Chapter 7 sensory system and perception Flashcards
What are the sensory areas of the cortex?
Primary – input mainly from thalamic relay nuclei
Example: Primary visual cortex receives input from the lateral geniculate nucleus (LGN) of the thalamus.
- Secondary –input mainly from primary and secondary cortex within the sensory system
- Association – input from more than one sensory system, usually from secondary sensory cortex
What principles guide the Interactions of Sensory Cortex?
In the context of sensory system organization, explain what is meant by each of the following terms: hierarchical organization, functional segregation, and parallel processing. Summarize the current model of sensory system organization.
Hierarchical Organization: a system whose members can be assigned to specific levels or ranks in relation of one another
*Based on specificity and complexity of function
*Each individual level receives input from a lower level
* Specificity and complexity increases with each level
Sensation – detecting a stimulus
Perception – understanding the stimulus
Functional Segregation: Sensory systems are characterized by functional segregation—each level contains distinct areas that specialize in different types of analysis.
*Primary, secondary, and association areas are no longer thought to be homogeneous but instead specialize in different functions.
Parallel Processing: occurs in sensory systems, meaning information flows through multiple pathways simultaneously, allowing for different types of analyses to happen at the same time.
Explain the Organization of the Sensory System
Multiple specialized areas, at multiple levels, interconnected by multiple parallel pathways
- The binding problem – how does the brain make sense of all this?
- While there is no final integrator of information, there are pathways that allow higher areas to influence lower areas
Talk to me about the visual cortex bitch
Primary (V1) – posterior occipital lobe
* Secondary
* Prestriate cortex – a band of tissue
surrounding V1
* Inferotemporal cortex
* Tertiary – various areas, largest single
area is in posterior parietal cortex
What are Scotomas?
Scotoma – an area of blindness
resulting from damage to visual cortex
* Blind in corresponding contralateral
visual field of both eyes
* Deficit may not be readily detected due to phenomenon of completion
What is blindsight?
How does it work
The ability to respond to a visual stimulus even with no conscious awareness of the stimulus (due to a scotoma)
* May be that some connections still exist in V1, allowing for reactions without awareness
* May be that message gets to the brain by connections that do not pass through the damaged area (i.e., LGN to V2)
Dorsal and Ventral Streams
Dorsal stream – “where”/control of behavior
* V1 to dorsal prestriate cortex to posterior parietal
* Ventral stream – “what”/conscious perception
* V1 to ventral prestriate cortex to
inferotemporal cortex
* Both “where”/“what” and behavior/perception distinctions are supported by effects of
damage
What are the two theories on the dorsal and ventricle streams, and what do they predict?
“Where” vs. “What” Theory:
Dorsal stream specializes in visual spatial perception,
Ventral stream specializes in visual pattern recognition
Predicts
* Damage to dorsal stream disrupts visual spatial perception
* Damage to ventral stream disrupts visual pattern recognition
“Control of Behaviour” vs. “Conscious Perception” Theory:
Dorsal stream specializes in visually guided behaviour
Ventral stream specializes in conscious visual perception
Predicts
* Damage to dorsal stream disrupts visually guided behaviour but not conscious visual perception
* Damage to ventral stream disrupts conscious visual perception but not visually guided behaviour
Expliain: “Control of behavior” vs. “conscious perception”
What is Prosopagnosia?
What is Agnosia?
Visual Agnosia?
- Agnosia – failure of recognition
- Visual agnosia – able to see, but unable to recognize
- Prosopagnosia – a specific type of agnosia for faces. Its face blindness, is a neurological condition that impairs a person’s ability to recognize faces.
ex. man who mistook his wife for a hat
This aligns with the idea that behavioural responses to stimuli can occur without conscious awareness, reinforcing the separation of conscious perception from unconscious visual processing.
Is Prosopagnosia limited to faces?
Prosopagnosics are unable to recognize
particular faces – they also are unable to recognize other specifics – which chair, which cow, etc.
* There is an inability to recognize specific objects belonging to a complex class of objects
* Note – some cases where deficits are limited to faces have been observed
How does Prosopagnosia occur?
