CH 7: Mechanisms of Perception Flashcards
List the 3 types of sensory cortex.
- Primary Sensory cortex
- Secondary Sensory cortex
- Association cortex
Define PRIMARY SENSORY Cortex
- Receives most input directly from the thalamic relay nuclei of that system
Define SECONDARY SENSORY Cortex
- Receives most input from the primary sensory cortex of the same system
Define ASSOCIATION Cortex
- Receives input from >1 sensory system
- Most input to areas of association cortex comes via areas of secondary system
WRT Sensory System organization, explain what is meant by the term, ‘HIERARCHICAL ORGANIZAITON’
- Organization into a series of levels ranked WRT one another
- ie) In sensory systems, primary cortex, secondary cortex, & association cortex perform progressively more detailed analyses
- Sensory structures org in hierarchy based on specificity & complexity of their function
- Each level of hierarchy receives inputs from lower levels & adds another layer of analysis before passing it up hierarchy
- The higher the level of damage
- -> ^specific & complex deficit
WRT Sensory System organization, explain what is meant by the term, ‘FUNCTIONAL SEGREGATION’
- Organization into diff areas, each of which has diff function
- Each of the 3 levels of cerebral cortex in each sensory system contains functionally distinct areas that specialize in diff kinds of analysis
- 3 levels of cerebral cortex = primary, secondary & association
WRT Sensory System organization, explain what is meant by the term, ‘PARALLEL PROCESSING’
- Simultaneous analysis of a signal in diff ways by the multiple parallel pathways of a neural network
- aka info flows through the components over multiple pathways
Summary Model of Sensory System Organization (2)
see Figure 7.1
- Sensory sys are hierarchical, functionally segregated, & parallel
- Sensory sys are characteristic by a division of labour = multiple specialized areas, at multiple levels, interconnected by multiple parallel pathways
Describe the neural mechanisms underlying SOUND LOCALIZATION.
- Sound localization is mediated by the lateral & medial superior olives (but in diff ways)
- Sound originates to (L) ear
- -> Sound reaches (L) ear first
- -> Louder in left ear
- -> some neurons in MEDIAL superior olives respond to slight diff in TIME OF ARRIVAL of signals
- -> some neurons in LATERAL superior olives respond to slight diff in AMPLITUDE of sounds
- Medial & lateral superior olives project to SUPERIOR COLLICULUS & INFERIOR COLLICULUS
- -> Receives auditory input
- -> Laid out acc. to map of auditory space
What is the function of SUPERIOR COLLICULI?
- Locating sources of sensory input in space
Describe the effects of AUDITORY CORTEX DAMAGE.
Bilateral vs. unilateral lesions.
- Bilateral lesions
- -> shock
- -> complete loss of hearing
- -> hearing recovers after weeks
- -> permanent effects = lose ability to localize sounds & impairment of ability to discriminate frequencies
- Unilateral lesions
- -> disrupt ability to localize sounds in space contralateral, but not ipsilateral, to the lesion
Describe CONDUCTIVE DEAFNESS.
- Damage to the ossicles
Describe NERVE DEAFNESS.
- Damage to the cochlea or auditory nerve
- Major cause = loss of hair cell receptors
- IF only cochlea damage
- -> Individual has nerve deafness for some frequencies but not others
List 4 types of CUTANEOUS RECEPTORS.
- Free Nerve Endings
- Pacinian Corpuscles
- Markel’s Disks
- Ruffini Endings
Describe FREE NERVE ENDINGS (3).
- Neuron endings w/ no specialized structures
- Sensitive to temp changes & pain
- Simplest cutaneous receptors
Describe PACINIAN CORPUSCLES (3).
- Adapts rapidly
- Responds to sudden displacements of skin but not to constant pressure
- Largest & deepest cutaneous receptors = onion-like
Describe MARKEL’S DISKS (2).
- Adapts slowly
- Responds to gradual skin indentation
Describe RUFFINI ENDINGS (2).
- Adapts slowly
- Responds to gradual skin stretch
Explain the functional significance of fast vs. slow receptor adaptation.
