Brain and Behaviour - Chapter 6: Hearing, Mechanical Senses, and Chemical Senses

Comprehensive vocabulary flashcards covering auditory processing, mechanical senses, somatosensation, pain mechanisms, gustation, olfaction, and synesthesia from Chapter 6 of Biological Psychology.

What do the sense organs in humans allow them do to?

Their sense organs enable them to survive and reproduce

The “thrifty” definition of evolution

When evolution solves one problem, it modifies that solution for other problems instead of starting from scratch

Sound wave

Periodic compressions of air, water, or other media, varying in amplitude and frequency

Amplitude

The intensity of a sound wave.

e.g. Sounds of greater amplitude seem louder

Frequency

The number of compressions per second in a sound wave, measured in hertz ($\text{Hz}$) and directly related to the perceived pitch.

Frequency (con’t)

It’s measured in hertz $\text{Hz}$ (cycles per second) and directly related to the perceived pitch.

Pitch

The aspect of auditory perception related to the frequency of a sound

e.g. Sounds higher in frequency are higher in pitch

The range at which humans can hear

About 15 to 20 Hz up to almost 20,000 Hz.

The range at which humans can hear (con’t)

Children hear higher frequencies, because the ability to perceive high frequencies decreases with age and exposure to loud noises

The rule about hearing capabilities

• Larger animals like elephants hear best at lower frequencies

• Small animals like mice hear higher frequencies, above what humans hear

Timbre

The tone quality or tone complexity of a sound.

e.g. Different musical instruments playing the same note sound different, as do people singing the same note

Timbre (con’t)

An instrument playing a note at any frequency also produces notes at multiples of that frequency (the harmonics of the principal note)

Prosody

The conveyance of emotional information through tone of voice, pitch, loudness, and timbre.

e.g. The way you say “that was interesting” could indicate approval (it really was interesting)

Pinna

The structure of flesh and cartilage attached to each side of the head in the outer ear that alters the reflection of sound waves into the middle ear and assists with sound localization.

Pinna (con’t)

All pinnas shaped differently

e.g. Rabbits have large movable pinnae that enable them to localize sound sources even more precisely

Tympanic membrane/ eardrum

The eardrum located in the middle ear, which vibrates at the same rate as the sound waves that strike it

The three bones the tympanic membrane/ eardrum connects to

1. Hammer/ malleus

2. Anvil/ incus

3. Stirrup/ stapes

Oval window

A membrane in the inner ear that receives transformed, amplified vibrations from the middle ear bones and transmits waves through the viscous fluid of the inner ear.

Cochlea

A snail-shaped structure within the inner ear containing three fluid-filled tunnels where auditory transduction occurs.

Hair cells

Auditory receptors positioned between the basilar membrane in the cochlea and excite cells of the auditory nerve by opening ion channels when displaced by fluid vibrations.

Frequency theory

A theory of pitch perception proposing that the basilar membrane vibrates in synchrony with sound waves, prompting auditory nerve axons to generate action potentials at that same frequency.

e.g. A sound at 50 Hz would cause 50 action potentials per second in the auditory nerve

Volley principle

The auditory mechanism whereby volleys of impulses across groups of auditory nerve fibers signal sound frequencies up to $4000$ per second.

Place theory

The second pitch perception theory stating that specific areas along the basilar membrane vibrate at distinct frequencies

e.g.

• Varying from stiff at the base where the stirrup meets the cochlea (sensitive to high frequencies)

• Floppy at the apex, or other end of the cochlea (sensitive to low frequencies).

Primary auditory cortex (area A1)

An area in the superior temporal cortex in which cells respond best to tones of a particular frequency

Primary auditory cortex (area A1) [con’t]

The cerebral destination in the superior temporal cortex for most auditory input, which is organized tonotopically and is essential for auditory imagery and processing complex sounds.

Primary auditory cortex (area A1) [III]

It becomes active when people view silent videos that suggest sound (imagined sounds)

e.g. Someone playing a piano or a glass vase shattering on the ground

The auditory system’s “what” pathway

Combines input from the auditory system and the visual system and it connects to systems for memory and decision-making

The auditory system’s “where/ how” pathway

Localizes sound sources and guides actions toward or away from them

Planum temporale

An area in the temporal cortex (strongly connected to area MT) that processes the experience you have of a sound source moving from one place to another

i.e. Helps one combine visual and auditory information to locate something accurately

The effect of damage to the planum temporale

Patients with damage in the planum temporale become motion deaf.

i.e. They hear sounds, but they do not detect that a sound source is moving

Tonotopic map

The systematic anatomical organization of cells in the primary auditory cortex, in which neighbouring neurons respond preferentially to specific, graded tone frequencies.