- A result of bilateral damage to the
ventral “what”/conscious perception
stream - Thus, unconscious recognition can be
preserved - altered skin conductance responses to
familiar vs. unfamiliar faces
Explain how we recognize Specific Classes of
Objects
* Fusiform face area
- Fusiform face area – activity increased
during face recognition but not
recognition of other objects
The ventral stream (the “what” pathway) contains regions that specialize in recognizing different categories, such as humans, animals (e.g., cats), and buildings (e.g., houses).
These areas respond preferentially to specific object classes but are not exclusively dedicated to them.
- Areas in ventral stream may be specific to humans, cats, or houses
- But – more than one area responds to
each class and there is great overlap
Wtf is the Fusiform Gyrus???
What is audation?
What is frequency?
What is pitch?
Audition:the sense of hearing
Frequency:the number of complete wavelengths that pass a point in a given time
Pitch: a tone’s highness or lowness
depends on frequency
Parts of the ear
Middle Ear:chamber between eardrum and cochlea containing three tiny bones (hammer, anvil,
stirrup) that concentrate the vibrations of the eardrum on the cochlea’s oval window
Inner Ear: innermost part of the ear, containing the cochlea, semicircular canals, and vestibular
sacs
Anatomy of the ear
Tympanic membrane - eardrum
Ossicles - bones in middles ear
malleus (hammer)
incus (anvil)
stapes (stirrup)
Cochlea - snail shaped structure which
contains hair cells
Oval Window - place on cochlea where the
stapes presses
What is the organ of corti
The primary sensory organ of hearing, located on the basilar membrane in the cochlea. It contains hair cells, which convert sound vibrations into neural signals.
What are hair cells?
The receptive cells of hearing. Their cilia bend in response to sound waves, triggering electrical signals sent to the brain.
What is the function of the basilar membrane?
Supports the Organ of Corti and vibrates in response to sound. Different regions detect different frequencies:
Base (near oval window) → High frequencies
Apex (far end) → Low frequencies
What is the tectorial membrane?
A gel-like structure above the basilar membrane. The cilia of hair cells push against it when the basilar membrane vibrates, leading to signal transduction.
Basilar membrane, tectorial membrane
ion channels of auditory nerve
How do these structures work together to process sound?
Sound waves enter the cochlea and vibrate the basilar membrane.
This causes hair cells to bend against the tectorial membrane.
Bending opens ion channels, generating electrical signals.
Signals travel via the auditory nerve to the brain for interpretation.
Overview of the cochlea
Organ of Corti - organ on the basilar
membrane which contains hair cells
Hair cell - receptive cell
Basilar membrane - a membrane in the cochlea that contains the organ of corti
Tectorial membrane - above the basilar membrane, cilia of hair cells move against the tectorial membrane
Where are hair cells located?
Inside cochlear coil
What are tip links?
Tiny protein filaments that connect the tips of adjacent stereocilia (cilia of hair cells). They help open ion channels when the hair bundle moves.
What happens when the hair bundle is straight?
When the bundle is straight there is a 10%
chance of ion channels being open
What happens when the hair bundle moves toward the tallest cilium?
As the bundle moves toward the tallest cillia the ion channels allow more K+ and Ca+ to enter and depolarize the cell
Cochlear nerve
What is it?
Are hair cells important to it?
Cochlear nerve - bipolar neuron
whose cell body is located in the
cochlear nerve ganglion
95% of neurons in the cochlear nerve
are from inner hair cells, which are
myelinated
The other 5% originate in outer hair
cells and are unmyelinated
The 6 steps of hearing (wowww)
Step 1: Sound Wave Entry
Sound waves enter the outer ear and travel down the auditory canal.
The tympanic membrane (eardrum) vibrates in response.
Step 2: Middle Ear Vibration Transmission
Vibrations pass through the ossicles:
Malleus (hammer) → Incus (anvil) → Stapes (stirrup)
The stapes transmits vibrations to the oval window, moving cochlear fluid.
Step 3: Cochlear Processing
The cochlea is a snail-shaped, fluid-filled structure housing the Organ of Corti (auditory receptor organ).
Pressure waves travel through the cochlear fluid, affecting the basilar membrane.
Step 4: Organ of Corti Activation
The Organ of Corti has two key membranes:
Basilar membrane – Holds hair cells (receptors).
Tectorial membrane – Rests above hair cells.
Vibrations bend hair cell cilia, opening ion channels.
Step 5: Neural Signal Transmission
Depolarization occurs as K+ and Ca²+ enter the hair cells.
