[W5] - CH11 Flashcards
The Neuroanatomy of Visuospatial Processes - The Primary Visual Pathway
Visual perception is distributed across two distinct subsystems:
- 90% of the optic nerve axons terminate in the lateral geniculate nuclei of the thalamus (the sensory relay station of the brain).
- 10% of the optic nerve axons terminate at other subcortical structures, including the superior colliculus of the midbrain and the pulvinar nucleus of the thalamus.
- The final axonal pathway leaves the lateral geniculate nuclei and terminates in the primary visual cortex of the occipital lobe.
The primary visual cortex within the occipital lobe has many specialized areas. While each of the visual areas within the primary visual cortex collectively help to provide a visual map of the external world, some Neuronal Areas are Sensitive to variations in colour, others to movement, and so on (a “divide and conquer” strategy). The specialized visual areas provide distributed and specialized analyses that are later integrated into perceptual wholes at higher levels of processing.
The Neuroanatomy of Visuospatial Processes - The Dorsal and Ventral Pathways
The outputs from the primary visual cortex follow two general pathways:
- The Inferior Longitudinal Fasciculus (a.k.a., the VENTRAL or occipito-temporal pathway): Called the “WHAT” pathway, as in, what we are looking at. Specialized for object identification and perceiving related movements (fibres terminate in the inferior temporal cortex).
- Superior Longitudinal Fasciculus (a.k.a., the DORSAL or occipito-parietal pathway): Referred to as the “WHERE” pathway. It is specialised for recognizing where an object is located, if it is moving, and its speed and direction of its movement. Both the “what” and the “where” aspects of visual perception are important (fibres terminate in the posterior parietal cortex)
Define Astereopsis
Inability to perceive the depth of objects.
Define Prosopagnosia; Simultanagnosia; Color; Integrative; Pantomime; Visual; Apperceptive; and Associative
Prosopagnosia: Impaired face recognition.
Simultanagnosia: Impaired recognition of the meaning of whole pictures or objects, but intact ability to describe the parts of the pictures/objects.
Colour agnosia: Inability to appreciate differences between colours; or an inability to relate colours to objects if colour vision is intact.
Integrative agnosia: A failure to integrate parts of an object into a coherent whole.
Pantomime agnosia: Inability to comprehend or recognise pantomimes/gestures, even when the ability to copy/imitate them is intact.
Visual agnosia: Impaired ability to recognize visual information/visually presented objects. A child with visual agnosia won’t be able to identify a pencil with sight alone; but may be able to quickly identify the pencil when it is placed in their hand.
Apperceptive agnosia: A subtype/form of visual agnosia in which the deficit is caused by impaired visual perception (i.e., failures in object recognition that are linked to problems with visual perceptual processing)
Associative agnosia: A failure of visual object recognition that cannot be attributed to perceptual abilities (i.e., the child has normal visual representations, but cannot use them to recognize an object)
Warrington’s (1985) Two-Stage Neuroanatomical Model of Object Recognition
Warrington proposed that visual processing would initially be bilateral and involve both occipital cortices.
- [Perceptual Categorization within the Right Parietal Hemisphere] - Incoming perceptual information (perceptual inputs) are aligned with visually stored representations of objects. This stage is thought to be pre-semantic (i.e., doesn’t require an understanding of the meaning of words).
- [Semantic Categorization within the Left Hemisphere] - In this stage, visual information is linked to knowledge in long-term memory containing the name and function of the object.
This model is grounded in Warrington’s finding that adults with lesions in their right hemisphere were likely to demonstrate apperceptive agnosia; while adults with lesions in their left hemispheres were more likely to demonstrate associative agnosia.
Neuroanatomy of Face Recognition
The inferior temporal lobe, specifically the Fusiform Gyrus, is involved in recognizing objects - especially faces.
When a face is recognized in the fusiform gyrus, the information is transmitted to the frontal lobes for processing.
Prosopagnosia rarely occurs with unilateral, left lesions; and is more likely associated with Bilateral Lesions caused by multiple strokes, head injury, encephalitis (brain inflammation) - OR Right Hemispheric lesions which include the ventral regions of the occipital and temporal lobes.
SAMPLE CASE - Alicia is a poor reader. She can name individual letters, but she has difficulty combining/integrating the letters to make a whole word. In art, she pays great attention to detail but lacks the ability to see any relationships between the details. Her teacher describes her as “not being able to see the forest for the trees.”