The perception of harmonics

People experience a tone with harmonics as “richer” than one without them

Damage to the auditory cortex

People with damage to it could indicate whether a letter array was a real word or not, except for words relating to sounds

i.e. They might look at something like “thunder” and indicate, “No, that is not a word”

Sound shadow

A sound localization cue resulting from an obstruction (such as the listener's head) that reduces sound intensity at the far ear; primarily used to localize high-frequency sounds.

Sound shadow (con’t)

The sound is louder in the closer ear as it’s reached first

Phase difference

A sound localization cue based on the discrepancy in the arrival phase of a sound wave between both ears, used by humans to localize low-frequency sounds.

Phase difference (con’t)

How much out of phase depends on the frequency of the sound, the size of the head, and the direction of the sound

Phase difference (III)

It can provide information that is useful for localizing sounds with frequencies up to about 1500 Hz in humans

Learning and localizing frequencies

Learning is required, because as a human head grows, the distance between ears increases, and humans need to recalibrate how they localize sounds

Amusia (tone deafness)

A condition characterized by the impaired detection of frequency changes occurring in approximately 4% of people

Amusia (tone deafness) [con’t]

It’s associated with fewer axonal connections between the auditory cortex and frontal cortex.

Absolute pitch (pitch perfect)

The ability to hear a musical note and identify it accurately without a reference pitch

Absolute pitch (pitch perfect) [con’t]

Is largely determined by early, extensive musical training, and is more prevalent among speakers of tonal languages.

Conductive deafness/ middle-ear difference

Hearing impairment caused by the failure of the middle ear bones to transmit sound waves to the cochlea

Treatment of conductive deafness/ middle-ear difference

It can be treated with surgery or amplifying hearing aids.

Nerve deafness/ inner-ear deafness

Hearing loss resulting from damage to the cochlea, hair cells, or auditory nerve, which can impair specific frequency ranges

Causes of nerve deafness/ inner-ear deafness

It may be inherited, caused by disease, or induced by loud noise exposure.

Tinnitus

A persistent or frequent ringing sensation in the ears that frequently accompanies nerve deafness or cochlear damage due to aberrant brain reorganization.

Tinnitus statistics

It is common in people who have lost their hearing but rare in people with lifelong deafness

Hearing, attention, and old age

Brain areas responsible for language comprehension become less active in older people

Hearing, attention, and old age (con’t)

As cochlear hair cells die because of the aging process or anything else, the auditory cortex receives less input than usual, and adjusts by facilitating the excitatory synapses and decreasing the inhibitory synapses to increase the sound, which amplifies all forms noise (including background noise)

Damage to the cochlea

It’s like an amputation: If the auditory cortex no longer gets its normal input, other axons invade the deprived area

Mechanical senses

All the body sensations (as well as vestibular sensation) which detect the position and movement of the head, which respond to pressure, bending, or other distortions

Vestibular sensation

Sensations from the vestibular organ detect the tilt of the head and the head’s acceleration

e.g. When you move your head, the vestibular organ adjacent to the cochlea monitors movements and directs compensatory movements of your eyes

Vestibular sensation (con’t)

One uses that information to guide eye movements and maintain balance

Otoliths

Calcium carbonate particles within the saccule and utricle of the vestibular organ that push against and excite hair cells when the head tilts.

Otoliths (con’t)

When the head tilts, the otoliths push against hair cells and excite them, telling the brain the direction of tilt

The vestibular organ

Consists of:

• Saccule

• Utricle

• Three semicircular canals

Semicircular canals

Three fluid-filled canals in the inner ear containing a jelly-like substance and hair cells that activate to detect acceleration and rotational movements of the head.

Semicircular canals (con’t)

Acceleration of the head at any angle causes the fluid in one of these canals to move, then pushes against the hair cells in the semicircular canals and setting up action potentials

The somatosensory system

A sensory network that monitors the surface of the body and its movements

The somatosensory system (con’t)

Spans many senses including touch, deep pressure, the position and movement of joints, pain, and temperature

Pacinian corpuscle

A somatosensory receptor featuring an onion-like outer structure that insulates against constant pressure while responding to sudden displacements or vibrations by opening sodium channels.

