By Max S. Chartrand Ph.D.
Binaural Hearing Aids: The Way Nature Intended.
An explanation of the cognitive advantages for hearing with both ears and both hemispheres of the brain.
Human hearing, language perception, and hemispheric function share an intricately entwined relationship. Understanding this relationship is crucial to a properly developed aural rehabilitation program.
From a perceptive standpoint, the 'learning process' of language (or the symbols we come to know as language) becomes markedly lateralized or specialized to various and specific parts of the brain where the information is processed and responded to. In other words, language comprehension is actually composed of essentially two different 'mental viewpoints,' verbal and non-verbal.
The verbal viewpoint is primarily processed in the left hemisphere of the temporal lobe in humans as evidenced by the physical location of Wernicke's area where language communication is expressed.(1) Both of these vital language processing areas reside in the left hemisphere.
The left hemisphere, therefore involves mainly abstract, logical, and technical interpretation of language, the 'what and whereof.'(2) Since the right ear primarily lateratlizes to the left hemisphere, we often refer to the phenomena of better speech utilization and retention in the right ear as the right ear advantage.(3) The right ear advantage aspect is particularly important in the rehabilitative process, in terms of fitting parameters and other considerations such as monaural vs. binaural applications.
The right hemisphere, via the left ear primarily, performs a different, yet vitally important, function in speech communication, albeit more subtly. From the right hemisphere, humans obtain spatial, holistic, contextual, and aesthetic interpretation of speech, The 'non-verbal' meaning of communication.(4) The right hemisphere is then more attuned to the emotions and is able to 'read into' language communication how a message was meant to be received, not getting lost in the logic (or lack of logic) of it all.(5) This ability, being the strong suit of the female of our species, is often referred to as "intuition."(6) In actuality, it appears to be more an innate ability to listen with both sides of the brain.(7) (Remember the larger corpus callosum in females?)
A Mental Tug-o-War
Another way to look at interrelationship of the two hemispheres is: To be verbally debating Einstein's Theory of Relativity vs. Newtonian Physical Laws in one's left hemisphere, while hanging by fingertips onto the edge of a sheer cliff, would come across as rather odd to the right side of the brain which keeps and eye out for the 'big picture' of events around us. Taking into consideration the 'context' of the situation, the right (holistic) side of the brain then forces the left (abstract) side to take a momentary backseat while it sizes up the situation.
The right hemisphere, once its wits are collected, may 'dole out' portions of the problem to be solved by the left hemisphere. As the adrenaline and the other powerful 'fight or flight' reactions come rushing to the rescue, however, the right brain will (in most cases) be fully in charge during the crisis! Once safely back upon solid terra firma, then the left side of the brain tends to take charge in taking remedial action to the (now past)crisis.
A more anecdotal illustration of the right/left brain relationship was humorously stated by Williams (8):
'The hemispheres do not ignore each other or act independently, like the fictional Dr. Jekyll and Mr. Hyde. Our strong left brain doesn't drag our weaker right brain around by his gray matter – it wouldn't dare – the right brain would kick the heck out of him while he's sleeping. No, our hemispheres, although they are functionally biased, work together through many inner cerebral roads and connections. Each plays a special part in the reception, selection and perception of the uncountable stimuli that bombards us each millisecond of our lives. Life without one hemisphere, or without full function of the other, would be hazardous and dull indeed, and we would miss a lot of incoming stimuli. Now, can you think of a better argument for wearing hearing aids on both ears?'
The Importance of Binaural Hearing Aids:
Since much of the acoustic information to the right hemisphere of the human brain is encoded and supplied form the left (contralateral) ear, we certainly cannot discount the importance of information from that ear. Together, the normal function of the right and left ears, primarily contralateral to the opposing brain hemispheres, are needed for normal development of verbal and non-verbal language communication. Hence, the most successful rehabilitation program in bilateral hearing loss, at the most symbolic level of hearing, would depend significantly upon binaural correction of the defective system.
Other binaural auditory functions, such as binaural summation, binaural squelch, binaural integration, spatial mapping and localization are also vital bi-hemispheric functions.(9) However, these auditory skills do not come genetically, but are developed through time exposure and maturation in the ongoing process of hearing, listening and communicating. In short, these are learned skills.
For instance, as an adjunct skill to developing language communication ability, it is often not until the age of six or seven years that most normally developing children acquire sufficient attention and auditory focusing skills to function well in challenging listening situations such as in classroom settings.(10) The ability to direct attention and to screen-out unrelated or unneeded sounds (or speech-in-noise ability) is developed as a result of continuous bilateral exposure to the aural environment.
Likewise, deprivation of hearing acuity (after language is attained) may cause a temporary central auditory processing condition called phonemic regression.(11) Phonemic regression is a speech understanding problem that is either out of proportion to the degree of hearing loss, or which persists for a period of time after amplification is first applied.(12) Resolution of this condition is dependent upon a carefully structured 'wearing schedule' for the new hearing instrument user, whereas it may require up to 12 weeks of acclimatization to the new acoustic signal before optimum speech understanding is realized."(13)
Conclusion:
Components of complete auditory communication involve both verbal and non-verbal viewpoints, which, in the binaural format, are manifest by specialization of each hemisphere via its contralateral ear. So, not only are we looking at time and spectral differences by virtue of dichotic listening., but also interpretative and conceptual differences as well. This is probably the most persuasive argument for binaural amplification correction in cases of bilateral hearing loss.
Human hearing, language perception, and hemispheric function share an intricately entwined relationship. A better understanding of this relationship is crucial to a properly developed aural rehabilitation program. By utilization of this concept, patients understand the importance of maintaining optimum hearing health and its indispensable connection to more effective language communication and meaningful social interaction.
References:
1. Graham R: Physiological Psychology, Belmont, CA: Wadsworth Publishing Co., 1990
2. Chartrand M: Hearing Instrument Counseling; Practical Applications for Counseling the Hearing Impaired, Livonia, MI. National Institute for Instruments Studies, 1990.
3. Hellige J: Hemispheric Asymmetry: What's Right and What's Left. Cambridge, MA University Press, 1993: 285-293.
4. Springer S and Duetsch G: Left Brain, Right Brain. New York, WH Freeman and Co., 1989.
5. Ley R and Bryden M: Hemispheric Differences in Recognizing Faces and Emotions, Brain and Languages 1979; 7:127-138.
6. Johnson G: Machinery of the Mind, Redmon, WA, Tempura Books, 1986:254-56.
7. Pool R: Eve's Rib: Searching for the Biological Roots of Sex Differences, New York, Crown Publishers, 1994.
8. Williams H: Thinking about our thinkers. Hear Instum, 1993; 44:4, 50.
9. Libby R: In Search of the Two-Eared Man, Binaural Hear and Amp, Vol 1, E. Robert Libby, editor. Chicago, Zenetron, Inc, 1980: 1- 36.
10. Phillips P: Speech and Hearing Problems in the Classroom. Lincoln, NE, Cliff Notes, 1975.
11. Delk J: Comprehensive Dictionary of Audiology, Maynard, MA, Laux Co. 1991.
12. Palmer C: Deprivation, Acclimatization, Adaption: What Do They Mean For Your Hearing Aid Fittings?. Hear J 1995; 47(5): 10, 41-45.
13. Gatehouse S and Killion M: HABRAT: Hearing Aid Brain Rewiring Accommodation Time, Hear Instrum 1993; 44(10): 29-32.
