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Lecture 9

Lecture 9 - chapter 11 notes

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Psychology 2043A/B
William Fisher

Lecture 9 Chapter 11 - Children with Visual Impairments For people depending on Sight ­ We think that we know what it would be like ­ Dark, scary, difficult to live independently o typically developing individuals, 50% of the information that the brain receives comes in through the eyes ­ People would seem socially cold o Eye contact, gestures, body postures, etc. What it can Be Like ­ Some individuals who are blind can still read and learn through the visual channel ­ Most people who are legally blind can see: o Shadow, light/dark, or moving objects ­ Can live independently o Can navigate their own homes o Can travel independently o Can be successfully employed o Can live active lives Perspectives form a blind man  Daniel Kish TESTBOOK Predicting Outcomes for Children with Vision Challenges 1. Presence/absence of co-occurring disability 2. Opportunities to learn AIM #1a: Definitions of blind/low vision - Very rare ­ Vision problems account for 0.4% (of the disabled population) of children receiving special education services. ­ Only 0.04% of children are legally blind ­ Difficult for evidence based recommendations due to the small sample sizes Co-occurring Disabilities ­ 50-75% of individuals also have co-occurring disabilities: o IDD (most common) o Autism o Emotional disorders o Learning disability Definitions ­ IDEA - who is entitled to receive services to support learning o Even with correction, the visual impairment affects a child’s educational performance and therefore the child is entitled to receive special services ­ Legal Definitions o Blind (Acuity): <20/200  Difficulties picking out details  Blurry image o Blind (visual field): have less then <20°  Tunnel vision  Normal person has: • 160°-180° Horizontal • 120° Vertical o Low-vision: 20/70 to 20/200 ­ Functional Definitions o Blind  Primary learning mode is through touch and/or audition o Low-vision  Primary learning mode is still through vision channel Classification by Age of Onset ­ Congenital blindness o Born blind o “I see nothing” ­ Adventitiously blind o Become blind sometime during their life o Accident of disease sometime after birth o “I see darkness all around me” o Still has the memory of light and dark AIM #1b: Causes of visual impairments in Children (7) Cause 1 Cortical Visual - Damage to the brain (occipital lobes) Impairment ­ Inadequate blood and oxygen supply to the brain at (CVI) or around the time of birth ­ Deficits in occipital cortex - Most common cause of visual impairment in developed countries 2 Retinopathy of - Mostly commonly in premature, low-weight babies (less Prematurity then 1500g) suffering from respiratory distress who need (ROP) high levels of oxygen over an extended period of time for survival - Incubators pumped with oxygen; at risk of having vision problems 3 Optic Nerve - Optic nerve doesn’t develop normally Hypoplasia/ ­ Or it degenerates Atrophy ­ Optic nerve does not connect to brain (no signals being sent) - Can’t connect the visual images received by the retina to the visual processing areas of the brain 4 Albinism - Congenital absence of pigmentation (including of the eye) that can lead to blindness 5 Glaucoma - Leading cause of blindness in adults ­ Can also occur in children (rare) - “Sneak thief of vision” ­ Slow onset problem - Fluid doesn’t drain properly à Build up of pressure and damage to the retina and optic nerve 6 Diabetic - Major cause of blindness in North America Retinopathy - Much more common in adults - Vision problems are particularly problematic the longer and individual has had diabetes (15 years = spike) regardless of age of onset or severity of diabetes 7 **Cataracts - Clouding of the lens of the eye - Children most common to have in both eyes - Adults usually have it in one eye - Preventable - Cause 5-15% of preventable childhood blindness throughout the world ­ Difficulty seeing the board clearly ­ May need increased lighting or high-contrast educational materials (i.e. white sheet with black print) AIM #1c: Visual processing in the brain Brain Plasticity ­ Brain tissue is expensive to maintain and valuable resource o Takes a lot of metabolic energy to produce and maintain o When visual cortex is not working; other regions adjacent to it can take up the space of the visual cortex o All senses competing for brain tissue ­ Visual cortex not getting a signal à cortical reorganization o Some are more sensitive to touch (Braille)  only 10% of blind population use braille  sense of touch takes over visual cortex o Rare, but some become extremely sensitive to sounds (Daniel Kish)  could navigate though echo location (i.e. bats)  send out clicks and receive clicks back  audition takes over visual cortex ­ Amazingly, these