I will always regret that I never met C.C. Bunch. I like to think of him as the very first audiologist. Toward the end of his life, he was a member of the faculty of my alma mater, Northwestern University, but he died three years before I entered the school as a freshman in 1945. He was well remembered by the older faculty, especially by voice scientist Paul Moore, who helped Bunch prepare his book, Clinical Audiometry, the first real tutorial on the techniques and interpretations of pure-tone audiometric testing. Bunch wrote the book while at Northwestern in 1941–1942, just before his untimely death in June of 1942.
The story of C.C. Bunch’s career as the first audiologist begins in 1917 at the University of Iowa. Psychologist Carl Seashore was dean of the graduate school and a lifelong student of music. He is perhaps best known for the Seashore Tests of Musical Ability. His wide interests included many other aspects of the auditory sense, especially the measurement of hearing loss. He shared this interest with local otologist Lee Wallace Dean. Together they embarked on a project to study “practical applications of methods of testing hearing.” In 1917, testing for hearing loss was still dominated by tuning fork tests, especially the Weber, Rinné, and Schwabach (Newby, 1958). These procedures were specialized for deciding what kind of hearing loss the patient had, but were not very good at estimating the degree of loss at various frequencies.
What Seashore and Dean had in mind was a device capable of presenting a pure-tone whose frequency and intensity could be controlled precisely, rather than by the imprecise manual stimulation from the stem of a tuning fork (i.e., nothing less than what we today call an audiometer). What they needed, they both agreed, was a bright young physicist who could carry the project through to the actual fabrication of such a device. They had both been impressed by Bunch, who had just completed his master’s degree in psychology and physics at Iowa. Dean described him as a brilliant young man. Supported by a five-year grant obtained by Seashore and Dean, Bunch pursued his PhD degree in psychology as he worked on the construction of what he termed the “pitch range audiometer.” Bunch succeeded in building a prototype audiometer but it was never commercially available. The range of frequencies was generated by a variable speed DC motor, driving a set of two rotating disks. Intensity level was varied by means of resistors. Bunch used this device in early studies of Dr. Dean’s patients, but in a few years the Western Electric 1-A audiometer, which took advantage of the capabilities offered by the recent development of the vacuum tube, was available. Bunch and Dean acquired one for the then-steep price of $1,500, and Bunch used it exclusively for the next two decades.
In 1920, Bunch was awarded the PhD degree in psychology and joined the Iowa faculty as associate professor of otology. He spent the next seven years testing Dean’s patients in the otology clinic. In 1927, Bunch moved to the Johns Hopkins University in Baltimore as an associate in research otology, working with the renowned otologic anatomist, Stacy Guild. Meanwhile his mentor, Dr. Dean, had moved from Iowa City to St. Louis to a post in otology at the Washington University School of Medicine. Dean immediately invited Bunch to join him as professor of applied physics. Bunch accepted and, in 1930, moved to St Louis. Here he continued to test all of Dean’s patients and to amass what must have been thousands of air-conduction audiograms. In 1938, Bunch became associate director of the highly-regarded Central Institute for the Deaf in St. Louis, then under the direction of the highly-respected educator of the deaf, Max Goldstein. Finally, in 1941, Bunch moved to Evanston, Illinois, where he joined the faculty of Northwestern University as research professor in Education of the Deaf in the School of Speech. Here, with the help of Paul Moore, he prepared the manuscript of his classic book, Clinical Audiometry, just before his death at the age of 57 in 1942. It was published posthumously by the C.V. Mosby Company in 1943.
Bunch’s untimely death left the course he was teaching in the School of Speech without an instructor. A young speech scientist, Raymond Carhart, was assigned to finish the course. Carhart’s subsequent interest in auditory matters may be traced to that event.
Bunch’s Incredible Achievement
To fully understand the remarkable achievement of C.C. Bunch, you must keep in mind that the Western Electric 1-A audiometer was capable of only one measure: air-conduction thresholds at octave and half octave intervals from 32 to 16,384 double vibration (d.v.). Double vibration has a long history in musical acoustics. It refers to the displacement of a musical string (e.g., violin, harp, or guitar) first in one direction from the position of rest, then in the opposite direction from rest, when plucked or bowed. This constitutes two displacements, or one double vibration. In the 1940s, d.v. morphed among physicists into “cycles per second” or c.p.s. Finally, in the 1960s the International Union of Pure and Applied Physics renamed it Hertz, abbreviated Hz, to honor Heinrich Hertz, a 19th century German scientist, who pioneered the study of electromagnetic radiation.
In describing losses and redoing audiograms to make them more suitable for publication, I have preserved the original terminology of the 1920s and 1930s for the sake of authenticity. TABLE 1 translates archaic terms into modern usage.
