I would like to know more about screening for central auditory processing deficits, specifically binaural interference after reading June's Pathways article, “Binaural Interference May Cause Ineffective Bilateral Amplification” (HJ 2012;6530; http://bit.ly/JunePathways). I have been a hearing instrument specialist in practice for 30 years, and I am still seeking to improve. Thank you in advance for your help.
Ralph T. Campagna, BC-HIS
Frank Musiek, PhD, and Jennifer B. Shinn, PhD respond: Screening for binaural interference is a concept that James Jerger, PhD, and others have written about over the years. (J Am Acad Audiol 1993;4:122; J Am Acad Audiol 2000;11:494; J Am Acad Audiol 2011;22:128.) The underlying factor in binaural interference, compared with the best monaural performance, is that a decrease in auditory performance occurs when both ears are simultaneously stimulated. This decrement is usually related to extremely poor performance in one ear (peripheral) or even one side of the auditory pathway (central).
The fusion of information at the central level results in the processing of the poorer side interfering with the better processing of the good side. This yields a decreased performance in the binaural condition compared with the best unilateral condition. This binaural interference phenomenon becomes most relevant in binaural versus monaural hearing aid fittings. The patient with true binaural interference may perform better with one rather than two hearing aids, which, of course, is contrary to accepted practice. (Int J Audiol 2003;42[Suppl 2]:2S63.)
No go-to test currently exists for assessing binaural interference, at least in our view, but relevant information can be obtained. First, testing in the monaural and then binaural condition, usually with speech stimuli, is required. The binaural score should be as good as or better than the best monaural score; if it is not, binaural interference may be a concern, though how much difference between the best monaural and binaural scores is difficult to say. It depends on a number of factors, and a discussion of these is beyond the scope of this response. This kind of testing with appropriate modification can be conducted with and without amplification and for one versus two hearing aids.
Sometimes binaural interference of a more central nature cannot be detected with standard peripheral tests. Simple dichotic listening procedures may be useful in this situation. Dichotic procedures that yield large differences for right and left ears might signal binaural interference, though predictability of such an approach to my knowledge has yet to be shown.
Dichotic listening is probably not the only type of test that can be applied for detecting binaural interference. A recent report has argued that masking level differences could also be a predictive tool. (J Am Acad Audiol 2011;22:181.) Various electrophysiologic procedures utilizing the binaural interaction component could hold promise for evaluating binaural interference. Dichotic testing maybe a useful procedure for the elderly who are hearing aid candidates or for general assessment of higher auditory function. A patient who demonstrates symmetrical pure-tone thresholds and bilaterally equivalent speech recognition scores, for example, could show dramatically different right vs. left ear scores on a dichotic paradigm. This dichotic information could be most revealing if this patient is not adjusting to binaural amplification, or be of help to the audiologist before fitting hearing aids.