cortical changes can happen within days o Blindfold sighted people for a week o This will boost their other sense o Not permanently altered; returns to normal ­ TEXTBOOK WRONG in saying that brain automatically adapt its other senses o this occurs but not automatically Brain Plasticity - Cats and Primates ­ Hubel and Wiesel  studies on taking away vision from one eye  kittens that were born were impaired of their vision in one eye until about 6 months (sexual maturity)  Found that the cats eye that had vision took over control  when the other eye was reopened, the brain was not receiving visual stimuli from the previously blinded eye ­ Cat critical period first 3 months ­ Primate critical period 6 months Children with Cataracts ­ Terri Lewis and Daphne Maurer o Optometry and Vision Science, 2009  5 principles on normal vision ? o McMaster University o Extensive research program of children with cataracts Treatment for Cataracts ­ For the last 100 years…. ­ Remove the cataract/cataracts o Bilateral has a better outcome o this is because the other eye cannot take over o treatment allows both eyes to develop normally after the cataract is removed ­ Eye patch on the unaffected eye prior sugary and after removal until 5-7 years of age o aids in better outcomes o aggressive patching: patching good eye for 3-4 hours per day ­ sugary should happen as soon as possible o want to correct visual balance a.s.a.p. o still important to patch eye until age of 5-7  used to believe that critical period for humans is 7 o 6 weeks is earliest possible age How does cataract treatment influence visual development? What can studies of these children tell us about normal vision development? 1. Low level vision ­ Low level vision = primary visual cortex ­ Systems that develop early in life are least influenced by abnormal visual experience o least affected by cataract ­ Systems that take longer to develop are more influenced by abnormal visual experience encountered later in life o most affected by cataract ­ Contrast sensitivity o Low spatial frequencies (2 months)  Rarely impaired by cataracts ­ High and medium spatial frequencies (2 years) o When cataracts are found, often impaired 2. Sleeper Effects of Cataracts ­ High spatial frequency vision only starts to emerge at 2 years of age thus might still see impairments o sets you up on a different developmental trajectory ­ Children with cataracts removed at 6 months of age, are still impaired at 2 years ­ Face processing o Adults really good - holistic processing o Typically developing infants take 4-5 months for face holistic processing to develop  Bilateral cataracts removed at 2-3 months, abnormal holistic processing still seen at 4-5 months ­ What is going on? o Early visual input is necessary to preserve the neural architecture for future visual learning o Touch, hearing, and language can move in and take over the visual cortex 3. Higher Visual Processing ­ Both require visual input for normal functioning o Dorsal Stream (green)  How/Action  Parietal region  Subconscious  Random dot Kinematograms • see dot patterns; determine what direction dots are moving • bilateral caterax - 40% • unilateral caterax - • normal vision - 10-15% o Ventral Stream (purple)  What/Cognition  Temporal  memory and object recognition  Glass Patterns • picking out global patterns • bilateral / unilateral caterax cannot see pattern as well as someone with normal vision ­ Blind site studies o studied people with brain injuries o no conious awareness that there is an object infront of you (ventral stream) but you are still able to operate object (dorsal stream) Vision is important for DORSAL and VENTRAL stream processing ­ Unlike low level visual processing, environmental input seems to be important for both dorsal and ventral processing of visual information, regardless if the visual process develops early or late ­ Global Motion: Dorsal o Develops early (before 4 months of age) o Is impaired ­ Global Form: Ventral o Develops late o Is impaired 4. Monocular vs. Binocular Cataracts ­ The relative effects of monocular versus binocular cataracts depend on the level of visual processing Low Level Visual Processing ­ Each eye competes for control of the visual cortex o Hubel and Wiesel o Kittens – one eye closed ­ Patching the “seeing” eye is very important Level of Vision Matters ­ Low level processing: o E.g. acuity, contrast sensitivity, peripheral vision o Left and right eye compete for control of visual cortex Higher Level Vision: Global Motion of the Dorsal Stream ­ Equal performance across better and worse eye ­ Left and right eye help each other out – complement each other 5. There are Multiple Sensitive Periods ­ Acuity is mature in children at 7 years ­ Led to the tradition view that: o Interventions before age 7 will help o Interventions after age 7 will not o Idea that
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