Hearing loss (sensation units)
HL in dB
There were no bone-conduction thresholds, no speech thresholds, no PB scores; there were only the air-conduction thresholds. With these limited data, Bunch managed to write 24 articles and a book on issues including age variations in auditory acuity, traumatic deafness, otosclerosis, deafness in aviators, conservation of hearing, late effects of otitis media in infancy, race and sex variation in auditory acuity, the acoustic nerve, and absence of the organ of Corti. And he did all of that over the space of only 22 years.
In the following sections, I describe some of Bunch’s insightful observations concerning percentage hearing loss, masking, audiometric technique, conductive hearing loss, perceptive hearing loss, and the fitting of hearing aids. They are all based on his 1943 book, Clinical Audiometry.
Percentage of Hearing Loss
Because patients so often ask, after being shown their audiogram, what is the percentage of hearing loss, Bunch gave the issue a good deal of thought before concluding that it was an exercise in futility. He illustrated his point by presenting the audiograms of three persons with congenital losses. Although the contours of the losses were strikingly different, the pure-tone averages, from which the percentage loss would be computed, were similar. Yet the ability of each patient to function in the auditory world differed substantially depending on both the shape of the audiogram and a variety of non-auditory factors. Bunch’s point was that three people with the same percentage loss had significantly different degrees of disability in real-world communicative events.
Bunch recognized, however, that there would be situations in which persons appeared before compensation boards or courts seeking monetary damages for hearing loss. He wrote the following:
The amount of award granted under present conditions is usually dependent on the relative skills of the opposing legal representatives. Fowler [Dr. Edmund Prince Fowler] has proposed a system for making such awards, but his plan has not as yet been accepted by otologists. It provides for awards on the basis of disability rather than upon the amount of hearing loss. His proposal is an attempt at a solution of this problem and indicates the trend of otological opinion (Bunch, 1943).
Unfortunately, the trend toward disability and away from loss never got much further. Three quarters of a century later, if you go to Google and enter the phrase “percentage of hearing loss,” you will encounter programs allowing you to calculate percentage loss by simply filling out a form that asks for the patient’s age, sex, air-conduction thresholds, handicap equation (there are eight different choices), and presbycusis equation (there are four choices). A final click completes the process. A computer program prints out the percentage loss summaries immediately. But there is not even a hint of how much disability this represents for the individual who generated the data.
In my years at the Baylor College of Medicine in Houston, my otologic colleagues sometimes talked about surgeons who operated on dead ears, thinking they were pure conductive losses because the opposite, normal-hearing ear was not masked when the dead ear was tested audiometrically. Bunch was very much aware of this kind of problem, as well as the need for masking the better ear whenever one encountered a substantial interaural asymmetry.
Noting that a masking noise was not available on all commercial audiometers, he suggested using a Bárány noise apparatus or even the sound from an alarm clock. His final recommendation, however, would meet with some opposition from present-day inspectors and regulators:
One who is mechanically inclined can construct an effective masking device by attaching a telephone receiver to a small toy transformer and connecting the transformer to a wall plug of the ordinary 60-cycle house current. (Bunch, 1943).
Please do not try this at home!
In Bunch’s time, it was usual to seek threshold by systematically lowering the level of a continuous test tone until it was no longer heard, then increasing the level until the continuous tone was heard again. Indeed, Bunch’s original pitch range audiometer, constructed during his PhD degree program at Iowa, had a motor-driven oscillator, providing a continuously changing frequency across the entire range of testing. It anticipated, in this regard, the original automatic audiometer of Békésy in 1947 and the Grason-Stadler E800 automatic audiometer in 1958. The tonal level could also be swept continuously from high-to-low and from low-to-high. Bunch’s training in psychology had made him acutely aware of the importance of attention when attempting to measure any kind of threshold. He included, therefore, an interrupter switch so that the test tone could be turned off as the level was changed from step-to-step. The fact that the control was labeled “interrupter” rather than “tone on” suggests, however, that in those early days of audiometry, the bias was toward a tone-on most of the time rather than a tone-off most of the time. As more experience was gained, Bunch realized that the onset of a sound is necessary to mobilize attention. In his words:
The threshold of auditory acuity is the faintest sound which the listener can hear, not when he is reading a newspaper or enjoying a nap, but when his attention is focused on that particular sound (Bunch, 1943).
Conductive Hearing Loss
Prior to the advent of audiometry, there was a long-standing dispute among otologists as to how conductive loss affected the frequency response of the total system. One school insisted that the greatest loss was in the low frequency region, with little or no loss at higher frequencies. The other school insisted that this was wrong, that the greater loss was at the higher frequencies. It is not recorded whether blows were exchanged, but each school staunchly defended its firm belief. What Bunch learned from his patiently gathered audiograms was that both schools were correct. It depended on the cause of the conductive loss. Anything that increased the stiffness of the ossicular chain, such as otosclerosis, produced greater loss for lows while anything that loaded the system down with more mass produced greater loss for highs.
