Lecture 6: Other Sensory Processes

Amplitude

Of a sound wave is its intensity. In general, sounds of greater amplitude seem louder, but a rapidly talking person seems louder than slow music of the same amplitude.

Frequency

Of a sound is the number of compressions per second, measured in hertz (Hz, cycles per second).

Pitch

The related aspect of perception. Sounds higher in frequency are higher in pitch.

Timbre

Meaning tone quality or tone complexity.

Prosody

Conveying emotional information by tone of voice.

Sound Waves

Pinna

Found in the outer ear.

The familiar structure of flesh and cartilage attached to each side of the head.

Tympanic Membrane (Eardrum)

Connects to three tiny bones that transmit the vibrations to the oval window (membrane of the inner ear).

Vibrates when sound waves reach the middle ear.

The Smallest Bones in the Body

Hammer, anvil, and stirrup.

Stirrup

When this vibrates the oval window, it sets into motion the fluid in the cochlea.

Cochlea

The snail shaped structure of the inner ear.

Hair Cells

The auditory receptors.

They lie along the basilar membrane of the cochlea.

Vibrations in the fluid of the cochlea displace them, which stimulate the auditory nerve.

Primary Auditory Cortex

As information from the auditory system passes through subcortical areas, axons cross over in the midbrain to enable each hemisphere of the forebrain to get most of its input, but not all of it, from the opposite ear. The information ultimately reaches this part of the auditory complex.

Planum Temporale

An area in the temporal cortex.

It processes the experience you have of a sound source moving from one place to another.

The Auditory Cortex

It is important not just for hearing but also for thinking about anything related to hearing.

Secondary Auditory Cortex

Surrounds the primary auditory cortex and other areas that respond mainly to meaningful sounds, such as animal calls, birdsong, machinery noises, music, and speech.

Time of Arrival

Is useful for localizing sounds with a sudden onset.

Humans can also localize whether a sound is coming from above or below, although less accurately than left vs. right.

Pinnae

Have an irregular shape that filters sound frequencies differently depending on their location (up or down, front or back).

Sound Travel

Faster in water than in air, so a sound arrives at the two ears almost simultaneously.

Amusia

An estimated 4 percent of people have this, commonly called “tone deafness”. Although they are not really unable to hear differences in tones, they do not detect a change less than about the difference between C and C-sharp.

The auditory cortex appears to approximate a typical structure, but it has fewer than average connections to the frontal cortex. The difference is evidently not in hearing itself, but in either memory for pitch or attention to pitch.

Absolute pitch (Perfect Pitch)

It is the ability to hear a note and identify it—for example, “That’s a B flat.” Genetic predisposition contributes, but early musical training is also important. Most people with this type of pitch had early musical training.

It is also common among people who speak tonal languages, such as Vietnamese or Mandarin Chinese.

The ability to recognize a pitch is common, even if the ability to name it is not.

Conductive Deafness (Middle-ear Deafness)

Diseases, infections, or tumorous bone growth can prevent the bones of the middle ear from transmitting sound waves properly to the cochlea.

This type of deafness is sometimes temporary.

Because people with this type of deafness have a normal cochlea and auditory nerve, they readily hear their own voices, conducted through the bones of the skull directly to the cochlea, bypassing the middle ear.

Nerve deafness (Inner-ear Deafness)

Results from damage to the cochlea, the hair cells, or the auditory nerve.

If it is confined to one part of the cochlea, it impairs hearing of certain frequencies and not others.

This type of deafness can be inherited, it can result from disease, or it can result from exposure to loud noises.

Tinnitus

Frequent or constant ringing in the ears.

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

It has many causes, but in some cases it resembles phantom limb.

Damage to part of the cochlea is like an amputation: If the auditory cortex no longer gets its normal input, other axons invade the deprived area.

Hearing, Attention, and Old Age

Many older people have hearing problems despite wearing hearing aids and have trouble understanding speech in a noisy room or when someone speaks rapidly - The brain areas responsible for language comprehension have become less active.

As cochlear hair cells die because of the aging process or anything else, the auditory cortex receives less input than usual.

Hearing improves if the listener watches the speaker’s face. We all do more lip-reading than we realize.

The Mechanical Senses

Respond to pressure, bending, or other distortions. They include all the body sensations as well as vestibular sensation, which detects the position and movement of the head.

Audition

It is also a mechanical sense, because hair cells are modified touch receptors. We considered it separately because of its complexity and importance.

