Biological Psychology - Chapter 6: Other Sensory Systems

Audition

• Hearing provides crucial information.

• Auditory signals are perceived as periodic compressions in a medium such as air or water.

Sound and the Ear

• Hearing occurs through detection of sound waves.

• Sound waves are periodic compressions.

• Sound waves are characterized by amplitude (intensity) and frequency (pitch).

Physics and Psychology of Sound

• Amplitude: Intensity of a sound wave perceived as loudness.

• Frequency: Number of compressions per second, measured in hertz (Hz), related to pitch.

• Timbre: Tone quality or complexity.

• Children can typically hear higher frequencies than adults.

• Ability to detect high frequencies decreases with age and noise exposure.

• Emotions are communicated through variations in pitch, loudness, and timbre.

Structures of the Ear

• Outer ear, middle ear, and inner ear.

• Outer Ear:

  • Pinna: Flesh and cartilage structure on the side of the head.

    • Modifies sound wave reflection into the middle ear.

    • Aids in locating sound sources.

• Middle Ear:

  • Tympanic Membrane: Eardrum, vibrates when struck by sound waves.

  • Malleus (hammer), incus (anvil), and stapes (stirrup): Three bones that transform waves into stronger waves to the oval window.

  • Oval Window: Membrane in the inner ear that transmits waves to the inner ear's fluid.

• Inner Ear:

  • Cochlea: Snail-shaped structure containing fluid-filled tunnels.

  • Hair Cells: Auditory receptors located between the basilar membrane and tectorial membrane.

    • Vibrations in the cochlea's fluid displace hair cells.

    • Displacement excites auditory nerve cells by opening ion channels.

The Auditory Cortex

• Primary Auditory Cortex (A1): Main destination for auditory information in the superior temporal cortex.

• Each hemisphere primarily receives information from the opposite ear.

• Organization:

  • Similar to visual cortex with "what" and "where" pathways.

  • Superior temporal cortex detects sound motion.

  • A1 is important for auditory imagery.

  • Development depends on experience; fewer axon connections develop in those deaf from birth.

• Functions:

  • A1 processes auditory information rather than being necessary for hearing itself.

  • Tonotopic map: Cells in A1 respond to preferred tones.

  • Some cells respond to complex sounds better than pure tones.

  • Damage to A1 doesn't always cause deafness unless it extends to subcortical areas.

• Additional Areas:

  • Areas around A1 respond to changes in sound.

  • Respond to auditory "objects" like animal cries, machinery noises, and music.

Individual Differences

• Amusia: Impaired detection of frequency changes (tone deafness); affects about 4% of people.

  • Associated with a thicker auditory cortex in the right hemisphere and fewer connections to the frontal cortex.

• Absolute Pitch (Perfect Pitch): Ability to identify a note by ear.

  • May have a genetic component.

  • Mainly determined by early and extensive musical training.

  • More common in tonal language speakers.

Hearing Impairment

• Two Categories:

  • Conductive/Middle Ear Deafness: Bones of the middle ear fail to transmit sound to the cochlea.

    • Caused by disease, infections, or bone growth.

    • Cochlea and auditory nerve are normal, so individuals hear their own voice clearly.

    • Corrected by surgery or hearing aids that amplify the stimulus.

  • Nerve/Inner-Ear Deafness: Damage to the cochlea, hair cells, or auditory nerve.

    • Varies in degree; can be confined to certain frequencies.

    • Inherited or caused by prenatal problems/early childhood disorders.

• Tinnitus: Frequent or constant ringing in the ears, common in nerve deafness, sometimes after cochlea damage.

Hearing, Attention, and Old Age

• Language comprehension areas become less active.

• Decrease in inhibitory neurotransmitters (e.g., GABA and/or Serotonin) leads to difficulty suppressing irrelevant sounds.

• Attention improves when watching the speaker’s face.

Mechanical Senses

• Respond to pressure, bending, or distortions of a receptor.

  • Include touch, pain, body sensations, and vestibular sensation.

• Vestibular sensation:

  • Detects head position and movement.

• Audition is a complex mechanical sense because hair cells are modified touch receptors.

Vestibular Sensation

• Detects head position and movement; directs compensatory eye movements and maintains balance.

• Vestibular organ is located in the ear, adjacent to the cochlea.

The Vestibular Organ

• Vestibular labyrinth is a bony cavity within the petrous portion of the temporal bone.

• It consists of the bony framework for the cochlea as well as the 3 semicircular canals.

• The bony labyrinth houses the 3 semicircular canals and the 2 otolithic organs (the utricle and saccule).

• Comprises otolith organs (saccule and utricle) and semicircular canals.

  • Otoliths: Calcium carbonate particles that stimulate hair cells when the head tilts.

