Spatial Attention Flashcards
Lectures: 9/29-10/13
Describe Attention
A set of processes that interact with other processes in the performance of different perceptual, cognitve, and motor tasks
What are some traits of attention?
- Alertness
- Concentration
- Selectivity
- Control
Why do we need Attention?
We have a limited capacity to process all information based on relevance to current goals
- Attention selects the stimuli that should be further processed
Describe the difference between early and late selection
Early Selection
- Processes that occur early on
ex. hear a noise when driving
Describe Late Selection
Selectivley ignoring stimuli to selectivley focus on a certain stimulus
- ex. looking for a street wign when driving
Describe the spotlight metaphor of spatial attention
- May move from one location to another
- Can zoom in & out; have a narrow or wide “beam”
- Attended location not necessarily same as where eyes are fixated
What does the pop-out effect say about feature binding?
A sinlge trait of a stimuli allows it to pop out quickly despite the set size
What does conjunction search say about feature binding
Spotlight of attention searches each item serially to bind features
- ex. look for the blue t in a set size of many orange T’s/L’s and blue L’s
Describe the Ventral stream
Primarily concerned with identifying what an object is
- Where objects are bound
Describe the Dorsal stream
- Specialized for spatial processing
- Attending to and acting on objects
How is the salience map of space organized?
Topographically
Where is the salience map of space located?
what does it do?
located in the parietal cortex
- allocates spatial attention to intergrate or bind visual information
- Re-enterant feedback; spotlight metaphor
- binding of “what” with “where”
what is the object discrimination task?
what does it reveal?
asks subject to distinguish between two objects, and choose the non-novel object
what is the landmark discrimination task?
what does it reveal?
Monkey has to choose the well that is closest to the stimuli, test spatial location.
- Monkey with lesion in ventral stream had issues with spatial location
Describe Bailnt’s Syndrome
- what parts of the brain are damaged
- what are the symptoms?
- what does it mean to be lost in space?
Bilateral Parietal lobe damage
Patients are “Lost in Space”
- Representing space
- Acting on space
- Allocating spatial attention
Describe Agnosia
Inability to distinguish between objects
Descirbe the lived experience of Private M. Holmes, who had bilateral lesions of the parietal lobe
- Normal visual percpetion
- Could see and recognize objects
- Could not determine location of objects
- Could not accuratley reach out to grasp objects
What are the Hallmark Charactersistics of Balint’s syndrome?
- Simultanagnosia
- Optic Ataxia
- Ocular Apraxia
What is Simultanagnosia?
- Impaired awareness of multiple visual objects or whoel scene
- Can recognize single objects but cannot compute spatial relationship between objects
What is optic ataxia?
- Impaired reaching behavior under visual guidance
Describe a test for Simultagnosia
Patient is asked what they can see
1) can see a comb and a spoon individually
1) can not see the objects together, can only see the comb or the spoon seperatley
Describe a test for optic ataxia
What types of errors could be observed?
What double dissociation might be observed with agnosia vs. optic ataxia patients?
Patient is asked to put their hand through a slot in a board. The patient could not put hand in slot successfully.
- Orientation errors
- Direction errors
Agnosia Patients = Can’t consciously describe an orientation of stimuli, but are able to act as if they understand the orientation
Optic Ataxia Patients = Can tell you orientation of stimuli, but cant act according to orientation
Describe Patient DF
What skill was she normal at?
What skill was she impaired in?
A 25 year old woman with carbon monoxide poisoning, that resulted in visual agnosia.
Normal = Visuomotor Posting
Impaired = Orientation Matching (often turns it the opposite way)
Describe the ventral vs. dorsal paths in terms of patient DF & RV
Ventral path
- Object perception
Ventral stream impairment
- Conscious perception problem, but intact action ability
Dorsal Path
- Object action
- Impaired action ability, normal conscious perception
What is Ocular Apraxia?
- Fixation of gaze without primary motor deficit
- Impaired ability to voluntarily shift gaze towards visual stimuli
Describe the grabbing and estimating experiment
How does a patient with Visual Agnosia perform on this task vs. a patient with optic ataxia?
Visual Agnosia (DF)
- Normal = Grasp Calibration
- Poor = Manual estimation
Optic Ataxia (RV)
- Poor = Grasp Calibration
- Normal = Manual estimation
How does Ocular Apraxia affect fixation patterns?
How can you evaluate whether someone might have Chaotic fixation patterns?
- Chaotic fixation patterns
- Failure to fixate on informative regions (irrelevant perceptual details capture gaze, which leads to erratic fixation patterns)
Healthy subjects eyes track along with the facial features of a given stimuli vs. Patient IR whose eyes track in an unorganized manner
Why do the what and where pathways interact?
To allocate spatial attention to integrate or bind visual information
How do the where and what interactions integrate and bind visual information?
- Re-entrant feedback
- Prevent illusory conjunctions
- Less critical for stored object representations (ex. a yellow banana)
Patient RM was a 54 year old man who suffered two strokes.
After the strokes he was impaired in binding objects under certain conditions.
Where what parts of his brain were damaged?
He has nearly symmetrical bilateral parietal-occipital damage
What task tested illusory conjunctions?
How did patient RM perform on this task?
