Chapter 6

Other Sensory Systems

Sound and the Ear

• Humans hear by detecting sound waves• Sound waves vary in amplitude and frequency• Hearing alerts us to useful information

Kolb & Whishaw, An Introduction to Brain and Behavior, Fourth Edition - Chapter 10

Sound Waves: Stimulus for Audition

• Sound Wave• Periodic compression of air

Kolb & Whishaw, An Introduction to Brain and Behavior, Fourth Edition - Chapter 10

Physical Properties of Sound WavesProperties of Sound-Wave Energy1) Frequency • Number of cycles that a wave completes in a given

amount of time• Measured in Hertz:

• cycles per second• Related to pitch

• Low pitch: low frequency• High pitch: high frequency• Different frequencies

Physical Properties of Sound Waves

• Most adult humans hear between 20 -20,000Hz• Children hear higher frequencies

• Ability decreases with age and exposure to noise

Kolb & Whishaw, An Introduction to Brain and Behavior, Fourth Edition - Chapter 10

Kolb & Whishaw, An Introduction to Brain and Behavior, Fourth Edition - Chapter 10

Kolb & Whishaw, An Introduction to Brain and Behavior, Fourth Edition - Chapter 10

Physical Properties of Sound Waves2) Amplitude • The intensity/strength of sound wave

• measured in decibels (dB)

• Relates to loudness• Soft sound: low amplitude• Loud sound: high amplitude

• Example of decibels

Kolb & Whishaw, An Introduction to Brain and Behavior, Fourth Edition - Chapter 10

Kolb & Whishaw, An Introduction to Brain and Behavior, Fourth Edition - Chapter 10

Structure of the Ear

Outer Ear• Pinna

• External structure • funnel sound waves into the ear canal • Helps us locate sounds

• External Ear Canal• Amplifies and directs sound waves to eardrum (tympanic

membrane)

Kolb & Whishaw, An Introduction to Brain and Behavior, Fourth Edition - Chapter 10

Kolb & Whishaw, An Introduction to Brain and Behavior, Fourth Edition - Chapter 10

Processing Sound Waves

Middle EarBegins with eardrum

• Air-filled chamber that includes the ossicles• Bones in the middle ear:

• Hammer (malleus)• Anvil (incus)• Stirrup (stapes)

• Connects the eardrum to the oval window of the cochlea• Transmits sounds to cochlea

The Ossicles

Kolb & Whishaw, An Introduction to Brain and Behavior, Fourth Edition - Chapter 10

Kolb & Whishaw, An Introduction to Brain and Behavior, Fourth Edition - Chapter 10

Kolb & Whishaw, An Introduction to Brain and Behavior, Fourth Edition - Chapter 10

Processing Sound WavesInner Ear• Cochlea

• Fluid-filled inner ear structure • receptor cells for hearing (hair cells)• auditory signals converted to action potentials

Processing Sound Waves

• Basilar membrane• Located in cochlea• Stimulated by staples and creates a wave in the fluid filling the cochlea• Contains about 25,000 fibers

• Fibers vibrate to specific frequencies and stimulate corresponding nerve cells

• We perceive pitch

Kolb & Whishaw, An Introduction to Brain and Behavior, Fourth Edition - Chapter 10

Basilar Membrane

Kolb & Whishaw, An Introduction to Brain and Behavior, Fourth Edition - Chapter 10

Kolb & Whishaw, An Introduction to Brain and Behavior, Fourth Edition - Chapter 10

Processing Sound WavesInner Ear• Hair Cells

• Sensory neurons embedded on basilar membrane• When moved by waves in the cochlear fluid outer hair cells

stimulate inner hair cells,• Inner hair cells are auditory receptor cells

• Visual of the Hearing Process

Electron Micrographs of the Hair Cells of Humans

Kolb & Whishaw, An Introduction to Brain and Behavior, Fourth Edition - Chapter 10

Detecting Loudness and Location• Loudness

• Greater amplitude of sound waves causes greater firing rate of cells in the cochlea.

• Ex: Youtube video• This is Spinal Tap

Kolb & Whishaw, An Introduction to Brain and Behavior, Fourth Edition - Chapter 10

Detecting Location• Location

• Cells receive info from both ears and calculate difference in arrival times.

• Superior olivary complex• More difficult to compare inputs when sounds move

toward the middle of the head.• the difference in arrival times is smaller.

• When we detect no difference in arrival times, we infer the sound is coming from directly in front of us or behind us.