This increases auditory nerve firing, sending signals to the brain.
Step 6: Frequency Coding in the Cochlea
Different frequencies activate different regions of the basilar membrane:
High frequencies → Base (near oval window).
Low frequencies → Apex (tip of cochlea).
Multiple auditory neurons carry frequency-specific signals to the brain for processing.
lecture version: Auditory pathway
Step 1: Cochlear Nucleus
First relay station in the brainstem.
Receives input from the auditory nerve.
Step 2: Superior Olivary Complex
Located in the medulla.
Codes for spatial location by comparing signals from both ears (sound localization).
Step 3: Lateral Lemniscus
A fiber tract that carries auditory information through the medulla and pons.
Sends signals to the inferior colliculus.
Step 4: Inferior Colliculus
Located in the midbrain.
Processes reflexive responses to sound and sound localization.
Step 5: Medial Geniculate Nucleus (MGN)
Located in the thalamus.
Acts as a relay station for auditory signals before reaching the cortex.
Step 6: Auditory Cortex
Located in the temporal lobe.
Responsible for sound perception, interpretation, and recognition.
What is the role of the Inferior Colliculus?
Located in the midbrain.
Processes sound localization and reflexive responses to auditory stimuli.
Relays auditory signals from the lateral lemniscus to the medial geniculate nucleus.
What is the Medial Geniculate Nucleus (MGN)?
Part of the thalamus.
Final relay station for auditory signals before they reach the auditory cortex.
Refines and processes auditory information, maintaining frequency selectivity.
What is the Auditory Cortex?
Located in the temporal lobe.
Responsible for sound perception, recognition, and interpretation.
Organized tonotopically—different areas process specific frequencies of sound.
What is Tonotopic Representation?
A topographical organization of sound frequencies in the auditory system.
High frequencies processed at the base of the cochlea and the front of the auditory cortex.
Low frequencies processed at the apex of the cochlea and the back of the auditory cortex.
Helps in distinguishing pitch and tone.
What is Phase Difference?
Phase difference refers to the difference in the arrival times of sound waves at each of the ear drums.
It helps the brain detect the direction of sound sources, especially for low-frequency sounds.
How is Phase Difference Detected?
Detected by the medial superior olivary complex (MSO).
The MSO compares the timing of sound arrivals at each ear to locate the sound source.
difference in arrival
times of sound waves at each of the
ear drums
What are Intensity Differences?
Intensity differences occur when a sound is louder in one ear than the other.
They help the brain determine the lateral location of a sound source, especially for high-frequency sounds.
How are Intensity Differences Detected?
Detected by the lateral superior olivary complex (LSO).
The LSO compares the intensity of sounds arriving at both ears to detect the direction of the sound source.
What are the three separate systems in somatosensory
Exteroreceptive – external stimuli
* Proprioceptive – body position
* Interoceptive – body conditions (e.g.,
temperature and blood pressure)
* Exteroreceptive – 3 divisions
Exteroreceptive System: 3 devisions
Touch (mechanical stimuli)
* Temperature (thermal stimuli)
* Pain (nociceptive stimuli)
* Specialized receptors respond to the
various stimuli
Cutaneous Receptors
- Free nerve ending:
- temperature and pain
- Pacinian corpuscles
- adapt rapidly, large and deep; onion-like
- sudden displacements of the skin
- Merkel’s disks – gradual skin indentation
- Ruffini endings – gradual skin stretch
Stereognosis – identifying objects by
touch
- Dermatome – the area of the body
innervated by the left and right dorsal
roots of a given segment of spinal cord
Story to help you with cutaneous receptors
When you touch an object, your skin acts as a sensory organ, detecting different types of stimuli. The cutaneous receptors in your skin play a key role in helping you feel and respond to the world around you.
First, as your skin encounters a change in temperature or pressure, free nerve endings spring into action. These simple, unprotected nerve endings are sensitive to pain and temperature, alerting you when something is too hot, too cold, or painful. For example, if you accidentally touch something sharp, these free nerve endings will immediately send a signal to your brain, causing a painful sensation.
Now, if you touch something more subtle, like the surface of a pillow, you have other receptors that help detect texture or the movement of the skin. The Pacinian corpuscles, which are deep and onion-like in structure, respond to sudden skin displacement—such as when you press into the pillow. These receptors adapt rapidly to vibrations or pressure, helping you feel even the smallest shift in your environment, like when the pillow shifts as you lay your head down.
