Constructing an Electronic-Oscillator-Based Model of the Human Ear

How do we perceive motion in music? It is the connection between motion and sound that has motivated our research and led us to focus our modelling efforts on hair cells—the sensory organs found in the inner ear which are common to both the vestibular and auditory systems. These tiny mechanorecpetors are found in the vestibule, where they detect accelerations, and in the cochlea, where they are individually tuned and arranged by frequency along a coiled membrane. To examine the essential properties of cochlear hair cells we looked at a type of circuit known as a Wien bridge electronic oscillator. This circuit contains ordinary resistors and capacitors as well as an op amp, a lightbulb which responds nonlinearly to heating, and a variable resistor that can be adjusted until threshold resistance is reached. Above this threshold, the system will spontaneously oscillate at its resonant frequency in what is known as a Hopf bifurcation. By swapping out components, the Wien bridge can be "tuned” to different resonant frequencies, many of which fall in the range of human hearing. We will discuss our experimental findings and mathematical descriptions of nonlinearity within the Wien bridge system, as well as relating our model to theoretical models of hair cell dynamics.