2. Hearing and Deafness 2. Ear as a frequency analyzer Chris Darwin

3. Frequency: 100-Hz Sine Wave Time (s) 00.05 1.0 0 Waveform Amplitude against time Spectrum Amplitude against frequency 1 100 Hz amp frequency

4. Frequency: 500-Hz Sine Wave Waveform Amplitude against time Spectrum Amplitude against frequency 1 500 amp frequency 1 100 amp frequency500 Time (s) 0 0.05 1.0 0

5. Amplitude: 500-Hz Sine Wave Spectrum Amplitude against frequency 1 500 amp frequency 1 100 amp frequency500 Time (s) 0 0.05 0 Time (s) 0 0.05 0

6. Phase: 500-Hz Sine Wave The amplitude spectrum does not show phase 1 500 amp frequency 1 100 amp frequency500 sine cosine

7. Phase Locking of Inner Hair Cells Auditory nerve connected to inner hair cell tends to fire at the same phase of the stimulating waveform.

8. Phase-locking

9. adding sine waves 1 amp frequency 1 amp frequency 1 amp frequency 1 amp frequency Spectrum of Sum

10. 100-Hz fundamental Complex Wave Waveform Amplitude against time Spectrum Amplitude against frequency Time (s) 00.05 -1.7 5.0 0 1 500 amp frequency 1 100 amp frequency500

11. Adding nine sine waves Frequency Time Frequency Time Spectrogram5s

12. The linear vs log scales Linear equal distances represent equal differences 0 100 200300 400 500 100 200 400 800 1600 3200 -1 0 1 2 3 4 Log equal distances represent equal ratios e.g. Piano keyboard frequencies Octave = doubling of frequency basilar membrane has log repn of frequency

13. deciBel (dB) scale Sound A is x dB more intense than sound B when: x = 10*log10 (energy of A / energy of B) or x = 20*log10 (amp of A / amp of B) So if A is 20 watts and B is 10 watts x = 10*log10 (20/10) = 10*0.3 = 3dB You can usually just hear a difference of 1dB (jnd)

14. Bandpass filtering (narrow) Time (s) 00.05 -1.7 5.0 0 1 500 amp frequency 1 100 amp frequency500 Time (s) 0 0.05 0 1 50 0 amp frequency 1 100 amp frequency500

15. Bandpass filtering (wide) Time (s) 00.05 -1.7 5.0 0 1 500 amp frequency 1 100 amp frequency500 1 amp frequency 1 100 amp frequency500

16. Beats 1 amp frequency 1 100 amp frequency500 Repetition rate is the difference in frequency between the two sine-wave components 1/3 second505 - 500 = 5 Hz

17. Beats 1 amp frequency 1 100 amp frequency500 Repetition rate is the difference in frequency between the two sine-wave components 1/100th second500 - 400 = 100 Hz 400

18. Reponse of basilar membrane to sine waves Each point on the membrane acts like bandpass filter tuned to a different frequency: high freq at base, low at apex. Each point vibrates at frequency of pure tone (-> phase locking)

19. Excitation patterns (envelope of excitation) Basilar membrane excitation pattern is like a spectrum

20. Auditory filter bandwidth (ERB)

21. Excitation pattern of complex tone on bm

22. Measurement of auditory bandwidth with band-limited noise Broadband Noise 1000 Hz 2000 Hz frequency 250 Hz Amadeus

23. A gardening analogy

25. Auditory bandwidth Noise bandwidth Detection mechanism Tone Noise

26. Wider auditory filter

27. Psychophysical tuning curves Bandwidth

28. Auditory tuning curves Healthy ear Inner hair-cell damage

29. Outer-hair cell damage

30. Human auditory bandwidth At 1 kHz the bandwidth is about 130 Hz; at 5 kHz the bandwidth is about 650 Hz. BW = freq / 8 roughly

31. Normal auditory non-linearities Normal loudness growth (follows Weber’s Law, which is logarithmic, not linear) Combination tones Two-tone suppression Oto-acoustic emissions

32. Combinations Tones (Tartini tones) 1 amp frequency 1 1000 amp frequency 1200 800

33. Two-tone suppression

34. Conductive vs Sensori-neural deafness Becomes linear, so No combination tones Or two-tone suppression Mostly a combination of OHC and IHC damage

35. Symptoms of SNHL Raised thresholds: helped by amplification Wider bandwidths: no help possible Recruitment (restricted dynamic range): partly helped by automatic gain controls in modern digital aids Often accompanied by tinnitus

36. Normal vs Impaired Dynamic Range