation view posits that this over-recruitment serves to compensate for age-related brain structural and biochemical declines and is associated with better performance (cf. Reuter-Lorenz and Lustig, 2005). In contrast, dedifferentiation suggests that over-recruitment is a sign of less efficient or specific neural representations with age (Li and Lindenberger, 1999). Recent findings support the Compensation-Related Utilization of Neural Circuits Hypothesis (CRUNCH), which posits that older adults reach their limits of cognitive and neural resources at lower levels of task difficulty (Reuter-Lorenz and Cappell, 2008; Carp et al., 2010; Schneider-Garces et al., 2010). That is, they exhibit over-activation as a compensatory mechanism at lower levels of task difficulty, and once they have reached their maximum capacity then activation declines. Functional brain over-activation is already apparent in individuals that are 60-years old (Burgmans et al., 2010). Moreover, studies investigating brain volumetric changes with age indicate that losses are evident in those within the range of 40–60-years old, particularly for brain structures involved in learning and memory (Ziegler et al., 2012). Thus, although behavioral changes may not be as marked in middle aged individuals as they are in older adults, brain structure and function are exhibiting evidence of age differences. United States Census data predict that there will be 88.5 million people in the US over the age of 65 by the year 2050. This dramatic shift in the population will increase the need for programs and interventions that can facilitate activities of daily living for older adults. Further investigation of neuroplastic changes within middle aged individuals will be important for providing prescriptions regarding the optimal time point for motor training interventions. Bezzola et al. (2012) have gotten us onto the fairway by providing evidence for neuroplastic changes in middle aged adults using a realistic and ecologically valid paradigm.

All data collection and analysis methods have limitations: Reply to Rabbitt (2011) and Raz and Lindenberger (2011).

The commentaries on my article contain a number of points with which I disagree but also several with which I agree. For example, I continue to believe that the existence of many cases in which between-person variability does not increase with age indicates that greater variance with increased age is not inevitable among healthy individuals up to about 80 years of age. I also do not believe that problems of causal inferences from correlational information are more severe in the cognitive neuroscience of aging than in other research areas; I contend instead that neglect of these problems has led to confusion about neurobiological underpinnings of cognitive aging. I agree that researchers need to be cautious in extrapolating from cross-sectional to longitudinal relations, but I also note that even longitudinal data are limited with respect to their ability to support causal inferences.

The relationships between cognitive aging and strategic variations in the cognitive procedural learning: an fMRI study

Event Abstract Back to Event The relationships between cognitive aging and strategic variations in the cognitive procedural learning: an fMRI study Gandini Delphine1, 2*, Eric Bertasi3, Benjamín Boller4, Philippe Fossati5 and Anne-Marie Ergis4 1 Centre de Recherche de l’Institut Universitaire de Gériatrie de Montréal (CRIUGM),, Canada 2 Centre de Recherche en Neuropsychologie et Cognition (CERNEC), Canada 3 Centre de Neuro-imagerie de Recherche (CENIR), France 4 Laboratoire de Psychologie et Neuropsychologie Cognitives (LPNCog), FRE 3292, CNRS, Université Paris Descartes, France 5 Centre Émotion, USR 3246, Hôpital de la Salpêtrière, France The ACT* theory postulates that cognitive skill learning comprises three main stages: cognitive, associative, and autonomous. During aging, learning is slowed but the sequence of each stage is spared. The present study addressed the roles of strategy variations and aging in procedural learning, at the behavioral and cerebral levels. We hypothesized that the strategic variability observed in the declarative stage could be responsible for cognitive learning slowing during aging. Moreover, this variability may explain the frequently observed difference in cerebral activations between young and older adults in cognitive learning tasks. Thirteen young adults and 12 older participants were tested in three experimental sessions: (1) a pretraining session (first fMRI scanning), (2) two behavioral learning sessions, and (3) a posttraining session (second fMRI scanning). The task used for the cognitive learning was an adapted version of the Tower of Hanoi. Results showed that the two age groups were comparable in the mean number of moves during the pre- and posttraining sessions, but older participants made more unwarranted moves and backward moves than younger ones. In addition, older adults more frequently used mixed perceptual strategies and mixed strategies (based on planning and perception) than did young adults. During the pretesting session, older adults exhibited distributed activation in right-lateralized cerebral network, including occipito-temporal and parietal areas whereas young adults activated the same regions but bilaterally. The same pattern of differences was found in the posttraining session whereas the two age groups reached the autonomous stage. Results will be further discussed regarding literature on cognitive neuroscience of aging and strategic variations. Keywords: Aging, fMRI Conference: XI International Conference on Cognitive Neuroscience (ICON XI), Palma, Mallorca, Spain, 25 Sep - 29 Sep, 2011. Presentation Type: Poster Presentation Topic: Poster Sessions: Cognitive Aging Citation: Delphine G, Bertasi E, Boller B, Fossati P and Ergis A (2011). The relationships between cognitive aging and strategic variations in the cognitive procedural learning: an fMRI study. Conference Abstract: XI International Conference on Cognitive Neuroscience (ICON XI). doi: 10.3389/conf.fnhum.2011.207.00611 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 15 Nov 2011; Published Online: 28 Nov 2011. * Correspondence: Dr. Gandini Delphine, Centre de Recherche de l’Institut Universitaire de Gériatrie de Montréal (CRIUGM),, Montreal, Canada, delphine.gandini@umontreal.ca Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Gandini Delphine Eric Bertasi Benjamín Boller Philippe Fossati Anne-Marie Ergis Google Gandini Delphine Eric Bertasi Benjamín Boller Philippe Fossati Anne-Marie Ergis Google Scholar Gandini Delphine Eric Bertasi Benjamín Boller Philippe Fossati Anne-Marie Ergis PubMed Gandini Delphine Eric Bertasi Benjamín Boller Philippe Fossati Anne-Marie Ergis Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Modeling Cognitive Trajectories Within Longitudinal Studies: A Focus on Older Adults

