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Georg von Bekesy conducting his research

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Georg von Bekesy and his 1961 Nobel Prize for his discovery of by which sound is analyzed and communicated in the cochlea

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Georg von Bekesy and his 1961 Nobel Prize for his discovery of by which sound is analyzed and communicated in the cochlea

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Georg von Bekesy lived from 1899-1972 and won the Nobel Prize in 1961 for Physiology after his discover of the ways in which physical sound is understood by our cochlea, part of the inner ear¹.
Georg received his early education in Munich, Constantinople, Budapest and in a private school in Zurich². He then studied chemistry at the University of Berne and then after serving in the military for a while went on to receive his PhD in Physics².
He did research at a Hungarian telephone system research laboratory as well as a few different large institution such as the University of Budapest, the Karolinska Institute, Stockholm, and Harvard University¹.
It had been known that the vibratory tissue most important for hearing is the basilar membrane since the mid-19th century¹. The basilar membrane reached the length of the snail-shaped cochlea and split into two tunnels¹. Bekesy used this known information to find out how sound worked and how we were able to perceive this information¹. He discovered that sound travels in waves through the basilar membrane¹. Meaning, that the sound would peaks at different places along the basilar membrane to indicate the frequency of the sound¹.
Additionally, he discovered that loudness and pitch of a sound is largely determined by the location of the nerve receptors and the number of receptors¹. These discoveries would become crucial in the attempt to treat and cure hearing loss.

1. https://emur.org/medicine/georg-von-bekesy.htm
2.https://www.nobelprize.org/prizes/medicine/1961/bekesy/biographical/
3.https://braintour.harvard.edu/wp-content/uploads/2016/05/img_TT_bekesy_portrait1.jpg

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Earliest Discovered Fossil Bones of the Ear

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Earliest Discovered Fossil Bones of the Ear

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The earliest known complete set of the the bones that make up the middle ear are dated back to a 2.0 million year old skull¹. This skull belonged to a distant human relative found in South Africa known as Paranthropus robustus ¹.
There is no evidence that they were studying these bones but it is the first time a discovery of these bones intact had been found. These bones help us to understand how our human hearing has evolved over time. Researchers have found that the malleus, one of the three ear bones, of P.Robustus to be very similar to the one in modern day humans¹. However, the other two bones were reportedly closer in relation to African and Asian great apes¹.
Consequently, they believe the reason for the malleus being more closely related to modern day human ear bones can correlate to our special sensitivity to the middle range acoustics frequencies which is very important for the development of spoken language¹.

1. https://www.science.org/content/article/scienceshot-earliest-ear-bones-sound-human-hearing

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ScienceShot: Earliest Ear Bones Sound Off on Human Hearing

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Two-million-year-old fossils from human relatives reveal insights to language development

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Francis bacon advocates for a new discipline of acoustics seventeenth century (1626)

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Francis bacon advocates for a new discipline of acoustics seventeenth century (1626)

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Francis Bacon has an enormous impact on English natural philosophers¹. He wanted to replace the Aristotelian physics system with his own new system¹. Through his works he believed that his duties as a natural philosopher began by understanding the roles of the senses and perceiving all external phenomena¹.
The next thing he had to do was move away from traditional Aristotelian ways and move towards the new pansophic and utopian theories where he will use technology for the benefit of mankind¹. Francis bacon did not just want to understand how the production, behavior, and direction of sound work but also to understand the properties of sound in order to help the wellbeing of humans¹. They could in-turn possibly help the range of hearing and use these properties in the development of communication, which will later be seen in the telephone¹.
Bacon has two works in which he gives his complete account on his acoustic and sound theories. His first is Sylva Sylvarum (1626) and the New Atlantis (1626) which were very popular with a lot of influence on the seventeenth century¹. In his work of the New Atlantis he dismissed the ideas of the Pythagorean dead, that the numbers 1 to 4 and their ratios underlie the structure of the universe including sounds in music². Instead he suggested that music was a "sonorous phenomenon of nature" which would be perceived by the senses and not mathematically².  Now that this principles of numbers giving guidelines to the universe was challenged, there would be a lot more realities that would be uncovered without the governing elements². This would completely change how the science of sound would be studied in the future.

