1. Sensory Systems: Auditory

2. What do we hear? Sound is a compression wave: When speaker is stationary, the air is uniformly dense Speaker Air Molecules

3. What do we hear? Sound is a compression wave: Speaker When the speaker moves, it compresses the air in front of it.

4. What do we hear? Sound is a compression wave: The speaker moves back leaving an area with less air behind - called rarefaction Compression Rarefaction

5. What do we hear? Sound is a compression wave: Speaker The speaker moves forward again starting the next wave Compression Rarefaction

6. What do we hear? Sound is a compression wave - it only “looks” like a wave if we plot air pressure against time time -> Air Pressure Period - amount of time for one cycle Frequency = number of cycles per second (1/Period)

7. Properties of a Sound Wave 1. Amplitude: difference in air pressure between compression and rarefaction (Sound Pressure Level)

8. Properties of a Sound Wave 1. Amplitude: difference in air pressure between compression and rarefaction (Sound Pressure Level) –What is the perception that goes along with the sensation of sound amplitude?

9. Properties of a Sound Wave 1. Amplitude: difference in air pressure between compression and rarefaction (Sound Pressure Level) –What is the perception that goes along with the sensation of sound amplitude? LOUDNESS

10. Properties of a Sound Wave 2. Frequency: how many regions of compression (or rarefaction) pass by a given point per second (expressed in Hertz)

11. Properties of a Sound Wave 2. Frequency: how many regions of compression (or rarefaction) pass by a given point per second (expressed in Hertz) –What is the perception that goes along with the sensation of frequency?

12. Properties of a Sound Wave 2. Frequency: how many regions of compression (or rarefaction) pass by a given point per second (expressed in Hertz) –What is the perception that goes along with the sensation of frequency? PITCH

13. Properties of a Sound Wave Pitch is complicated by the fact that sound waves can be complex –Made up of more than one frequency

14. Properties of a Sound Wave A 1 second, 1 Hz sound wave:

15. Properties of a Sound Wave A 1 second, 2 Hz sound wave:

16. Properties of a Sound Wave A 1 second, 3 Hz sound wave:

17. Properties of a Sound Wave What would happen if two or more sound waves were happening at the same time?

18. Properties of a Sound Wave Sounds superpose (they add together)

19. Properties of a Sound Wave Sounds superpose (they add together)

20. Properties of a Sound Wave Another way to think of this is that any complex wave can be decomposed into its component frequencies

21. Properties of a Sound Wave A spectrogram shows us a picture of this decomposition

22. Sensing Vibrations

23. Outer ear transmits and modifies sound (critical for sound localization)

24. Sensing Vibrations Middle ear turns compression waves into mechanical motion oval window stapes

25. Sensing Vibrations Middle ear turns compression waves into mechanical motion Ear Drum Oval window

26. Sensing Vibrations Middle ear turns compression waves into mechanical motion Ear Drum Oval window Compression Wave

27. Sensing Vibrations The cochlea, in the inner ear, is a curled up tube filled with fluid. Auditory Nerve to Brain

28. Sensing Vibrations Inside the cochlea is the basilar membrane Movement of the oval window causes ripples on the basilar membrane

29. Sensing Vibrations Basilar membrane measures the amplitude and frequency of sound waves –amplitude (loudness) –frequency (pitch)

30. Sensing Vibrations Basilar membrane measures the amplitude and frequency of sound waves –amplitude (loudness) - magnitude of displacement of the basilar membrane –frequency (pitch)

31. Sensing Vibrations Basilar membrane measures the amplitude and frequency of sound waves –amplitude (loudness) - magnitude of displacement of the basilar membrane –frequency (pitch) - frequency and location of displacements of the basilar membrane

32. Sensing Vibrations Basilar membrane measures the amplitude and frequency of sound waves –frequency (pitch) - frequency and location of displacements of the basilar membrane

33. Sensing Vibrations Bundles of “hair cells” are embedded in basilar membrane

34. Sensing Vibrations When hair cells sway back and forth, they let charges inside This flow of charges is converted to action potentials and sent along the auditory pathway

35. The Auditory Pathway The auditory pathway is complex and involves several “stations” along the way to the auditory cortex in the brain Lots of processing must be done in real- time on auditory signals!

36. How Can You Localize Sound? Ponder this: –Imagine digging two trenches in the sand beside a lake so that water can flow into them. Now imagine hanging a piece of cloth in the water in each trench. Your job is to determine the number and location and type of every fish, duck, person, boat, etc. simply by examining the motion of the cloth. That’s what your auditory system does! - Al Bregman