Historical Biographies in Acoustics:

Georg von Békésy

 

Elle O’Brien

Acoustics Today Intern 2018

 

 

One of the most exciting things a student learns about the ear is that the cochlea, the snail-shell shaped organ in the inner ear where sound is transduced into an electrical signal carried by the auditory nerve, is arranged very particularly. In humans, high frequency sounds (e.g., sounds above 7000 Hz) excite the base of the cochlea’s spiral, while low frequency sounds (e.g., sounds below 400 Hz), excite the apex (top) of the spiral. How the cochlea could accomplish this feat of engineering was the source of great debate for decades among leading acousticians until the Hungarian scientist Georg von Békésy settled the debate, for which he was awarded the 1961 Nobel Prize in Physiology or Medicine. The Acoustical Society of America awarded Bekesy its highest honor, the Gold Medal, and later created the von Békésy award for outstanding research in psychological or physiological acoustics.

Georg von Békésy, born in Budapest in 1899, spent much of his life studying how the cochlea is able to “sort” sounds before they ever reach the auditory (eighth) cranial nerve. When he began his work, scientists knew that sound—vibrations of air particles—was converted into vibrations of the basilar membrane, a flexible tissue within the cochlea, that stimulated the sensory hair cells, which, in turn, stimulated the auditory nerve (Robels and Ruggero 2001, Brownell 2017, Manley et al. 2018). The exact way that the basilar membrane responded to sound, though, was controversial. Some researchers believed that vibrations travelled as standing waves, like the motion of a plucked guitar string (for an explanation of waves, see Acoustics Today’s World Through Sound series, and animated tutorials by acoustician Dan Russell)Others believed that the entire cochlea moved up and down, not just the basilar membrane, or that only specially tuned resonators along the basilar membrane responded to a given frequency. And still others believed that traveling waves, like ripples in a pond, were at work (Olson et al. 2013). Von Békésy realized that all four hypotheses were related: each was possible, depending on how flexible the basilar membrane was (von Békésy 1961 pp. 743). Once he made this insight, solving a decades-old mystery became a matter of understanding the mechanical properties of the basilar membrane. Von Békésy was the first to definitively show that the vibrations of sound were converted to traveling waves along the basilar membrane. Thanks to his work, we know exactly how any given sound will excite the cochlea—a breakthrough that’s been critical for understanding hearing and its many disorders.

The road to this discovery was, as it so often is in science, winding. As a newly minted Ph.D. in physics from the University of Budapest in 1926, von Békésy first searched for a job in optics. When a skilled and salaried position in his chosen field didn’t materialize in his native country, he began working with the Hungarian Telephone and Post Office Laboratory in Budapest, which managed all the telephone lines in the country. Similar to the work of Harvey Fletcher at Bell Labs (who became the first president of the Acoustical Society of America) across the Atlantic Ocean, Von Békésy set about understanding the factors that limited the faithful transmission of sound over the telephone. Soon, he became fascinated by the inner ear, which bested the highest quality telephone receiver in performance (von Békésy 1961 pp. 740). The Telephone and Post Office Laboratory was mostly happy to accommodate his interest: according to the Nobel Foundation, “Soon he became a nuisance to the autopsy rooms of the hospitals and the mechanical workshops of the Post Office. There they did not like to find their drill press full of human-bone dust in the morning.”  This circuitous road to discovering his life’s work is perhaps why, when asked which major influences had determined his particular body of work, he replied, “Pure accident” (Ratliffe 1976, pp. 25).  

            Von Békésy’s training as a physicist, and his willingness to pick up a drill when necessary, led him to think about the cochlea differently than many of his contemporaries. In 1947, von Békésy moved to Boston, Massachusetts to work at the Psycho-Acoustic Laboratory at Harvard University. There, he built 3D mechanical models of the cochlea. His main model was a modification of one developed in the lab of the great German acoustician Erwin Meyer (The Nobel Foundation 1964, pp. 743): the cochlea was modeled as a 30-cm long plastic cylinder, which was filled with water, and contained a flexible “basilar membrane” (pictures can be seen here). By vibrating the membrane, the pattern of excitation could be studied—and the traveling wave could be seen. Even more, by holding up his arm to the cylinder, von Békésy could feel the way the auditory nerve would be excited on his skin. Although von Békésy also worked with various techniques to capture the movement of the basilar membrane through photography, it’s important to remember that for soft (but still audible) sounds, the basilar membrane moves less than the diameter of a hydrogen atom. Hence one reason why a larger-than-life model was of use! When he accepted the Nobel Prize, von Békésy told the audience in Switzerland,