Alicia is having difficulties with the perception of a part-to-whole relationship - which is a subcomponent of visuospatial functions.
Identifying Visuospatial Processing Concerns with the NPCC-3:
- Confusion with directions (e.g., gets lost easily).
- Shows right-left confusion or directions (up-down).
- Difficulties with putting puzzles together.
The classifications of Visuospatial Processes within the Integrated SNP/CHC Model
Broad: Visuospatial Processes
Second-Order: (2)
- Visual-spatial perception
- Visual-spatial reasoning
Third Order:
Visual-spatial perception (3):
- Visual discrimination and spatial localization
- Visual-motor constructions
- Qualitative behaviours
Visual-spatial reasoning (3):
- Recognizing spatial configurations
- Visual gestalt closure
- Visuospatial analyses with and without mental rotations
A Typical Visuospatial Processing Test
- The Block Design test from the WISC-V/WISC-V Integrated
The Neuroanatomy of Auditory Processes
The auditory cortex is responsible for phonological processing, by allowing us to identify what a word is based on the way that it sounds. Input from each ear is received and processed in different hemispheres, passing through the thalamus on its way. While it is the ear that receives auditory input, it is the brain that hears.
Auditory Pathway:
- The ears receive sound waves
- these travel into the ear canal where they vibrate the ear drum
- the vibration of the eardrum moves tiny bones in the middle ear, which in turn carry the vibrations through the fluid filled cochlea
- in the cochlea a series of tiny hairs (a.k.a., cilia) vibrate; which are attached to the cochlear nerve
- the movements of the cilia stimulates the cochlear nerve which sends signals to the brain
- the cochlear nerve passes through the medulla in the brainstem and then onto the inferior colliculus
- the auditory pathway divides; such that input from each ear is received and processed in different hemispheres
- the auditory pathway is then processed through the thalamus (the sensory relay station of the brain) and onto the auditory cortex.
Identifying Phonolgical/Auditory Processing Concerns with the NPCC-3
Difficulty with sound discrimination.
Difficulty with blending of sounds to form words.
Difficulty with rhyming activities.
Omits sounds when reading or speaking.
Substitutes sounds when reading or speaking.
The classifications of Auditory Processes within the Integrated SNP/CHC Mode
Broad:
Auditory Processes
Second-Order (2):
- Sound Discrimination
- Auditory/Phonological Processing
Testing Basic Sound Discrimination vs. Auditory/Phonological Processing
A student should first be referred for a speech language assessment (with a speech and language pathologist) when deficits in this area are suspected. A student with deficits in basic sound discrimination will have difficulty learning to read using a phonological approach.
Auditory and/or phonological processing can be assessed by school psychologists/school neuropsychologists, or via speech and language assessment batteries.
How Do Auditory/Phonological Processing Deficits Manifest? - [APD]
Students with deficits in auditory/phonological processing will struggle with reading acquisition (when taught using purely phonological instruction). Students with severe deficits in this area may have to learn how to read based on memorizing the whole word visually rather than applying a sound-it-out, phonetic approach to reading.
A disorder of relevance to neuropsychological assessment of auditory processing is central auditory processing disorder (CAPD), as it represents a primary difficulty with processing auditory information. CAPD, also referred to as auditory processing disorder (APD), is defined as the efficiency and effectiveness of the central nervous system in using auditory information.
Children with APD have difficulty processing auditory input. APD manifests as poor performance in listening tasks, understanding speech, developing language, and learning. Such children may have trouble with auditory attention, sound discrimination in the presence of background noise or distortion, difficulties with auditory integration needed for skills like phonological awareness, and poor overall receptive, expressive, and pragmatic language skills.
They do not process what they hear in the same way that other children because their ears and brain do not fully coordinate. Something interferes with the brain’s recognition and interpretation of sounds.
The brain stem has been implicated in APD as the first point of convergence of input from the two ears, with important points of convergence in the pons (superior olives) and midbrain (inferior colliculi) which are responsible for binaural processing. Children with APD are often misdiagnosed as having attention difficulties (i.e., inattentive) or labelled as “not motivated to learn”. Many are at risk for developing specific learning disabilities or reading problems.
