Chapter 5 pt1

Sensation vs Perception

• Sensation: the act of using out sensory systems to detect environmental stimuli

  • what stimuli does our body detect

• Perception: the conscious recognition and identification of a sensory stimulus

  • How does our brain make sense of the information our sense have detected

Types of sensory systems and their physical stimuli

• Olfactory (smell) - Odourants

• Somatosensory (touch) - Pressure or damage to skin

• Gustatory (taste) - Chemicals

• Auditory (hearing) - Sound waves

• Visual (sight) - Light (photons)

What are sensory receptor cells

• Specialized cells that convert a specific form of environmental stimuli into neural impulses (sensory transduction)

What is sensory transduction

• Process of converting a specific form of environmental stimuli into a neural impulse that our brain can read

What is Absolute threshold

• Smallest amount of stimulus that one can detect

  • Smell - drop of perfume

  • Taste - 5ml of sugar in 9L of water

  • Touch - an insect wing falling on your cheek from 1cm

  • Hearing - tick of a watch at 6m away

  • Sight - candle flame 50 km away in a dark room

What is the difference thresholds

• The minimal difference needed to notice a difference between 2 stimuli

• Sensory sensitivity depends on experience, expectations and consequences for failure

  • someone who notices a faint smell has a high sensory sensitivity

  • If you listen to music on your iphone, how much do you have to turn up the volume before you notice the music getting louder

What is signal detection theory

• response to a signal in every situation depends on an individual’s ability to differentiate between the signal and noise, and on their response criteria

What is sensory adaptation

• Repeated stimulation of a sensory cell leads to a reduced

  response

  • E.g. The tag in your shirt that bothered you in the morning but you don’t feel anymore

  • E.g. Olfactory adaptation - when you walk into a coffee shop and you slowly stop smelling the coffee

What is bottom-up processing

• Perception that proceeds by transducing environmental stimuli into neural impulses that move successively into more complex brain regions

What is top-down processing

• Perception processes led by cognitive processes, such as memory or expectations

What is perceptual sets

• Example of Top-down processing

• Readiness to interpret a certain stimulus in a certain way

• usually occur when faced with ambiguous stimuli (multiple interpretations)

Processing sensory information

• Bottom-up Processing

  • Physical stimuli from the environment → neural impulses sent to CNS → perception

• Top-down Processing

  • Previously acquired knowledge → perception

• Perception typically involves both types of processing

  • e.g. recognizing objects/songs/faces

What are the 5 main senses

• Smell, taste, touch, sound and sight

• BUT there’s

  • Kinesthetic (body’s movement, posture)

  • Vestibular (head’s position and movement)

What are the two senses “touch” can be separated into

• Separated into thermoception (temperature detection) and nociception (pain detection

What sensory receptors are designed to detect chemicals

• Olfactory sense (smell) and Gustatory sense (taste)

What is the pathway of chemical sense (smell)

• Odourants: airborne chemicals bind to receptors that are detected as odours

• Olfactory receptor neurons: sensory receptor cells that convert chemical signals from odourants into neural impulses that travel to the brain

  • Reach the amygdala and hippocampus

• Continuous exposure to a specific smell will result in fatigue of olfactory receptor neurons

What is the pathway of chemical sense (taste)

• Papillae - bumps on the tongue that contain clumps of taste buds

• Taste buds - clusters of sensory receptor cells that convert chemical signals from food into neural impulses that travel to the brain

Taste is actually called flavour (combination of small and taste)

What are the five taste receptors on your tongue

Taste receptors have cilia that contain actual receptors

1. Sweet

2. Sour

3. Bitter

4. Salt

5. Umami - taste of MSG

What other sense is activated when you eat

• Tactile sense

• The consistency of a particular food is not relayed to the brain via the taste receptors but rather by inputs from touch receptors located on the tongue

How do we experience spice

• The sensation we experience when eating spicy food is related to tactile systems that communicate information about pain

• Capsaicin (spicy chemical) activates pain receptors located in the tongue

  • Some people enjoy it and some people dont

What makes sensory receptors of taste different

• When you eat hot (temperature) food it burns you mouth and damages the taste receptors

• These receptors are able to regenerate

When is smell and taste developed

• Smell is developed at birth

  • Newborns show preference for the odour of their mother’s milk

• Taste is also developed at birth (preference towards sweet)

  • Taste buds are not evenly distributed across the tongue (most are the top of the tongue)

• Around age 7 children start to like sour tastes (e.g. sour patches)

Why are kids typically more picky

• Due to the higher number of taste buds

• The taste of certain foods may seem too strong because of the large amount of taste buds produce more neural impulses than adults would

How does the brain process smell and taste

• Signal from olfactory receptor neurons travel to the brain via olfactory nerve

• Info is carried along olfactory nerves → olfactory bulb (located base of the front brain beneath the frontal lobes) → olfactory information is sent to regions of cerebral cortex (piriform cortex)

What is an olfactory bulb

• The first region where olfactory information reaches the brain on its way from the nose

• Sends information to the amygdala (emotions & fear) and indirectly to the hippocampus (learning & memory)

  • Smells evoke memories

What is the piriform cortex responsible for

• Primary area for processing smell

• This cortex is plastic (changeable in adulthood)

Do taste receptors have axons?

