Justice Obiahuba

• Introduction
• Definitions and Distinctions
• Types of Visual Agnosia
• Visual Processing Model
• Neuroanatomy of Agnosia
• Neglect
• Neuroanatomy of Neglect
• Models
• Neuropsychological assessment
• Treatment

• Left Brain  Language, Planned movements,
• Right Brain 

• https://www.youtube.com/watch?v=T1qnPxwalhw

Agnosia is the inability to process sensory information
Visual Agnosia  visual disorder of perception and recognition
Neglect: inability of a person to process and perceive stimuli on one side of the body or environment, where that inability is not due to a lack of sensation

• Sensation
• Perception
• Naming
• Recognition

• Intact visual acuity and other visual abilities
• CANNOT form a whole mental representation of an object
• Can perceive elements of an object but cannot integrate them
• Can recognize objects via different sensory modalities

• Recognition impairment not attributable to decline in intelligence, memory, language or attention
• CAN form mental representation of an object
• Patients can accurately distinguish between objects
• Can’t identify object, its features, or functions

• Superordinate level
• Basic Level
• Subordinate level

• Differential impairment of categories of objects
• Ranges from narrow to broad categories of impairment
• Eg. Human faces, living things, non-living things

• Impaired facial recognition
• Not only human faces
• Can identify face using different sensory modalities

• Apperceptive  Stroke, anoxia, and carbon monoxide poisoning
• Associative  damage to the inferior temporo-occipital junction
• Infarction of the posterior cerebral artery, tumour, haemorrhage

• Generalized category-specific recognition deficits (eg.
Living objects) are associated with diffuse hypoxic damage like carbon monoxide poisoning
• The more specific category deficits are associated with isolated damage due to focal stroke

• Visual agnosia prevalent in Alzheimer’s patients
• Neuronal degeneration, via neurofibulary tangles (NFT), of brain regions involved in vision

• Associative agnosics cannot connect the mental representation of an object to its semantic information
• Apperceptive agnosics have impaired formation of the mental representation of an object
• Integrative agnosics  have symptoms of both

• Cognitive Psychology
• Extract elements/features of visual object  Form mental representation of that object  Recognition

• Dense coding  All neurons in the visual pathway are involved in the mental representation of a stimulus
• Sparse coding  Mental representation of object is encoded by relatively small number of neurons

• Bilateral damage along ventral stream of processing
• Severe Visual object Agnosia
• Perceptive tasks impaired
Size discrimination  choosing larger of two objects
Manual estimation  Judging size of an object by shaping hand correctly
• Intact parahippocampal place area (PPA)
• Region of limbic cortex bordering the ventromedial temporal lobe
• Activated by scenes and backgrounds

• Location of Striate cortex (primary visual cortex)
• Areas V1 spared
• Areas V2 largely damaged

• Perceptual grouping and figure-ground discrimination
• Internal substructure that can be visualized by labeling cytochrome oxidase
• 3 functionally distinct compartments:
• Thick Stripes  disparity- and motion-sensitive cells
• Thin stripes  unoriented-colour sensitive cells
• Pale stripes  orientation sensitive cells for form vision

• Highest level of the ventral stream of the visual association cortex
• Involved in perception of objects, including people's bodies and faces

• Located on the fusiform gyrus, on the base of the temporal lobe
• Greater activation for faces than other categories of visual stimuli
• Also selective for objects a person is highly familiar with
• Individuals with congenital prosopagnosia have a smaller fusiform gyrus and a decreased connectivity within the occipital temporal cortex

• https://www.youtube.com/watch?v=VdIC-x6UZg0

• Lack of attention on one side of the world
• Can affect sensory modules such as visual, auditory, somatosensory, etc

• Sensory Neglect
• Motor neglect
• Representational neglect

• Strokes
• Unilateral brain damage
• 80% of visual neglect on the left-hand side
• Right-sided spatial neglect is rare
• Memory and recall perception affected

• Caused by damage to structures involved in arousal and transmission of sensory information to the cortex
• Leads to decreased attention to the contralateral side of lesion

• Right hemisphere specialized for attention to both left and right visual fields
• Left hemisphere only attends to the left
• Thus, damage to right leads to loss of control of left-side attention

• Difficulty in detaching or disengaging attention from rightsided stimuli
• Stimulus on right side appears sufficient to inhibit a similar stimulus on the left side

• Imbalance in brain activation with each hemisphere having specific cognitive and perceptual functions
• Left hemisphere activated by language
• Right hemisphere activated by spatial tasks
• Both act mutually to achieve inhibitory inbalance
• Damage to the right causes increased activity of the left and decreased spatial functioning

• Occurs more commonly and with greater severity after right- than left hemisphere-lesions
• Right hemisphere involved in attention and spatial representations Temporo-parietal junction
• Posterior parietal cortex

• 12/18 patients at acute stage of neglect had lesions at middle temporal gyrus and/or the temporo-parietal paraventricular white matter
• high correlation between persisting neglect and a lesion involving the paraventricular white matter in the temporal lobe

• Planning, organization, problem solving, selective attention
• Mesial and dorsolateral portions of frontal lobe

• Relay of sensory information

• Coordination of voluntary motor movements and eye movements

• Usually elderly patients
• Use of fMRI and/or diffusion tensor imaging (DTI) for localization of brain damage
• Patients usually have cortical damage not exclusive to visual processing areas
• No two cases of Agnosia are the same (Symptoms or localization of brain damage)

• Ability to name drawings of living things impaired, while ability to name man-made things intact
• Early visual processes of shapes intact
• Ability to identify overlapping man-made objects intact

1. Rule out other conditions that might lead to recognition impairment
2. Scope and specificity of recognition impairment
• Specific sensory modality
• Specific category of stimuli
• Conditions which recognition is possible
3. Associative or Apperceptive agnosia

• figure-ground discrimination

• Awareness of patient’s deficits
• Repetitive training of impaired ability
• Coping strategies
• Use of other sensory modalities
• Take more time on tasks
• Visual Tracing

• Involves large team of professionals
• Progressive incremental use of neglected side

• Job loss
• More likely to Depend on others (eating, getting around)

• https://www.youtube.com/watch?v=cP6hfLJq8ng

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