by Nicole Denny, Alyssa Everett, and Frank Musiek, The University of Arizona
Binaural Improvement in Normal and Defective Ears in a Background of Other Voices is a classic article from 1971 by J. D. Harris and C. Myers. Previous research by Harris in 1965 demonstrated that when a subject is asked to answer a set of questions in a room with three loudspeakers transmitting background speech babble, the subject usually answered the questions better using any binaural mode rather than using the better ear alone. The 1971 article we will be discussing in this review further investigated the findings in the original study by testing in a more realistic environment. The microphones in the original study were 12 inches apart and 15 feet away from the loudspeakers which yielded exaggerated timing differences in comparison to what you find with the human head. Therefore, to represent a more realistic recording of temporal cues, interaural intensity cues, timbre, and spatial localization the placement of the microphones were arranged on a dummy head to replicate the position of the eardrums. A comparison between performance in soundfield and under headphones in the original study did not show any differences so for this article, testing was performed at ear level with headphones.
The subjects were divided into two groups: 1) “normal” and 2) “defective.” (The authors of this study refer to one of their groups as “defective”; however, the current authors and much of the more recent literature would argue that this is no longer a suitable term to describe a group of people with hearing loss. The term defective will be no longer be used throughout this review and will be replaced with “experimental group”.) The experimental group consisted of subjects who had monaural hypacusics. Multiple conditions were used in testing the subjects for this study and both groups were tested under four different conditions. Normal group conditions: 1) “Monaural Mode”- channel 1 directed to the subject’s preferred ear; 2) “V-Cord Mode”-channel 1 and 2 directed to the preferred ear; 3) “Stereo Mode”-channel 1 to one ear and channel 2 to the other ear; and 4) “Double V-Cord Mode”-channel 1 and channel 2 to both ears. Experimental group conditions: 1) Channel 1 directed to the better ear; 2) Channel 1 directed to the worse ear; 3) “Stereo mode”; and 4) “V-Cord Mode” directed to the worse ear. Each group had their respective conditions presented to them at 0 dB SNR, -4 dB SNR, -8 dB SNR, and -12 dB SNR. Interestingly, the findings of this study would pave the way to hearing research on this topic as we know it today. In the normal group, performance was reduced from the Monaural Mode to the V-Cord Mode, and from Stereo Mode to Double V-Cord Mode. Stereo Mode always resulted in increased performance compared to all other conditions. These results are suggestive of two principles, The Principle of Blurring, where background noise smears the level of clarity of the desired speech, and The Principle of Binaural Gain (also termed Binaural Enhancement) which highlights binaural listening over monaural listening. For the experimental group, The Principle of Blurring and The Principle of Binaural Gain were also corroborated. In fact, Stereo Mode resulted in performance that was up to 30% better when compared to the Monaural Mode to the better ear. These results were important due to the common complaints of patients not hearing well in noise, especially those with only one good hearing ear. Although this was a common complaint at the time of this article being published, it has remained to be the most common complaint that audiologists hear during clinical practice today. During the time of this article, there were no tests available that allowed quantification of hearing deficits in complex everyday listening situations. The authors suggested the use of the taped tests they developed for this study in order for clinicians to be able to quantify these deficits, assess improvements, and to investigate binaural hearing and aid in the recommendation of a binaural hearing aid fitting. The test that they created simulated three speakers talking at one time from three different areas under headphones. The voices were raised to a range of 12 dB SNR. From these tests, the researchers again found that a Stereo Mode (binaural listening) always led to better intelligibility. The importance of these findings have been used to quantify a patient’s ability to understand one person in a background of voices, predict whether binaural hearing aid fitting should be considered, and assess the effect of binaural hearing aid fittings in dB. From here, we have since been using these answers to address treatment plans and counsel our patients. The well-known phenomenon of the “cocktail party effect” is still widely studied today and has brought attention to a better understanding of binaural hearing ability in noise.
More recently, the role of binaural benefit in bimodal (hearing aid and cochlear implant) or bilateral cochlear implant users has become a topic of considerable interest in clinical practice. Several studies have shown a significant binaural advantage for speech understanding in complex listening situations compared to listening with either ear alone. Ricketts and colleagues (2006) investigated speech intelligibility performance in the presence of uncorrelated noise sources in bilateral and unilateral cochlear implant modes. Their findings revealed a significant advantage in speech-in-noise performance in the bilateral cochlear implant mode compared to the unilateral mode. Furthermore, a study looking at binaural advantage for speech-in-noise performance and localization ability in adult and pediatric bimodal users found significant benefits in speech performance and localization when using both the cochlear implant and the hearing aid in comparison to using the cochlear implant alone (Ching, Incerti, Hill, & van Wanrooy, 2006). The authors attribute this binaural advantage as a result of access to head shadow effect (spatial separation cues) and binaural redundancy cues, similar to the findings of Harris and Myers (1971).
This classic article by J. D. Harris and C. K. Myers has added to the acoustical and audiological literature. Specifically, it highlights the significance of speech-in-noise testing in a clinical setting in order to evaluate more realistic amplification outcomes. An important take away from this literature is to understand the difference in spatial listening abilities between monaural and binaural conditions. A binaural condition has been historically shown to be most advantageous for speech recognition in noise and continues to hold true in current research and clinical practice.
Alyssa Everett is a 3rd year Au.D./Ph.D. at the University of Arizona. She is originally from Bel Air, Maryland and graduated from Towson University with a B.S. in Speech, Language, and Hearing Sciences. Currently, Alyssa is working on multiple research projects with Dr. Frank Musiek, Dr. Barbara Cone, and Dr. Nicole Marrone. These projects involve central auditory processing, electrophysiology, cost/benefit of hearing aids, and aural rehabilitation. She spent a summer at Washington University participating in a T35 with Dr. Kevin Ohlemiller. Alyssa has 2 publications, one of which is peer-reviewed and has been the lead author on 3 posters presentations.
Nicole Denny is a third year AuD student at The University of Arizona. She is from Northern California and received her Bachelor of arts in Speech, Language, and Hearing Sciences from San Diego State University. Throughout her graduate studies, Nicole has been involved in various research projects focused in Neuroaudiology and humanitarian audiology. She is involved in Dr. Frank Musiek’s Neuroaudiology Lab. Additionally, she has developed an interest in the delivery of hearing healthcare through a binational non-profit organization known as the Arizona Sonora Borders Project, established and registered in Nogales, Sonora, MX. Nicole is also a co-author on a peer-reviewed article.
- Ching, T. Y., Incerti, P., Hill, M., & van Wanrooy, E. (2006). An overview of binaural advantages for children and adults who use binaural/bimodal hearing devices. Audiology and Neurotology, 11(Suppl. 1), 6-11.
- Ricketts, T. A., Grantham, D. W., Ashmead, D. H., Haynes, D. S., & Labadie, R. F. (2006). Speech recognition for unilateral and bilateral cochlear implant modes in the presence of uncorrelated noise sources. Ear and hearing,27(6), 763-773.