If you apply a more gradual pressure, like gently pressing your hand against a smooth surface, Merkel’s disks are the receptors that detect that gradual skin indentation. These receptors are sensitive to light touch and help you feel things like the texture of a fabric or the detailed surface of an object.
Stereognosis
vs
* Dermatome
Stereognosis – identifying objects by
touch
* Dermatome – the area of the body
innervated by the left and right dorsal
roots of a given segment of spinal cord
What is the Dorsal-Column Medial-Lemniscus System?
It processes touch and proprioception (sense of body position).
The first synapse occurs in the dorsal column nuclei of the medulla.
It carries information about fine touch and vibration.
What is the Anterolateral System?
It processes pain and temperature sensations.
The first synapse occurs immediately upon entering the spinal cord.
What Are the 3 Tracts of the Anterolateral System?
Spinothalamic tract – carries pain and temperature information to the thalamus.
Spinoreticular tract – involved in arousal and attention to painful stimuli.
Spinotectal tract – directs attention to painful stimuli, particularly related to visual and sensory processing.
Somatosensory cortex:
Where is the Primary Somatosensory Cortex (SI) Located?
How is it organized?
Contralateral impute?
Role of SII?
Output to Association Cortex?
Location of SI:
The Primary Somatosensory Cortex (SI) is located on the postcentral gyrus of the brain.
Somatotopic Organization:
The sensory areas of the body are mapped onto the cortex. This mapping is somatotopic, meaning that each area of the body has a corresponding area on the cortex.
Areas of the body that are more sensitive (like the fingertips or lips) have a larger cortical representation.
Contralateral Input:
Sensory input to the SI is contralateral—meaning that the left side of the body sends sensory information to the right SI, and vice versa.
Role of SII:
The Secondary Somatosensory Cortex (SII) receives input from SI.
SII also follows a somatotopic organization but receives input from both sides of the body.
Output to Association Cortex:
The output from SI and SII is directed to the association cortex in the posterior parietal lobe, where higher-level processing and integration of sensory information occurs.
What is Asterognosia ?
inability to recognize
objects by touch
* pure cases are rare – other sensory deficits
are usually presen
Asomatognosia what is it?
The failure to
recognize parts of one’s own body – the
case of the man who fell out of bed
Descending Pain Control Circuit
* 3 discoveries made this possible
Electrical stimulation of the periaqueductal
gray (PAG) has analgesic (pain-blocking)
effects
- PAG and other brain areas have opiate
receptors - Existence of endogenous opiates (natural
analgesics) - endorphins
chemical senses what two does food act on
Olfaction (smell)
* detects airborne chemicals
- Gustation (taste)
- Responds to chemicals in the mouth
- Food acts on both systems to produce
flavor
Pheromones
Chemicals that influence the behavior of conspecifics (members of the same species)
* Evidence of human pheromones?
* Changes in olfactory sensitivity across and menstrual cycle
* Synchronization of menstrual cycles
* Sex differences in odors
* Men can identify menstrual stage by smell
Olfaction
Receptors embedded in the olfactory
mucosa of the nose
* Thousands of olfactory receptor proteins
* New receptors are created throughout
life
Gustation
Receptors in tongue and oral cavity in clusters
of about 50 called taste buds
* > 4 (sweet, sour, salty, bitter) primary tastes – 5th
is umami, meat or savory
* Many tastes not created by combining
primaries
* Salty and sour don’t have receptors, they merely act on ion channels
Anosmia and Ageusia what are they?
- Anosmia – inability to smell
- Most common cause is a blow to the head that
damages olfactory nerves - Incomplete deficits seen with a variety of disorders
- Ageusia – inability to taste
- Rare due to multiple pathways carrying taste
information
Selective Attention:
What is it?
What are the types?
What is Change Blindness?
Selective attention is the process by which we focus on certain pieces of information while ignoring others.
Endogenous Attention: Driven by internal cognitive processes (e.g., focusing on a task or goal).
Exogenous Attention: Driven by external events or stimuli (e.g., something catching your eye in the environment).
Change blindness refers to the phenomenon where people fail to notice changes in a visual scene because they were not attending to the area where the change occurred.
This occurs because there is no memory of what was not attended to, and the brain does not retain information about it.