Bunch went on to show that in some patients there were high-frequency perceptive loss as well as conductive loss. Lacking calibrated bone conduction capability, he nevertheless reasoned it from the fact that, in cases treated for suppurative otitis media, the low tones recovered more rapidly than the highs. One such case is illustrated in FIGURE 1 of his book (modified from Bunch, 1943). Three successive audiograms showing recovery over a four-month period are shown. From these successive contours, Bunch reasoned that there might be a perceptive component in some cases of middle-ear disease. He wrote:
The striking feature in these records lies in the fact that the recovery in the acuity for low tones took place much more rapidly than that for high. This phenomenon has been interpreted to indicate that a certain portion of the high tone loss was due to secondary involvement of the inner ear (Bunch, 1943).
There had long been speculation among otologists that such secondary perceptive loss might be present in disease processes such as otosclerosis or otitis media, but Bunch was surely the first to demonstrate it audiometrically.
It was generally accepted in otological circles that high-frequency losses tended to be perceptive rather than conductive, but Bunch’s audiograms convinced him that there were at least two subtypes—abrupt and gradual. He linked the abrupt drops in the high-frequency range to trauma of some kind, and the gradually sloping losses to aging. Eventually, however, he noted what he believed to be yet a third type of perceptive loss based on the shape of the threshold contour. FIGURE 2 (modified from Bunch, 1943) shows the audiograms of a 26-year-old woman. This is neither a low-frequency nor a high-frequency loss. It extends from 256 d.v. to 4096 d.v. but disappears at very low and very high frequencies. While noting that this unusual shape was rare Bunch insisted that it be catalogued as a third type of perceptive loss. It has since been described as a “cookie bite” audiogram and has been associated with a form of otosclerosis that invades the inner ear while sparing the ossicular chain and stapes footplate. Many also associate the cookie-bite audiogram with congenital hearing loss. Bunch appears to have been the first to observe the “cookie bite” audiometric contour and to suggest its genesis.
If you only test down to 256 d.v., when you do audiograms, you will consistently miss such contours. Bunch thought it important to test as low as 32 d.v. Although thresholds at 32, 64,and 128 d.v. are usually redundant, here is a situation in which they are important to a full audiometric picture.
The late 1930s saw a minor revolution in hearing aids, with the introduction of the mini vacuum tube. Now the case could be reduced in size, and the sound quality was substantially improved. Bunch became an enthusiastic fitter, relishing the new insights he gained from interviews with his patients. One such interview, in 1938, reveals the extent to which Bunch sought to understand why some patients were helped less by hearing aids than others. FIGURE 3 (modified from Bunch, 1943) shows the audiograms for the two ears of a 42-year-old man with a relatively flat, bilaterally symmetrical, moderately severe loss. Bunch first suggested that the man procure, on a trial basis, an aid with a flat frequency response fitted to the right ear. The man complied and reported that it was wonderfully helpful. Bunch noted, however, that when he spoke with his back to the patient at a distance of only a few feet, there was no response.
Bunch next thought that sending the amplified signal to both ears, via a Y-cord, might produce a better result. The patient tried this and liked it so much that he purchased the aid. But alas he still could not understand speech when only a few feet from the talker. Bunch now decided that he needed to know more about this hearing loss than the audiograms could convey. He took the sensible step of asking the patient how the various test tones were actually perceived. He found that all tones up to 512 d.v. retained their natural tonal quality and were appropriately ordered in pitch. Surprisingly, however, all tones above 512 d.v. “sounded alike and had no tonal quality” (Bunch, 1943). The aid that he had purchased did help him to hear low frequency sounds, like the buzz of an airplane propeller, but he still could understand no speech. Bunch concluded that:
Cases of this type are undoubtedly quite rare. The nature of the pathology is food for speculation. It is sufficient to say that, had simple speech tests been done, the discrepancy between his audiogram and his ability to understand speech could have been detected, and the patient saved the expense of purchasing a hearing aid which was of no practical value.
Of course, there was no such thing as standardized speech audiometry in 1938, but Bunch was prescient in anticipating the need for such measures.
We can discern, from the account of this patient, the principal reason that Bunch was able to publish so much on so many aspects of hearing loss. He talked to his patients. If they were having trouble he certainly wanted to help them, but beyond that he wanted to know why they were having trouble, and how he could use that knowledge to help future patients with the same complaints. He asked questions and carefully weighed the answers.
Today’s students can learn a good deal from a study of C.C. Bunch, the first audiologist, and his remarkable book.