Cognitive Neuroscience

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)

• anosagnosia
• 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

• line bisection
• copying
• spontaneous drawing
• matching
• implicit processing
• memory tasks
• posner cuing paradigm

• 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

Bisect every slanted line on a page

patient does not bisect appropriately (bisection is off)

patient ignores the entre one side of the page

• 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

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

• memory is intact
• but reporting requires attention

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.

• 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

• 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.

• 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

• VAILD: contralesional and ipsilesional normal
• INVALID: ipsilesional normal, contralestional very long RT

cannot disengage from invalid cue

bilateral damage to parietal lobes

balint's syndrome

• 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

• Only reports seeing one of the two objects
• needs to close his eyes to see the other object

• 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

• 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

move system

• 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

• No problem selecting single object when it is alone
• difficulty when multipe objects are present
• cuing doesn't help

Engage

• VALID: contralesional slower but ok RT, ipsilateral looks normal
• INVALID: contralesional same as valid, ipsilateral looks normal.

no help for cuing effect

large (big difference for invalid and valid)

difficult to assess

small ( no diff for invalid and valid)

small (no diff for valid and invalid)

Parietal lobes-superior colliculus- pulvinar nucleus

• 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

when attention is on pink bar on the left than when attending to pink bar on the right

• yes!
• P1 amplitude greater for stimuli appearing on the left

• No!
• P1 amplitude is comparable for green and pink bars on the left

Another ERP component that is sensitive to color

• Location-based selection preceds color-based selection
• so hierarchical selection process

• 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

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

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?

• anatomical & neurophysiological evience
• neuropsychological evidence
• brain imaging (fmri, pet)

• 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

(Triesman proposed)

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

• Infero-temporal (ventral) - the WHAT
• Parietal (dorsal) - WHERE/HOW

Spatial attention

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

• 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

• For feature target search, the # of distractors doesn't matter, same RT.
• For conjunction search, as # of distractors increase, RT increases

Reaction time should nto be affected by increasing # of distractors (bc it is a feature search task)

Reaction time is a function of the # of distractors bc it is a conjunction task

• Pre-attentive Stage
• Attentional Stage

• Pop-out effect
• primitive features of vision are detected in parallel
• (feature search- parallel search)

• Increasing RT with # of distractors
• complex objects are detected through serial processing through attentional resources
• (conjunction search- serial search)