PSY 214 Lecture 16 Topic: Sound, Auditory System & Speech Perception Chapter 11, pages 270-289 Corrections: None Announcements: CD is available outside Dr Achtman s office if you would like to see demonstrations of audio function. Lecture Notes: OUTLINE Inner Ear How do nerve fibers signal tone frequency? 1. INNER EAR Three major parts of the inner ear 1. Outer ear 2. Middle ear 3. Inner ear cochlea and auditory nerve Written by: Sue Allen-Mazzatti, sallenm9@naz.mail.edu Page 1 of 5
Function - Where transduction happens The stapes rocks against the oval window. The vibration of the oval window triggers waves in the fluid of the cochlea. This causes the basilar membrane to vibrate and the tectorial membrane moves up and down in a shearing fashion that causes the cilia to bend and outer hair cells to move. This bending action changes into an electrical signal that leaves the cochlea through the auditory nerve. Cochlea & organ of corti Transduction happens in the inner ear in the hair cells. How do nerve fibers signal tone frequency? It is coded in the basilar membrane in 2 different ways. There are 2 theories and both are true. Neural signals for frequency 1. Place Theory Which/Where nerve fibers fire Where on the basilar membrane are the hair cells firing? Hair cells fire action potentials and signal the frequency of the tone. 2. Frequency Theory - How nerve fibers fire - the pattern - how quickly they are firing signals the frequency of the tone Written by: Sue Allen-Mazzatti, sallenm9@naz.mail.edu Page 2 of 5
How inner ear helps us hear different tones low and high high frequency - signal quickly, higher pitched, toward the base low frequency - signal slowly, lower pitched, toward the apex Bekesy - researcher that experimented with cochlea Which neurons fire? Place theory (Bekesy) Tonotopic map in cochlea Basilar membrane response to complex tones Written by: Sue Allen-Mazzatti, sallenm9@naz.mail.edu Page 3 of 5
2. HEARING LOSS Types 1. Conductive hearing loss - Sound never reaches the receptor cells, not passing on the signal - Usually can be helped 2. Sensorineural hearing loss - Problem with hair cells which are responsible for transduction or - Damage to the auditory nerve which carries the signal or - Damage to brain - Usually permanent - Most common type of hearing loss is presbycusis (the cumulative effect of aging) - Can also be caused by exposure to loud noise 3. COCHLEAR IMPLANTS - Electrode goes through the middle ear and into the cochlea where it gives direct input to the cells that make up the auditory nerve - Controversial - they don t help everybody - are they necessary? Written by: Sue Allen-Mazzatti, sallenm9@naz.mail.edu Page 4 of 5
For more information: The CD provided in some cases with the book is a rich source of demonstrations for this topic. NIOSH (National Institute for Occupational Safely and Health) Hearing Loss Simulator http://www.cdc.gov/niosh/mining/products/product47.htm This website gives a good overview of different aspects of sound with hearing and loudness concepts including attack and decay and harmonic content http://hyperphysics.phy-astr.gsu.edu/hbase/sound/timbre.html Real-life example: This is an important concept for everyday living and one thing to really keep in mind is that hearing loss is cumulative. This has not become an issue yet but as a young person I attended many concerts and recall waking up with my ears still ringing so I know that is working against me. I also use a hair dryer almost every day and have started to wear ear plugs when I use it because I don t want to lose my hearing! Written by: Sue Allen-Mazzatti, sallenm9@naz.mail.edu Page 5 of 5