Pacinian corpuscle (con’t)

Responds to a sudden displacement of the skin or high-frequency vibrations on the skin

Capsaicin

A chemical, found in hot peppers, that produces a painful burning sensation that could be used to relieve pain

Somatosensory sensations in the central nervous system

Information from touch receptors in the head enters the central nervous system through the cranial nerves and 31 spinal nerves

Somatosensory sensations in the central nervous system (con’t)

They then travel through the spinal cord in separate pathways toward the thalamus

Dermatome

An area of the body connected to a particular spinal nerve

e.g. When the fingers touch something, people are conscious of only those that produce enough arousal in the primary somatosensory cortex

The primary somatosensory cortex (S1)

An area essential for touch experiences

Numbsense

When some people correctly “guess” the location of a touch while insisting that they didn’t consciously feel it, either because of damage or because of temporary suppression

Numbsense’s cause

The likely explanation is that the thalamus sends enough input to areas surrounding S1 for location identification, but not enough for conscious perception.

The benefits of itching

Itch is useful because it directs you to scratch the itchy area and remove whatever is irritating your skin, as the brain isn’t satisfied until you scratch hard enough to produce mild pain, because pain inhibits itch

The causes of itching

When skin releases histamines that dilate blood vessels and produce an itching sensation as a part of healing from tissue damage, antihistamines are released to relieve the itch

The thing about itching

Itch is a separate sensation from pain and touch

The correlation between pain and depression

Pain and depression are closely linked.

e.g.

• People in pain become depressed and unmotivated.

• People who are depressed become more sensitive to pain.

Gender differences among pain and depression

Depression is more common in women than in men, and women tend to experience more pain than men

Where does pain begin?

Pain begins with a bare nerve ending (the least specialized of all receptors)

Axons and pain

The thicker and faster axons convey sharp pain, whereas the thinner ones convey duller pain, such as postsurgical pain

Emotion and pain

Input to the hypothalamus, amygdala, and anterior cingulate cortex pertains to the unpleasant emotional aspect of pain

Emotion and pain (con’t)

The emotion-relevant areas react not only to feeling your own pain but to watching someone else in pain, especially someone you care about

Axons and pain (con’t)

It’s conducted the range of 2 to 20 meters per second

The cingulate cortex

An area responsive to the emotional aspects of pain that sees increased activity during moments of hurt

The cingulate cortex (con’t)

Sensations of hurt can be remedied with acetaminophen (Tylenol)

Opioid mechanisms

Systems that respond to opiate drugs and similar chemicals

Opioid mechanisms (con’t)

They act on the nervous system rather than the injured tissue

Periaqueductal gray area

An area of the brainstem that is rich in endorphin synapses

Merkel's disks

Somatosensory receptors found across all skin regions that respond to light touch.

Meissner's corpuscles

Somatosensory receptors located in hairless skin areas (principally the fingertips) that respond to discriminative touch and low-frequency vibration.

Ruffini endings

Somatosensory receptors that are scarce in humans and respond to skin stretch and surface roughness.

Substance P

A neuropeptide released alongside glutamate in the spinal cord during intense or strong pain.

Periaqueductal gray area (con’t)

A midbrain region surrounding the cerebral aqueduct where opiate receptors and electrical stimulation suppress pain signals.

Endorphins

A group of endogenous neuropeptides that attach to morphine-sensitive opiate receptors in the brain and spinal cord to relieve pain.

Inescapable pain

A sensation that’s especially potent at stimulating endorphins and inhibiting further pain

Inescapable pain’s evolutionary function

Intense pain accomplishes nothing when you already know about the problem and escape is impossible

Gate theory

A model proposing that non-pain touch stimuli and descending cortical signals can close spinal gating mechanisms by releasing endorphins, thereby diminishing pain transmission.

Neuropathic pain

A condition of chronic pain that lasts long after the original cause of pain has ended

Placebo

A drug or other procedure with no pharmacological effect(s)

Placebo (con’t)

They have little influence on most illnesses, but they often relieve pain, depression, and anxiety

Nocebo

The opposite of placebo

Itch

A sensation initiated by the skin's release of histamines that travels slowly ($0.5\,\text{m/s}$) along a distinct spinal pathway that maintains an inhibitory relationship with pain.