The Vestibular Sensation

Sensations from the vestibular organ detect the tilt of the head and the head’s acceleration. You use that in formation to guide eye movements and maintain balance.

People with impairments of the vestibular system stagger and fall.

The Vestibular Organ

Consists of the saccule, utricle, and three semicircular canals. Like the hearing receptors, the vestibular receptors are modified touch receptors.

Otoliths

Calcium carbonate particles lie next to the hair cells. When the head tilts, the they push against hair cells and excite them, telling the brain the direction of tilt. When you move, they tell the brain which direction you are moving.

Three Semicircular Canals

They are oriented in perpendicular planes and are filled with a fluid and lined with hair cells.

Acceleration of the head at any angle causes the fluid in one of these canals to move, just as the water in a bucket will splash if you jerk the bucket from side to side.

The Somatosensory System

The sensation of the body and its movements, is not one sense but many, including touch, deep pressure, the position and movement of joints, pain, and temperature.

Somatosensory Receptors

Suppose you feel objects with thin grooves like these, without looking at them, and try to feel whether the grooves go left to right or up and down:

The Pacinian Corpuscle

Detects vibrations or sudden displacements on the skin. On the inside is the neuron membrane.

The onion-like outer structure provides mechanical support that resists gradual or constant pressure, insulating the neuron against most touch stimuli.

Only a sudden or vibrating stimulus bends the membrane, enabling sodium ions to enter and start an action potential.

Somatosensation

The body has receptors for temperature, a critical variable because overheating or overcooling the body can be fatal.

Cold-sensitive neurons in the spinal cord exhibit little response to a constant low temperature, but they respond to a drop in temperature.

Heat-sensitive neurons in the spinal cord respond to the absolute temperature, and they do not adapt.

Our temperature receptors also respond to certain chemical stimuli. Capsaicin, found in jalapeños and other hot peppers, stimulates the receptors for painful heat. Menthol and mint stimulate the coolness receptor.

Dermatome

Each spinal nerve innervates (connects to) a limited area of the body.

Various types of somatosensory information—such as touch, pressure, and pain—travel through the spinal cord in separate pathways toward the thalamus, which sends impulses to different areas of the primary somatosensory cortex in the parietal lobe.

Information from skin sensations also goes to the anterior cingulate cortex, which respond to the pleasantness or unpleasantness of the sensation.

Pain

___ and depression are closely linked. People experiencing this become depressed and unmotivated. People who are depressed become more sensitive to pain.

Economic insecurity leads to depression and makes a pain feel worse.

Depression

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

Much of the biological research on pain has relied on just males— sometimes humans, sometimes rodents. The reasoning was that females were assumed to be more variable, because of their hormonal cycles.

Emotional Pain

Hurt feelings do resemble physical pain.

Increased activity in the cingulate cortex, an area responsive to the emotional aspects of pain but also the sensory areas responsive to physical pain.

Hurt feelings are like real pain in another way: You can relieve hurt feelings with pain-relieving drugs such as acetaminophen (Tylenol®).

Endorphins

The transmitters that attach to the same receptors as morphine— a contraction of endogenous morphines.

The brain produces several types, which relieve different types of pain, such as the pain from a cut versus the pain from a burn.

They are also released during intense pleasures, such as orgasm and when you listen to thrilling music that sends a chill down your spine. Those experiences tend to decrease pain.

Cannabinoids

They have demonstrated promise for treating neuropathic pain, a condition of chronic pain that lasts long after the original cause of pain has ended.

Gate Theory

Proposed decades ago, was an attempt to explain why some people with stand pain better than others, and why the same injury hurts worse at some times than others. When you have an injury, you can decrease the pain by gently rubbing the skin around it or by concentrating on something else.

Placebos

People who receive these do not just say the pain decreased; scans of the brain and spinal cord also exhibit a decreased response.

These can reduce pain even when people know they are receiving them.

If someone expects an unpleasant reaction to a drug, the nervous system increases that response also—a nocebo effect (opposite of placebo).

Itch

Two causes of itch. One, if an insect crawls slowly across your skin. The other cause is tissue damage, such as when your skin is healing after a cut. Your skin releases histamines that dilate blood vessels and produce an itching sensation.

It is useful because it directs you to scratch the itchy area and remove whatever is irritating your skin.

