Can you ear me?? Hearing & the ear

1. Can you ear me??Hearing & the ear A brief discussion CHAPTER 7 – Measured Tones

2. Let’s Design an ear

3. The Path Where did the ear come from???

4. We probably came from green slime …

5. An Important Question WHY do we need to hear? WHY did ears evolve in most (not all) species??

6. Physical Design Requirements • Must hang on the head in a place where it usually won’t be tightly covered. • iPods etc. excluded • It should be very sexy. • It can’t be too heavy. • It should be sensitive. • It should be able to sense direction of the sound’s origin. (Why?) • It should be able to distinguish a range of frequencies. (Why?)

7. Component Definition • A sound “collector” to channel as much of the sound as possible to the actual collector.

9. More Component Definitions • A sensor that collects the sound and converts it into something that moves. • A membrane at the end of the collector would work because it will move in response to the pressure changes in front of it as long as the pressure at the back of the membrane remains the same. • A converter to adjust the amplitude to the desired strength of the signal. Transmits forward into the process. • A frequency sensor/discriminator • An “electrical signal” producer • A “wire” or connection to the brain. • A Brain • A program in the brain’s computer (cortex) that converts the signal into something perceived as sound.

10. Walla… an ear! The Ear

11. It can be sexy …. as in:

12. Put together Balance Brain collection wire sensor adjustment freq. separate

13. Some Interesting FactsFrom Robert Jourdain, “Music, the Brain and Ecstasy”, Morrow (1997) • In the beginning … • Paramecia patrol the ooze of early life • A spot detects levels of light (not yet an eye) • She chemically senses her environment (not yet a nose) • She can sense collisions with objects (but not a sense of touch) • During first 80 % of the 3.5 billion years that evolution proceeded • Flatworms, mites and rotifers (whatever they may be) • eyes, sense of touch, chemical receptors (taste?) • No sound at all. • 200,000,000 years later, the ear began to emerge.

14. Hearing has been around for a LONG time:

15. The ugly outer ear: pinna 1 in 4 have a bump here Catches, reflects snd. canal to inner ear Deflects sound in Pinna amplifies (resonance) the higher frequencies – consonants

16. 100 1.0 Frequency Amplification – PinnaC. D. Geisler – “From Synapse to Sound” – Oxford Press (1998) Ear canal resonance Later! Minimal Amplification

17. The Ear Drum Pinna Ear Drum Ear Canal Eustachian Tume

18. Amplify Some More? The Inner Ear Atm. Pressure

19. The real deal … Cochlea

20. Where are we? • We have collected the sound and applies a bit or resonance via the pinna folds. • We sent the sound down the ear canal. • We have moved the eardrum with the sound. • We connected the eardrum to the cochlea. What the heck is a cochlea? It is NOT a dirty word!

21. Oh where, oh where, has my cochlea gone? Location Balance Frequency & Transmission to the brain. AS COILED IN THE EAR

22. The Cochlea

23. Rock and Unroll the Cochlea High response Low

24. The Basilar Membrane high frequency low frequency cross section f high frequency (Stiff) low frequency What would a wave traveling down the basilar membrane do to the shape of the membrane??

25. The almost real deal RESONANCE

26. Cross-sectioned Incompressible compressible

27. Hair Cells Outer Inner

28. Fire One Brain Many fire at the same time

29. The Signal to the Brain • Neurons can spontaneously fire at a rate of a few tens of Hz. • It is the CHANGE in rate that IS the neural message. • The collector nerves are often in contact with more than one hair cell. • If a cell fires, there is a time before it can fire again.

30. The “message”

31. This may not work …

32. Things that can go wrong with this process ….. • Long exposure to loud (later) music can literally fracture the hair cells. • Those cells no longer respond to sound. • This can lead to deafness. • There is a “Society for Deaf Musicians” that is a result of this. Modern bands usually take precautions. • Very loud noise can shatter an eardrum • May recover, may not. • Nerves can die. Bad news.

33. The ear gets old along with the body. • Age 40 • Ear is only 10% of what it was when you were younger. • Age 80 • You have lost most of your high frequency hearing so the “quality” of what you hear changes significantly. • Consonants sound in the high frequency region which explains why older people have difficulties hearing (without any pathology).

34. The Death Slide • You lose ½ Hz. per day in high frequency hearing. • 20,000 Hz.  10,000 Hz.  7000 Hz.  Dead • Most music is in the <4000 Hz. range so it is ok to put a stereo in your casket. • As you age, you lose sensitivity to the higher harmonics of some instruments.

35. Localization - Animals Move to find direction

36. Slight delay due to different distances. Pinna “bouncing” leads to different quality that the brain can sense Can’t do this for long wavelengths Localization Humans

37. The Ear • Distance Effect • Phase • Amplitude • Pinna Effect • Large l • Amplitude and Phase differences are minimal • Localization is difficult. • Very Low frequencies, hearing doesn’t work too well (next slide) so • DANGER!!!

38. Hearing Normal Response loudness (soon) Interesting Tidbit. • Loudness Recruitment • Cells lose sensitivity to low or moderate sound intensities but respond normally at high intensities. • Beethoven had this problem!

39. Loudness Scale – A Preview Log of a number (for our purposes) is the number of zeros that it contains when written as an integer. Let I0 be the lowest intensity (defined next time … use your imagination for now) of sound that you can hear. db or decibel definition:

40. Hearing Range