HEARING

SOUND• Sound is vibrations of molecules• Amplitude, wavelength, and purity affect qualities of loudness,

pitch, and timbre

HUMAN HEARING CAPACITIES• Frequency (wavelength): measured in cycles per second, hertz

(Hz)• Higher frequency creates higher pitch• Humans hear btwn 20 Hz and 20,000 Hz

HUMAN HEARING CAPACITIES• Amplitude affects loudness• Measured in decibels (dB)• Perceived sound doubles every 10 dB• Loudness requires an interaction of frequency and amplitude

HUMAN HEARING CAPACITIES• Purest sound has only a single frequency of vibration• Most sounds are mixed

SENSORY PROCESSING IN THE EAR• External ear depends on vibrations of molecules• Consists of the pinna• Pinna collects sound and funnels it down the auditory canal to

the eardrum

SENSORY PROCESSING IN THE EAR• Middle ear consists of the hammer, anvil, and stirrup• Hammer, anvil, and stirrup are called ossicles• Ossicles amplify changes in air pressure

SENSORY PROCESSING IN THE EAR• Inner ear consists of the cochlea: fluid filled, coiled tunnel that

contains receptors for hearing• Sound enters through the oval window• Ear’s neural tissue lies in the cochlea; it sits on the basilar

membrane: runs the length of the cochlea, holds auditory receptors

• Auditory receptors are called hair cells• Waves in fluids in the inner ear stimulate the hair cells, which

convert the motion into neural impulses• Impulses travel to the thalamus, then to the auditory cortex

AUDITORY PERCEPTION: PLACE THEORY• Holds that perception of pitch corresponds to the vibration of

different portions, or places, along the basilar membrane• Frequency is detected by specific regions of the basilar

membrane

AUDITORY PERCEPTION: FREQUENCY THEORY• Holds that perception of pitch corresponds to the rate, or

frequency, at which the entire basilar membrane vibrates• Ex: 3000 Hz would cause the membrane to vibrate 3000 times

per second

RECONCILING PLACE AND FREQUENCY THEORIES• Both are valid but both have flaws• Volley Principle: holds that groups of auditory nerve fibers fire

neural impulses in rapid succession, creating volleys of impulses

• Improves frequency theory

PERCEIVING SOURCES OF SOUND• Auditory localization: locating the source of a sound• 2 cues: intensity and timing of arrival at each ear

OUR CHEMICAL SENSES: TASTE AND SMELL

TASTE: THE GUSTATORY SYSTEM• Physical stimuli for taste are based on chemical substances

that are soluble• Taste buds are clusters of taste cells• Taste buds absorb chemical dissolved in saliva, which trigger

neural impulses

PRIMARY TASTES• Sweet, sour, bitter, and salty• Some preferences are innate, some are learned• Sensitivity to certain tastes depend on density of taste buds• Women more likely to be supertasters than men

SMELL: THE OLFACTORY SYSTEM• Olfactory cilia are tiny hairlike structures located in the upper

portion of the nasal passages• These receptors have axons that synapse directly with cells in

the olfactory bulb at the base of the brain• Only sense not routed through the thalamus

SMELL• Humans can distinguish about 10,000 different odors• Identifying odors can be difficult• Females tend to be more accurate with identifying odor

SENSE OF TOUCH

FEELING PRESSURE• Skin has receptive fields where CNS cells are most sensitive• Nerves route through the spinal cord to the brainstem• Then project through the thalamus and onto the

somatosensory cortex in the parietal lobe• Some cells in the somatosensory cortex respond to specific

features of touch

FEELING HOT AND COLD• Skin has warm and cold receptor nerves• When warmth is applied the warm receptors fire rapidly and

cold receptors cease and vice versa for when cold is applied

FEELING PAIN• Pain travels to the brain through 2 pathways• Fast pathway registers localized pain---sharp pain---depend on

myelinated neurons called A-delta fibers• Slow pathway conveys longer-lasting, aching, or burning

pain---depends on unmyelinated neurons called C fibers

PAIN PERCEPTION• Very subjective• Pain can be blocked• Gate-control theory: holds that incoming pain sensations must

pass through a “gate” in the spinal cord that can be closed, thus blocking ascending pain signals

• Studies suggest that the release of endorphins creates the analgesic effect

• Discovery of a descending neural pathway that originates from the periaqueductal gray (PAG) in the midbrain; endorphins initiate activity in the PAG

OTHER SENSES

KINESTHETIC SYSTEM• Monitors the positions of the various parts of the body• Some receptors are in the joints---indicate bending• Others reside in the muscles---register tautness, or extension

VESTIBULAR SYSTEM• Responds to gravity and keeps you informed of your body’s

location in space• Provides sense of balance (equilibrium)• Located in the inner ear• Semicircular canals make up largest part