Rob van der Willigen

1. Auditory Perception Rob van der Willigen http://www.mbfys.ru.nl/~robvdw/DGCN22/Anatomy_Physiology/DGCN22_2011_Anatomy_Physiology_Part1.ppt

2. General Outline P4 P4: Auditory Perception - Cochlear Mechanotransduction - Neuroanatomical Organization

3. Sensory Coding and Transduction Mammalian Auditory Pathway Cochlear Mechanotransduction

4. Sensory Coding and Transduction 6 critical steps

6. Physical Dimensions of Sound Summary Amplitude - height of a cycle - relates to loudness Wavelength (λ) - distance between peaks Phase (Φ) - relative position of the peaks Frequency (f ) - cycles per second - relates to pitch Recapitulation previous lectures

7. The Adequate Stimulus to Hearing Summary Sound is a longitudinal pressure wave: a disturbance travelling through a medium (air/water) Recapitulation previous lectures http://www.kettering.edu/~drussell/demos.html

8. The Adequate Stimulus to Hearing Type of waves Transverse waves Longitudinal waves http://www.physics.usyd.edu.au/~gfl/Lecture/GeneralRelativity2005/

9. The Adequate Stimulus to Hearing Summary Compression Duration Decompression Particles do NOT travel, only the disturbance Particles oscillate back and forth about their equilibrium positions Compression Distance from source Recapitulation previous lectures http://www.glenbrook.k12.il.us/GBSSCI/PHYS/Class/sound/u11l2a.html

10. Physical Dimensions of Sound Amplitude (A) High http://www.physpharm.med.uwo.ca/courses/sensesweb/ LOUD sound Large change in amplitude Pressure Amplitude Low SOFT sound Small change in amplitude Time or Distance from the source In air the disturbances travels with the 343 m/s, the speed of sound Amplitude is a measure of pressure

11. Physical Dimensions of Sound Frequency (f) ; Period (T) ; Wavelength (λ) LOW pitched sound Lowfrequency Long wavelength Pressure changes are slow HIGH pitched sound Highfrequency Short wavelength Pressure changes are fast One cycle High Pressure Low Time or Distance from source T is the Period (duration of one cycle) λ is wavelength (length of one cycle) f is frequency (speed [m/s] / λ[m]) or (1/T[s])

12. The Mathematics of Waves Phase is a relative shift in time or space

13. The Mathematics of Waves Fourier’s Theorem Jean Baptiste Fourier (1768-1830) Any complex periodic wave can be “synthesized” by adding its harmonics (“pure tones”) together with the proper amplitudes and phases. “Fourier analysis” Time domain Frequency domain “Fourier synthesis”

14. The Mathematics of Waves Fourier’s Theorem Linear Superimposition of Sinusoids to build complex waveforms If periodic repeating

15. The Mathematics of Waves Fourier synthesis “Saw tooth wave”

16. The Mathematics of Waves Fourier synthesis “Square wave”

17. The Mathematics of Waves Fourier synthesis “Pulse train wave”

18. The Mathematics of Waves Fourier Analysis Transfer from time to frequency domain Time domain Frequency domain Superposition

19. The Mathematics of Waves Superposition Waves can occupy the same part of a medium at the same time without interacting. Waves don’t collide like particles. Two waves (with the same amplitude, frequency, and wavelength) are traveling in opposite directions. The summed wave is no longer a traveling wave because the position and time dependence have been separated.

20. The Mathematics of Waves Superposition Waves can occupy the same part of a medium at the same time without interacting. Waves don’t collide like particles. Waves in-phase (Φ=0) interfere constructively giving twice the amplitude of the individual waves. When the two waves have opposite-phase (Φ=0.5 cycle), they interfere destructively and cancel each other out.

21. The Mathematics of Waves Superposition Most sounds are the sum of many waves (pure tones) of different Frequencies, Phases and Amplitudes. At the point of overlap the net amplitude is the sum of all the separate wave amplitudes. Summing of wave amplitudes leads to interference. Through Fourier analysis we can know the sound’s amplitude spectrum (frequency content).

23. Sensory Coding and Transduction

24. Sensory Coding and Transduction A Sensor Called Ear

25. Sensory Coding and Transduction Peripheral Auditory System Outer Ear: - Extents up to Eardrum - Visible part is called Pinna or Auricle - Movable in non-human primates - Sound Collection - Sound Transformation Gives clues for sound localization

26. Sensory Coding and Transduction Peripheral Auditory System +60 +40 +20 Elevation (deg) 0 -20 -40 Frequency The Pinna creates Sound source position dependent spectral clues. “EAR PRINT”

27. Amplitude (dB) Sensory Coding and Transduction Peripheral Auditory System In humans mid-frequencies also exhibit a prominent notch that varies in frequency with changes in sound source elevation (6 – 11 kHz) Elevation +60 +40 +20 Elevation (deg) 0 -20 -40 Frequency kHz

28. Sensory Coding and Transduction Peripheral Auditory System Barn Owls have Asymmetric Ears and Silent Flight. One ear points upwards, the other downwards.