1. Gouk, Penelope. “Vol. 36, No. 2 (Feb., 1982), Pp. 155-175 (21 Pages).” Acoustics in the Early Royal Society 1660-1680.
https://www.jstor.org/stable/531772?seq=1
2.http://www.thomaspatteson.com/uploads/7/3/8/8/7388316/sound_between_magic_and_science_-_toward_an_understanding_of_early_modern_aurality.pdf

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Mathematician Marin Mersenne conducted experiments to determine properties of sound (1640)

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Mathematician Marin Mersenne conducted experiments to determine properties of sound (1640)

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Mersenne was very fascinated by the humans brain and its musical appreciations. He correlated this appreciations to being attuned to mathematical harmonies¹. The difference between Mersenne and Bacon was that he not only proposed these ideas but conducted experiments to test his proposals. His proposals took a more radical Pythagorean stance on musical science, relating his knowledge more on acoustic experiments². Mersenne studies the vibrational stitched strings which would be summarized in his three Mersenne's Laws³. One of his experiments was one of the first experiment to attempt to measure the speed of sound². Mersenne is credited with discovering the second and third law of strings². The work he published was in Mershenne's Harmonicorum Libri(1636)¹.

1. https://plato.stanford.edu/entries/mersenne/
2.http://english.ioa.cas.cn/psk/201410/t20141027_130145.html
3. https://www.britannica.com/science/acoustics/Early-experimentation
4. https://www.lindahall.org/wp-content/uploads/sites/5/2020/09/mersenne1.jpg

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Understanding sound medium and transmission with Robert Boyle (1660)

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Understanding sound medium and transmission with Robert Boyle (1660)

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Aristotle and his suggestion of sound wave propagation back in the 4th century B.C. did come in handy when Robert Boyle went to conduct his experiments¹. Robert Boyle was an Anglo-Irish scientist, who had worked with the vacuum technology to improved it capabilities¹. He had improve it so much to the point where he could observe sound intensity decreasing virtually to nothing as all of the air is removed¹.
Boyle concluded that such phenomenas was a result of the lack of medium for sound to track upon cause the decrease and elimination of sound¹. Boyle concluded that air is required for sound wave transmission¹. This essentially helped us to understand that sound was traveling as a wave rather than a singular particle which would be crucially to the later technological advancements with sound technology.
We can further understand how we perceived sound by understanding how the sound is created and travels. Even though there were other contributing factors that effected the outcome of the sound and the way Boyle had perceived its at the time his understanding was still correct.

1. https://www.britannica.com/science/acoustics/Early-experimentation
2. https://www.sciencehistory.org/sites/default/files/styles/distillations_modern_issue_cover_phone/public/robert_boyle_engraving.jpg?itok=fKYitO0Y&timestamp=1620910002

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Hearing Science in the Mid-Eighteenths Century

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Hearing Science in the Mid-Eighteenths Century

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English natural philosopher, Benjamin Martin and a French Surgeon by the name of Claude-Nicolas Le Cat publish work on the auditory physiology and function¹.
Le Cat's published work provides original engravings of the ear's anatomy¹. Le Cat's treaties came directly from his surgical work in the elite intellectual world of the corporative mid-eigteenth century surgical establishment¹. His main drawing is a startlingly realistic three-dimensional cross-sectional image of the whole ear mechanism¹.
Benjamin Martin used the ear as a part of a scientific demonstration¹. Martin had a successful career and business with eyeglasses established in 1755, so the hearing science was an addition to his image¹. Martin presented music as the lynchpin of rational hearing science opposed to a mathematical by-product of man's sensory nature¹. Martin used Le Cat's drawing of "The Organ of Hearing on the Right Side" in his own treaties¹.
Both Le Cat and Martin's interpretations of hearing functions included that the cochlea was the most important element of the ear mechanism that contributed heavily to the perception of sound¹. There is a debate still whether the hearing science emerged as a discipline from England and France¹. Le Cat nor Martin was simply a "hearing scientist"¹. They both worked under broader domains of medicine and natural philosophy. Hearing science was a neglected subject of the time¹.

1. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3182046/

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Miller Reese Hutchinson was interested in mechanics and technology since the beginning of when he attended mobil public school¹. He graduated with a doctorate in Electrical Engineering at Alabama Polytechnic Institute at Auburn¹. While he was a student he hoped to benefit a friend who was deaf and mute from childhood bout with scarlet fever¹.
This led him to study hearing at Alabama  Medical College and work hard for four years doing research to develop his technology¹. His invention was one of the first know portable electrical hearing aid which he called the "Akouphone"¹. Hutchinson was able to improve his friends hearing very successfully but unfortunately his friend was not able to speak after multiple attempts.
As the time went on this became a state of the art piece of equipment with only a limited number of them being produced until it was able to be produced and sold at $60 which at the time was still very expensive¹. This instrument became very crucial and also the only available instrument that could amplify the sound which was also wearable which made it convenient1. Hutchinson received a patent in 1898 for his creation¹. The way the hearing aid worked was that it amplified the sound for the person¹.
This would later be a very big contribution to further research to help accelerate advancements for the deaf or hard of hearing community. These devices would be another way for these individuals to be apart of the community and not feel so outcasted by society.

