Unit 4: Sensation & Perception

1. Unit 4: Sensation & Perception Module 14: Hearing

2. Hearing (Audition) • Audition:the sense or act of hearing. • Sound waves result from mechanical vibration of molecules from a sound source (e.g. instrument or voice).

3. Hearing (Audition) • Amplitude: The height of the sound wave the determines the loudness. • The bigger the amplitude, the louder the sound.

4. Hearing (Audition) • Frequency: the number of complete wavelengths that pass a point in a given amount of time.

5. Hearing (Audition) • Pitch: the highness or lowness of a sound. Higher Frequency Shorter Wavelength Higher Pitch = = Lower Frequency Longer Wavelength Lower Pitch = =

7. Hearing (Audition) • We are most sensitive to frequencies that correspond to the range of human voices.

8. Hearing (Audition) • Decibels – measuring unit for sound energy. Prolonged exposure above 85 decibels produces hearing loss.

10. The Ear • Outer Ear: visible part of the ear; channels the sound waves through the auditory canal to the eardrum. • Middle Ear: the chamber between the eardrum and cochlea. • Inner Ear: innermost part of the ear, containing the cochlea, semicircular canals, and vestibular sacs.

11. Middle Ear • Hammer, anvil, and stirrup: a piston in the middle ear made up of containing three tiny bones that concentrate the vibrations of the eardrum on the cochlea’s oval window (membrane). • Eardrum: a tight membrane that vibrates with the waves.

12. The Inner Ear • Cochlea: a coiled, bony fluid-filled tube in the inner ear through which sound waves trigger nerve impulses. (Looks like a snail!) • The vibrations on the cochlea’s oval window cause vibrations that move the fluid in the tube.

13. The Inner Ear • Basilar membrane: lined with hair cells that are bent by the vibrations from sounds and triggers impulses in the adjacent nerve fibers that converge to form the auditory nerve. • The neural messages travel via the thalamus to the temporal lobe’s auditory cortex – and we hear!

14. The Ear • Semicircular canals: three fluid-filled bony channels in the inner ear. They provide information about orientation to the brain to help maintain balance. • Auditory nerve: axons of neurons in the cochlea converge transmitting sound messages through the medulla, pons, and thalamus to the auditory cortex of the temporal lobe.

15. Human Ear Video

16. The Ear • Loud sounds damage the hair cells which accounts for most hearing loss. • We detect sound by the number of hair cells activated.

17. The Ear

18. Determining Pitch • How can you discriminate small differences in sound frequency or pitch? • Place theory: we hear different pitches because different sound waves trigger activity at different places along the cochlea’s basilar membrane. • Works best with high pitched sounds.

19. Determining Pitch • Waves that peak near the close end are perceived as high-pitched. • Waves that peak near the far end are interpreted as low-pitched.

20. Determining Pitch • Frequency theory: we sense pitch by the basilar membrane vibrating at the same rate as the sound. • Frequency theory explains how you hear low-pitched tones. • Place theory explains how we sense high pitches and frequency theory explains how we sense low pitches.

21. Locating Sounds • Sound localization: the process by which you determine the location of a sound. • With ears on both sides of our head, you can locate a sound source. • The side closest to the source of the sound hears it louder.

23. Locating Sounds • Using parallel processing, your brain processes both intensity and timing differences to determine where the sound is. • It is hardest to locate a sound directly in front, behind, above, or below you because the sound hits both ears at the same time.

24. Hearing Loss • Conduction hearing loss: loss of hearing that results when the eardrum is punctured or any of the tiny bones in middle ear lose their ability to vibrate. A hearing aid may restore hearing. • Nerve (sensorineural) deafness: loss of hearing that results from damage to the cochlea, hair cells, or auditory neurons. Cochlear implants may restore some hearing.