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The developing visual brain
Concepts and Contexts
Concepts and Contexts
• Neuroscience
• Perceptual and cognitive psychology
• Nature-nurture
Visual Systems
• Two streams in development– where and
what
• Three streams of processing – where, what
and how
Ventral and Dorsal Streams
• One stream for perceptual processing and
one stream for controlling actions
• Ventral Pathways – contain specialised
areas for face perception (who)
• Dorsal Stream – controls eye movements,
reaching and grasping (how)(action)
Development
• Different rates of functional development
within the two cortical streams
Dorsal - Action
• Multiple action modules
• First action module used for making
exploratory eye movements from one object
to another followed by reaching and later
grasping – increasing need for more
complex spatial information
Infants born preterm (born before
37 weeks from conception)
• Neurological problems – rupture of the
fragile capillaries around spaces in the brain
(ventricles) – if severe baby may die or
survive with cerebral palsy
Retinopathy Of Prematurity
(ROP)
• ROP rare in preterm infants with
birthweights greater than 2000g but infants
born weighing less than 1500g at birth are
vulnerable to ROP whilst those born less
than 1250g at birth with a gestational age
less than 28 weeks are especially
vulnerable.
CVI
Children with CVI and ocular visual loss radically differ in their ability
to process visual message. With ocular disorders, the signals may
be incomplete, but the process of analysis is sound. Thus, visual
enrichment and training in scanning more efficiently when the
information is complex are successful techniques.
For children with CVI, this approach does not work; in fact, visual
input must be controlled to avoid "visual overloading…if the
amount of visual information is increased, it becomes much more
difficult for the children to process visual input. Visual images
should be simple in form and presented in isolation.
CAUSATION
• Prenatal (before birth)
Toxaemia, Intra-uterine infection
• Perinatal (birth to 28 days of life)
Asphyxia, Intra-cerebral haemorrhage,
Meningitis/Encephalitis
• Acquired
Shunt malfunction, trauma, meningitis,
cortical vein thrombosis, Cardiac arrest
APPEARANCE
• Does not look blind
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Blank facial expression
Lack of visual communication skills
Eye movements smooth, but aimless
Nystagmus (rapid eye movement) rarely seen
VISUAL FUNCTION
• Visual function varies from day to day or hour
to hour
• Limited visual attention and lacks visual
curiosity
• Aware of distant objects, but not able to
identify
• Spontaneous visual activity has short
duration
• Visual learning tiring
• Closes eyes while listening
Visual Function
• Balance improved with eyes closed
• Looks away from people and objects
• Consistently looks to either side when visual
looking
• When visually reaching looks with a slight
downward gaze
• Turns head to side when reaching, as if using
peripheral fields
• Uses touch to identify objects