Visual Inattention

1
Visual Inattention

• Lecture A

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Evaluation and Treatment of Visual Attention
Deficits
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Lecture Objectives

• Differentiate between visual inattention caused
  by right and left hemisphere lesions
• Describe the effect of visual inattention on
  occupational performance
• Differentiate between left visual field deficit
  and hemi inattention
• Demonstrate correct testing procedure for
  measuring visual attention
• Select appropriate treatment interventions

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Attention is Critical to Learning

• How closely you attend to something determines
  your level of assimilation
• Example watching TV while reading
• 90 of all learning is completed through the
  visual channel
• Divide attention between two areas of the visual
  world
• Central field
• Peripheral field

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• Central field
• Information from macular visual field
• Used for focal perceptual processing
• Responsible for identification
• Peripheral field
• Information from peripheral visual field
• Used for ambient visual processing
• Responsible for awareness of position in space in
  relation to objects
• Contributes to balance and orientation
• To move and interact with environment must
  constantly attend to and process visual
  information through both areas
• Only conscious of central processing

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• Visual attention is expressed through visual
  search and scanning

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• Saccadic eye movements are used to
• shift visual attention from object to object
• Attention is shifted between visual stimuli
• by a three step process
• Disengage step
• Stop attending to present target/object
• Move step
• Initiate saccade to new target/object
• Compare step
• Initiate saccades between targets to compare
  present target
• with past target

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Example of the three step process of shifting
attention
Attention is focused first on TMT 1
after identification is made, attention is
disengaged and moved to TMT 2 a comparison
saccade is made between the two Faces to ensure
that another TMT is being seen, then attention is
disengaged from 2 and moved to 3 and so onon
completion, the viewer is able to state that
there are 4 TMT in the picture.
2
3
1
4
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Normal Search Strategy

• Driven by need to know
• Efficient
• Designed to acquire the greatest amount of
  information in the least amount of time
• Normal, effective search strategies
• Linear strategy for structured arrays
• Left to right and top to bottom
• Clockwise strategy for unstructured arrays
• Initiate search upper left quadrant of scene
• Symmetrical search pattern
• Predictable search pattern
• Thorough and comprehensive
• Resilient
• Consistent accuracy

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• All Visual Search is Influenced by Global
  Attention
• Mediated through brainstem
• 4 As arousal sequence-Asleep, awake, alert,
  attending
• Two components
• Tonic
• Level of visual attention increases and decreases
  throughout day reflecting the sleep wake cycle
  controlled by circadian rhythms
• Phasic
• Level changes- triggered by an event or memory
• Event Seeing a bloody hand pop out from behind
  this screen can increase visual attention
• Memory Approaching a busy intersection when
  driving and remembering past experiences with
  intersections triggers increased attention and
  scanning of intersection
• Memory Seeing the teacher write a formula or
  story problem on the board causes person to zone
  out

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Neuroanatomical Basis for Visual Attention
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• CNS has developed an extensive neural network
  for control and modulation of visual attention
• 5 major cortical players
• Visual cortical relay centers
• Posterior temporal circuitry
• Posterior parietal circuitry
• Prefrontal circuitry
• Limbic circuitry
• Brainstem

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Cortical Relay Centers

• Lateral geniculate nucleus
• Tunes CNS into salient feature
• Occipital pole
• Receives input directly from retina
• Refines and enhances retinal input
• Sorts out input and sends it on to temporal and
  parietal circuitry for processing

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Posterior Temporal Circuitry

• Visual object center
• Involved in recognition
• and classification of
• objects
• Utilizes information
• from the macula
• Utilizes selective visual
• attention to organize
• visual details

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Posterior Parietal Circuitry

• Visual spatial center
• Internal maps that
• direct orientation to body
• and surrounding space
• on contralateral side
• Utilizes peripheral visual
• field input and global
• attention

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Prefrontal Circuitry

• Combines visual input with
• other information for cognitive
• application
• Directs visual search
• of contralateral space
• Maintains attention on task through activation of
  working visual memory

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Limbic Circuitry

• Supplies short term and
• long term memory circuits
• for storage of visual images
• Prefrontal areas use these
• memories to direct visual
• search

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Hemispherial Differences in Direction of Visual
Attention

• Directing visual attention is a huge task
• One way CNS accomplishes the task is by dividing
  responsibility between the two hemispheres
• First division is in engagement and direction of
  attention
• Second division is in strategy used to direct
  attention

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Engaging/Directing Attention

• Left hemisphere
• Directs visual attention towards right half of
  visual field only
• Right hemisphere
• Directs visual attention towards both right AND
  left halves of visual field
• Global direction of
• attention

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Strategy Used to Focus Attention

