The Best of 2007 (2008)

FigureThere are exciting happenings in hearing science: genetics, hair cells, cortical connections, imaging, tinnitus, noise, age… and the list goes on and on. Basic science discoveries and insights in these areas underlie our clinical practice—both today and in the future. The published research is found in an array of journals. Journal of the Association for Research in Otolaryngology, Hearing Research, and Journal of the Acoustical Society of America are among those that focus on hearing research. Topics of interest to audiologists encompass many areas and disciplines, so we also find ourselves reading articles in journals that focus on genetics, biology, neurology, engineering, and many other topics. Here, I will focus on the audiology journals, which contain many informative articles related to the hearing science underlying audiologic practice. The topics of papers in 2007 encompass a wide range of research areas, and what follows are just some selections from the many excellent articles that I read in the audiology journals last year. As always, I join with Gus Mueller, Brad Stach, and David Wark in commending all the 2007 authors for their excellent contributions to our audiology literature. GREAT FOR THE CLINICIAN Contrary to the claim I sometimes hear that we already know everything about how best to use the ABR for screening and threshold determination, I believe our work in that area is unfinished. We should strive to improve test efficiency, response detection, frequency specificity, and incorporation of cochlear and neural processing characteristics into the development of refined paradigms. In support of this idea is an article in the Journal of the American Academy of Audiology (JAAA) by Mario Cebulla, Ekkehard Stürzebecher, Claus Elberling, and Jochen Müller that evaluates a new stimulus for ABR testing. They present a click-like stimulus that compensates for frequency dispersion of the cochlea and compares it to clicks and to studies of chirp stimuli. Along with a finding of increased response signal-to-noise ratios, response detection improved and detection time decreased. This study also lays the groundwork for further developments in frequency-specific application of the methods. A two-part article in Ear and Hearing that's a must-read for pediatric audiologists in particular comes from Mary Pat Moeller and nine co-authors. The need for so many contributors becomes obvious when one considers how much work went into acquiring and analyzing the data reported in these articles. Development of vocalizations of infants with hearing loss and infants with normal hearing are explored longitudinally across the ages of 10 to 24 months. The investigators found, for example, that consonant sound development was delayed with hearing loss, but not qualitatively different from that in children with normal hearing, and that this may influence early word-learning rates. The authors present a wealth of carefully collected, analyzed, and presented data, which helps explain why these articles received Ear and Hearing's 2007 Editor's Award. Another article for this category was written by Carol Mackersie in the Journal of Speech, Language, and Hearing Research (JSLHR). She addresses the topic of masking effects on speech recognition and the effects of hearing loss. Subjects in this study had either normal hearing, flat or gradually sloping sensorineural hearing losses, or steeply sloping sensorineural hearing losses. Temporal masking effects on consonants from adjacent vowel components were evaluated by testing consonants in isolation and in vowel-consonant-vowel sets where format transition information was removed. This is important for the clinician because the author found that the group of subjects with steeply sloping hearing losses performed worse than the other two groups, which suggests that the steepness of a hearing loss may dictate different considerations in the signal processing strategies used in rehabilitation. BEST QUICK READ I could probably have placed most of the articles I selected for this category into another category, since one is often hard-pressed to find any real “quick reads” in hearing science. But these three seemed to fit here, perhaps because they make relatively straightforward points. One that caught my attention comes from the Blue Mountains Hearing Study, a longitudinal study of aging in the Australian population. In the vein of full disclosure, I'll state that I have the privilege of being involved in this hearing study (though not the particular article cited here). In their Ear and Hearing article, Gerald Liew and his five co-authors examine potential relationships between retinal microvascular abnormalities and age-related hearing loss based on the hypothesis that microvascular changes in the eye might have relationship to changes in hearing. Retinal microvasculature and hearing sensitivity quantified by pure-tone thresholds were examined in 1511 adults aged 54 years and older. Interestingly, the authors found a relationship in women but not men, and a particular association with low-frequency hearing loss. As you will see here, as well as in other articles discussed below, we can learn about the auditory system by studying other sensory systems and the interactions among them. In another population study, Amanda Hall, Kevin Munro, and Jon Heron discuss developmental changes in word recognition in children 2 to 5 years with varying middle ear status. As they report in the International Journal of Audiology (IJA), word-recognition threshold was measured