The Auditory System June 3 , 2014

1. The Auditory SystemJune 3, 2014

2. Sensory Processing • Similar to vision • Receptors  thalamus  1o cortex  2o cortex  association • Parallel processing, crosstalk • Multimodal

3. Auditory Information

4. Why Hearing? Interact w/ environment Ex. for ours/other species? • Identify, locate Similarities to visual arrangement

5. Do You Hear what I Hear? Perception based on interpretation of sensory info • Sound waves Variability w/in species

6. Sound Vibration of an object  distorts molecules in particular medium Creates sound waves of energy at particular frequency Humans detect freq. of 20-20000 Hz (cycles/second) • Other species higher or lower

8. Sound Greater vibration, greater displaced energy • Decreases w/ distance from source Patterns of vibrations interpreted as sound

9. Sound Sensory receptors in inner ear Sensory vibrations  components for perception Amplitude – loudness Frequency – pitch (high/low) Timbre – complexity

11. The Ear Collects, directs info to CNS Outer ear (pinna)  middle ear inner ear Inner ear contains sensory receptors Comparable to the eye/retina

12. The Middle Ear Eardrum and small bones Sound waves vibrate tympanic membrane (eardrum) - durable, tight membrane Eardrum vibration moves small bones

13. The Middle Ear Malleus (hammer), incus (anvil), stapes (stirrup) Malleus attached to eardrum, stapes to inner ear Amplifies sound wave Pressure in middle ear equalized Ruptured eardrum, congestion

14. The Inner Ear Inner ear - cochlea & auditory nerve Vibration of stapes -- oval window Transfer vibration to cochlea

15. The Inner Ear Cochlea – coiled organ, fluid & auditory receptors Organ of Corti– membrane containing receptors Sound wave disrupts fluid, triggers receptors Wave dissipated at end of cochlea - round window

16. The Inner Ear Basilar membrane on Organ of Corti – hair cells (receptors) Hair cells rest against stiff tectorial membrane Disruption from sound wave (fluid) bends hairs Basilar moves in relation to tectorial

18. The Inner Ear Hairs sensitive to particular frequency Opening of ion channels Activation of hair cell – action potential Auditory nerve

19. The Inner Ear Sound “coded” by which hairs are displaced Where wave travels on membrane Diff frequencies, different distances Thousands of cells – distinguish slight differences Combinationsof hair cells

21. Thresholds Large range of frequencies, higher freq. lost w/ age Upper limit audible to under 25 “Mosquito Tone” Decibel scale – intensity of sound

22. Decibel Levels http://www.physicsclassroom.com/class/sound/u11l2b.cfm

23. Processing Sound at the Cortex

24. From Ear to Cortex Auditory nerve - inner ear to brainstem Subcortical auditory pathways Pathway to primary auditory cortex

25. Subcortical Pathways Superior olives in hindbrain • Crossover To inferior colliculi • Sound localization Copies to superior colliculi • Eye mvmnt to sounds

26. Auditory Cortex To perceive, travel to auditory cortex • Via thalamus Inferior colliculi medial geniculate thalamus  auditory cortex • Primary auditory cortex in primates – temporal lobe

28. Auditory Cortex • Tonotopic (neighboring cortex/adjacent hair cells) • Auditory discrimination less understood than visual • Why might this be?

29. Auditory Cortex • Can respond to imagined sounds • Does not respond as well to pure tones (unnatural) • Feedback from cortex  cochlea • Receptor sensitivity • Dampen further response

30. Binaural Processing Copies of each ear to both hemispheres • Combined at level of brainstem Very accurate sound localization • Louder in ear closest to sound • Timing of arrival of soundwaves(which ear first)

31. Secondary Processing Greater specificity and complexity • Recognizable or important sounds • Anterior association cortex (prefrontal cortex) • Identify sounds (what is it) • Posterior association cortex (posterior parietal) • Localization (where is it)

33. Secondary Processing • Superior temporal (combine w/ visual) • Motion of sounds (and objects) • Where is it going? • Perception of music, musical training • Importance of experience

34. Auditory Dysfunction

35. Disorders of the Auditory System Conduction loss – bones, loss of sound amplification Sensorineuralloss - damage to hair cells • Specific frequencies • Sound discrimination • Cochlear implants bypass the cochlea

36. Disorders of the Auditory System Acoustic neuroma – input to brainstem • Diseases, toxins during pregnancy Tinnitus – ringing in the ears • Cortical or cochlear damage

37. Disorders of the Auditory System Auditory Cortex – sensory deficits • Localization, discrimination • Rare in humans Amusia – impaired change detection (freq/pitch) • Recognition of music, sequences of sounds • Abnormal auditory, frontal connections

38. Species Differences

39. Use of Auditory Information How do other species view the world? Relation to CNS organization, evolutionary development, survival… • Uses of sound in different species? • Mating • Warnings • Navigation

40. Use of Auditory Information • Owls -- sound location • Nocturnal hunting • Bats -- echolocation • Reflection of ultrasonic sound waves off objects • Approximate speed/distance from delay, change in frequency • Navigation, hunting

41. Use of Auditory Information • Many species - higher frequencies (ultrasound) • Humans – 20 000Hz • Dogs – 45 000 Hz • Cats – 85 000 Hz • Bats – 120 000 Hz • Dolphins – 200 000 Hz • Elephants – infrasound (5Hz)