• No, the connect with sensory neurons on the tongue to send information to our brains

  • Sent to the thalamus and cerebral cortex

What is the insula

• Part of the cortex that receives taste information

• Associated with emotion of disgust

  • Activates with bad smell, taste and repulsive visual images

What are some smell and Taste disorders

• Ageusia - inability to taste (rare)

• Anosmia - inability to detect odours

• Hyposmia - reduced ability to smell

• Reflex epilepsy - seizure occurs only after exposure to a specific odour

• Migraine headaches - specific odours trigger migraines

Disorders may implicate dysfunction in the brain, sensory receptors, or both

What is the tactile or somatosensory system composed of

• Combination of skin senses

  • Pressure

  • Touch

  • Temperature

  • Vibration

  • Pain

• The tactile senses rely on variety of receptors located in different parts of the skin

Different somatosensory receptors

• Free nerve endings

  • Located near the surface of the skin

  • Detect touch, pressure, pain and temperature

• Meissner’s corpuscles

  • located in the fingertips, lips and palms

  • Transduce information about sensitive touch

• Merkel’s discs

  • located near the surface of the skin

  • transduce information about light to moderate pressure against the skin

• Ruffini’s end-organs

  • located deep in the skin

  • register heavy pressure and movement of the joints

• Pacinian corpuscles

  • located deep in the skin

  • respond to vibrations and heavy pressure

What are the steps to perceiving touch

1. Tactile receptors respond to touch and pressure and send information to the spinal cord

2. Information is relayed up to the spinal cord to the thalamus

3. The thalamus sends the information to the somatosensory cortex

4. The somatosensory cortex receives the information

Our brain processes tactile information contralaterally (opposite side of the brain from the body where touch occurred)

What are the two pathways of pain

• Fast pathway (myelinated): sharp, localized pain is felt quicker because it travels along myelinated neurons to the brain

• Slow pathway (unmyelinated): inputs communicate with brain regions involved in processing emotions; pain we perceive via the slow pathway is more often burning pain than sharp pain

How are tactile senses developed

• Developed at birth

• After birth the ability to respond to somatosensory stimuli is dependent on brain development and learning

• Physical contact is required for healthy development in infancy (Harry Harlow)

What is an example of activation of somatosensory pathway?

• Tickling, usually an enjoyable somatosensory input

• Causes an uneven, uncontrollable, and unexpected manner

What are the three different tactile sense disorders

• Chronic pain - common

• No pain (familial dysautonomia) - rare genetic condition associated with an inability to detect pain or temperature & produce tears

• Phantom limb sensations - tactile hallucinations of touch, pressure, vibration, and pain in the body part that no longer exists

How does the body reduce pain, and how do pain-relief drugs work?

• The body uses endorphins and enkephalins to block pain naturally.

• Opiate drugs like morphine and oxycodone copy these chemicals to relieve pain.

• Touch (like rubbing a sore area) can also reduce pain using the gate control theory.

What is the gate control theory of pain

• Theory that certain patterns of neural activity can close a “gate” to keep pain information from travelling to parts of the brain where it is perceived

What are sound waves, and how do frequency and amplitude affect what we hear?

• Sound waves - vibrations of the air in the frequency of hearing

• Frequency - the number of cycles per second in a wave

  • Determines pitch of sound

  • Measured in units called Hertz which represent cycles per second

  • We hear best in the range of 2000-5000Hz

• Amplitude - magnitude (height of a wave)

  • determines loudness

  • Measured in units called decibels

How does the ear hear

1. Sound wave enter ears and deflect tympanic membrane

2. Waves pass into the middle ear, which contains the three smallest bones in the human body the ossciles (composed of maleus, incus, and stapes)

3. Stapes hits the oval window, causing a wave to form in the fluid in the cochlea

4. The fluid deflects the basilar membrane, bending its hair cells that transduce the fluid sound wave into electrical activity

5. As hair cells move, neural impulses are created and sent to the brain

6. Signal travels to the brainstem, thalamus, and auditory cortex

7. In the auditory cortex, sound is received in a tonotopic map

8. Certain frequencies are always received by specific areas of auditory cortex

How do you identify frequency and pitch

• Frequency theory

  • different sound frequencies are converted into different rates of action potentials

  • High-frequency sounds produce a more rapid firing than do low-frequency sounds

• Place theory

  • Differences in sound frequency activates different regions of the basilar membrane

  • The brain equates the place activity occurred on the basilar membrane with a particular frequency

What is absolute pitch

• Ability to recognize any notes on a musical scale

• Develops between 3 and 6 years of age

• People who speak tonal languages are more likely to have absolute pitch

How does sound adaptation occur

• Muscles around our ears can contract so less of the sound wave enters the ear

• Our ears become less sensitive to continuous noises

• Our brains filter out sounds that are not important

What is the cocktail party effect

• The brain picks up on relevant sounds, even in a noisy environment

• Ear ringing could be a sign of irreversible damage

How do we localize sounds

• General loudness - louder sounds seem closer

• Loudness in each ear - the ear closer to the sound hears a louder noise than the ear farther from the sound

• Timing - sound waves will reach the ear closer to the source of the sound before they reach the ear farther away

How does hearing develop

• Babies can hear before they are born

• Ability to recognize and respond appropriately to sounds develops in the first few months after birth

• Infants prefer speech (especially mom’s) to non-speech

What are the two types of hearing loss

• Deafness - Loss of hearing (partial or complete)

  • Can be genetic, cause by infection, physical trauma (headphone use), exposure to toxins, high doses of common medications (aspirin)

• Tinnitus - ringing in the ear

  • Due to abnormalities in the ear

  • 1 in 200 experiences tinnitus

What devices aid with hearing loss

• Medical devices that are implanted in the ear and are wired to the nerves that send sounds information to the brain

  • e.g. cochlear implants