“I think the happiest period of my research was when I started to repeat all the great experiments that have been done on the ear in the past… All the small details could be duplicated on the skin. Nothing has been more rewarding than to concentrate on the little discrepancies that I love to investigate and see them slowly disappear. This always gives me the feeling of being on the right track, a new track.” (The Nobel Foundation 1964, pp. 744-745)

            While so many other thinkers in hearing science and acoustics relied on mathematical models, von Békésy saw those as an almost artistic abstraction. His strength was not in symbolic reasoning, but in mechanics, and this may have been the key to his insight on the question of the basilar membrane.

After winning the 1961 Nobel Prize, von Békésy continued on at Harvard for six more years until his inevitable retirement loomed. Having always preferred solitude (he never married, and in his entire career had only a single postdoctoral student, ASA Silver Medal recipient Richard R. Fay), he accepted a position as far from Harvard as one could get in the United States: directing the Laboratory of Sensory Sciences at the University of Hawai’i at Manoa (now the Békésy  lab). There, a lab was specially built for von Békésy, carefully constructed so that extremely precise measurements of the basilar membrane could be taken without interference from vibration or electromagnetic radiation. This is the reason why the facility has incandescent lighting everywhere instead of fluorescent lighting. Here, von Békésy could continue building models with von Békésy worked in Manoa until his death in 1972. Walter Karplus remained at the lab for some time so that he could reconstruct all of the von Békésy models so they could be preserved for posterity. Mr. Karplus passed away just hours after he had just finished reconstructing the last model (personal communication, A. Popper). 

It is easy to assume that a man like von Békésy was first and foremost passionate about physics or sound, perhaps even music. But when the National Academies of Sciences asked him to list his major interest for their records, he replied, “Art” (Ratliffe 1976, pp. 25). In fact, his Nobel Acceptance lecture contained 12 scientific figures and 10 photographs of works of art, from the ornate casket of a mummified ancient Egyptian baboon to da Vinci’s drawings of the natural world. He was a collector all his life, and his biography in the National Academy of the Sciences remarks that

“His closest friends, from which he drew both solace and inspiration, were the art objects he had collected over the years. These filled his laboratory, secreted here and there in drawers and filing cabinets where one might ordinarily expect to find only tools, supplies, and records of data.” (Ratliffe 1976, pp. 31)

            When von Békésy died, he gifted his expansive collection of works from the ancient Far East to Renaissance Europe to the Nobel Foundation (photographs of his collection can be seen here). His love of art was not so much in competition with his appetite for science as it was an inspiration. Looking at artifacts of other cultures, von Békésy wondered about the limits of the human imagination and decided that the richest ideas came from studying nature itself. In his own words,

“I found the inner ear so beautiful under a stereoscopic microscope that I decided I would just stay with that problem. It was the beauty and the pleasure of beauty that made me stick to the ear.” (Ratliffe 1976, pp. 36)

 

REFERENCES

Brownell, W. E. (2017). What is electromotility? – The history of its discovery and its relevance to acoustics. Acoustics Today 13(1), 20-27.

Manley, G. A., Lukashkin, A. N., Simoes, P., Burwood, G. W. S., & Russel, I. J. (2018). The mammalian ear: physics and principles of evolution. Acoustics Today 14(1), 8-16. 

Olson, E. S., Duifhuis, H., and Steele, C. R. (2012). Von Békésy and cochlear mechanics. Hearing Research 293(1-2), 31-43. https://doi.org/10.1016/j.heares.2012.04.017

Robles, L., and Ruggero, M. A. (2001). Mechanics of the mammalian cochlea. Physiological Reviews 81(3), 1305-1352. https://doi.org/10.1152/physrev.2001.81.3.1305

Ratliff, F. (1976). Georg von Békésy. Biographical Memoirs 48, 25-36

The Nobel Foundation (1964). Nobel Lectures, Physiology or Medicine 1942-1962, Elsevier Publishing Company, Amsterdam. https://bit.ly/2PFYbXi

 

 

FURTHER READING

A compilation of essential papers by von Békésy, Experiments in Hearing, can be purchased through the Acoustical Society of America for $23.