Fundamentals Of Human Neuropsychology. Kolb.- Visual Perception And Dysfunction

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Cornea

Back 1

transparent layer

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Pupil

Back 2

light enters through hole in eye

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iris

Back 3

colored section

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lens

Back 4

refracts light to the back of the eye on the retina (image is flipped  inverted)

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Retina

Back 5

photoreceptors that collect light info at the back of the eye

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optic nerve

Back 6

* create the blind spot
* carry info

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Cataracts:

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blurring of the lens, resulting in a general blurry image (not clear) -> can put in an artificial lens to fix

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Glaucoma

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increased pressure in the eye, may result in tunnel vision (loss of peripheral vision, much more limited)

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Macular degeneration:

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* degeneration of the macula (area of the eye that processes when you are staring directly at something), cannot focus directly at something, see a swirl/distortion of central part of the image (peripheral vision is intact)

*Vascular problems (hypertension, diabetes) can increase the chance of macular degeneration

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Papilledema

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swelling in the brain that pushes optic nerve into the eye

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Cone-based colorblindness

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may be born without certain type of cone
Red-Green (sex-linked): cannot distinguish b/w red and green, more common in men

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Optic chiasm

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X : cross point at which some visual information (peripheral vision) crosses to the opposite side of the brain -> critical

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Where does optic chiasm impairment happen and what does it do?

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* Impairment: can occur with tumors of the pituitary gland that press on the optic chiasm
Results in visual impairment: tunnel blindness, no peripheral vision, therefore peripheral vision is what crosses at the optic chiasm

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What is the process of visual info info from eye to visual cortex?

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Info then connects to thalamus and then goes to primary visual cortex in occipital lobe

Eye -> optic chiasm -> thalamus -> visual cortex

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Damage to the occipital lobe

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leads to partial or full cortical blindness -> blind spots (scotomas) occur

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upper left blind spot = damage to which part of frontal lobe?

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Damage to lower right occipital lobe

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Retinotopic organization of visual cortex:

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map of the world on our brain (inverted vertically at the lens and inverted horizontally at the optic chiasm) -> both upside down and backwards

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Cortical blindness:

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specifying that blindness is due to brain dysfunction (NOT eye dysfunction)

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residual blindness :

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Residual [subconscious] vision despite full cortical blindness


Ex. Are cortically blind but can catch a ball (respond to visual info)
90% of info goes along pathway to occipital lobe but 10% of fibres go down to the brain stem (to areas for basic visual processing)
Can respond to things in the environment even though we don’t consciously see them

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Area V4

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in the occipital lobes processes and interprets color information from the cones in the eye

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Damage V4

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= impaired ability to process color (see everything in black and white)

* Strong social effects -> find no joy in eating, may develop nutritional deficiencies, no longer want to engage in sexual relations

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Damage to right V4

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black and white on the left side of vision

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Area V5

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in the occipital lobes processes and strings together visual input to create one coherent, smooth visual scene
Critical for movement

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Damage to V5

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reduce ability to see continuous movement (visual info updated much more slowly, seeing snapshots of reality)
Ex. Like being around a strobe light all the time and only seeing snapshots

* Very rare, usually occurs in people w/ extensive brain injury (often other impairments as well)
* Cannot adequately judge speed, heights -> ex. Difficult to cross an intersection, difficult to pour a cup of coffee
* Can be almost functionally blind and require extensive support

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Dorsal Stream

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“where pathway”, identify where you are relative to space around you, occipital lobe to parietal lobe, used to engage in actions and interact w/ objects in environment

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Ventral Stream

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“what pathway”, connects memory to vision, identify what we are seeing, connects occipital lobe to temporal lobe