19 Central Visual Processing

19 Central Visual Processing - Central Visual Processing...

Info iconThis preview shows pages 1–3. Sign up to view the full content.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Central Visual Processing Optic Chiasm- Optic nerves project from eyeball into brain thru blind spot - Each retina ‘sees’ both visual hemifelds (visual world)- Must be coalesced (aligned) in brain- Half of retinal efferents must join up w/ efferents from other eyeball -> cross at chiasm- Each half of brain processes only contralateral Feld- Half-brain concerned w/ opposite half of visual Feld- L half brain is concerned w/ R hemiFeld- R half brain concerned w/ L hemiFeld- Half of afferents in each optic nerve cross at optic chiasm- The rest project to same side of brain- After chiasm, optic nerve becomes optic tract- Diagram: black arrows = visual info from R hemiFeld- R hemiFeld inputs -> L retina on both eyes - Efferents travel to L brain hemisphere- Inputs from R eye must cross chiasm to join w/ inputs from L eye- Vice versa for L hemiFeld inputs (gray lines)- Causes motor system to also cross -> cerebral cortex looks at opposite side of body to match w/ visual system Visual Nuclei- Afferents in optic tract have many targets: 1) Thalamus: interface btwn sensory systems + cerebral cortex- lateral geniculate nucleus (LGN):- “Geniculate” refers to way it sticks out of thalamus like a knee, on top of SC- Responsible for guiding eye-head mvts- Concentrates on M- & P-stream afferents 2) Superior colliculus (SC) : on brainstem; one of the bumps on midbrain- Directly receives retinal afferents- Concentrates on rapidly adapting afferents ( M-stream /magnocellular pathways) 3) Pretectal nuclei : “in front of colliculus” on brainstem- Responsible for autonomic fxns, i.e. pupillary light re¡ex, and accessory optic system for motion detection (M-stream); used for postural corrections 4) Suprachiasmatic nucleus (SCN): in hypothalamus, sits on top of optic chiasm- Target for small group of afferents -> responsible for circadian cycle- “Master clock” of body- Also , V1 cortical sensory region in cortex: receives signals from LGN - Right of back of occipital lobe, medial wall of cortex btwn hemispheres- About the farthest you can get from eyeball in cortex! PSL302Y: Lecture 19, by Prof. MacKay Wed., Oct.27, 2010 1 of 7 Lateral geniculate nucleus (LGN)- 6 layers (like cortex): align neuronal r.f.’s- 1-2 for M-stream - 3-6 for P-stream- Alternate layers receive afferents from different sides of retina (of one eyeball)- We don’t merge inputs from both eyeballs yet- So: 3 layers from 1 eyeball, 3 for other eyeball- Organize mappings of retina->contiguous btwn layers- R.f.’s of neurons in all layers, lying on radial axis, are the same (see “ common r.f. ” line)- All refer to same pt in visual Feld- Bigger r.f.’s than they are for ganglion cells of retina, due to synaptic convergence- General rule for all somatosensory systems: primary afferents have tiny r.f.’s, but at cortex have much larger r.f.’s- Note: Ipsi-> “same side”, vs. contra-> “opposite side”- Ipsilateral retinal afferents -> layers 2,3,5- Contralateral retinal afferents -> layers 1,4,6...
View Full Document

This note was uploaded on 03/27/2012 for the course PSL PSL300 taught by Professor Mackayfrench during the Fall '11 term at University of Toronto.

Page1 / 7

19 Central Visual Processing - Central Visual Processing...

This preview shows document pages 1 - 3. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online