  • Semicircular Canals: Filled with a jelly-like substance and hair cells that are activated by head movements.

    • Action potentials travel to the brain stem and cerebellum.

Somatosensation

• Sensation of the body and its movements.

  • Includes discriminative touch, deep pressure, cold, warmth, pain, itch, tickle, and joint position/movement.

Somatosensory Receptors

• Touch receptors:

  • Simple bare neuron endings.

  • Modified dendrites (Merkel disks).

  • Elaborated neuron endings.

  • Bare endings surrounded by non-neural cells.

• Stimulation opens sodium channels to trigger an action potential.

Somatosensory Receptors and Probable Functions

• Free nerve Ending:

  • Location: Any skin area

  • Responds to: Pain and temperature

• Hair-follicle receptors:

  • Location: Hair-covered skin

  • Responds to: Movement of hairs

• Meissner’s corpuscles:

  • Location: Hairless areas

  • Responds to: Movement across the Skin

• Pacinian corpuscles:

  • Location: Any skin area

  • Responds to: Vibration or sudden Touch

• Merkel’s disks:

  • Location: Any skin area

  • Responds to: Static touch

• Ruffini endings:

  • Location: Any skin area

  • Responds to: Skin stretch & Thermoreceptor for warmth

• Krause and bulbs:

  • Location: Mostly hairless areas

  • Responds to: Thermorecptor for cold

The Pacinian Corpuscle

• Detects sudden displacement or high-frequency vibrations.

  • Onion-like structure resists gradual pressure.

  • Sudden stimuli bend the membrane, increasing sodium ion flow and triggering action potentials.

Merkel Disks

• Respond to light touch.

• Men and women have the same number, but women have smaller fingers, resulting in disks being compacted into a smaller area and being more sensitive to feeling the distances between grooves.

Somatosensation in the Central Nervous System (CNS)

• Touch receptor information from the head enters via cranial nerves.

• Information from receptors below the head enters the spinal cord and travels through 31 spinal nerves to the brain.

Somatosensation in the Spinal Cord

• Each spinal nerve has sensory and motor components and connects to a limited body area.

• Dermatome: Body area innervated by a single sensory spinal nerve.

• Sensory information travels in distinct pathways (e.g., touch vs. pain).

The Somatosensory Cortex

• Body sensations remain separate through the cortex.

• Areas of the somatosensory thalamus send impulses to different areas of the somatosensory cortex (parietal lobe).

• Sub-areas respond to different body areas.

• Damage can impair body perceptions.

Pain

• Experience evoked by a harmful stimulus, directs attention to danger.

• Pain sensation begins with bare nerve endings.

• Some pain receptors respond to acids, heat, or cold.

• Axons carrying pain information are unmyelinated or have little myelin, so impulses travel slowly.

• Mild pain triggers glutamate release in the spinal cord.

• Stronger pain triggers glutamate release and several neuropeptides including Substance P and CGRP.

• CGRP (calcitonin gene-related peptide) causes inflammation of the meninges and could cause migraines.

Emotional Pain

• Activate a path that goes through the Reticular Formation of the medulla, and then to several of the central nuclei of the thalamus, the amygdala, hippocampus, prefrontal cortex, and cingulate cortex

• Experimenters monitored people’s brain activity and found hurt feelings activate similar pathways as physical pain.

Relieving Pain

• Opioid mechanisms: Systems sensitive to opioid drugs and similar chemicals.

  • Opiates bind to receptors in the spinal cord and periaqueductal gray area of the midbrain.

• Endorphins: Chemicals that bind to the same brain receptors as morphine (brainstem & medial thalamus).

  • Different types of endorphins for different types of pain.

• Gate Theory: Spinal cord areas receive messages from pain receptors, touch receptors, and descending axons from the brain. Non-pain stimuli can modify the intensity of the pain

  • Other areas that provide input can close the "gates" by releasing endorphins and decrease pain perception.

More Ways of Relieving Pain

• Placebo: A drug or other procedure with no pharmacological effect which decreases the brain’s emotional response to pain perception, not the sensation itself.

• Cannabinoids: Chemicals related to marijuana that block certain kinds of pain, mainly act in the periphery of the body.

• Capsaicin: Produces a temporary burning sensation followed by a longer period of decreased pain (such as Muscle relaxing creams).

Sensitization of Pain

• Mechanisms to increase sensitivity to pain.

• Damaged or inflamed tissue releases histamine, nerve growth factor, and other chemicals that increase the responses of nearby pain receptors.

• Certain receptors become potentiated after an intense barrage of painful stimuli.

  • Leads to increased sensitivity or chronic pain later.

Itch

• Histamine release by the skin produces itching sensations.

  • Activates a distinct pathway in the spinal cord to the brain.

