Organization. The physics of sound. Measuring sound intensity. Fourier analysis. (c) S-C. Liu, Inst of Neuroinformatics 1

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1 Audition: Biological and Silicon cochleas; Localization Shih-Chii Liu Institute of Neuroinformatics University of Zurich/ETH Zurich Organization Thursday: Biological and silicon cochleas; lab with spike-based VLSI cochlea Friday: Localization; lab expts on localization and tone discrimination GANGLION CELLS COCHLEA The physics of sound Measuring sound intensity We are sensitive to an enormous range of intensities, so a logarithmic scale works well intensity in db=2 x log (P1/P2) where P2 is 2 icropascal remember log(1)=, log(1)=1, log(1)=2 (and also, log(.1)=-1) system neuroscience, fall 29 system neuroscience, fall 29 Fourier analysis Any complex waveform can be represented as the sum of a series of sine waves of different frequencies and amplitudes system neuroscience, fall 29 (Neuroscience. 2nd edition. Purves D, Augustine GJ, Fitzpatrick D, et al., editors. Sunderland (MA): Sinauer Associates; 21) (c) S-C. Liu, Inst of Neuroinformatics 1

2 (Neuroscience. 2nd edition. Purves D, Augustine GJ, Fitzpatrick D, et al., editors. Sunderland (MA): Sinauer Associates; 21) (Neuroscience. 2nd edition. Purves D, Augustine GJ, Fitzpatrick D, et al., editors. Sunderland (MA): Sinauer Associates; 21) The Inner Hair Cells IHC response Flexion 3 Scala media + 8 mv High K + Response (mv) % Full Response 25 mv mv High K a.c. component 1 d.c. component 2 Scala tympani To spiral ganglion cells Displacement ( m) 12.5 mv ms (Kelly, 1991) (Pickles, 1988) (Hudspeth and Corey, 1977) (Palmer and Russell, 1986) Auditory Nerve Fiber responses ANF Response to Speech SPL (sound pressure level) = 2 log (pm/pref) db Pref = 2 upa (rms) Response from 275 fibres from an anesthetized cat to first 5 ms of syllable da (Miller and Sachs, 1993, Shamma, 1985) (c) S-C. Liu, Inst of Neuroinformatics 2

3 Cochlea BW The Outer Hair Cell 12 db 33 db When depolarised, the outer hair cell shortens; when hyperpolarised, it elongates. The change in length is up to 4% of the cell body. Can vibrate up to about 25kHz. When pushed upwards, the stereocilia deflect in the direction of depolarising. The OHC further pulls-up the basilar membrane, enhancing its motion. a) and b) adopted from Fragnière (1998) BM gain (db) Nonlinear Cochlea db 7 1 db 2 db 6 3 db 5 4 db 4 5 db 3 6 db 2 7 db 1 8 db Frequency (khz) (Ruggero, 1992) Switch to Silicon Cochleas Event-based silicon cochlea Introduction to cochlea and history of silicon cochlea designs and architectures. Circuit and architecture of the binaural spikebased AEREAR2 chip. Features of the AEREAR2 board. Possible applications. 199 Spike-based cochleas (includes hair cell and ganglion cell model) Furth, Kumar, Andreou Lazzaro Liu, van Schaik Wen, Boahen Abdalla, Horiuchi AEREAR Lyon, Mead Wyatts Liu, Andreou Sarpeshkar van Schaik, Vittoz Fragniere, Vittoz 25 Sarpeshkar Hasler Hamilton, van Schaik Katsiamis, Drakakis, Lyon Analog cochleas (c) S-C. Liu, Inst of Neuroinformatics 3

4 BM Responses Chosen BM model on AEREAR2 Relative Amplitude mm 28mm24mm 2mm 17mm13mm from stapes 2 1 High f Low f Frequency (Hz) (von Békésy, 196) Gain (db) Frequency (Hz) (van Schaik, 1997) AEREAR2 cochlea AEREAR2 architecture Basilar membrane LF Inner hair cells (a) Spiral ganglion cells HF (b) (c) AEREAR2 characterization AEREAR2 board Best center frequencies Response to a chirp (3 Hz to 3kHz) Rate is 17keps The fox jumped over the lazy dog (c) S-C. Liu, Inst of Neuroinformatics 4

5 Possible applications Auditory tasks like speaker verification and speech recognition. Front-end for exploring ideas about neuralinspired speech processing. Binaural information used for source localization. Spike-based multi-modal motor system. Auditory Scene Analysis Knowing the where Knowing the what Spatial Auditory Cues Two basic types of head-centric direction cues binaural cues Interaural time difference cues (ITD) Interaural intensity difference cues (IID) spectral cues Interaural Time Differences (ITD) ITD increase with directional deviation from the median plane. It is about 6-7 s for a source located directly to one side. Humans are sensitive to as little as 1 s ITD. For pure tones, phase based ITD is ambiguous. At low to moderate frequencies, phase difference can be detected. At high frequencies, one can use the ITD in the signal envelope. (Grothe, 21) Interaural Intensity Differences (IID) With lateral sources, head shadow reduces intensity at opposite ear Effect of head shadow most pronounced for high frequencies. IID cues are most effective above about 2kHz. IID of less than 1dB are detectable. At 4kHz, a source located at 9 gives about 3 db IID (Matlin and Foley, 1993) system neuroscience, fall 29 Spectral Cues Pinnae or outer ears and head shadow each ear and create frequency dependent attenuation of sounds that depend on direction of source. Pinnae are relatively small, spectral cues are effective predominately at higher frequencies (i.e. above 6kHz). system neuroscience, fall 29 (c) S-C. Liu, Inst of Neuroinformatics 5

6 Localization model (Knudsen, 22) Jeffress model (Grothe, 23) Birds (Grothe, 23) (NL neurons) (Carr, Konishi, 199) Localization Pathway in Mammals ILD ITD Midbrain Cochlear Nucleus Superior Olivary Complex (Young, 23) (c) S-C. Liu, Inst of Neuroinformatics 6

7 Calyx of Held (Grothe, 23) The End (Grothe, 23) (c) S-C. Liu, Inst of Neuroinformatics 7