The natural history of life span cognitive performance and its late-life determinants have been studied from an array of perspectives. Significant insights come from psychological disciplines, including cognitive, developmental, and neuropsychology, as well as from medical specialties, such as geriatrics, neurology, psychiatry, neuroradiology, and neuropathology, that contribute to the growing interdisciplinary scientific field: cognitive neuroscience of aging. This survey of longitudinal studies of aging suggests that disease-oriented investigations commonly do not adequately consider normative cognitive changes, whereas developmental studies do not sufficiently measure and model nonnormative cognitive aging. This article argues for an integrative perspective that considers both of these influences on cognitive trajectories and presents a series of methodological concerns that have not been addressed comprehensively. Interdisciplinary methods from longitudinal observational studies should be leveraged to enable translational interventions to promote brain longevity.

Culture and the Aging Brain


 
 
 
 Research in the cognitive neuroscience of aging has revealed several significant changes that alter the functioning of the brain over an individual’s lifetime. Particularly, some of these discoveries have contributed to our understanding of age-related degenerative diseases and cognitive decline. Most of these studies have, however, been conducted in Western (North American and Western European) populations, casting doubt on the universality of these findings. Cross-cultural investigations allow for the distinction between changes in the brain that are a consequence of aging and those changes that are due to the impact of life experiences. Research suggests that different cultures place emphasis on distinct aspects of information and use different strategies for processing this information (Nisbett and Masuda, 2003). Therefore, performing cognitive studies taking into account cultural context may provide an effective avenue for differentiating between age-related neural changes that persist across cultures and those that are driven by culture specific life experiences.
 
 
 

Cognitive Neuroscience of Aging

The number of reports on the cognitive neuroscience of aging has increased in recent years, and most of these studies have found many similarities in the patterns of activity in young and old adults, indicating that basic neural mechanisms are maintained into older age. Despite these overall similarities, older adults often have less activity in some regions, such as medial temporal areas during memory processing and visual regions across a variety of cognitive domains. It seems clear that age reductions in cognitive function can be tied, at least in part, to these reductions in brain activity. On the other hand, older adults typically also overrecruit some brain areas, mainly the ventral or dorsal prefrontal cortex during memory tasks, as well as both the frontal and parietal regions during tasks engaging cognitive control processes, such as attention. Sometimes this overrecruitment appears to be in response to altered function in other brain regions and is often seen in those older adults who perform better on the task at hand. These findings have provided rather convincing support for the idea that overrecruitment can be compensatory in the elderly. Nevertheless, not all age increases can be interpreted as compensatory, and some are more indicative of neural inefficiency. The challenge facing future research will be to understand the task conditions that promote compensation in older adults, the role of the various brain areas in aiding cognitive function, and how these compensatory mechanisms can be elicited to enhance quality of life in the elderly.

The Cognitive Neuroscience of Aging and Culture

Research into the cognitive neuroscience of aging has revealed exciting and unexpected changes to the brain over the lifespan. However, studies have mostly been conducted on Western populations, raising doubts about the universality of age-related changes. Cross-cultural investigation of aging provides a window into the stability of changes with age due to neurobiology, as well as into the flexibility of aging due to life experiences that impact cognition. Behavioral findings suggest that different cultures process distinct aspects of information and employ diverse information-processing strategies. The study of aging allows us to identify those age-related neural changes that persist across cultures as well as the changes that are driven by culture-specific life experiences.

Effects of age on auditory and cognitive processing: implications for hearing aid fitting and audiologic rehabilitation.

Recent advances in research and clinical practice concerning aging and auditory communication have been driven by questions about age-related differences in peripheral hearing, central auditory processing, and cognitive processing. A "site-of-lesion'' view based on anatomic levels inspired research to test competing hypotheses about the contributions of changes at these three levels of the nervous system. A "processing'' view based on psychologic functions inspired research to test alternative hypotheses about how lower-level sensory processes and higher-level cognitive processes interact. In the present paper, we suggest that these two views can begin to be unified following the example set by the cognitive neuroscience of aging. The early pioneers of audiology anticipated such a unified view, but today, advances in science and technology make it both possible and necessary. Specifically, we argue that a synthesis of new knowledge concerning the functional neuroscience of auditory cognition is necessary to inform the design and fitting of digital signal processing in "intelligent'' hearing devices, as well as to inform best practices for resituating hearing aid fitting in a broader context of audiologic rehabilitation. Long-standing approaches to rehabilitative audiology should be revitalized to emphasize the important role that training and therapy play in promoting compensatory brain reorganization as older adults acclimatize to new technologies. The purpose of the present paper is to provide an integrated framework for understanding how auditory and cognitive processing interact when older adults listen, comprehend, and communicate in realistic situations, to review relevant models and findings, and to suggest how new knowledge about age-related changes in audition and cognition may influence future developments in hearing aid fitting and audiologic rehabilitation.