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Frames of reference
a means of conceiving how space and spatial relations are coded in the brain
location of objects and body parts is defined relative to the viewer's body (i.e. trunk)
- failure to detect and/or use contralesional limbs
- denial of hemiplegia or minimizing its impact
- recognition of hemiplegia- but failure to claim ownership of contralesional limbs
inability to move one side of the body
location of objects relative to one another and relative to fixed environmetnal boundaries
- there is a top and a bottom
- a left and a right
- objects parts are computed in relation to its own structure
Common tasks used to index neglect
- line bisection
- spontaneous drawing
- implicit processing
- memory tasks
- posner cuing paradigm
Line Bisection Task
- draw a line to separate a horizontal line into 2 halves
- patient with neglect draws this line off center
- can determine the magnitude of the neglect by he distance of the ignored space
Line cancellation Task
Bisect every slanted line on a page
Object-based neglect in a Line Cancellation Task
patient does not bisect appropriately (bisection is off)
Scene-based neglect in a Line Cancellation Task
patient ignores the entre one side of the page
Target detection task
- barbell drawing and subjects have to ID if there is an X
- Object-based neglect will not be able to ID X if it is on the right OR switched to the left
- Scene-based neglect will only see the X when it is on one side or the other
subjects won't draw one side of what they were asked to copy
asked to draw whatever they want and don't draw one side
Asked if two pictures are alike which are actually the same on the right side but different on the left side. patient w hemineglect says they are the same
Example of implicit processing in neglect
pts Id'ed that houses were the same, then when pts asked which house prefer to live in always answered the one without the flames
Will neglect influence memory for space?
- memory is intact
- but reporting requires attention
Memory and Neglect
Italian researchers- stand in piazza- had the pt turn around to make sure it was the neglect of that side rather than the fact that just had more interest for the other side.
Summary of Neglect
- 1. Individual ignores info contralateral to the lesion
- 2. Can occur for perceptual info, memory, motor actions, and parts of the body
- 3. Info is ignored although person is not blind, deaf, or paralyzed
- 4. usually results from R parietal lesion of vascular origin
Why is damage to the right parietal lobe more likely to cause neglect than damage to the left?
- because the right parietal lobe is involved with attention in both visual fields
- The left is only involved with the right visual field
- A residual effect of Neglect
- can ID a flashbulb on either side separately, but when both are presented at the same time the stimulus on the right leads the one on the left to be extinguished from awareness.
Normal subjects in teh posner cuing paradigm have an advantage for stimuli on which side
- stimuli on the right side (valid or invalid)
- becuase info on the right side is attended to in both of the L and R hemispheres
- so smaller attentional cuing effect for right
Deficits in disengage will look how on Posner cuing paradigm?
- VAILD: contralesional and ipsilesional normal
- INVALID: ipsilesional normal, contralestional very long RT
cannot disengage from invalid cue
bilateral damage to parietal lobes
bilateral damage to parietal lobes is called
- Severe attentional disorder- pts are functionally blind
- stare at single dixated object and difficult to disengage
- have to close their eyes to disengage
- bil. damage to parietal lobes
Bob's symptoms are
- Only reports seeing one of the two objects
- needs to close his eyes to see the other object
Four characteristics of Balint's syndrome
- 1. Occular apraxia
- 2. simultagnosia
- 3. Spatial disorientation
- 4. Optic ataxia
(fine movements) inability to change fixation from one object to another
Inability to ID more than one object per fixation
Inability to perceive spatial layout of objects around them
(coordination and movement control) inability to handle objects in space
unilateral damage to the superior colliculus
Sam's exhibits symptoms of
- does not look at you when he speaks
- does not look at the plate when he eats
- can't keep his attention steady
- cuing doesn't help
unilateral damage to superior colliculus is deficit in which orienting system
How would someone wtih unilateral damage to the superior colliculs perform on posner cuing paradigm
- VALID: contralesional very long RT, ipsilesional looks normal
- INVALID: contralesional same as for valid, ipsilesional looks normal.
cuing does not help so contralesional side same long RT for valid and invalid conditions
unilateral damage to the pulvinar nucleus of the thalamus
Paul exhibits symptoms of
- No problem selecting single object when it is alone
- difficulty when multipe objects are present
- cuing doesn't help
unilateral damage to the pulvinar nucleus of the thalamus is a deficit in what orienting system
how woudl someone with unilateral damage to the pulvinar nucleus of the thalamus perform on the posner cuing paradigm?