• Left hemisphere
• Employs a strict sequential item by item search
  strategy
• Gives it an advantage in discriminating minute
  differences in objects-detail processing
• Very focal
• Can only process a limited number of items at a
  time
• Sees the trees
• Right Hemisphere
• Breaks down visual array into groups of items
• Simultaneously processes several items
• Less spatially selectively and more broadly
  receptive
• Gives it an advantage for configural processing
• Sees the forest

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Ls example
L L L L L L L L L L L
Right hemisphere Sees the single large L. Left
hemisphere Sees the individual Ls that make up
the design
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Brainstem controls visual attention by setting
the attentional tone of the entire CNS

• Sets the level of arousal and receptiveness to
  sensory stimulation
• Visual
• Somatosensory
• Auditory
• Vestibular

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Effect of Brain Injury on Attentional Processing
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Creates Gaps and Breakdowns in the Network

• Damage to brainstem
• Person cant be aroused sufficiently to attend
• Attentional capability wavers with arousal
• Unable to engage attention
• Damage to the cortical relay structures and
  primary visual cortex
• Image is incomplete, garbled
• Input may not be sufficient to engage attention

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Brain injury

• Damage to parietal circuitry
• Internal maps are disrupted creating challenges
  attending to extrapersonal and personal space
• Map no longer contains representation of space
• May not know where you are, where youve been or
  where you are going
• Disruption of body image
• May not recognize body parts
• Greater deficit if it occurs in the right
  parietal lobe
• Creates condition known as neglect

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Brain Injury.

• Damage to prefrontal circuitry
• Alters the cognitive application of visual search
• Difficulty engaging and shifting attention to
  acquire information from environment needed for
  problem solving
• Impairs anticipation of visual stimuli
• Slows visual search
• Reduces speed of information processing
• Significant affect on performance in dynamic
  environments where anticipation and speed is
  critical to success
• Driving
• Impairs working visual memory
• Cant retain information long enough to search
  for it
• Impairs motivation and judgment
• Lacks desire or doesnt see need for visual
  search

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• Because development of prefrontal circuitry is
  dependent on experience, person with significant
  experience completing an activity has greater
  capacity to direct attention for that activity
  even after brain injury
• Example two persons with same brain injury
• One is a 16 year old with 6 months driving
  experience
• The other is a 30 year with 10 years of
  experience as an over the road truck driver
• Which one will likely perform better on a behind
  the wheel driving assessment?
• Because visual search capability is learned in
  context, person demonstrates better attentional
  skills in a familiar context
• Patient searches home environment more
  effectively than clinic environment

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Brain injury

• Damage to temporal circuitry
• Doesnt attend to details sufficiently
• Impairs object identification
• More severe if occurs in left hemisphere
• Hemisphere is detail detail
• Damage results in alexia and agnosia
• Damage to limbic circuitry
• Person doesnt search and attend to objects in
  the environment because they do not hold any
  emotional relevance
• To engage attention, object must have significant
  emotional relevance
• Pets, babies, loved ones

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Changes in Visual Search Caused by Visual
Inattention Right Hemisphere Lesions

• Primary change is a reluctance or inability to
  direct visual search towards the left side
• Capability of right hemisphere to direct search
  both left and right enables patient with left
  hemisphere lesion to continue to initiate search
  of the right visual field using capabilities of
  right hemisphere
• In right hemisphere lesions, no back up
  capability exists to search left field
• Patient is unable to direct visual search towards
  left

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• Right hemisphere lesions
• Patient may over attention to right visual field
• Balance between attention to two fields is
  disrupted causing over stimulation from right
  visual field
• Patient engages attention first to most
  peripheral stimuli on right
• Oculomotor performance changes
• Saccades take longer to initiate and complete
  towards the left
• Have difficulty disengaging from stimulus
  especially if it is located in the right visual
  field
• Saccades towards left are less accurate
• Inability to fixate gaze on target in the left
  visual field
• Uses an asymmetrical search pattern
• Person initiates search from right side
• Confines search to right half of array

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• Creates hemi-inattention
• Inattention to one half of the visual space
• At least two forms of hemi-inattention
• Person is hypo-attentive toward left half of
  visual space
• Unable to activate attentional mechanism in that
  direction
• Person is hyper-attentive towards right half of
  visual space
• Attention is captured by stimuli on right and
  person is unable to break away
• Most severe form of hemi-inattention is visual
  spatial neglect
• Person is unaware of the left visual space and
  unable to direct attention towards the left
• Often created by the combination of a primary
  sensory loss-hemianopsia-with hemi-inattention
• Occurs only with right hemisphere lesions

