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Lecture 5

Psyb65 - lecture 5.docx

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Zachariah Campbell

Psyb65 – lecture 5 Sensory Motor Functions and Dysfunctions Visual System - Look at this from bird’s eye view – tip: draw the diagram on the back of exam paper for midterm - Involved with seeing and recognizing things in your universe - General organization o Function is dependent on its anatomy and organization o Retinas (each of your eyes) anatomically, are divided right down the centre in each eye o Your world (what you see when you look out) is your visual field divided right down the centre where your nose is  Also divided into right visual half field and left visual half field (the word half is rarely used) (must look straight ahead for this to make sense) o Portion of retina toward the outside portion of your head is referred to the temporal portion of your retina (temporal – side) o Portion which is closest to your nose is referred to the nasal portion of your retina o Anatomy of them is completely different because the way they are connected is very different o Information from each retina leaves through an optic nerve (nerve as it leaves the retina)  The 2 nerves cross (known as an optic chiasm) – point where the nerves from the back of your eyes come together  Portions cross and meet and then separate again (optic tract) o The part of your retina from the temporal portion (outside portion), as it continues back, it comes to the optic chiasm and stays on the same side of the brain – meaning it does not cross *  Nerves coming from the temporal portion, hit the optic chiasm and keep going on the same side of the brain o Nasal portion of each retina (part closest to your nose), that half, whenever they go toward the optic chiasm, they cross over to the opposite side of the brain * o This creates a system o Retina is part of your nervous system o If something is in your right visual field, it will hit the nasal portion of the right eye and temporal portion of the left eye and vice versa  Everything in your right visual field ends up in your left cortex; left visual field goes into right cortex o Everything from the temporal portion continues to the same side of the brain while everything from the nasal portion crosses over - Damage o Tell the person to close one eye and look the other person right in the nose – ask them if they see any fingers moving – ask them what they can see  By figuring out what they can see, you can tell where the tumor is o Refer to slide* - right side of picture is person’s actual visual field – what the person can see/ what is damaged in person’s visual field, not in the retina  Have to look at one eye at a time – close one eye  o 2. Left eye is not infected (can see everything perfectly normal)  If you cover your left eye, you will be completely blind in your right eye o 3. If you slice through the optic chiasm (tumor blocking that area) you are cutting off the fibres that cross over not the ones on the outside – nasal portion of each eye will be blind  Right eye, outside portion will be blind, left outside portion will be blind therefore lesion is in the centre o 4. Tumor on the right temporal side – left visual field of outside of the right eye will be blind – if temporal portion of right eye is dead, you can’t see off to the left o 5. Losing right hand side of right eye – therefore right eye is blind in the left (severed temporal portion)  Severed fibres that cross (nasal) therefore also blind to the left nasal portion o 7. If you go all the way to the cortex and there is damage, you will be blind in the opposite visual field of each eye however there is a small part in the middle called macular sparing - What kind of function do things have as we move down this system o The more central the neuron, o Neurons and retina are able to detect a single spot of light on a single receptive field  Is light shining on this particular field  Each neuron builds upon information from neuron beneath it  Area 17 of cortex (bottom of image – primary receptive area) neurons respond to bars of light that is oriented in a particular direction  Will not respond to bars of light in different orientations o When you get to the associational cortex (in temporal area) a neuron responds to complex images (ie. hand or face) and recognizes it  Taken information from simpler neurons and puts them together o When you get up to damage of visual cortex  Complete damage leads to blindness of opposite visual field  Won’t be quite blind – little part in centre that you see but shouldn’t be able to – macular sparing o If you have small areas of damage in the level of occipital cortex – you will lose portions of your opposite visual field – certain areas where you will be blind  *always opposite visual field o If damage is very small, it can result in a schotoma – small area of blindness caused by damage to occipital cortex  If it’s very small you may not even notice it o Person has difficulty in visualization of complex objects if damage is in areas 20/21 - Perceptual disorders/ visual agnosias o Visual agnosia – although you can see the object and pick it up, you don’t know what it
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