1.https://hearinghealthmatters.org/hearinginternational/2015/the-road-to-the-first-electric-portable-hearing-aid-and-beyond/
2. https://hearinghealthmatters.org/hearinginternational/files/2015/07/mrh2.jpg

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Nikola Tesla and Guglielmo Marconi and The Radio (1903)

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Nikola Tesla and Guglielmo Marconi and The Radio (1903)

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There is a big debate over who was the actual inventor of the radio as the patent application of Tesla was made in 1897 and they were granted in 1900¹. However, Marconi's first patent went out in America in 1900 which was turned down¹.
However, more important the establishment and discovery of the radio was a Hugh. milestone in the sound technology community. Tesla created coils that would receive and transmit powerful radio signals  when they were tuned to resonate at the same frequency¹. The full function of a radio started with changing sounds or signals into radio waves². These waves travel through air, space, and solid objects and the receiver on the radio has the ability to change the waves back o sounds, words, and the music that we hear².
It is a crazy phenomena to think about that we experience every day almost without thought. The understanding of sound and how it is transmitted is a major contributor in the creation of this radio. Additionally it helps to understand how these sounds can be changed and transmitted back and forth in a reasonable method. Radios truly set the groundwork for a lot more communication systems involving transmission and reception of sounds.

1.https://www.pbs.org/tesla/ll/ll_whoradio.html
2. https://www.knowitall.org/document/history-radio-kids-work
3. https://image.jimcdn.com/app/cms/image/transf/dimension=origxorig:format=jpg/path/s40c423127565d23a/image/ifcc75f8f6dddebc3/version/1401406283/image.jpg

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Publication of clinical Audiometry by Cordia C. Bunch (1943)

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Publication of clinical Audiometry by Cordia C. Bunch (1943)

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In the year of 1943 a man by the name of C.C. Bunch published a paper which included his first prototype pf an audiometer². An audiometer is a machine that evaluates hearing acuity². C.C. Bunch was a graduate student in psychology at the University of Iowa in 1919, when a famous Seashore Musical Aptitude test intrigued Bunch to make a piece of equipment that measure the threshold of frequencies³.
Bunch did not just create the device for other to use, he also used the device on patients at the local otolaryngologist³. His reports and all his studies were documented in his clinical audiometry that includes the development and his use of the audiometer as well as countless audiograms¹.
All of this work is to later contribute into how we analyze what sound is and how it works and how we can control sound for the benefit of human beings and those who may be suffering from a hearing loss or deafness. This would go into helping us understand language and how different sounds come across differently to a listener.

1. https://www.science.org/doi/10.1126/science.99.2578.431.c
2. https://www.audiology.org/news-and-publications/audiology-today/articles/c-c-bunch-the-first-audiologist/
3.https://hearingreview.com/practice-building/practice-management/continuing-education/ten-highlights-history-audiology

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Perspective | May 2019 Hearing Review

A top-10 list of events and achievements in audiology during the last 75 years

The measurement and management of hearing disorders has a long history. As early as the 4th century BC, Hippocrates wrote extensively on the causes of hearing disorders. Later, the Enlightenment brought a flurry of activity focused on tests to differentiate among the various causes and types of hearing loss. Throughout most of recorded history, however, the measurement and management of hearing loss remained the province of medical professionals.

Dr Jerger highlights 10 great events in our field's rich history, ranging from C.C. Bunch's early audiometric work to the establishment of the first AuD training program.

The modern era of audiology is only 75 years old. It began with a book on clinical audiometry by Cordia C. Bunch in 1943. Over the next seven decades audiology grew rapidly to its present strong position in the family of healthcare professions. Several signal milestones mark the progress of audiology over the past three quarters of a century. This article highlights 10 of the most important events that, in my opinion, have guided the direction of our profession since that seminal publication by Bunch. I have restricted the coverage to events impacting audiology in the United States and Canada. I also acknowledge that any such list is highly subjective. It would be relatively easy to come up with a dozen more events, and I invite readers to chime in, either via comments in the online version of this article or via email, about what you might include.

Event #1
1943: The Publication ofClinical Audiometry by C.C. Bunch

Cordia Bunch was a graduate student in psychology at the University of Iowa in 1919 when Carl Seashore, creator of the now famous Seashore Musical Aptitude Tests, convinced Bunch to construct a device to measure auditory thresholds across a broad frequency range. Bunch not only built the device but went on to test the patients of a local otolaryngologist, L.W. Dean. When Dean moved from Iowa City to St Louis, Bunch agreed to move with him and to continue the testing, now with an early Western Electric 1A audiometer.