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• Additional changes in visual search
• Disruption of compare phase of visual search
• Reluctant to rescan for information especially on
  the left side
• Can display diminished global awareness of
  environment
• Doesnt search environment for details or
  landmarks needed for orientation
• Doesnt pick up on cues
• Example if told there is chocolate pudding
  sitting on the left side of the food tray,
  patient still will not look for the pudding

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To SummarizeCharacteristics of Hemi Inattention

• Patient will have difficulty searching for and
  using information from the environment
• Unable to initiate scanning towards the left
• Sometimes unable to cross midline towards left
• Demonstrate asymmetrical, incomplete search
  pattern confined to the right side
• May be overly attentive to right or does not look
  for information towards the left
• Cognitive involvement in that when information on
  the left is pointed out, person is unable to use
  it

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Changes in Visual Search Caused by Visual
Inattention Left Hemisphere Lesions

• Symmetrical loss in searching visual arrays for
  details
• Related to disruption of item by item search
  strategy and inability to locate details in
  visual arrays
• Patient has difficulty with the disengage, move
  and compare phases of visual search
• Limits processing of detail from the visual array
• Can impair ability to discriminate between
  objects with discrete differences
• May not obtain sufficient information from a
  scene to complete competent decision making

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• Tyler
• (1969) Defective Stimulis Exploration in Aphasic
  Patients. Neurology, 19105-112.
• Compared search patterns in persons with left
  hemisphere lesions with control subjects
• Black dots on figure indicate foveal fixation and
  gaze shift
• Subjects asked to search pictures and describe
  what is happening
• Normal subjects moved through the three phases of
  visual search
• Scanned pictures focusing on the most informative
  parts of the picture first (A)
• Then repeated scanning to extract more detail (B)
• Returned to action part of the scene to confirm
  impression (C)
• On completion of search subject was able to
  describe what was happening in the picture
  including specific details of the scene

A
B
C
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• Subjects with anomnia (word
• finding problems) and mild
• aphasia demonstrated the
• same pattern as normals
• Subjects with severe expressive
• aphasia demonstrated breakdown
• in the three phases of search

A
B

• Scanned normally for 2-10 seconds,
• seeking out most informative areas
• A and B

C

• But then stopped and did not scan
• for further detail, instead just repeated
• initial scan pattern eventually fixating in one
• area C and D
• On completion of search, subject able to
• give general description but unable to
• describe any details of the scene

D
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Changes in Visual Search in Persons with Cortical
Lesions

• As a whole persons with both right and left
  hemisphere lesions are slower in scanning and
  show more erratic fixation
• Causes them to get only part of the picture
• Experience particular difficulty engaging
  selective attention and applying an organized
  search strategy to view complex visual arrays

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• Selective attention is vulnerable because it
  requires implementation of a focal search
  strategy and the ability to tune out extraneous
  input
• Serial search becomes increasingly difficult as
  the number of distracters in a display increases
  and/or if the distracters are difficult to
  discriminate from the target
• Example searching for a single person in the
  picture of a football team of 45 players all
  dressed in their suits with their helmets on
• Research on normal adults has shown that this
  kind of visual processing is limited by
  attentional capability
• Requires concentration and effort

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• Research completed by Weintraub and Mesulam on
  subjects with milder head injury demonstrates
  these limitations in search
• (1988) Visual hemispatial inattentionstimulus
  parameters and exploratory strategies. J Neuro,
  Neurosurgery Psych 51 1481-1488.

Subjects with and without brain injury were asked
to cross out the no sun symbol on two
cancellation tasks with different arrays
Symbols with structured array
Symbols with random array
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• Findings
• Subjects with brain injury showed a specific
  pattern of breakdown in selective attention
• Scanned adequately on task with structured array
• Insignificant asymmetry observed
• Breakdown in visual search capability occurred
  when asked to cross out symbols on the more
  complex unstructured visual array task

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• Findings
• Normal subjects were able to impose an organized
  search strategy on the unstructured array in
  order to ensure that all targets were identified

Example
Direction of visual search
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• Subjects with brain injury were unable to impose
  an organized search strategy and instead
  demonstrated random and often asymmetrical search
  which resulted in cancellation of fewer targets

• They also cancelled out figures which were
  similar
• to the no sun target but not correct
• Indicating a breakdown in working visual memory

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Implications of Visual Search Research

• Inability to efficiently and completely scan a
  visual array may cause patient with inattention
  to make errors on tasks which measure complex
  perceptual processing
• Example Embedded figures test used to measure
  figure ground perception given to a subject with
  hemi-inattention and left hemianopsia secondary
  to right hemisphere stroke

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Example Performance of patient with left VFD and
hemi- Inattention on figure ground perception test

