PSY 215 Lecture 10 Topic: Hearing Chapter 7, pages 189-197 Corrections: NTC 09-1, page 3, the Superior Colliculus is in the midbrain (Mesencephalon). Announcements: Movie next Monday: Case of the frozen addict Monday the 28 th : We will be going over the mechanical sense and reviewing Lecture Notes: Outline Auditory Stimulus Auditory system (ear) Pitch perception Auditory system (ear to cortex) Auditory Localization Hearing loss 1
Auditory Stimulus Frequency: How many cycles that can fit into one second. The higher the frequency, the greater the amount of waves in one second, which tends to sound higher in pitch. Not a direct relationship. -Frequency (#waves/sec) similar to pitch (range: 15-20,000 Hz). As we age we lose upper range of hearing. Amplitude: Distance from peak to bottom of wave. The higher the amplitude the louder it sounds. Not a direct relationship. -amplitude similar to loudness range: 10-90 db. - 100-140 db can cause damage. -25% of kids today have some damage already due to how loud music is listened too. (from lecture) *Speech: combination of multiple frequencies 2
Ear: Outer: Pinna: part you can see, directs sound waves into ear Auditory Canal Boundary between Outer and Middle Ear Tympanic membrane/ear drum: pulled tight to vibrate when a pressure wave hits it Middle Ear Osicles: 3 smallest bones in body: hammer, anvil, & stirrup -hammer touches tympanic membrane, membrane causes osicles to vibrate -Amplifies the vibrations (from lecture) 3
*Boundary between middle and Inner Ear Oval window: stirrup causes this to vibrate Inner Ear Cochlea: Where transduction (When you convert 1 type of energy into another type) occurs, looks like a snail: coiled -Basilar membrane travels length of cochlea -Hair cells(has cilia) on top of basilar membrane bending cause signal -Boney structure filled with fluid -Has 3 Semicircular Canals: maintain balance -3 separate compartments: Scala vestibule, Scala tympani, Scala media -Tectorial membrane: jelly like material on top of hair cells, makes hair cells bend when vibrations pass through basilar membrane. Transduction: 1. Bending of hair cells 2. This causes K+ channels to open & K+ rushes into the cell 3. The influx of K+ depolarizes the hair cells. 4. The depolarization causes Voltage dependent Ca++ channels to open, Ca goes into cell, 5. The calcium entering causes Neurotransmitters to be released, 1 AP at most *Fluid around hair cells has a lot of K+, not much in cell. -signal leaves cochlea via the Auditory Nerve Pitch Perception (Happens in inner ear) Theories of Pitch perception: 1. Place theory: It is the place/ location on the basilar membrane where the peak of the vibration occurs that is signaling the different pitches. Basilar membrane stiffer and narrower where it touches oval window (higher frequencies), Apex is wider & more flexible (lower frequencies). -Better for high frequencies 2. Frequency theory: Frequency of firing of Action Potentials = frequency of Sound, works up to 500-1000 Hz -anything higher, AP can t fire fast enough because of refractory period. 4
Auditory System (ear-cortex) Signal goes from the Cochlear to the Cochlear Nucleus (2 of them, each receives info from single ear) Then to the Superior Olive Nucleus(bilateral, split equally) Then go to the inferior colliculus (info passed to both sides) Then Middle Geniculate Nucleus (in Thalamus), Then goes to Primary auditory Cortex(A1), A2 surrounds A1 -Have a Tonotopic map in A1, (tones are mapped) where low frequency and high frequency stimulate different parts of A1 Auditory Localization *Sound coming from side travels different distances to reach each ear (phase difference: different part of wave) *Azimuth: sound source coming from left or right *Sound coming from straight ahead has no phase lag *Phase difference works best with low frequency sounds *High frequency has problems *Superior Olive codes for phase differences 5
Hearing Loss 1. Conduction Deafness -problems with bones of the middle ear, eardrum -caused by tumors, infection, disease -Usually corrected by surgery or hearing aids 2. Nerve Deafness -damage to cochlea, hair cells, auditory nerve -caused by genetics, disease -potential treatment with cochlear implants For More Information: http://www.noiseaddicts.com/2009/03/can-you-hear-this-hearing-test/ This link takes you to a site where you can test yourself to see how high of a frequency you can hear. This video describes transduction and goes over the anatomy of the ear while discussing it. It does go into a little more depth then we covered in class, but it s quite helpful. http://www.youtube.com/watch?v=petrigtenoc Real Life Example: As we age, we naturally lose some of ability to hear high frequency sounds. This generally doesn t interfere with normal conversation until much later. For our generation, it may start occurring earlier due how loud we listen to music. Noise induced hearing loss may also cause a loss of ability to hear lower frequency sounds as well as higher frequency. 6