in approximately 1000 children at age 31, 43, and 61 months, and the data were analyzed with respect to the presence of OME in one or both ears or previous history of OME. Children without OME showed a 5-dB improvement in word-recognition threshold between 31 and 43 months. While present OME influenced results, at 61 months a history of OME did not influence word threshold. Large studies such as these are an excellent resource for understanding population trends related to hearing. My final “quick read” explores the feasibility of expanding applications of auditory steady-state responses (ASSR) to frequencies below or above the 500-to-4000 Hz range where this method is typically applied. As they report in IJA, Abreena Tlumak, John Durrant, and Lionel Collet tested young adults via the 80-Hz ASSR technique with carrier frequencies of 250 and 12,000 Hz. The value of understanding test characteristics has implications as consideration is given to using high-frequency ASSR for monitoring ototoxic effects and perhaps expanding to lower frequencies to better describe hearing sensitivity across the hearing range. While the investigators demonstrated overall efficacy of the ASSR over a broad range of frequencies, they found reduced accuracy at the audiometric extremes. The study's thoughtful approach and interpretation add to our understanding of the applications and limitations of this objective test method. NOT READY FOR MEDLINE Leading off this section is an outstanding two-part article from Walter Nance and Kelley Dobson in Audiology Today. Dr. Nance, a pioneer and world leader in genetics and hearing, focuses on genetics as it relates to hearing loss and its early identification and management. Along with a thorough review of various forms of genetically based hearing loss, Dr. Nance poses some very provocative and important observations about how newborn hearing screening could be improved. This is must reading for anyone involved in newborn hearing screening programs and/or pediatric audiology… or really audiology in general. Another article of interest in this category is The Hearing Journal Page Ten entry from Beverly Wright. Dr. Wright looks very systematically at the basic parameters, such as frequency or duration cues, involved in learning and neural plasticity. While this line of research addresses basic questions about learning and perception primarily in young adults, it likely has implications for individuals of all ages. It also has important implications for clinical management related to device use, follow-up, and training programs designed to maximize auditory effectiveness. “A Moment of Science,” which appears regularly in Audiology Today, continues to provide insightful commentary on recent breakthroughs in hearing science. All these articles are interesting, but since I have to pick favorites I'll cite two from 2007. Shimon Francis and Lisa Cunningham discuss research related to the role of anti-oxidant activity in protecting the inner ear. Free radicals play important roles in signaling functions, but an over-accumulation can be toxic. Antioxidants are important in control and, as the authors state, may be important scavengers for maintaining hearing. In another “Moment of Science,” Kathleen Faulkner and Kelly Tremblay discuss the effects of noise in infancy on hearing ability later on. They focus on the work of Aizawa and Eggermont (2006, JARO 7:71–80) that found that noise-exposed infant animals had poorer ability than adults to discriminate gaps in sounds and voice onset time. These findings should send us a strong message to guard against noise at all ages. Readers of the Hearing Review can find useful leads to new articles in the “Research Roundup,” a recurring column that reviews articles on basic science and clinical topics. Hearing science topics reviewed here in 2007 included origins of hair cell motility, the role of the tectorial membrane in hearing, stem cell research, and the role of the planum temporale in spatial hearing. Oh, and 260-million-old ears, too. Surely that one is worth looking up! MOST THOUGHT PROVOKING Quite a few articles about event-related potentials (ERPs) were published last year, which may reflect growing interest in relationships between auditory evoked potentials and behavioral measures of perception. I had to make some hard decisions to avoid turning this into a “heavy evoked potentials” section, both because of the number of articles and my confessed interest in this area. One article on this topic that I enjoyed and recommend as an excellent review of the role of ERPs in assessing central auditory processing was published by Claude Alain and Kelly Tremblay in JAAA. The topic of auditory processing always draws a lot of interest and we are seeing more and more discussions of objective as well as behavioral approaches to evaluating this elusive hearing problem. I especially liked this article because it explores neural correlates of behavioral perception and provides insight into the neural processes that underlie auditory perception. The authors examine the role of ERPs in investigating the processing of complex acoustic events such as speech and music, how hearing loss can affect these events, and how cognitive factors and training can compensate for difficulties. Finally, they consider how auditory scene analysis can be used as a framework for understanding perception of sound thorough the components of detection, discrimination, grouping, and separating of incoming signals. This article offers a very clear and thoughtful discussion of foundation knowledge for