ABR, OAEs, and Cortical-Evoked Responses: Interview with James (Jay) W. Hall III, PhD
Douglas L. Beck, AuD, spoke with Dr. Hall about his new book, eHandbook of Auditory-Evoked Responses, middle latency, late latency, and more.
Academy: Good morning, Jay. As always it's a joy to speak with you.
Hall: Thanks, Doug. Great to catch up with you again, too.
Academy: By way of disclosure, I should note we've done a few projects together over the last decade or two and we've written and lectured together…so I admit, I may have a bias, but I have to say your books on otoacoustic emissions (OAEs) and auditory brainstem response (ABR) are the gold-standard textbooks in audiology education, and it was a surprise to see the brand new 2015 eHandbook of Auditory-Evoked Responses.
Hall: Yes, I've heard that from a few other people, too. Nonetheless, the thing to understand about the e-version is the content is all new. I know the title seems familiar, but this is a totally new book.
Academy: Fantastic. I've got a copy in front of me, and I have noticed some important changes.
Hall: Right. First of all this e-version is organized quite a bit differently. That is, the e-version has been re-organized such that each evoked response has its own area of the book, and so it's well organized and the data is easier to find. Even though it sounds like the previous title, the content is brand new.
Academy: I see that…Chapter One is now titled "Introduction to Auditory-Evoked Responses." What does that include?
Hall: Chapter One is a very basic explanation and review of stimulus parameters and acquisition and recording parameters. And to be clear, in this overview, I cover everything you need to know to record any evoked response, with a focus on the major evoked responses audiologists need to know such as electrocochleography (ECochG), the auditory brainstem response (ABR), the auditory middle latency responses (AMLR), and I placed the P-300 and the mismatch negativity in this chapter, too.
Academy: And I saw that you also addressed the cortical responses here?
Hall: Right. And the cortical responses have really come a long was in the last decade. That is, their clinical utility is becoming more feasible and more apparent.
Academy: Yes, I saw in the chapter where you wrote if one were to do a Pub Med search of cortical responses, there are 100 times more peer-reviewed publications on cortical responses that there are on ABR—that's stunning.
Hall: It really is—and the thing is most of the research on cortical responses is being done by non-audiologists such as physiologists, cognitive psychologists, neurologists, basic hearing scientists and other scientists. And with regard to the late responses, these have an increasing bearing on infants, particularly when you're working with an infant and trying to decide if the sounds running through the hearing aid are audible to that child. That is, the late responses help us to see whether the brain is stimulated in a difficult case—and the changes in the late responses can give us important information to help answer that question—and so it's less esoteric than it was a decade ago.
Academy: And so one might have a child with normal hearing or substantial hearing loss, who happens to also present with auditory neuropathy spectrum disorder (ANSD), and so we're not going to have an ABR we can use reliably to tell us very much…and so we do behavioral tests and we gather electrophysiological information to make our best estimate as to the hearing thresholds. Of course those estimates are then used to program the hearing aid, but that doesn't tell us whether the child's brain is perceiving sound. Even the best NAL or DSL protocol and even with Real Ear and RECD—we need to measure brain activity in this child to see if the brain is being stimulated with sound.
Hall: That's exactly correct. Clearly most audiologists will be able to ascertain this type of information from the patient, or from ABR or ASSR…but in these difficult cases and in infants, we need more sophisticated tools. In fact, sometimes these late responses will tell us the hearing aid isn't really helping and it may be the pivotal information which leads us to recommend a cochlear implant for that child.
That is, there are cases in which an ABR isn't present, yet the cortical response may be significant and revealing—particularly for children under one year of age. Doug, you know that our friend Harvey Dillon has already shown that for adults and older children, cortical evoked responses are very useful and they can be automated very accurately—and the automated version can be just as good as an expert audiologist reading the same tracings—so yes, they are becoming more clinically useful and we all need to be up to speed on this.
Academy: Jay, I know auditory chirps are commonly used across the globe now. Sometimes chirps are used in addition to tone-bursts and clicks, and sometimes instead. What are your thoughts on chirps as the stimulus for ABR and related auditory evoked responses?
Hall: Chirps represent an excellent advance in auditory science and clinical audiology. I could give a three-hour lecture on the advantages of chirp stimuli for ABR measurement in infants and young children…in fact, I often do.
Academy: We'll save that topic for another day. Thank you for telling us about the new e-book.
Hall: Thank you for the opportunity.
James (Jay) W. Hall III, PhD, is a professor of audiology at Salus University and extraordinary professor at the University of Pretoria in South Africa.
Douglas L. Beck, AuD, Board Certified in Audiology, is the Web content editor for the American Academy of Audiology and the director of public relations with Oticon, Inc.