Kolb & Whishaw, An Introduction to Brain and Behavior, Fourth Edition - Chapter 10

Kolb & Whishaw, An Introduction to Brain and Behavior, Fourth Edition - Chapter 10

Detecting Location

• Source of sound is detected by loudness on the left or right side of the head

• High frequency sound waves do not easily bend, the head acts as an obstacle.

• higher frequency sound waves on one side of the head are louder than on the other.

Kolb & Whishaw, An Introduction to Brain and Behavior, Fourth Edition - Chapter 10

Theories of Pitch Perception

• Place theory• basilar membrane has hair cells sensitive to only one specific frequency of

sound wave

• Frequency theory• basilar membrane vibrates in synchrony with sound • causes auditory nerve axons to produce action potentials at the same

frequency

Pitch Perception• Current pitch theory combines both

• Low frequency sounds best explained by the frequency theory

• High frequency sounds best explained by place theory

Variations in Sensitivity to Pitch

• “Amusia”• the impaired detection of frequency changes (tone deafness)• Video clip (4 minutes)• thicker than average auditory cortex in right hemisphere but fewer

connections from auditory cortex to frontal cortex

Variations in Sensitivity to Pitch

• Absolute pitch• (“perfect pitch”) ability to hear a note and identify it• Genetic predisposition • The main determinant is early and extensive musical training• More common among people who speak tonal languages such as Vietnamese

and Mandarin Chinese

The Auditory Cortex

• Primary auditory cortex (area A1) • Located in the superior temporal cortex

• Area A1 is important for auditory imagery• Hearing in the absence of vision

• Requires experience to develop properly• Axons leading from the auditory cortex are less developed in people deaf

since birth • Damage to A1 does not necessarily cause deafness unless damage extends to the

subcortical areas

• Auditory Illusions

Can You Trust Your Ears?

Hearing Loss

• Two categories of hearing impairment• Conductive or middle ear deafness• Nerve deafness or inner ear deafness• Examples of hearing loss

Tinnitus

• Frequent or constant ringing in the ears• Experienced by many people with nerve deafness• Examples

• Sometimes occurs after damage to the cochlea

Vestibular Sensation

• The vestibular sense: system that detects the position and movement of the head

• Directs movements of the eye and helps to maintain balance

• The vestibular organ is in the ear and is adjacent to the cochlea

The Vestibular Organ

• Made up of• two otolith organs

• calcium carbonate particles that push against different hair cells and excite them when the head tilts

• three semicircular canals• filled with a jellylike substance and hair cells that are activated when the head moves

• Action potentials travel to the brain stem and cerebellum

Structures for Vestibular Sensation

Somatosensation

• Refers to the sensation of the body and its movements• Includes tickle sensation

• Can’t tickle self• our brain expects the stimulation and generates a weaker

response

The Somatosensory Cortex

• Aspects of body sensations remain separate all the way to the cortex• somatosensory thalamus sends impulses to different areas of the

somatosensory cortex• Where is this cortex located?

• Damage to the somatosensory cortex can result in the impairment of body perceptions

• Phantom limb phenomenon (13 min.)

Somatosensory Cortex

6.3 The Chemical Senses

• The first sensory system of the earliest animals was a chemical sensitivity

• enables a small animal to find food, avoid danger, locate mates

Taste

• Taste has one simple function – to tell us whether to swallow something or spit it out

• We like sweet tastes even in infancy• We dislike bitter and sour, but will accept in small amounts• We vary in our like of salty flavors

Taste and Smell• Taste buds

• receptors on the tongue

• Perception of flavor is combo of taste and smell• Taste and smell axons converge in the endopiriform cortex

Papillae and Taste Buds

• Papillae • structures on tongue that contain the taste buds• may contain up to ten or more taste buds

• Each taste bud contains approximately 50 receptors• Most taste buds are located along the outside edge of the tongue in

humans

Taste Buds

Taste Perception – Taste Receptors

• Sweet, sour, salty and bitter, glutamate• Some substances that can modify tastes

• Miracle berries – miraculin

Mechanisms of Taste Receptors

• The saltiness receptor permits sodium ions to cross the membrane• Results in an action potential

• Sour receptors detect the presence of acids • Sweetness, bitterness, and umami receptors activate a G protein

• Transmits information from outside to inside the cell

Bitter Receptors

• Bitter tastes are associated with toxic substances• About 25 types of bitter receptors

• sensitive to a wide range of chemicals with varying degrees of toxicity

• sensitive to range of harmful substances, but not highly sensitive to any single one