The Auditory Process

Stimulus  Distal Stimulus- in our environment produces a proximal stimulus  Proximal Stimulus- form of sound waves reaching the ear  Sound waves are vibrations of molecules & can be made by vibrating objects or air pushing past a chamber or by a sudden release of burst of air.

Wavelengths vs. Frequency  Wavelengths (frequency) is measured in cycles per second or hertz  Frequency is another name for pitch  People can only hear a portion of the sounds out in nature, ranging from 20Hz to 20, 000 Hz  Amplitude equals loudness and is measured in decibels  Pitch equals timbre  Most sounds are a mixture of frequencies  The purest sound is one that has only one frequency vibration

Three sections of the ear

Vibrations and the ear parts  Can be divided into three sections  External Ear: Depends on the vibration of air molecules  Middle Ear: Depends on vibration of movable bones  Inner ear: depends on waves in a fluid which are converted into a stream of neural signals

External Ear  Consists of the Pinna, the sound collecting cone.  Auditory canal which funnels the message along to the eardrum

Middle Ear  Eardrum: membrane that vibrates in response to the sound  Ossicles: made up of the hammer, anvil and stirrup  Vibrations of the eardrum are transmitted inward by a mechanical chain made up of the 3 smallest bones in your body-the ossicles which serve to amplify tiny changes in air pressure

Inner Ear  Made of semicircular canals, which help you keep your balance  When your head moves around and moves the tiny hairs that line each canal, it triggers the nerve messages that are then sent to your brain.  Cochlea:Fluid filled, coiled tunnel contains receptors for hearing.

Cochlea  Within the cochlea is the basilar membrane which holds the auditory receptors  These receptors are called hair cells because they LOOK like little hairs  Waves on the fluid of the inner ear stimulate the hair cells and convert the message into neural impulses that are sent to the brain  The signal is routed to the temporal lobe

One of the theories  Place Theory (Herman von Helmholtz)  The perception of pitch is determined by the vibrations of different places (hair cells) along the basilar membrane. (like a guitar or harp)  Different sets of hair cells are vibrated by different sound frequencies  The brain the detects the frequency according to which area along the membrane is most active

Theory # 2  Frequency Theory (Rutherford, 1886-)  Perception of pitch corresponds to the rate at which the entire basilar membrane vibrate (like a drum)  The brain detects tone by the rate at which the auditory nerve fiber fire

Reconciling Place & Frequency Theories  Both are valid  Hair cells are not independent, they vibrate together (Frequency Theory)usually fire a  The pattern of vibration travels as a wave along the membrane  Wave peaks DEPEND on the frequency of the sound wave (Place Theory). Neurons usually fire at about 1000 impulses per second.  Volley Principle: groups of auditory nerve fibers fire neural impulses in rapid succession, creating volleys of impulses  # of impulses (see notes)

Taste- Gustatory System  Physical Stimuli- chemical substances  Receptor cells and saliva  Life Span  4 primary taste: sweet, sour, bitter and salty  Most respond to more than one taste  Complex patterns of neural activity

Cultural Influence vs Genetic  Taste preferences are largely learned  Density of taste buds  Supertasters -4X  Evolutionary reason  Ability to identify flavors declines w/out odor cues

Olfactory System  Olfactory cilia  Life span (30-60)  Synapse in the olfactory bulbs  Only sense not routed through the thalamus  No primary odors  Distinguish 10,000 odors but can’t name  Female better

Sense of Touch