Physiology Lab: Transfer Functions
This application is designed to help you understand how the outer and middle ear modify and transfer sound energy before cochlear stimulation.
1. Chart Overview
The graph displays simplified, frequency-dependent transfer functions in decibels (dB) relative to frequency (Hz) on a logarithmic scale from 200 Hz to 16,000 Hz.
Yellow Curve — Outer-ear Transfer: Shows the frequency-dependent enhancement produced mainly by the pinna, concha, and ear-canal resonances.
Green Curve — Middle-ear Transfer: Represents a simplified model of the frequency-dependent transmission characteristics of the tympanic membrane and ossicular chain, including the middle ear's impedance-transforming function.
Red Curve — Combined Relative Transfer: Represents the sum of the two modeled transfer terms. It is intended as a teaching representation of the overall frequency-dependent response of the outer- and middle-ear system.
The red curve should therefore be interpreted as a relative transfer function, not as a direct measurement of sound pressure inside the cochlea.
2. Interaction & Controls
You can manipulate the acoustic input using the control panel:
Input Level (dB SPL): Adjusts the level of the external acoustic stimulus.
Frequency (Hz): Selects a specific frequency. The dashed vertical line on the chart tracks the selected frequency.
Dynamic Data Box (Tooltip): When you move the cursor over the graph, the tooltip displays the modeled Outer-ear Transfer, Middle-ear Transfer, and Combined Relative Transfer at that frequency.
Hovering: Moving across the graph allows you to compare how the modeled transfer changes with frequency.
3. Reading the Results
As you adjust the sliders, the Results Card updates in real time:
Outer-ear Transfer: The modeled contribution of the outer ear at the selected frequency.
Middle-ear Transfer: The modeled contribution of the middle ear at the selected frequency.
Illustrative Downstream Level Index: The selected input level plus the two modeled transfer terms.
This value is provided only as a teaching index. It should not be interpreted as a measured cochlear SPL, oval-window pressure, or clinically calibrated physiological quantity.
Basilar Membrane Tonotopic Map
Below the graph, a color-coded track represents the tonotopic organization of the cochlea.
Base: Associated with higher characteristic frequencies.
Apex: Associated with lower characteristic frequencies.
The marker moves according to the selected frequency to illustrate approximately where that frequency is represented along the basilar membrane.
Scientific Notes for Students
Outer-ear resonance
Notice that the outer-ear transfer reaches its maximum in the region of approximately 2–4 kHz in this simplified model.
This reflects the frequency-dependent resonances of the pinna, concha, and ear canal and contributes to enhanced sensitivity in a frequency region that is important for speech perception.
Middle-ear transfer
The middle ear does not simply amplify sound by a fixed number of decibels.
Its transfer characteristics vary with frequency because of the combined effects of mass, stiffness, damping, tympanic-membrane mechanics, ossicular coupling, and impedance transformation between air and cochlear fluids.
Model limitations
This application uses simplified log-Gaussian functions to illustrate the general frequency dependence of outer- and middle-ear transfer.
The curves should therefore be interpreted as conceptual teaching models rather than precise physiological measurements.
The combined curve is formed by adding the modeled transfer terms in dB. It illustrates how their frequency-dependent effects may combine, but it does not represent a direct measurement of cochlear input.
Question for Students
How does the combined modeled transfer change as you move from the middle-ear transfer peak near 1.2 kHz toward the outer-ear transfer peak near 3 kHz?
Which of the two components contributes most to the combined response at each frequency?