For the next 20 years Bunch gathered air-conduction audiograms on patients and wrote articles about them. His publications spanned an amazingly diverse subject matter. Here is only a partial list of the topics covered:

Use of the audiometer;

Effect of age on audiometric thresholds;

Importance of measuring thresholds at frequencies above the conventional audiometric range;

Occupational and traumatic deafness;

Progression of loss in otosclerosis;

Deafness in aviators;

Conservation of hearing in industry;

Race and gender variations in hearing thresholds;

Hearing aids;

Otitis media;

Calculating percentage of loss for medico-legal purposes;

Effect of removal of one cerebral hemisphere, and

Effect of absence of organ-of-Corti on the audiogram.

A truly impressive oeuvre! Bunch laid the foundation of audiology by vividly demonstrating the many contributions that an audiological specialist could offer to hearing-impaired persons.

In 1943, in the midst of WWII, the Army assigned Captain Raymond Carhart to head the acoustic division at Deshon General Hospital in Butler, Penn. He was ordered to provide aural rehabilitation and to dispense hearing aids to army personnel coming home with hearing loss. Guidelines, however, did not exist.

As a trained speech scientist, Carhart looked beyond the technical engineering aspects of hearing aids, sidestepped the issue of selective amplification, and focused instead on how aids actually helped users in everyday speech communication. Using the spondee words and 50-item single-syllable PB words developed at the Harvard Psycho-Acoustic Laboratory to evaluate ground to aircraft radio systems, Carhart devised a method for evaluating how well the hearing aid user could understand speech: the spondee words to determine the speech reception threshold (SRT), and the PB lists to evaluate how well the user could understand single words presented well above the (SRT).

Bunch, in his book on clinical audiometry, had earlier suggested the need for some clinical measure of speech understanding but never carried the idea further. Carhart used his speech-oriented approach as he evaluated and, where needed, dispensed heaing aids to more than 16,000 returning veterans.

Carhart made many other contributions to our profession but the invention of speech audiometry remains his towering achievement.

The observations that producing and receiving language could be degraded by brain injury, the aphasias, had been analyzed and debated extensively by the end of the 19th Century. During WWI, however, the abundance of head wounds caused by various projectiles led Henry Head, a British neurologist, to study lower level perceptual disorders, the agnosias.

Helmer Myklebust, an American psychologist with a particular interest in hearing-impaired and deaf children, studied Head's published works closely. When he came to Northwestern University in the early 1950s, Myklebust set up a children's hearing clinic. Testing the hearing of young children was certainly primitive by today's standards, but he supplemented the extant audiological measures with various psychological analyses and with keen observation of the child's behavior.

Myklebust identified what might be expected in hearing-impaired and deaf children; in the process, however, he observed that there were other children, referred for possible deafness, who appeared to have difficulty processing auditory input in spite of relatively normal audiometric threshold levels. For these children Myklebust coined the term "auditory disorder." Eventually this morphed into the current term "auditory processing disorder" or "APD." Based on Head's work with head injury, Myklebust viewed the problem as a centrally-based auditory perceptual disorder.

Much of today's interest in auditory processing disorder, especially in children, can be traced to Myklebust's pioneering observations.

Event #4
1953-58: The Transistor and the Integrated Circuit
The invention of the transistor by John Bardeen, Walter Brattain, and William Shockley-and the subsequent creation of the integrated circuit by Jack Kilby-changed hearing aids substantially. Prior to these historic events miniature vacuum tubes provided electronic amplification. These tubes required considerable battery power; a 6-volt battery for the heating elements of the vacuum tubes and a 20-40 volt battery for their controlling grids. All of this was packed into a box about the size of a package of cigarettes, typically carried in a shirt pocket, or in a harness suspended from the neck. The amplifier box was connected to the ear via a long cord attached to a transducer mounted in a fully occluding earmold.

But the electrical power requirement of transistors was only a single 1.5-volt unit, and the space it occupied was much smaller than a single miniature vacuum tube.

These two reductions-battery capacity and physical dimensions-made possible an aid that could be fitted on the head or in the ear canal. All of this made actual binaural hearing aids a reality. The importance to the hearing aid user can scarcely be imagined.

We can date the identification and treatment of hearing-impaired infants and young children into two eras: before Marion Downs and after Marion Downs. Before Marion Downs, there was a widespread philosophy that, since you could not actually test the hearing of children until at least age 3, intervention for children suspected of substantial hearing loss was potentially dangerous and should be avoided. But as early as 1959, Downs was fitting aids to children as young as 6 months with suspected severe losses. She was guided by the strong belief that, if you waited 3 years before intervening, you had forever lost the most important years of language learning.

In 1962, at the University of Colorado Health Sciences Center, she initiated the first infant screening program, designed to identify hearing loss at the earliest possible age. She based it on a series of systematic observations of the infant in a controlled listening environment-the first such program in the nation.