Feature binding task
- He could only see one stimulus at a time
- He misbound the features of an the stimulus
Patient GK suffered two strokes at age 48, that resulted in bilateral parietal lesions.
How did he respond to the following questions?
1) Are the small circles at the top or bottom of the oval shape?
2) Are the eyes at the top or the bottom of the face?
1) 50% accuracy
2) ~90% accuracy
His FFA area was activated to perceive the circles as eyes
- when circles were changed to squares he could not perceive them as faces - lines for a nose and mouth had to be added
What do gestalt grouping effects on extinction reveal?
One item trials
- could accurately describe features despite strong or weak grouping
Two items trials
- The stimulus that went extinct was the weak grouping
- He saw the strong group
What area of the brain is damaged to result in neglect syndrome?
Unilateral parietal lobe damage
Usually seen in patients with right parietal damage
What does right parietal damage lead to?
Which side o
Right parietal damage = Neglect on the left side of space
- Left parietal damage leads to milder symptoms
What are the Clinical Characteristics of Neglect Syndrome?
1) Hemispatial Neglect
2) Extinction to Simultaneous Stimuli
3) Hemiakinesia, Motor Exctinction Impersistence
Describe Hemi-spatial Neglect?
- Fail to report or respond to stimuli
- Neglect of hemispace when asked to perform tasks
- Fail to recognize contralateral extremities as their own
Describe extinction to simultaneous stimuli?
Multiple stimuli compete with each other and leads to the extinction of one stimuli
Describe Hemiakinesia, Motor extinction and Impersistence
Neglect syndrome is not visual – also extends to motor function.
- Patients neglect one half of the body
Describe Allesthesia
- Pain referred to the non-neglected side of the body
Describe Anosognosia
Unawareness of the deficit
- They see nothing wrong in their world and perceive their world as normal
- The brain creates an illusion of wholeness
What are the the three theories on what might drive neglect?
1) Primary Sensory Disorder
2) Attentional Disorder
3) Representational Disorder
Why is Hemi-neglect not a Sensory Disorder?
- Objects in neglected space activate the appropriate visual regions in occipital lobes
- Neglect affects auditory and tactile judgements as well as vision
- Phenomenon of visual extinction suggest different perceptual representations are competing for attention (& visual awareness)
Burning house experiment, when presented with a regular house and burning house patient chose to live in the regular house 81% of the time.
- This means - that the ventral stream continues to process neglect objects up to the stage of object recognition and possibly semantics
Findings from the Tactile Maze Experiment, where even with non-neglected arm – patients showed neglect
Describe why Hemi-neglect might be an attentional disorder
- Line bisection test
Hemi-neglect patients are impaired in disengaging and moving attention to a target location
Ex. a patient had damage on the right hemisphere
- The right hemisphere can’t compete with the left hemisphere. it wants to shift attention to the left visual or motor field, but attention is stuck to the right visual field because the unimpaired left hemisphere is dominant.
If systems are seemingly symmetrical, why is there a right hemisphere dominance of spatial neglect?
- Might reflect corresponding asymmetry in spatial attention
- Standard Theory of Neglect
What does the standard theory of neglect argue? in terms of right hemisphere dominance
- Right hemisphere controls shifts of attention to both left and right space
- Left hemisphere controls attention to only right space
- RH damage will impair attention to left space, while LH damage can be compensated
The problem with the Standard Theory of Neglect is that –there is no clear evidence that the brain network mediating spatial attention is either
1) asymmetrical
2) actually damaged in neglect
Describe the Dorsal attention network
- Preparatory and voluntary goal-directed spatial attention
-Bilateral distribution (not symmetric)
Describe the ventral attention network
- Detection of salient unexpected stimuli
- Arousal and vigilance
- Mediates interruption of attentional focus controlled by the dorsal system (disengagement/reorienting attention)
Where is the ventral attention network located?
- Lateralized to the right hemisphere
The area of the brain that is damaged in most hemineglect patients is associated with what network?
The ventral attention network
What is the source of the deficit found in neglect patients?
The damage is located in
- The alerting network that stops the shifting of attention to allow the other hemisphere to control attention
SINCE THIS NETWORK IS REPRESENTED MORE IN THE RIGHT HEMISPHERE THAN THE LEFT –> primary neglect in right parietal lobe damage
Describe the difference between attentional disorder and representational disorder
Attentional Disorder
- Intact representation, but can’t attend to the left half
Representational Disorder
- You cant create the left half of your representation, and therefore cant shift or scan that half of the representation because it doesn’t exist
What did the piazza de Dumo Study argue?
Argued that subjects can not create a mental image of their left hemi space and therefore can not attend to it
What is perceptual neglect?
- The inability to attend to visual, auditory, or olfactory stimuli in the contralesional side of the perceptual domain
What is representational neglect?
- The inability to represent, describe, or explore the contralesional side of a mental image
Describe the relationship between Perceptual and Representational neglect
RN is almost always observed in association with PN
Describe the traits of the relationship between PN and RN
- Both represent core deficits of neglect
- But a few dissociations have been observed
What is a factor that might
could be due to differential involvement of visuospatial memory
- RN caused by a deficit in the interaction between working memory and attention
- Overlap in brain regions mediating RN and PN
