Introduction to Auditory Simulation Methods Applicable to NIHL Study June 22, 2009 Won Joon Song and Jay Kim Mechanical Engineering Department University of Cincinnati

Contents Network model Transfer function model Applicability of simulation models to NIHL study

Auditory pathways in conventional network models External ear TM Ossicular chain Inner ear Mechanical transmission Acoustic transmission Bone conduction Generally replaced by cochlear input impedance B.C Modeled as independent block ME air space Skull

Schematic of network ear model

Classical middle ear network model Tympanic membrane & ossicular chain up to I-S joint Two-port network of conductive pathway Middle ear cavity Decoupled from mechanical pathway Stapes complex & cochlear input impedance Impedance B.C. for ME transmission Network sub-structures and parameter values are different, but three- impedance-block concept is common in typical network models.

Available outputs from network model Time-domain response: Steady state response: Inner Ear Middle Ear External Ear Source U ST (t)d BM (x, t)P TM (t) Z ME Z C0 H UP (ω) P C0 (t) HP (ω)HP (ω)H C (x, ω) ZEEZEE H FT (ω) P FF (t) H DP (ω) d ST (t)

Limitations of middle ear network models Complex vibrational mode of the tympanic membrane: single-piston or mechanically coupled two-piston modeling Rocking motion of the stapes footplate: translational motion only Variable middle ear transformer ratio –Moving axis of rotation –Flexible ossicular joints: rigid M-I joint assumed –Effective area change in TM and stapes footplate Nonlinear acoustic reflex characteristics –Time-frequency dependent –Threshold, adaptation, and saturation features Nonlinear mechanical properties of the annular ligament Highly complicated cochlear input impedance: over-simplified

Network model simulation example : Simulink version of AHAAH TM input pressure Stapes displacement Acoustic wave Nonlinear model block

Network model simulation example : Human cochlear model in AHAAH BM characteristic freq.-time BM location-time d ST (t) d ST (ω)d BM (x,ω)d BM (x,t) FFT IFFT H C (x,ω) Network model (Simulink) Cochlear model (Matlab) Cochlear model (Matlab)

Transfer function method : An alternative to network model Free from modeling artifacts Wider valid frequency range Responses only up to stapes Linear concept Inner Ear External Ear Source Middle Ear Replaced by measured TFs

Transfer function method : Stapes response calculation FFT TF from free-field sound pressure to stapes volume velocity Stapes response in frequency domain Stapes response in time domain IFFT

Available transfer functions Human H FT H UP ChinchillaGuinea pigCat Shaw, E. A. G. (1974)** Mehrgardt & Mellert (1977) Bismarck & Pfeiffer (1967)* Murphy & Davis (1998) Sinyor & Laszlo (1973)** Wiener et al. (1965)** Ruggero et al. (1990) Guinan & Peake (1967) Nuttall (1974) Kringlebotn & Gundersen (1985) * Azimuth: 0° ** Phase data not available

Currently available data : Magnitude of H FT Chinchilla: Bismarck & Pfeiffer (1967) Chinchilla: Murphy & Davis (1998) Cat: Wiener et al. (1965) Guinea pig: Sinyor & Laszlo (1973) Human: Shaw (1974) Human: Mehrgardt & Mellert (1977)

Currently available data : Phase of H FT Chinchilla: Murphy & Davis (1998) Human: Mehrgardt & Mellert (1977)

Currently available data : Magnitude of H UP Chinchilla: Ruggero et al. (1990) Cat: Guinan & Peake (1967) Guinea pig: Nuttall (1974) Human: Kringlebotn & Gundersen (1985); Rosowski (1994) Human: Kringlebotn & Gundersen (1985); Rosowski (1991)

Currently available data : Phase of H UP Chinchilla: Ruggero et al. (1990) Cat: Guinan & Peake (1967) Guinea pig: Nuttall (1974) Human: Kringlebotn & Gundersen (1985); Rosowski (1994) Human: Kringlebotn & Gundersen (1985); Rosowski (1991)

Transfer function reconstruction Target –Spectral range up to 25 kHz –Species: human and chinchilla (due to insufficient data for guinea pig and cat) Within measured frequency range –Approximated by spline function passing through the measured data points Out of measured frequency range –Curve-fitting of measured data subset –Extrapolation of the fitted curve

Transfer function reconstruction example: H FT Human: Mehrgardt & Mellert (1977) Chinchilla: Murphy & Davis (1998) Gauss2 (0.96, f<1 kHz) Poly1 (0.91, f> 8 kHz) Sin4 (0.97, f<1 kHz) Fourier6 (0.92, f>15 kHz)

Transfer function reconstruction example: H UP Human: Kringlebotn & Gundersen (1985); Rosowski (1994) Chinchilla: Ruggero et al. (1990) Poly7 (0.99, f<1 kHz) Exp2 (0.99, f>1 kHz) Poly5 (0.99, f<1 kHz) Power2 (0.84, f>1 kHz)

Reconstructed transfer function Chinchilla Human

TF model simulation example :Stapes response to complex noise Human Chinchilla Complex (G-44)

TF model simulation example :Stapes response to impulsive noise Human Chinchilla Test impulse ±20 μm

Velocity-based metric Displacement-based metric Application to NIHL study : Auditory response metric Network / TF model EARM curve NIHL study EARM curve NIHL study

Questions?