Development of Hearing Tests
No specific event or development can be considered the origin of hearing tests as we identify them today. Still, in the early 19th century, a couple of separate developments opened a pathway. On one hand, there was a growing need for improved diagnoses and description of disease entities, and as a result, some simple, but practical hearing tests had been presented. The inventors are unknown, but these consisted of allowing a person to repeat spoken sentences or having patients listen to a pocket watch, and even some refinements of these.
A second development was rapid progress in the natural sciences, especially in the separate disciplines of acoustics and sensory physiology. Cooperation and exchange of ideas between the two disciplines led to a first culmination point. Edelmann, a physicist, developed a set of instruments for hearing testing that he presented to an otologist named Bezold. The latter, in turn, referred to the theoretical concepts of the physiologist Helmholtz to help in interpreting his clinical test results. This cooperation set a standard for the future of hearing tests and, eventually, the discipline of audiology. Essentially, the development of audiology as we know it today could not have occurred without the combined efforts of Physics, Physiology, and Otology.
Mechanical Acuity Meters
Perhaps the first such measurement device for testing hearing was described by Wolke (1802) {{1}}[[1]] Wolke. Nachricht von den zu Jevere durch die Galvani-Voltaische Gehörgenbekunst beglückten Taubstummen. Oldenburg 1802[[1]]. The instrument consisted of a wooden board placed upright; attached to it was a drumstick that could be dropped onto the board from various heights, and which could be read from a related scale (Figure 1). Wolke tested the usefulness of this “acuity meter” on deaf mutes. It was with this that Wolke initiated the development of “instrument” hearing tests. Variations of this were introduced at times until the end of the 19th century.
Figure 1. Wolke's measurement device for testing hearing. The drumstick could be dropped from various heights and related to a scale, with the height of the drop providing different levels of sound. (Author rendering).
Figure 2. Itard's accumeter. The copper ring, which is suspended by a string, is struck by the ball at the end of the pendulum with a strength that depended upon the latter’s initial displacement.
Itard (1821) constructed a device he called the “accumeter” which was similar to Wolke’s, but the difference was that Itard’s acuity meter used a tuned ring made of copper as the sound source {{2}}[[2]] Itard, J. M. G. Traité des maladies del’oreille et de l’audition. Paris, 1821[[2]] (Figure 2). The copper ring, which is suspended by a string, is struck by the ball at the end of the pendulum with a strength that depended upon the latter’s initial displacement.
This instrument found widespread acceptance during the first half of the 19th century. What helped is that Itard was Director of the Paris Institute for the Deaf and, as a result, had access to many hearing-impaired persons and was able to conduct well-conceived and systematic studies, which had a significant influence on further developments in the discipline of hearing. And, because he was aware of the need to differentiate between mental retardation and deaf-mutism, for small children he recommended an arousal test to be performed by means of graded noises (banging of doors, etc.). He also devised a classification for deafness, even though he was not aware at the time of the diagnostic tests of bone-conduction.
Politzer (1877) {{3}}[[3]] Politzer, A. G., Gradenigo, und Delsaux. Wahl einer einfachen und praktischen akumetrischen. Formel, 7. Int. Otol.-Kongr. Bordeaux 1904. Ref. Z. Ohrenheik. 49 (1905) 63-69 [[3]] developed an acuity meter that he referred to as a “standard auditory meter.”
Figure 3. Politzer accumeter. See text for explanation for use.
The device was held vertically between the thumb and index finger of the right hand at places b and b’. The right middle finger would push h’ down until it met the angled iron resistance, then released, and the mallet h would fall to strike the small steel cylinder c – always from a constant height. Bone-conduction testing was accomplished by placing disk p in contact with the mastoid.
Other acuity meters utilized spring devices – most being little more than loud watches (Schmalz, 1846) {{4}}[[4]] Schmalz, E. Erfahrungen über die Krankheiten des Gehörs and ihre Heilung. G. G. Teubner, Leipzig 1846[[4]]. One incorporated the chime of a large clock housed in a wooden box, while another used an ordinary pocket watch with the housing perforated (Figure 4).
Figure 5. Rau sound generator with retractable ruler for distance heard measurement.
Figure 4. Watch-like sound generator with perforations for sound to escape.
Another device consisted of a mallet driven by a spring that beat against a wooden box with a force that could be regulated (Yearsley, 1855) {{5}}[[5]] Yearsley. Gazette méd. Paris 41, 1855, 650; zit. Nach W. Rau, Lehrbuch der Ohrenheilkunde für Ärzte and Studierende, Peters, Berlin 1856[[5]]. Even the metronome, patented by J.N. Mälzel in 1916, had been used on occasion as a hearing test.