The importance of the earliest possible intervention for suspected hearing loss in infants and young children has been repeatedly confirmed over the next five decades and has since become standard orthodoxy in our profession. When Marion Downs died in 2014 at the age of 100 years, audiology lost one of its most beloved heroes.
Event #6
1964: The Birth of Immittance Audiometry

We can thank four of our Scandinavian colleagues for leading the world in the introduction of what is now called immittance audiometry. Two Danish investigators, Knud Terkildsen and K.A. Thomsen, and a German working in Denmark, Otto Metz, were responsible for the ultimate development of the first electro-mechanical impedance bridge by the Madsen Company in Copenhagen in the early 1960s. Metz built the first practical device for objective measurement of the middle-ear muscle reflexes; Terkildsen and Thomsen developed the Madsen Z0 60, and later, the Z0 70 impedance bridges, the first to make routine clinical measurements of middle-ear status possible. Terkildsen further gave the name "tympanometry" to the process of plotting immittance as a function of air pressure in the closed external ear canal. Gunnar Liden of Sweden later described the three basic tympanometric shapes. Together, tympanometry and the detection of middle-ear muscle reflexes, now collectively named "immittance audiometry," have had a profound influence on diagnostic audiometry for many years.

Barry Elpern practiced audiology at the University of Chicago in the 1960s. One wintry night he drove home from work in a raging blizzard. His car soon became mired in deep snow, and Barry was forced to walk the rest of the way home. It was a transformative event for him. Throughout the trek he kept asking himself "Is this any way for a reasonable person to live?" Finally reaching home, cold and wet, he announced to his family that they were moving to Arizona.

And they did. After wrapping up his affairs in Chicago, Barry moved his entire family to Phoenix. But no jobs were available in audiology. There was, however, a small company attempting to design a better hearing aid. To stay in business they needed the income from selling their no-longer-needed experimental aids. Because they wanted to be sure that the aids were fitted appropriately they enlisted Barry to fit and dispense them. But the American Speech-Language-Hearing Association (ASHA) had decreed that members were in violation of the ASHA code of ethics if money changed hands. Barry, they pronounced, was no longer a member of ASHA. He had lost his professional home.

Many of his colleagues thought that Barry had been treated badly (indeed, others would find themselves in the same fix). For some time a number of influential audiologists argued that the ASHA edict signaled the permanent prevention of the development of private practice, one of the bases of a viable healthcare profession. They saw Barry's ouster from ASHA membership as an ominous sign that would forever limit the scope of practice of the fledgling field. This single event accelerated a growing sense that audiologists needed their own professional home, free of the constraints imposed by an organization oriented toward the wants and needs of the overwhelming majority of the ASHA membership, speech-language pathologists. As these murmurings multiplied, ASHA-finally, in 1979-revised its code of ethics to permit the dispensing of hearing aids. This opened the door to the growth of private audiological practice, now one of the pillars of the profession.

Don Jewett, an electrophysiologist at the University of California San Francisco, is credited with the first observation of the auditory brainstem response (ABR). Initially recording from the region of the auditory nerve in cats, he observed four small bumps in the recording within the first 10 msec after signal onset. Because they were unexpected at such an early latency, he turned to human recordings. Here he found the same four "bumps," as well as a fifth bump. We now know these as the five classic peaks of the human ABR.

At the time Jewett wondered why these peaks had never been reported by other investigators studying early evoked responses to auditory signals. The answer, of course, was that researchers tended to be interested in a particular response at a known frequency, and in order to improve signal-to-noise ratio, bandpass filtered the ongoing EEG narrowly around the frequency region of interest. This was particularly true of individuals studying the middle-latency response (MLR), located at about 40 Hz on the frequency spectrum. Jewett discovered the ABR because, as an experienced electrophysiologist, he kept the bandpass of his recording system as wide as possible, especially at the low end of the frequency spectrum, in order to avoid phase distortion of the evoked response, wherever it might be.

The ABR literally revolutionized the evaluation of babies and young children because it is state-independent. It does not matter whether the child is asleep or awake: if the click gets through to the brain, those five peaks will appear. This has made it possible to test even newborn babies with comparative ease. Hearing loss can now be detected not at 3 years but at 3 hours after birth. Marion Downs' goal of genuinely early detection was finally realized.

In 1978, David Kemp, a British physicist then working at the Royal National Throat, Nose and Ear Hospital in London, was the first to demonstrate that auditory input generated a response in the cochlea which could be measured and recorded. These "otoacoustic emissions" have had a profound effect on auditory diagnosis, especially in screening infants.

In the preface to the first edition of Otoacoustic Emissions, 1 Ted Glattke and Martin Robinette eloquently summarize the importance of OAEs: "We have at our disposal a measure of preneural function in the inner ear that can be accessed using noninvasive techniques that do not require sedation. This acoustic otoscope allows us to scan the cochlear epithelium from the base to the apex and produces acoustical images that are revealing secrets long hidden from view or obscured in electrical recordings."

