The Best of 2009: Hearing Science

It is significant and comforting to see the quality and quantity of hearing research appearing in our audiology journals. We know that research underlies and advances a profession. We can take comfort that audiologists, hearing scientists, and others interested in hearing and hearing loss are actively providing that much needed research.

I've had a great time reading all of the articles this year and focusing on those that fit into the hearing science category. I congratulate all the authors—those included here and those not—for their fine work. I would also like to extend appreciation to the editors of our audiology journals as well as the associate editors and the many reviewers, who all work very hard to be sure we are reading articles of the highest quality. Theirs is a task that takes countless hours, often without thanks for their commitment and contributions.

As always, there are many, many more articles I'd like to tell you about than space permits. So, think of these as simply “teasers.” I hope that as you look at the articles cited below you will also peruse the rest of the issue and find your own favorites. And, look beyond the audiology journals; PubMed is a good place to start. The search engine there has undergone some significant changes, making searches on the topics you select even more likely to bring you to the articles of interest and relevance to your work.

GREAT FOR THE CLINICIAN

It is well known that words in sentences are easier to identify than isolated words due to contextual and linguistic information. While this is true in a general sense, an article in the Journal of the American Academy of Audiology (JAAA) by Raj Stewart and Arthur Wingfield demonstrates the importance of considering the complexity of a sentence, particularly in older listeners. In their study of hearing loss and cognitive effort, the authors presented words and sentences with two levels of complexity and thus of cognitive demand to younger and older listeners with normal hearing as well as to a group of older listeners with hearing loss. Subjects were well matched on several factors. Stewart and Wingfield found the expected better performance for sentences than words in all groups. However, the more complex sentences with higher cognitive demands yielded poorer performance than the easier sentences in both of the older groups of listeners, and, notably, the difference was greater in the older subjects with hearing loss. This study highlights the increasingly recognized importance of considering cognitive effects in working with older patients and how cognitive ability may affect communication and effectiveness of management.

How many of you have seen a patient, perhaps “middle-aged,” who complains of difficulty hearing but was found to have normal hearing sensitivity and normal results on diagnostic site-of-lesion measures? I have. Despite the fact that the tests show normal hearing by current audiometric definitions, these individuals experience difficulty. When we look to the literature on the effects of aging on auditory function, studies traditionally have focused on the extremes, examining early developmental aspects in infants and children or declining hearing ability in elderly listeners.

Two articles I'd like to discuss focus on auditory function in middle-aged listeners and highlight the importance of considering changes across the life span, not just at the extremes. The first of these, by Karen Helfer and Megan Vargo in JAAA, focuses on speech recognition and temporal processing in middle-aged women. In this study, they found decreased speech-recognition ability with a competing speech masker and reduced temporal resolution in the middle-aged subjects compared to younger subjects, despite similar pure-tone thresholds in the two groups. These results provide some evidence to support the idea that middle-aged individuals reporting difficulty listening in adverse conditions may indeed differ from younger listeners.

Another article in JAAA on this theme of middle-aged hearing related to processing of interaural phase cues. Here Ilse Wambacq and colleagues evaluated ability to separate sounds, perhaps as in speech in a competing signal background, in the context of sound segregation. These investigators compared cortical auditory evoked potentials in young and middle-aged subjects where sudden phase shifts in components of a harmonic complex were the cue of interest. Their results provide evidence of changes in neurophysiologic responses in middle age. With studies such as these, we see converging evidence of behavioral and neurophysiologic differences in auditory function in middle-aged listeners.

While it is possible that central auditory changes might also be a factor, these studies highlight the fact that more sensitive measures of auditory function, particularly at supra-threshold levels, are needed to identify subtle changes in function. I hope we will see more of these assessment methods in clinical use in the near future. And, an important additional benefit shown by these studies, as noted by James Jerger, editor of JAAA, in his editorials, is that studies of middle-aged subjects avoid the confounding issues of pure-tone sensitivity losses that are nearly universal in more elderly subjects. I always make it a point to read Dr. Jerger's editorials.

BEST QUICK READ

I know that putting a genetics article in the Quick Read category may seem a bit risky. However, the reason I liked this article and put it in this category is because it provides a succinct update on what scientists are learning about noise-induced hearing loss (NIHL) from genetics studies. Writing in Ear and Hearing, Annelies Konings, Lut Van Laer, and Guy Van Camp review the characteristics of NIHL and discuss the roles of various genes associated with oxidative stress, potassium recycling, and heat shock proteins in NIHL. They review human and animal studies supporting these gene associations, along with studies supporting the protective effects of antioxidants. NIHL is a complex disorder, induced by environmental and genetic factors. This article includes consideration of environmental factors and some discussion of protective effects. You are probably thinking that discussion of all of these aspects of NIHL would result in a nice review article of 50 or more pages. Well, it certainly could, but in this case the authors have condensed a highly complex topic into a clear summary of the most salient points related to current knowledge in fewer than 10 pages.

NOT READY FOR PUBMED

The memorable photo of Baylen Brees in the arms of his father, New Orleans Saints (Geaux Saints!!) Quarterback Drew Brees, brought the potentially harmful effects of noise on hearing to the popular press. In research circles as well, the effects of noise exposure at a young age on hearing in later life is a hot topic. Two articles in the Moment of Science series in Audiology Today address this issue.