Patient is instructed to identify the three
overlapping objects that comprise the top
picture. The pt does not see or attend to the
left half of the page (indicated with orange
shading). Based on what he can see, he selects
the pitcher the key and the mallet. All
salient target features are located on the left
side so the pt selects the correct objects and
gets a perfect score.
(next slide)
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The patient is then shown this picture. Once
again because of the left VFD and hemi-inattentio
n, he only searches the right half of the
picture. This time two of the figures (the plane
and bird) are located on the left side and he
does not see them. He doesnt see enough of the
third figure (the egg) to be able to select it so
he selects the whale, the moth and the bowl and
scores 0 on the test. All in all on the
entire test, the patient only gets 3/8
figures correct.
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DOES THIS PATIENT HAVE A FIGURE GROUND
DEFICIT? OR DID THE
IMPAIRMENT IN VISUAL SEARCH CREATED BY THE VFD
AND INATTENTION PREVENT THE PATIENT FROM
SEEING THE CORRECT OBJECTS? HOW WOULD YOU KNOW
IF YOU DIDNT FIRST EVALUATE THE LOWER LEVEL
PROCESSES ??
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Affect of Visual Inattention on Occupational
Performance

• Creates gaps and asymmetry in visual information
  sent to CNS
• Quality of adaptation decreases because CNS does
  not have sufficient visual information to make an
  appropriate decision
• Severe effect on cognitive performance because
  80 of all learning is reinforced through vision
• Can affect performance of all ADL
• But especially ADLs completed in dynamic
  environments
• Driving, work, community

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The Affect of Deficits in the Lower Level
Processes of the Hierarchy on Higher Level
Processes of Pattern Recognition, Memory and
Cognition
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• Disruption of lower level processes can cause
  incorrect or incomplete visual input to be sent
  to CNS
• This will have a domino effect, first altering
  pattern recognition which then alters storage of
  visual memory
• Which ultimately impairs cognition

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• There are three requirements for object
  recognition and storage in memory
• Must be able to construct a three dimensional
  model of the object from the two dimensional
  image falling on the retina
• So the CNS can recognize the object
• Must have access to an organized memory bank of
  such descriptions and models and
• Must have a way of associating the new model with
  those in storage
• So that object can be categorized and stored in
  memory
• Presence of VFD, poor acuity, oculomotor
  impairment or visual inattention can affect step
  1 causing failure to accurately construct the
  visual model

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• If the model is not accurate
• The CNS may not recognize it
• Example the word delicious may be seen as
  licious by a person with a left hemianopsia
• Delicious makes sense to the CNS and is stored
• Licious does not make sense to the CNS and is
  discarded as a nonsense word
• The CNS may misidentify it
• Example the word Eight may be seen as Fight by a
  person with poor acuity
• The word eight makes sense in the context of the
  sentence Eight muffins were left on the plate
  and is stored
• The word fight does not Fight muffins were
  left on the plate and the sentence is discarded
• The person will be unable to use the visual input
  to complete cognitive processing

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• Fortunately we dont store or learn everything
  exclusively through the visual channel
• Models are stored three ways
• Visually
• By color, contrast and detail
• Physically
• By somatosensory qualities of weight, size,
  texture
• Verbally or Semantically
• By name and definition of purpose

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• Objects can be identified through more than one
  sensory mode and through modes other than those
  through which they were originally coded and
  stored
• Example An apple can be identified three ways
• I can show you an apple
• I can have you close your eyes and put an apple
  in your hand to feel
• I can describe the qualities of an apple to you
• Its round, red, smooth, juicy and keeps the
  doctor away
• In real life information about objects is
  available via several modes and one sensory mode
  is used to verify another
• I see the apple
• I pick it up and smell it
• I say apple

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• Because of multi-sensory processing, a patient
  may show deficits in object recognition only in
  situations where processing is limited to the
  visual mode
• Example a testing situation where the patient is
  shown a picture of an object and asked to
  identify it
• The patient may fail this task but if allowed to
  tactually explore the object or if given a verbal
  description of the object, may be able to
  successfully identify it

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• There are two common daily activities that
  require a person to obtain information
  exclusively through the visual mode

Can you name them????
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Reading Driving
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Affect on Visual Cognition

• Deficits in visual cognition result in difficulty
  identifying the spatial properties of objects and
  mentally manipulating these properties for the
  purpose of decision making
• Visual cognitive deficits include agnosias,
  alexias, disorders of figure ground perception,
  position in space etc.

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Visual Cognition cont

• Disorders were originally thought to occur as
  isolated, pure perceptual disorders without other
  associated deficits
• Now known that most visual cognitive deficits are
  accompanied by subtle deficits in lower level
  visual processes, other sensory processes and
  memory
• Impairment in visual cognition occurs because the
  CNS is receiving insufficient or inaccurate
  visual input due to deficiencies in lower levels
  of visual processing