The combination of the ABR and otoacoustic emissions comprises a set of tools for the early detection of hearing loss in infants and young children with an accuracy unimaginable in the early days of our profession.

Event #10
1994: The First AuD Training Program
The concept of raising the level of the profession by offering a doctorate in clinical audiology had been shared by several individuals during the decades of the 1970s and 1980s. It arose from three ongoing concerns: 1) A growing discontent with the fact that the PhD degree, the measure of research competence, was being awarded to individuals whose career path was clearly clinical rather than investigative; 2) The fact that many excellent clinicians were reluctant to enter a PhD program because of the perceived challenge of the dissertation requirement, and 3) The perception that a viable healthcare profession required that the majority of members operate at the doctoral rather than at the master's degree level.

These 10 highlights vividly reflect the growth of audiology from its fledgling origin only seven decades ago to its present full membership in the healthcare family.

What Would You Add?
Let us know what you might add to the list in the Comments section below!
Correspondence can be addressed to Dr Jerger at: [email protected]

Original citation for this article: Jerger J. Ten highlights from the history of audiology. Hearing Review. 2019;26(5):10-14.

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Ten Highlights from the History of Audiology

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The measurement and management of hearing disorders has a long history. As early as the 4th century BC, Hippocrates wrote extensively on the causes of hearing disorders. Later, the Enlightenment brought a flurry of activity focused on tests to differentiate among the various causes and types of hearing loss.

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Speech Audiometry for Hearing Aid Selection (1946)

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Speech Audiometry for Hearing Aid Selection (1946)

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During World War 2 the head of the army gave Captain Raymond Carhart the appointment to the head of the acoustic division at Deshon General Hospital¹. They were treating and rehabilitating personnel who had come home with hearing loss and were giving out hearing aids to the army1.
There were no guidelines as to how and who should be given a hearing aid and Carhart, a a trained speech scientist, did not feel satisfied with this. He went on to look into the technical engineering of the hearing aids in hope to find a way to selectively amplify things instead of just helping the patients on daily communication¹. Carhart created a way to understand what a hearing aid users could understand as speech¹. He did this by the speech reception threshold(SRT)¹. This became instrumental for how they would understand the patient and what their capabilities consisted of¹. Carhart used his speech oriented approach as he evaluated and dispensed hearing aids to all of 16,000 men who were coming home from war¹.
These hearing aids were not going help a tremendous amount for a lot of the veterans however, the most crucial part of this story is the understanding of thresholds in which our ears can hear. There are different capabilities that naturally occur but having a way to measure these capabilities come from research of how the sounds are made.

1. https://hearingreview.com/practice-building/practice-management/continuing-education/ten-highlights-history-audiology
2. https://images.fineartamerica.com/images-medium-large-5/raymond-carhart-national-library-of-medicine.jpg

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The vacuum tube with the diode invited by John Ambrose Fleming (1904)and the triode (1906) by Lee DeForest aid in amplification

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The vacuum tube with the diode invited by John Ambrose Fleming (1904)and the triode (1906) by Lee DeForest aid in amplification

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The First Vacuum Tube was introduced in 1904 by a British engineer by the name of John Ambrose Fleming who created the thermionic valve¹. Even though the Supreme Court declined his patent since they believed this technology was already known, he is still recognized as the inverter of the vacuum tube and diode which had two electrodes that would go way beyond what he had ever imagined¹.
Later the discovery of the triode by Lee DeFrost would also contribute to the keys to amplification and hearing aids specifically². The electron flow by is controlled by a varying grid voltage which in turn is called amplification². The smaller sizes of these and the lower current consumptions led to development of smaller batteries and smaller hearing aids².
Understanding this type of technology is crucial to understand how it can be used for the benefit of human beings. If we understand how to amplify sound and do this on an electronic scale it would be a lot more precise and effective for the patients. Additionally this will later impact the technologies that evolve to help the deaf or hard of hearing community.

1. https://www.wired.com/2009/11/1116fleming-thermionic-valve-vacuum-tube/
2. https://hearinghealthmatters.org/waynesworld/2014/hearing-aid-technology-evolution/

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Factors that Drive Hearing Aid Development

Starting with the first hearing aids developed, and continuing today, three factors have driven hearing aid technology and development. These three factors, in their historical ranking, are:

1. Cosmetics

2. Technology leading to miniaturization, and

3. Packaging

Patients have always been interested in the most cosmetically appealing hearing aid - translated as "invisible" or "smallest." This is evident by reviewing hearing aid sales. This means that they are interested in the most inconspicuous hearing aid that can possibly be coupled with the technology at the time. Stories abound about the individual who says, "I don't care what the hearing aid looks like, as long as it provides the significant listening performance I'm interested in." But then, when the instrument is presented to the patient, the first thing they ask is, "Yes, it works as expected, but can't it be made smaller?" All one has to do is look at hearing aids over time to confirm that "smaller" and "invisible" have dominated much of the development. Many patients have not been fitted as well as they could have been because cosmetics, and not performance, drove the sale.