Antihistamines

Relieve this type of itch, but not the itch you get from something crawling over your skin. The two types of itch sensation travel in parallel paths to the brain.

Taste

Results from stimulation of the taste buds (receptors on the tongue).

Taste of food, we generally mean flavor (Combines taste and smell).

Taste and smell axons converge onto many of the same cortical cells, enabling them to combine their influences.

Mammalian Taste Receptors

Are in taste buds located in papillae on the surface of the tongue.

A given papilla may contain up to 10 or more taste buds and each taste bud contains about 50 receptor cells.

Adaptation

A phenomenon that reflects the fatigue of receptors sensitive to sour tastes.

Cross-adaptation

Reduced response to one taste after exposure to another.

Umami

The tongue has a glutamate receptor that resembles the neurotransmitter receptors for glutamate.

Glutamate tastes somewhat like unsalted chicken broth.

The English language had no word for this taste, so it adopted a Japanese word.

The Saltiness Receptor

It is simple. Recall that a neuron produces an action potential when sodium ions cross its membrane.

This receptor simply permits sodium ions on the tongue to cross its membrane, and thereby detects the presence of sodium.

The Sour Receptors

Detect the presence of acids.

The Sweetness, Bitterness, and Umami Receptors

Resemble metabotropic synapses.

After a molecule binds to one of these receptors, it activates a G protein that releases a second messenger within the cell.

People have two types of sweetness receptors and two types of umami receptors, each with somewhat different sensitivities.

The Bitter Receptor

Bitter taste used to be a puzzle because bitter substances include a long list of dissimilar chemicals. Their only common factor is that they are to some degree toxic.

We have not one bitter receptor but a family of approximately 30 that respond to different sets of compounds. Our large number of bitter receptors enable us to detect a great variety of dangerous chemicals.

Most Taste Receptors

Respond only to one type of chemical, but some respond to both sweet and salty, or sweet and umami.

The receptors feed into neurons that might respond just to one taste, or to several.

Taste Receptor Cells

On your tongue, you have taste buds, and these cells are inside them. They are specialized to detect different chemical compounds in food.

Two Main Ideas for "Coding": Labeled Line

This idea suggests that certain taste cells and the nerves they connect to are dedicated to a single taste.

So, a "sweet" pathway only tells the brain "sweet," a "bitter" pathway only "bitter," and so on. It's like having separate, labeled phone lines for each taste.

Two Main Ideas for "Coding": Across-Neuron Pattern (or Ensemble Coding)

This idea is more complex. It suggests that while some cells might be "best" at detecting a particular taste, all taste cells respond to varying degrees to different tastes.

The brain then "reads" the unique pattern of activity across many different taste cells to figure out the overall taste.

Taste Sensitivity

Some people have three times as many taste buds as other people do on the fungi form papillae near the tip of the tongue.

Supertasters - Greatest number

Tasters or Non-tasters (a misleading term) - Average or below-average numbers

Olfaction

The sense of smell, is the response to chemicals that contact the membranes inside the nose.

Olfactory Cells

The neurons responsible for smell that line the olfactory epithelium in the rear of the nasal air passages.

Orthonasal Olfaction

They detect both the chemicals of the air you inhale.

Retro-nasal Olfaction

The chemicals given off by food in your mouth.

Olfactory Receptors

Vulnerable to damage because they are exposed to the air. Unlike your receptors for vision and hearing, which remain with you for a lifetime.

It has an average survival time of just over a month. At that point, a stem cell matures into a new olfactory cell in the same location as the first and expresses the same receptor protein.

Damaged Olfactory Surface

However, if it is damaged at once by a blast of toxic fumes so that the system has to replace all the receptors at the same time, many of them fail to make the correct connections, and olfactory experience does not fully recover.

Olfactory Cell

Each of them have only one receptor type, and most receptors respond to either just one chemical or several closely related chemicals.

It's much more complex than simply having a separate sensor for every single smell, because there are millions of different possible odors, and we only have a few hundred types of smell receptors.

Synesthesia

The experience some people have in which stimulation of one sense evokes a perception of that sense and another one also.

They have increased amounts of gray matter in certain brain areas and altered connections to other areas.

Fisher-Price refrigerator magnets - red A, yellow C, and green D.

“To me, the taste of beef is dark blue. The smell of almonds is pale orange. And when tenor saxophones play, the music looks like a floating, suspended coiling snake-ball of lit-up purple neon tubes.”