- Having receptors that adapt quickly vs. slowly
- -> Provides info about the dynamic & static qualities of tactual stimuli
- ie) don’t feel constant pressure of clothes on skin unless focus
Describe how receptors generally function.
- Stimuli applied to skin
- -> Change chemistry of receptor
- -> Change permeability of receptor cell membrane to various ions
- -> Neural signal
List the 2 major somatosensory pathways.
- Dorsal-Column Medial-Lemniscus System
2. Anterolateral System
Describe the Dorsal-Colum Medial-Leminiscus System
- Carries info about touch & proprioception
- It’s sensory neurons enter spinal cord via dorsal root
- -> Ascend inspiralaterally in the dorsal columns
- -> Synapse in dorsal column nuclei of medulla
- Proprioception = awareness of position & movement of body
Describe the Anterolateral System
- Carries info about pain & temp
- see pg 178
Name the areas of association cortex that somatosensory signals are sent to, & describe the functional properties of one of those areas.
- Sent to areas of association cortex in prefrontal & posterior parental cortex
- Posterior parental cortex contains bimodal neurons
- BIMODAL NEURONS respond to activation of:
1. Somatosensory stimuli
2. Visual stimuli - Visual & somatosensory receptive fields of each neuron are spatially related
- ie) if somatosensory receptive fields centred in (L) hand, its visual field is adjacent (L) hand
- -> If (L) hand moves, visual receptive field of the neuron moves w/ it
List the 2 major types of somatosensory AGNOSIA.
- ASTEREognosia
2. ASOMATognosia
Describe Astereognosia
- Inability to recognize objects by touch
Describe Asomatognosia
- Failure to recognize parts of one’s own body
- Usually unilateral (only affects (L) side of body)
Describe the RUBBER-HAND ILLUSION
- Feeling that an extraneous object (in this case, a rubber hand) is actually part of one’s own body
- Hide healthy person’s hand from their view via screen
- Place rubber hand beside real hand but in clear site
- Stroke both healthy & rubber hand
- Person thinks rubber hand is their own
- -> Temp in hidden real hand drops
Explain why the 1st reason why the perception of pain is said to be paradoxical.
- ADAPTIVENESS OF PAIN
- There’s no stimulus to pain
- Pain = response to potentially harmful stimulation of any type
- Pain warns us not to engage in dangerous activities
- -> important for survival
Explain why the 2nd reason why the perception of pain is said to be paradoxical.
- LACK OF CLEAR CORTICAL REPRESENTATION OF PAIN
- Pain has no obvious cortical rep
- Pain stimuli activate many areas of cortex, though none of these areas seem necessary for perception of pain
- ie) removal of one of those areas isn’t ass w/ change in pain threshold
Explain why the 3rd reason why the perception of pain is said to be paradoxical.
- DESCENDING PAIN CONTROL
- Pain can be suppressed by cognitive & emotional factors
- Descending analgesia pathways
- see pg 183
Describe NEUROPATHIC PAIN & when it commonly develops.
- Severe chronic pain in absence of a recognizable pain stimulus
- Commonly develops after injury
- -> Injury heals & seems to be no reason for further pain but patient experiences chronic excruciating pain
Describe some of the putative neural mechanisms of neuropathic pain.
- Unknown exact mech
- Somehow caused by pathological changes in NS induced by the original injury
- -> Caused by abnormal activity in CNS
- -> Thus cutting nerves from perceived pain location doesn’t bring comfort
Describe 2 adaptive roles of the chemical senses.
- EVALUATION OF POTENTIAL FOODS
- = ^consumption of E sources & nuts while avoiding toxins
- ie) in natural environment where food isn’t labelled - REGULATING SOCIAL INTERACTIONS
- Many sp release pheromones (chemicals)
- -> influences physiology & behaviour of conspecifics
Define OLFACTION
- Smell = response of olfactory sys to airborne chemicals that are drawn by inhalation over receptors in nasal passages
- see Figure 7.18
Describe OLFACTORY MUCOSA.