Technology and Miniaturization

Technology, often evidenced by miniaturization of hearing aid components, has complemented the driving force for cosmetics. In other words, improved cosmetics most often has come about because of miniaturization of components. But, technology is not only miniaturization; it also means providing the best sound quality possible using existing developments. And, part of this consists of attempts to mimic human hearing as closely as possible.

Packaging involves the design and manufacture of the hearing aid itself. Design goals are to make construction and use of the instrument as simple and straightforward as possible. One has to wonder, however, if some of the current designs have lost their way when it comes to this important factor - perhaps not so much with respect to construction, but conceivably when it comes to consumer use. We have instruments that have multiple functions and accessories - and usually with small controls for the patient to manipulate. This is not always easy when approximately 65% of the people wearing hearing aids are 65 years of age or older. So, remotes are added, which means that now the patient can lose or break two devices rather than one. Developments that enable the hearing aid to make decisions and adjustments for the patient based on the incoming signal are promoted heavily, but they might be questioned. What happens to hearing aid performance when multiple parameters are adjusting at the same time? Do we really know? Could they be interfering with each other, especially as more parameters are being manipulated? The hearing aid circuitry is making decisions based on physical input sound pressure. Unfortunately, actual hearing needs are often based on psychoacoustics, emotion, or patient preference - all of which can change from moment to moment. Self-adjusting hearing aids cannot manage these mood changes.

Major Developments

The development of a hearing aid consists of a series of compromises. A more powerful hearing aid requires a larger power supply and most likely larger transducers as well as other components, leading to a larger physical size of the hearing aid. How many microphones are desired? What about streaming, telecoil, volume control, other user controls, connection options, Bluetooth, wireless, etc.? With hearing aids, the wheel is reinvented frequently - most often as a result of smaller component availability or improvements in existing features.

To illustrate the three main factors involved in hearing aid development, the remainder of this post will highlight major developments (primarily hardware) that shaped the changes to hearing aid design. This post is intended primarily for those who are not familiar with the historical development of hearing aids, although it was a featured presentation by this Editor at the American Academy of Audiology in 2013.

Mechanical Enhancements

Devices relying on mechanical enhancement of sound transmission reception gained prominence in the 17 th century, but continued into the early 1900s. These consisted primarily of ear trumpets, listening tubes, speaking tubes, etc.

Electrical Amplification

Current flow, and control, is the heart of the electrical hearing aid amplifier. The function is to efficiently deliver amplified power to a speaker (often called a receiver in hearing aid terminology). The historical development of hearing aid amplifiers involved three distinct developments:

Carbon microphones/amplifiers (1900-1939)

Vacuum tubes (1921-1953)

Transistors (1953 - and continuing)

Carbon Microphones/amplifiers - 1900-1939

The carbon microphone (carbon transmitter) was developed in 1938. This was the first electrical hearing aid. The carbon microphone consisted of two metal plates separated by granules of carbon. Carbon movement was made to amplify electrical current. This essentially boosted weak signals (amplification). In functioning as both a microphone and an amplifier, the carbon microphone was ahead of its time. If greater power was required with the carbon microphone, the battery voltage could be increased, additional microphones could be added, or a resonating box could be employed.

From an historical view, the following companies manufactured carbon hearing aids. The only company still in existence as an original manufacturer is Siemens. Older practitioners in the discipline of hearing might remember the names of those companies with gold color emphasis.

Vacuum Tube Hearing Aids - 1921-1953

The principle of the vacuum tube is that heat escapes from a filament (cathode) and is captured by a plate (anode). The hearing aid required two supply voltages:

One to heat the cathode (the heater), called the A battery

One to provide power to the plate, called the B battery

The vacuum tube itself had an earlier introduction, with the diode (1904) invented by John Ambrose Fleming, and the triode (1906) by Lee DeForest. The latter development was the real key to amplification in general, and for hearing aids specifically. DeForest placed a grid between the filament and plate. This allowed for control of electron flow by varying the grid voltage. This controlling feature is called amplification.

Continued smaller size and lower current consumption led to the development of smaller batteries, and hence, smaller hearing aids. Early units were table models carried in cases - like early camera boxes.

