Exam 2 Flashcards
Function of the corpus callosum
Major pathway between hemispheres
Major fiber tract for inter hemispheric communication
Transcallosal info transformation takes time (20 ms delay)
When CC is cut or disrupted
Each hemisphere still gets contralateral sensory input (e.g., info from left visual field goes to right hemisphere
Motor cortex in each hemisphere still controls contralateral effectors (e.g., commands from left M1 control right hand)
BUT hemispheres CANNOT communicate
Provides opportunity to present info to only one hemisphere and see if it gets processed
Split brain patients
Surgery for epilepsy (cut CC to prevent seizures from jumping to other hemisphere)
Perform visual search task twice as fast as normal
-suggests that each hemisphere has its own mind
Posterior CC cut
Transfer of sensory (visual, tactile, and auditory) info disrupted, but higher-level (semantic) info can still be transferred
Opposed to full CC cut -> no (or close to no) data transfer
Split brain study contributions
Functional specifications
LH: language production, analytic
RH: visual-spatial processing and action
Each hemisphere can function independently (to some degree)
-even double cognitive capacity
No cross-hemisphere communication, with some residual cross-task via subcortical pathway
Limitations to split brain studies
Patients not “normal” prior to study
Findings are from a handful of patients
Brain imaging studies show that both hemispheres contribute to all functions but to a different degree
Global vs local processing
specialization in ventral stream
Global letter captures attention
RH better at global level (low spatial freq info; perception of whole)
LH better at local level (high spatial freq; perception of details)
but either can do task
Double disassociation
Local level based on HIGH spatial frequencies
Global level based on LOW spatial frequencies
Categorical vs coordinate reps
specialization in dorsal stream
Categorical (LH- abstract, top/bellow, left/right- verbal terms)
-specify the RELATIVE position between objects or between object and viewer
Coordinate (RH- specific metric, relative distance- visual-spatial)
-specify the EXACT positions and distances between objects or between objects and viewers
Functional asymmetry in dorsal pathway
Attention
Limited capacity to process information
-> competition between items for precessing (bottleneck/ capacity limits)
Attention is the mechanism that SELECTS the most important/ behaviorally relevant info at the COST of others
-> what is important changes depending upon goals of moment
Normally keeps the bias to processes info balanced, which involved a network of areas that integrate sensory and goal info (shown from spatial neglect)
Studies through:
visual search
Ponser cueing
Stroop
Two mechanisms of selection
Voluntary attention
- select info relevant to current goals and ignore irrelevant info (top-down)
- > ex. finding a friend wearing red in crowd
Reflexive attention
- re-orienting towards unexpected, but potentially important info (bottom-up)
- > ex. turning towards sound of sirens OR novel stimuli
NOT mutually exclusive
Eye movements and visual attention
We can see details only at center of gaze
Make frequent eye movements to inspect objects of interest
- 3 per second
- called overt attention
Most eye movements are sudden jumps (saccades)
-each preceded by a covert shift of attention
Attention ALWAYS precedes eye-movements, but NOT all shifts of attention are followed by eye-movements
-> covert attention (without eye movement)
Voluntary Attention
Effects of ERPs
Early in time
Effects on fMRI
Late in processing hierarchy?
Late selection
What goes to memory
What we act upon
Stroop effect
Attentional blink
Flankers task (ignore letters on sides, focus on middle letter)
[semantic processing of distractors]
Feature integration theory
We perceive simple features (e.g., color) without focused attention, but we need attention to perceive objects defined by multiple features
Attention is used to INTEGRATE (“glue”) the FEATURES of an object
Preattentive stage
- visual input is decomposed into maps of simple features
- > separate for each color, orientation, etc.