- VALID: contralesional slower but ok RT, ipsilateral looks normal
- INVALID: contralesional same as valid, ipsilateral looks normal.
no help for cuing effect
Ned's cuing effect is
large (big difference for invalid and valid)
Bob's cuing effect is
difficult to assess
Sam's cuing effect is
small ( no diff for invalid and valid)
Paul's cuing effect is
small (no diff for valid and invalid)
Disengage-Move-Engage corresponds w which brain regions?
Parietal lobes-superior colliculus- pulvinar nucleus
Pink bar/green bar task instructions
- your task is to respond to the target: pink bar on the left side.
- right occipital lobe electrode
- ERP is time-locked to the pink bar on left
For pink bar/green bar task, P1 component is larger where?
when attention is on pink bar on the left than when attending to pink bar on the right
Does P1 care about Attention- to Space?
- P1 amplitude greater for stimuli appearing on the left
Is P1 sensitive to Attention-to-color?
- P1 amplitude is comparable for green and pink bars on the left
Another ERP component that is sensitive to color
which preceds which? Location or color?
- Location-based selection preceds color-based selection
- so hierarchical selection process
What is the evidence that spatial attention is special?
- 1. ERP evidence: the P1 component for location occurs prior to Selection Negativity component for color
- 2. Illusory conjuctions: in the absence of spatial attention, object features are combined
Task: remember colors of letters and digits. What errors?
Miscombinations: Illusory conjuctions
- Without focused attention, features appear to be combined at random
- The miscombination of features form illusory objects in the absence of attention
The Binding Problem
How are features that are registered separately reunited to produce our inified experience of the world??
- Features are coded by separate systems
- -direction, motion, location, color, orientation
- So how do we experience the coherent world? what goes with what?
How do we know that features are coded by separate systems?
- anatomical & neurophysiological evience
- neuropsychological evidence
- brain imaging (fmri, pet)
Feature Integration Theory
- Attention is used to bind features together
- Code one object at a time on the basis of its location
- Bind together whatever features are attended at that location
Solution to the Binding Problem
Feature Integration Theory
Example of Feature Integration Theory
- When you have just a color that is different, this is a basic feature that is coded automatically without the need for attention.
- However, when you have different colors and sizes, you need attention to focus on all the features in that area so they unite together
Where and What pathways
- Infero-temporal (ventral) - the WHAT
- Parietal (dorsal) - WHERE/HOW
What binds object features together?
1 red T in the display (all T's diff colors). According to FIT this should pop-out and not require attention since it is defined by a single feature.
- 1 red T in display (T's and X's, X's are red too)
- Target now defined by shape and color
- so this involves binding features so according to FIT demands attention to each item
Visual Search experiments
- Record the time taken to determine whether target is present or not
- Vary distractos
- Search for features should be independed of # of distractors
- Conjunction search should get slower with more distractors
Findings for Visual Search Experiments
- For feature target search, the # of distractors doesn't matter, same RT.
- For conjunction search, as # of distractors increase, RT increases
Parallel Search RT
Reaction time should nto be affected by increasing # of distractors (bc it is a feature search task)
Serial Search RT
Reaction time is a function of the # of distractors bc it is a conjunction task
Triesman's two stage Theory of Visual Attention
- Pre-attentive Stage
- Attentional Stage
Triesman's pre-attentive stage
- Pop-out effect
- primitive features of vision are detected in parallel
- (feature search- parallel search)
Triesman's Attentional Stage
- Increasing RT with # of distractors
- complex objects are detected through serial processing through attentional resources
- (conjunction search- serial search)
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