1. Getting an Earful Winter 2017 Peter Woodruff
Brainwaves

2. How can one sense movement of a fluid?

3. How to sense movement of a fluid?
Hair versus hair cells

4. How to sense movement of a fluid?

5. How to sense movement of a fluid?

6. Sensitive Sharks

7. Sensitive Sharks

9. Linear Acceleration Coding by Maculae
Tilt causes shearing forces on some hair cells which depolarize as others hyperpolarize.

10. Rotational Coding by Semicircular Canals
As one of the canals moves in an arc with the head, the internal fluid moves in the opposite direction, causing the cupula and stereocilia to bend. Brain interprets relative activation of all six canals to give precise indication of head movement.

12. Sound attributes
Pitch determined by frequency: vibrations per second, in hertz, Hz
Loudness determined by amplitude: height of sound wave a sound intensity, as in decibels, dB
Timbre: determined by
“complexity and shape” of sound wave
Tone: simple sound

13. Sound attributes
Pitch determined by frequency: vibrations per second, in hertz, Hz
Loudness determined by amplitude: height of sound wave a sound intensity, as in decibels, dB
Timbre: determined by
“complexity and shape” of sound wave
Tone: simple sound

14. Fun Facts about Hair Cells
Hair cells can detect deflections of 0.3 nanometers (< size of atom!)
Threshold of hearing: 1 billionth of atmospheric pressure
Can convert stimulation into nerve impulse in 10 microseconds
Threshold of pain at 130 dB is 1013 times more intense than threshold of hearing, at 0 dB!

15. Tasks of the auditory system
Resolve intensity (loudness) and frequency (pitch, timbre) components of sound stimuli
Localize sound sources in space

16. Human Hearing

17. How would YOU code?
Frequency?
Loudness (Amplitude)?

18. Cochlear animation

19. With every sound wave, the cell shortens and then elongates.
When the stereocilia are bent in response to a sound wave, an electromotile response occurs.
With every sound wave, the cell shortens and then elongates.
This pushes against the tectoral membrane, selectively amplifying the vibration of the basilar membrane.

20. Frequency segregation in the cochlea – an initial sort of sound frequencies

21. Sound Frequency -> Position -> specific neurons
Pitch to Position: tones of 20,000 Hz and 20 Hz activate different neurons, leading directly into the auditory nerve.

22. The spatial layout of frequencies in the cochlea is repeated in other auditory areas in the brain. This is called tonotopic organization.

23. Tonotopic Mapping through Auditory Pathway

24. http://www. adsx. co. za/wp-content/uploads/2013/11/sound_spectrum2

25. Minimum sound pressure
Perceived for each frequency
audible
inaudible

26. Human Hearing Ranges

27. Sound Spectrua of Various Instruments

28. Sound Spectra of Various Animals

29. Coding of Auditory Information
In Cochlear Nerve:
Firing rates of neurons
Number of active neurons
Together correlate with perceived loudness
Relative location (tonotopic)
Preserved throughout auditory pathway
Converts frequency (tone) to position
Not whole story
The main pathways and nuclei are shown for both cochleae.

30. Max response rate of neuron: ~1000 firings/second
For sounds of higher frequency, coding carried by many neurons together, here neurons a - e

31. Harmony
Why do tones whose frequencies are in ratios of small numbers sound good together? See Pythagoras

32. Harmony
Why do tones whose frequencies are in ratios of small numbers sound good together? See Pythagoras
Consonance
A Feeling for Harmony:

33. Processing Auditory Information
Arrival of auditory message in brain:
Processed
as reflex: jump if loud sound
In auditory cortex
In other brain regions

34. Auditory Cortex

35. Humans use at least two strategies for sound localization
Strategy 1. for frequencies below 3 kHz: time of arrival differences can be detected. The threshold of detection is as small as 10 microsec. This translates to a sensitivity of about 1o of arc.

36. Spatial Localization also Distance

37. Processing in the brainstem: sound localization by coincidence cells in the olivary nuclei
Q. How can time delays as small as 10 microsec be measured by neurons that have to operate in the msec time domain?
A. The medial superior olive (MSO) receives bilateral inputs from the anteroventral cochlear nuclei. These inputs enter a chain of coincidence cells.

38. Time is measured by conduction time in the network

39. Strategy for higher frequencies
Strategy 2. for higher frequencies, intensity differences between the two ears must be used. At these frequencies, the sound wavelength is so short that the waves cannot bend around the head, so the head creates a sound shadow that enhances the effect.

40. Sound localization
The sound arriving at the ear that is furthest from the sound source is delayed (time difference) and lower in amplitude (intensity difference). Both cues used.
“Wiring” in brain consistent with this function.
The timing difference never exceeds .8 msec

41. Detection of intensity differences in the brainstem
Whichever ear receives the loudest stimulus can also shut off activity in the ascending pathway from the less stimulated ear
The players here are the lateral superior olive (LSO) and the medial superior nucleus of the trapezoidal body (MNTB).

42. Hearing Loss

45. Causes:
ear malformation,
abnormal bone growth,
fluid accumulation due to infection,
poor drainage
hole in eardrum

47. Treatments: varies with circumstances surgery, antibiotics,
hearing aid

48. Causes:
usually cumulative, slowly
often loud noise exposure
some medications & health conditions

49. Treatments:
hearing aids
possibly cochlear implant

51. Mixed Hearing Loss

52. https://s-media-cache-ak0. pinimg

53. Electrodes placed on the surface of the cortex can be used to stimulate the brain of a conscious patient or record its activity.

54. Corrected Somatosensory Homuculus