29. Sensory Coding and Transduction Peripheral Auditory System Middle Ear: (Conductive hearing loss) - Mechanical transduction (Acoustic Coupling) - Perfect design for impedance matching Fluid in inner ear is much harder to vibrate than air - Stapedius muscle: damps loud sounds Three bones (Ossicles) A small pressure on a large area (ear drum) produces a large pressure on a small area (oval window)

30. Sensory Coding and Transduction Peripheral Auditory System Inner Ear: The Cochlea is the auditory portion of the ear Cochlea is derived from the Greek word kokhlias "snail or screw" in reference to its spiraled shape, 2 ¾ turns, ~ 3.2 cm length (Humans)

31. Sensory Coding and Transduction Peripheral Auditory System The cochlea’s core component is the Organ of Corti, the sensory organ of hearing Cochlear deficits cause Sensorineural hearing loss Its receptors (the hair cells) provide the sense of hearing

32. Sensory Coding and Transduction Peripheral Auditory System The Organ of Corti mediates mechanotransduction: The cochlea is filled with a watery liquid, which moves in response to the vibrations coming from the middle ear via the oval window. As the fluid moves, thousands of hair cells are set in motion, and convert that motion to electrical signals that are communicated via neurotransmitters to many thousands of nerve cells.

33. Sensory Coding and Transduction Hair Cells The Organ of Corti mediates mechanotransduction: (A) Scanning electron micrograph of hair bundle (bullfrog sacculus; David P. Corey's Lab.). This top view shows the stereocilia arranged in order of increasing height. (B) Model for mechanotransduction. Deflection of a hair cell's bundle causes the stereocilia to bend and the tip links between them to tighten. (C) Ion channels attached to intracellular elastic elements (ankyrin repeats) open in response to tension on the rather inextensible tip link.

34. Sensory Coding of Sound Cochlear anatomy

35. Sensory Coding of Sound Cochlear anatomy (straightened)

36. Sensory Coding of Sound Tonotopic coding Pressure waves distort basilar membrane on the way to the round window of tympanic duct: - Location of maximum distortion varies with frequency of sound - Frequency information translates into information about position along basilar membrane

37. Sensory Coding of Sound Travelling Wave Theory Periodic stimulation of the Basilar membrane matches frequency of sound Travelling wave theory von Bekesy: Waves move down basilar membrane stimulation increases, peaks, and quickly tapers Location of peak depends on frequency of the sound, lower frequencies being further away

38. Sensory Coding of Sound Cochlear Fourier Analysis High f Periodic stimulation of the Basilar membrane matches frequency of sound Med f Location of the peak depends on frequency of the sound, lower frequencies being further away Low f BASE APEX Position along the basilar membrane

39. Sensory Coding of Sound Place Theory Travelling wave theory von Bekesy: Waves move down basilar membrane Location of the peak depends on frequency of the sound, lower frequencies being further away Location of the peak is determined by the stiffness of the membrane

40. Sensory Coding of Sound Sensory Input is Tonotopic Thick & taut near base Thin & floppy at apex TONOTOPIC PLACE MAP LOGARITHMIC: 20 Hz -> 200 Hz 2kH -> 20 kHz each occupies 1/3 of the basilar membrane

41. Sensory Coding of Sound Sensory input is tonotopic

42. Sensory Coding of Sound Sensory input is tonotopic

44. Sensory Coding of Sound Processing of Sounds: Anatomy

45. Sensory Coding of Sound Sensory Input is Non-linear The COCHLEA: Decomposes sounds into its frequency components Represents sound TONOTOPICALLY Has direct relation to the sounds spectral content Has NO linear relationship to sound pressure Has NO direct relationship to the sound’s location in the outside world

46. Cochlear nonlinearity Active processing of sound Effects of an “active”cochlea Iso-level curves show sharp tuning at low sound levels, broader tuning at high levels. Response is strongly compressive around the so-called characteristic frequency (CF). Requires functioning outer hair cells. The response of the BM at location most sensitive for ~ 9 KHz tone (CF). The level of the tone varied from 3 to 80 dB SPL (iso-intensity contours).

47. Cochlear nonlinearity Active processing of sound CF= 9 kHz OUTPUT Response in dB ~4.5kHz INPUT level (dB SPL) Frequency [kHz] The response of the BM at location most sensitive for ~ 9 KHz tone (CF). The level of the tone varied from 3 to 80 dB SPL (iso-intensity contours). BM input-output function for a tone at CF (~9 kHz, solid line) and a tone one octave below (~4.5 kHz) taken from the iso-intensity contour plot.

48. Cochlear nonlinearity No nonlinearity post mortem Rugero et al. (1997) 1) Reduced gain: Higher thresholds in quiet; loss of audibility as measured with pure-tone audiogram 2) Loss of nonlinearity: Reduced dynamic range; quiet sounds lost but loud sounds just as loud: Loudness Recruitment Basilar-membrane intensity-velocity coding functions for a chinchilla using a tone at the 10 kHz GAIN equals DAmplitude of motion divided by D Amplitude of stimulus pressure

49. The Problem of Hearing Tonotopie blijft in het auditief systeem tot en met de auditieve hersenschors behouden. “De samenstelling van een geluid uit afzonderlijke tonen is te vergelijken met de manier waarop wit licht in afzonderlijke kleuren uiteenvalt wanneer het door een prisma gaat .” John A.J. van Opstal (Al kijkend hoort men, 2006; p. 8)‏

50. The Problem of Hearing Mapping can be an important clue to the function of an area. If neurons are arrayed according to the value of a particular parameter, then that property might be critical in the processing performed by that area. Neurons within a brain area may be organized topographically (or in a map), meaning that neurons that are next to each other represent stimuli with similar properties. Neurons do not need to be arranged topographically along the dimensions of the reference frame that they map, even if its neurons do not form a map of that space.