Where does its output go to?
- Mucous membrane lining upper nasal passages
- Contains olfactory receptor cells
- -> Each receptor cell contains only 1 type of receptor protein molecule
- -> Sends signals to olfactory bulbs
Describe OLFACTORY BULBS
Where does its output go to?
- Receives signal sent from olfactory mucosa
- Its output goes primarily to amygdala & piriform cortex
- PIRIFORM CORTEX = area of medial temporal cortex adjacent to amygdala
Describe OLFACTORY GLOMERULI
- Clusters of axons of olfactory receptors that lie near surface of olfactory bulbs
- Receives input from 1000s of receptor cells
Define GUSTATION
- Taste = response of gustatory system to chemicals in solution in oral cavity
Describe TASTE BUDS & how its output is communicated.
- Clusters of taste receptor cells (50-100)
- On tongue & parts of oral cavity
- In each bud, only 1 receptor cell (=presynaptic cell) synapses onto neuron carrying signal away from bud
- -> communication via gap junctions
- -> send signal to primary & secondary gustatory cortex
WRT the Gustatory System, explain what’s meant by BRODLY TUNED.
- Each receptor cell responds to wide range of tastes
- 5-primary component processing theory of tastes implies that each gustatory receptor & neuron is ‘broadly tuned’
WRT the Gustatory System, explain what’s meant by NARROWLY TUNED.
- Each receptor cell responds to only 1 taste, or at least to very few of them
- via ^^^accumulating list of receptor molecules & mechanisms
List 2 potential effects of brain damage on the chemical senses.
- Anosmia
2. Ageusia
Describe ANOSMIA
- Inability to SMELL
- Common cause = blow to head causing brain displacement w/in skull
- -> Shears olfactory nerve where pass through cribriform plate
- Less complete deficits in olfaction liked to neurological disorders
- ie) AD, down syndrome, epilepsy, etc.
Describe AGEUSIA
- Inability to TASTE
- Rare bc sensory signals from mouth are carried via 3 separate pathways
- Partial ageusia = limited to anterior 2/3 of tongue on 1 side
- -> after damage to ear on same side
- -> bc branch of facial nerve that carries gustatory info from anterior 2/3 of tongue passes through the middle ear
Describe SELECTIVE ATTENTION
- Ability to focus on a small subset of the multitude of stimuli that are received at any one time
Describe the 2 characteristics of Selective Attention.
- Improves perception of the stimuli in focus
2. Interferes w/ perception of the stimuli not in focus
Explain what’s meant by EXOGENOUS vs. ENDOGENOUS Attention.
Attention can be focussed in 2 diff ways:
- ENDOGENOUS Attention = by internal cognitive processes
- ie) attention focused on tabletop bc searching for keys
- Mediated by TOP-DOWN neural mech (from higher to lower levels) - EXOGENOUS Attention = by external cognitive processes
- ie) attention can be drawn to tabletop bc cat tipped over a lamp
- Mediated by BOTTOM-UP neural mech (from lower to higher levels)
Describe the phenomenon of CHANGE BLINDNESS.
- Difficulty perceiving major changes to unattended-to parts of a visual image when the changes are introduced during brief interruptions in the presentation of the image
- Occurs bc when we view a scene, we have no memory for parts of the scene that aren’t in focus of our attention
- see pg 190 for explanation
Describe the neural mechanisms of attention (2).
- Selective attention works by strengthening the neural responses to attended-to aspects & weakening the responses to others
- -> this dual mech = push-pull mechanisms
- Attention is activated by circuits in prefrontal & parental cortex
- -> Enhances activity in task-relevant sensory circuits & suppress activity in irrelevant sensory circuits
Describe the disorder of attention known as SIMULTANAGNOSIA.
- Difficulty attention to >1 stimulus at a time
- ie) patient can identify objects in any part of his visual field if they were presented individually
- -> Thus he isn’t suffering from blindness or other visual field defects
Simultanagnosia is usually ass. w/ damage to what part of the brain?
- Bilateral damage to posterior parental cortex