However, perhaps the first device to incorporate multiple features for hearing testing and which may have driven the future development of hearing measurement devices was that of Rau (1856) {{6}}[[6]] Rau, W. Lehrbuch der Ohrenheilkunde für Ärzte und Studierende. Peters, Berlin 1856 [[6]]. He devised a spring-driven clockwork that actuated a small varnish-coated (for damping purposes) bell, the intensity of which could be set to any of eight levels, and the period of the bell could be regulated with the aid of an adjustable screw. He recommended the use of a tape measure (marked in centimeters) contained in a metal housing that could be pulled out of its capsule to measure the distance at which tests were run, and fixed in position by a toothed wheel. When finished, it would be rolled back into its capsule by pressing a spring (sounds familiar, doesn’t it?). A device built by Bing (1875) {{7}}[[7]] Bing, A. Über eine praktische Modifikation der Uhr als Hörmesser. Allg. Wien. Med Z. 1875. Zit nach A. Bing, Verlesungen über Ohrenheilikunde, Braunmüller, Wien. 1890, 40[[7]] incorporated these features, being essentially a copy, even to the fine details. Figure 6 provides an example as to how this device with its ruler, were used clinically.
Figure 6. Reporting results of a Rue-type device showing how distance "heard" was used in diagnostic and rehabilitation.
These early hearing testing devices relied on subjective response to various tones and sounds that were generated by the instruments. They were soon complemented by the invention of Wheatstone (1827) {{8}}[[8]] Wheatstone. Quart. J. Med. Sci. 1827, 67; Forieps Notizen 19, 1827. Zit nach A. Politzer, Geschichte der Ohrenheilkunde, Bd 1, 413[[8]], Weber (1834) {{9}}[[9]] Weber, E. H. De pulsu, resorptione, auditu et tactu. De utilitate cochleae in organo auditus. Lipsiae 1834[[9]], and Muller 1838) {{10}}[[10]] Müller, J. Handbuch der physiologie, 1938, Bd. 2. 393, 437[[10]] of instruments that employed tuning forks (invented by the English musician John Shore in 1711) to generate sounds of different frequencies.
Hearing Testing Related to Hearing Aids
That hearing testing and hearing aids had at least a theoretical relationship was identified already in Beck’s (1827) {{11}}[[11]] Beck, K. J. Die Krankheiten des Gehörorganse. Ein Handbuch zum Gebrauche seiner Vorlesungen. K. Groos, Heidelberg und Leipzig 1827[[11]] textbook in otology, where he devoted an entire paragraph. “In the same manner as glasses are employed for certain visual defects in order to re-establish normal visual function, hearing tubes are being utilized in cases of auditory disorders. The state of the art in Optics makes it relatively easy to prescribe glasses suitable for any given visual defect. After defining the distance at which a target must be seen, there is no difficulty in selecting a lens of the proper focal length. Due to our limited knowledge of Acoustics, however, a hearing tube capable of transmitting all the variously modulated tones cannot be made at this time. [Vidus Vidius (died 1569) had already compared the support one obtains from hearing tubes with that provided by glasses.] The more strongly a sound is transmitted the more it loses its definition and becomes an indistinguishable noise. The instrument designed by Itard for the measurement of hearing acuity might be applied for the present purpose, that is, for making a hearing tube exactly fitting the magnitude of the hearing loss. As one has to define the focal length of glasses, one may find something suitable with respect to magnitude and type of hearing tubes through actual practice.”
It was 100 years later that Brünings (1825) voiced similar ideas. He championed the utilization of the “rebirth of Acoustics,” with all its technical potentials, for the building of hearing aids and trying to make them prescription instruments. {{13}}[[13]] Dembe, A.E. Occupation and Disease: How Social Factors Affect the Conception of Work Related Disorders, Chapter 4. Noise induced hearing loss, Yale University Press, 1996, 334 pages [[13]]
Electronics Era Incorporation
A number of electronic sound-generating devices were built in the late 19th century because of technological advances in electronics – especially the development of the induction coil by E. Du Bois Reymond in 1848, and the telephone by Bell and Gray in 1876. The telephone especially influenced otologists and acoustical engineers to visualize in that device the potential to generate standardized tones and speech for medical testing purposes. Within two years after the telephone breakthrough, sound-generating instruments for the medical testing of hearing were built by A. Hartmann (1878), E. Högyes (1878), J. Blyth (1878), and D.E. Hughes (1879) {{13}}[[13]] Dembe, A.E. Occupation and Disease: How Social Factors Affect the Conception of Work Related Disorders, Chapter 4. Noise induced hearing loss, Yale University Press, 1996, 334 pages [[13]].
This blog will be continued with the development of the audiometer up through the Western Electric 4A audiometer.
