Читать книгу Engineering Acoustics - Malcolm J. Crocker - Страница 147

Pythagoras in the sixth century BCE was perhaps the first to recognize that sound is an airborne vibration [10]. Hippocrates in the fourth century BCE recognized that the air vibrations are picked up by the eardrum but thought that the vibrations were transmitted directly to the brain by bones. In 175 CE, Galen of Pergamum, a Greek physician, realized that it was nerves that transmitted the sound sensations to the brain. Galen and most other early scientists and philosophers proposed, mistakenly, however, that somewhere deep in the head was a sealed pocket of implanted air which was the “seat” of hearing. This view was popularly held until 1760 when Domenico Cotugno declared that the inner ear (cochlea) was completely filled with fluid [10].

In 1543, Andreas Vesalius published his treatise on anatomy giving a description of the middle ear and in 1561 Gabriello Fallopio described the cochlea itself.

In 1605 Gaspard Bauhin put forward a resonance theory for the ear. In his model, different air cavities were excited by different frequencies. However, he knew little of the construction of the inner ear. Du Verney, in 1633, developed a more advanced theory by postulating that different parts of the ridge of bone which twists up the inside of the cochlea resonated at different frequencies which depended upon its width. Du Verney's theory was held until 1851 when Alfonso Corti, using a microscope, discovered that the thousands of hair cells on the basilar membrane were attached to the ridge of bone in the cochlea.

A few years later, Hermann von Helmholtz used Corti's findings to suggest a new theory of hearing. In Helmholtz's theory, as it became refined, different parts of the basilar membrane resonated at different frequencies. Later workers showed that Helmholtz was not exactly right (the basilar membrane is not under tension). However, in 1928 Georg von Békésy did show that waves do travel along the basilar membrane and different sections of the basilar membrane do respond more than others to a certain sound. The region of maximum response is frequency‐dependent and as Helmholtz had predicted, von Békésy found that the high‐frequency sound is detected nearer to the oval window and the low‐frequency sound, nearer to the apex (Figures 4.3 and 4.4).