- parallel, with NO capacity limitations
- only “pooled activity” from feature map is available to awareness (“approximately”)
Attentive stage
- attention is focused onto a location
- > features can be LOCALIZED and BOUND TOGETHER (conjoined)
- > form object file (abstract representation of current features of object)
- serial (one location at a time)
- output is available to AWARENESS
- can DIRECTLY control behavior
Feature vs. conjuncture search
Feature:
Only look for specific feature (green rectangle)
Conjuncture:
Look for specific target with more than one feature (vertical green rectangle)
Spatial neglect
Ignore contralesional space
Sensory perception is INTACT
CAN direct voluntary attention to neglected side
Sensory-driven (reflexive) attention very impaired
Extinction
-problem only occurs when competition over visual fields
IM, STM and LTM differences
Capacity
- IM: unlimited (spelling partial reports)
- STM: limited, 3-4 items
- LTM: infinite
Lifetime
- IM: <500 ms (typically 150 ms)
- STM: short-lived; 50% at 4 seconds
- LTM: lifetime memory; forgetting = retrieval failure
Retrieval
- IM: fragile, eliminated by eye movements
- STM: fast, parallel
- LTM: slow
Retrograde amnesia
Amnesia for past
Intact ability to store new memories
Anterograde with some retrograde amnesia
Partial recall of memories for events prior to the amnesia onset, but their ability to form new memories is impaired
Amnesia case study: H.M.
Unable to form new long term memories (anterograde amnesia)
Some loss of events 1-3 years prior to surgery (retrograde amnesia) [memory recall]
No ability to form new episodic memories
Star mirror experiment (implicit memory/ procedural memory)
-gradually improved, but could not remember previous events
Can amnesiacs learn new semantic knowledge?
Some newly acquired knowledge, although more difficult to learn
- can learn facts (pop culture, news events, etc.)
- > semantic memory (maybe relies less on medial temporal lobe [MTL] for encoding)
Can amnesiacs learn procedural skills?
Serial reaction time task (implicit sequence learning)
No different from control, no episodic memory
Similar to mirror tracing task
Dual-process theory of recognition
Recollection and familiarity
-memory retrieval can be based on either
Recollection (Hippocampus)
- relatively slow search process
- qualitative info about prior events retrieved
- re-experiencing the encoding event at the time or recall
- true EPISODIC memory
Familiarity (Perirhinal cortex)
- relatively fast
- ‘sense of recency’ is used as basis for recognition
- feeling seen before, but not remember exact encoding event
- NOT implicit because is conscious
Dissociation between recollection and familiarity
- single dis (hippo and recollection)
- kind of double dis, but not most clear
Nondeclarative memory
Explicit memory tests
-tasks that explicitly instruct subjects to use memory (e.g., recall, recognition)
Implicit memory tests (priming)
- tasks that do not explicitly instruct subjects to use memory
- > measure the unconscious influence of experience without asking to recall the past
Vowel counting task, followed by stem completion task
Implicit memory task
- increased likelihood of solving the words that have been studied
- likely related to “activation” parts of sensory cortex
Results:
Free recall [C > A] lowest results
Cued recall [C > A] highest results
Stem completion [C < A] A results same as A cued
False memories
Memory is reconstructive
-may “remember” something that never actually happened
Unaware of how unreliable our memory can be and overly confident in the accuracy of our memories
Semantic rep. of sleep, even though specific word never shown
Recall
~40% recalled “sleep”
Recognition
-remembering lure (sleep) during recall strengthened participants memories of the lure during recognition (vs. “knowing” it had been on the list”
Basic emotions
[Ekman’s universal facial expressions]
Anger Fear Disgust Happiness Sadness Surprise
(innate)
Emotion dimensions
Describe emotions as reactions to events where each emotion is a continuous state
- Characterization based on 2 continuous variables
- valence (pleasant/unpleasant; good/bad)
- arousal (intensity of the emotion; low/high) - Characterization based on ACTIONS and goals that MOTIVATE the person to:
- approach/engage OR withdraw
Amygdala & fear - Patient S.M.
Doesn’t fear (social behavior overly trusting and friendly)
-lesion of all nuclei of amyg. bilat.; most all other subcortical structures intact
Cannot draw fear
Does not used info from eyes for any emotion (sadness and fear)
Amygdala & fear - facial processing
Sadness and fear most detectable when look at eyes, so if do not look there, unable to identify
Insula & disgust
Functional role: avoidance
Plays role in mapping bodily states with emotional experiences
Emotional decision making
Part of limbic system