the newcomer as well as concepts to stimulate further discussion among those experienced in ERPs. With the big picture in mind, a specific example of investigation of neural correlates of behavioral responses is demonstrated in a study by Jennifer Lister, Nathan Maxfield, and Gabriel Pitt published in Ear and Hearing. Dr. Lister has studied gap detection, both within and across channels, using psychophysical approaches and has shown that the task is more difficult when listening across different frequency regions or channels. In this paper, cortical responses to gaps in noise are quantified, again comparing within and across channel conditions. ERP findings were consistent with predicted results, showing higher amplitude cortical responses where acoustic cues were most salient (such as larger gaps and frequency differences). Studies like this provide information about relationships between behavioral and objective methods, underlying mechanisms, and the potential for developing measures that don't depend on behavioral responses. The remaining thought-provoking studies I've selected address the topics of aging and understanding speech. I don't know an audiologist who hasn't wondered why most people with SNHL have difficulty understanding speech in noise. Interestingly, one factor related to these difficulties is reduced ability to discriminate fundamental frequency differences. In JSLHRTara Vongpaisal and Kathleen Pichora-Fuller expand this finding to issues in aging, even in older individuals with normal hearing. As expected, young adults could detect smaller differences than older adults could, even those with good hearing in the speech range. The authors provide a thoughtful discussion of factors related to this difficulty and suggest that the problems experienced by older listeners may relate to changes in processing of temporal information, which also occur with aging. Problems listening in noise may not be due to peripheral hearing loss alone; central auditory processing and cognitive factors might also play a role. Larry Humes, Matthew Burk, Maureen Coughlin, Thomas Busey, and Lauren Strauser addressed this subject in a JSLHR study comparing age-related differences in auditory speech recognition and visual text recognition. Along with studying function via both auditory and visual modalities to help in separating cognitive issues, the authors also evaluated rate of presentation of stimuli. They found that performance in the auditory modality was closely associated with visual performance and that older adults, whether with normal hearing or hearing loss, had more difficulty with fast presentation of speech in the auditory tasks. Research like this should help us better understand the sources of difficulty that older listeners experience. It also should lead to appropriately targeted management of their difficulties, whether peripheral or central in nature. As we learn more about the nature of listening-in-noise problems and age-related hearing loss, we also want to know why they occur. What are the underlying mechanisms? Despite having learned much about the function of the cochlea as a non-linear system, we do not yet have a good understanding of how these cochlear non-linearities affect our ability to understand speech in noise. To further this understanding, Judy Dubno and colleagues have undertaken a number of studies. In one of them, published in Ear and Hearing, Judy Dubno, Amy Horowitz, and Jayne Ahlstrom evaluate masking effects on tones and speech in persons with normal hearing and a range of quiet thresholds. Findings from this research related to individual differences and effects of maskers support the hypothesis that non-linear cochlear effects have an important role in understanding speech in noise. ALL-AROUND FAVORITE I'm coming back to the topic of evoked potentials for my all-around favorite article. A perk of belonging to HJ's Journal Club is that sometimes I get to pick an article on a topic of particular personal interest. This is one of those years, but even when I made sure to be as objective and unbiased as possible, this article still kept showing up as my favorite. It also was a favorite of Journal Club member Brad Stach, so I do have some unbiased validation! This article examines divided and directed attention, a paradigm used in some dichotic listening experiments. Writing in JAAA, Jeffrey Martin, James Jerger, and Jyutika Mehta examined behavioral and electrophysiological responses in children, some of whom showed ear differences on a dichotic listening task and some of whom showed no such differences. The authors compared behavioral responses and ERPs (specifically N400 and a late positive component) in a dichotic listening task requiring either divided attention between two signals or directed attention toward one of the signals. For the task paradigms used in this study, divided attention was the condition where differences were clearly demonstrated between the two groups of children. This is a well-planned and executed study, which one expects from the Jerger group. What makes it of particular interest is its clear presentation of the background information and issues and the insightful discussion of results, including careful consideration of limitations and potential applications. Anyone interested in auditory processing, children, brain function, or related areas should find this article of interest. As one who is interested in all those areas, I certainly did. CONCLUSION That's it for this year. I've enjoyed reading all of these articles from 2007 and more. Hope you do, too!