In the first of these, Chris Clinard and Kelly Tremblay describe the work of Sharon Kujawa and Charles Liberman examining how age at the time of exposure to noise in mice, even with recovery of thresholds to normal, may interact with age-related hearing loss developing at a later age. The notable finding in this study was a decrease in spiral ganglion cells in young-exposed aged mice, despite otoacoustic emissions and outer hair cells that were similar to the non-exposed control group. These data support the potential importance of considering noise history at a younger age when working with our older patients with hearing loss.

In another Moment of Science entry, Shimon Francis, Judy Dubno, and Lisa Cunningham discuss findings on the topic of noise and aging in gerbils, the need to understand noise effects on spiral ganglion immediately after exposure, and the difficulties in exploring these issues in humans, and the conflicting results in some of the retrospective human studies. Clearly, this is a provocative topic with much work remaining to be done.

On another topic, Frank Musiek introduces an interesting idea in the Pathways series in The Hearing Journal. Here the concept of auditory neglect, well known in other health areas, is discussed as it might affect the auditory system. Dr. Musiek describes a condition known in neurologic circles as neglect syndrome in patients with brain damage and asks if such conditions may exist in the auditory system. He uses poor performance of individuals on dichotic listening and localization tasks as evidence supporting the existence of auditory neglect and reminds us that basic auditory tests will not identify such problems. Is the demonstration of auditory neglect minimized by the presence of ipsilateral and contralateral pathways to the brain? Will the inclusion of more sensitive measures and development of new ones in the future identify and characterize auditory neglect? Perhaps only time will tell.

MOST THOUGHT PROVOKING

Thought-provoking articles are ones that make me think about things differently, and perhaps challenge current thinking on a topic. I found quite a few articles that did just that, including these two.

Naturally, evoked potentials would be something that would catch my eye so I couldn't resist including a couple of articles that suggest new ways to think about responses. In the first of these articles, appearing in the International Journal of Audiology, Jyutika Mehta, Susan Jerger, James Jerger, and Jeffrey Martin investigated ways in which auditory evoked potentials may help us understand the processes involved in word comprehension. Given the complexities of this process, one would not expect the answer to be straightforward. And while that's true, this article provides data supporting potential separation of contributing processes. In this study, young adults judged semantic categories for a range of words, and their event-related potentials (ERP) were recorded. Through independent components analysis (ICA), the researchers isolated four components interpreted as representing four factors involved in processing of the speech stimuli. The framework described by their data includes components in discrete and overlapping time periods that relate to detection and allocation of cognitive resources, phonological processing, semantic processing, and decision processing. In addition to the primary findings of the study, the authors provide a thoughtful discussion of complex considerations in ERP and ICA analyses. As we strive to understand the neural representation of speech, studies such as this provide model approaches using tools that should be very useful in elucidating complexities of neural processing.

My other selection in this category has implications for understanding the impact of hearing loss as well as planning management strategies. In a study reported in Ear and Hearing, Gabriella Musacchia et al. provide biological evidence that hearing loss can reach beyond the auditory domain through their demonstration of poorer multisensory (audio/visual) integration in persons with hearing loss. Theoretically, if one can successfully integrate auditory and visual information, then responses to combined auditory/visual stimuli should differ from the sum of the responses to each modality obtained individually. While this effect is demonstrated in older listeners with normal hearing, responses to auditory/visual signals in subjects with hearing loss showed a lack of sensory integration. As a control, cortical responses to auditory-only stimuli and visual-only stimuli were similar for both groups studied, which isolates the finding to integrative properties. I liked this article for several reasons. First, it's a well-controlled study from an experienced group of researchers. Second, it addresses a topic, multisensory perception, that has a rich literature with growing consideration related to audiologic issues. And finally, this study provides another demonstration of how physiologic evidence can further understanding of the characteristics of hearing loss and considerations that are important in its management.

ALL-AROUND FAVORITES

This year's All-Around Favorite is an article, by Michael Epstein and Mary Florentine in Ear and Hearing, which could easily have fit into the Quick Read category. But it's an All-Around Favorite because it makes several important points. First, the researchers demonstrate that data obtained under earphones cannot necessarily be generalized to real-world listening. In this case, they measured binaural loudness summation for speech and tones through earphones and loudspeakers. They tested the premise that binaural loudness summation reflects a near-perfect summation where a binaurally presented signal is twice as loud as the sum of monaural stimuli. They found that binaural loudness summation was less for live voice presentation with visual cues than recorded spondees and less for speech than tones. Further they found less summation for signals presented through a loudspeaker than through earphones. And, when they included a visual condition—again a more real-life circumstance where a listener can see the speaker—they found that summation was even lower with a visually present speaker. From this work we learn that what happens under earphones in auditory-only situations may not accurately reflect the real world of a listener, that some binaural phenomena may not be accurately represented by addition of responses from the two ears, and that we must consider all possible factors when making generalizations. Finally, the authors discuss the fact that this study grew out of their classroom demonstrations of binaural summation where they observed less summation than expected. This demonstrates the importance of not simply accepting or rejecting an observation, but formally testing that phenomenon to better understand what is happening and why.

I hope that you've found this discussion interesting. More importantly, I hope it prompts you to dig deeper on some of the topics discussed and to leaf back through the journals to find your own “Best of” articles from the past year. Clearly, the studies mentioned here are just a small sample of what awaits you. Happy reading!