Body-worn hearing aids appeared in the mid 1930s, consisting of a multi-piece design (because of large battery sizes). One part consisted of the amplification electronics, the other two parts included one battery that supplied the heater vacuum tube, and the other supplied the power vacuum tubes.

One-piece hearing aids were developed in 1945 as a direct result of battery design improvements, allowing batteries to be made in smaller size. They still required two batteries, one for the heater, and the other for power. Vacuum tube improvements allowed for finer control of volume, and potentiometers were added leading to the use of a volume control wheel, control of tone (frequency response), and to AGC (automatic gain control).

Companies that made vacuum tube hearing aids are listed in the following table, with those still manufacturing in black and underlined, and others no longer manufacturing under their original umbrella, but names one might be familiar with, in gold.

The transistor performs in many ways like the vacuum tube amplifier, but with the following differences:

It controls current, whereas the vacuum tube controlled voltage.

It is smaller, and stable under vibration and mechanical hazards.

There is no filament to heat, and so, no need for an "A" battery.

It has lower inherent noise and increased amplification. However, the transistor required greater operating voltage, and hence, the development of the silver-oxide hearing aid cell.

The transistor amplifies sound, and as such, eliminated vacuum tubes. The first use of an all-transistor hearing aid occurred in 1953. It was a body-worn aid. Eyeglass, behind-the-ear (over-the-ear, post-auricle), in-the-ear, in-the-canal, and other hearing aid configurations followed. The Table below lists the names of companies that made transistor body hearing aids, and then continued with ear level units. Again, those in Black continue to exist today, those in gold are most likely recognized by those who have been in the field for several years, and those in blue are no longer in business, and that readers are less prone to identify.

Printed Circuits

These first appeared in hearing aids in 1948, but were not commonly used in hearing aids until the 1970s. These printed circuit boards reduced the assembly time, which previously involved assembling many small individual components that required around 65 soldering connections. Soldering was not eliminated with printed circuit boards, but it was reduced substantially, as many "cold solder" connections were no longer needed.

Integrated Circuits (1958-1959)

Integrated circuits consist of an entire circuit created in a single step. All individual components (capacitors, resistors, transistors, wires) soldered into a printed circuit, were now made from silicon. The first integrated circuits were considered "solid state" in that they were made from a single crystal. Integrated circuits (ICs) allowed for substantial miniaturization of hearing aids.

The IC concept was developed by Jack Kilby of Texas Instruments in 1958. He found a way to place individual components on a crystal. In 1959, Robert Noyce (Fairchild Semiconductor) enhanced the concept by integrating all into a unitary, or Integrated Circuit (IC).

The concept is based on building masked "layers" from bottom up in silicon. This allows for millions of transistors to be placed on a small chip. When being fabricated, hundreds are made on a single wafer at the same time, and then sliced apart later. ICs made for dedicated performance are known as ASICs (Application Specific Integrated Circuits).
(Next week's post wills finish this "ride through history" of hearing aid technology and techniques).

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Starting with the first hearing aids developed, and continuing today, three factors have driven hearing aid technology and development. These three factors, in their historical ranking, are: Cosmetics Technology leading to miniaturization, and Packaging Patients have always been interested in the most cosmetically appealing hearing aid - translated as "invisible" or "smallest."

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Contemporary: The Benefits of Younger and Longer use of Cochlear Implantation

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Contemporary: The Benefits of Younger and Longer use of Cochlear Implantation

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Research done by the Washington University School of Medicine took 76 children from 23 different states¹. Each child received a cochlear implant between their 1st and 3rd birthday (+-2 months)¹.
This purpose of this study was to determine if getting an implantation at a younger age contributed to their language development¹. Additionally, they sought to see if it was realistic for children with severe hearing loss to receive a cochlear implant and an oral language method of education to achieve age appropriate language development during the preschool years¹.
What they found was that children who did receive cochlear implantations prior to a substantial delay in spoken language development were more likely to achieve age-appropriate spoken language¹. Advanced technology has given us the opportunity to implement a universal newborn hearing screening program and technology to improve the hearing experience for all¹. For families of the 90% of deaf children who have no previous experience with deafness and whose native languages are expressed primarily through speech this a huge accomplishment and advancement¹. Cochlear implantations have been around for a few centuries now but this new research showing its benefit from proactive action has shown improvements on language development at an earlier age¹.
I chose this artifact as it related to the neuroscience of hearing and the hearing mechanism that I chose to make this mini-museum centered around. This research development show how our technology can not only change someones life but also improve their quality of life. For some parents, hearing that their child is deaf or hard of hearing it may be a scary reality for them so having ways that this can be detected early to help ensure quality of life is a very promising course of treatment for those who are detected early. Of course, those in the deaf and hard of hearing community should embrace their differences as well! Technology of today does not change

1. https://doi.org/10.1044/1092-4388(2007/073)