  • C (unmyelinated) fibers & PAG may be involved

  • Impulses travel slowly.

• Pain and itch have an inhibitory relationship.

  • Opiates increase itch, antihistamines decrease itch.

Taste and Smell

• Taste: Stimulation of taste buds (receptors on the tongue).

• Flavor: Combination of taste and smell.

  • Taste and smell axons converge in the endopiriform=Piriform cortex

Taste Receptors

• Modified skin cells with excitable membranes that release neurotransmitters.

• Replaced every 10–14 days.

• 10,000 taste buds replaced every 2 weeks.

Papillae and Taste Buds

• Papillae: Structures on the tongue that contain taste buds.

  • Each papillae may contain up to 10 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 Perception

• Western societies have traditionally described sweet, sour, salty and bitter tastes as the “primary” tastes and the four types of receptors.

• Procedures that alter one receptor but not others can be used to identify taste receptors

• Some substances that can modify tastes

  • Miracle berries—miraculin

  • Gymnema sylvestre tea

• Umami: Fifth type of glutamate receptor.

  • MSG (monosodium glutamate).

  • Tastes like unsalted chicken broth.

• Oleogustus: Ability to taste fats, a potential sixth type of taste.

Mechanisms of Taste Receptors

• Saltiness receptor permits sodium ions to cross the membrane, resulting in an action potential.

• Sour receptors detect the presence of acids.

• Sweetness, bitterness, and umami receptors activate a G protein that releases a second messenger when a molecule binds to a receptor.

Taste Coding in the Brain

• Taste information from the anterior two-thirds of the tongue is carried by different nerves than from the posterior tongue and throat.

• CT or Chorda Tympani Nerve innervates the ant. 2/3

• Taste nerves project to the nucleus of the tractus solitarius (NTS) in the medulla, which then projects to various brain areas.

• The somatosensory cortex responds to the touch aspect of taste.

• INSULA (within the Lateral Sulcus) is the Primary Taste Cortex

• Each hemisphere of the cortex is also responsive to the ipsilateral side of the tongue

Variations in Taste Sensitivity

• Genetic factors and hormones account for some differences.

• Related to the number of fungiform papillae near the tip of the tongue.

• Supertasters have higher sensitivity to all tastes and mouth sensations.

• Women have higher sensitivity to taste while pregnant.

Olfaction

• Sense of smell: Detection/recognition of chemicals contacting membranes inside the nose.

• Critical for finding food/mates and avoiding danger in most mammals.

  • Rats/mice avoid smells of cats/foxes.

Olfaction in Social Behavior

• Humans prefer smells of potential partners who smell different from themselves/family.

  • Decreases inbreeding risk.

  • Increases offspring immunity range.

Olfactory Receptors

• Olfactory cells line the olfactory epithelium in the rear of the nasal passage and are the neurons responsible for smell.

• Olfactory receptors are located on cilia extending into the mucous surface of the nasal passage.

• Vertebrates have hundreds of receptor types, highly responsive to related chemicals; unresponsive to others.

Olfactory Receptors and Proteins

• Proteins in olfactory receptors respond to chemicals outside the cells and trigger changes in G protein inside the cell.

• G protein then triggers chemical activities that lead to action potentials.

Olfaction in the Brain

• Axons from olfactory receptors carry information to the olfactory bulb.

  • Similar smells excite neighboring areas; different smells excite separated areas.

  • Coding is determined by which part of the olfactory bulb is excited.

• The olfactory bulb sends axons to the cerebral cortex, where messages are coded by location.

Olfactory Damage

• Receptors are replaced approximately every month due to vulnerability to air contact.

• Massive damage can cause permanent impairment à Anosmia, loss of smell.

Differences in Olfaction

• Women detect odor more readily than men.

• Ability to detect faint odor and become more sensitive to it is characteristic of young adult women; seems to be influenced by hormones.

• Mice with a gene that controls a channel through which most potassium (K+) travels to reach the olfactory bulb developed a sense of super smell.

Pheromones

• Chemicals released by an animal to affect the behavior of others of the same species.

• The vomeronasal organ (VNO) is a set of receptors found in most mammals located near the olfactory receptors that are sensitive to pheromones.

The VNO and Pheromones

• The VNO and pheromones are important for most mammals, but less so for humans.

• The VNO is tiny in human adults and has no receptors and is considered vestigial.

• Humans unconsciously respond to some pheromones through receptors in the olfactory mucosa.

  • Example: synchronization of menstrual cycles in women.

Synesthesia

• The experience of one sense in response to stimulation of a different sense.

  • An example would be seeing a number or a letter as a specific color. Or smelling bleach before a headache.

• Tends to cluster in families that also have perfect pitch.

  • Genetic predisposition.