L2 Visual System 2024 OJ PDF

Representation in the visual system Recommended Reading: Gazzaniga et al chap 5 Key Concepts: Primary cells of retina Phototopic vs scotopic vision Optic nerve Photosensitive Retinal Ganglion Cells Synaptic transmission Neurotransmitter-gated ion channels Lateral inhibi...

Representation in the visual system Recommended Reading: Gazzaniga et al chap 5 Key Concepts: Primary cells of retina Phototopic vs scotopic vision Optic nerve Photosensitive Retinal Ganglion Cells Synaptic transmission Neurotransmitter-gated ion channels Lateral inhibition Opponent processes Colour vision Approach-Avoidance conflict Homeostasis What mechanism underlies this phenomenon? Kayahara’s ‘Spinning Dancer’ illusion The Retina Rods and Cones in the retina Cone-mediated vision – phototopic high acuity colour vision in good illumination Rod-mediated vision – scotopic poorer acuity achromatic vision in low-light levels Distribution of rods and cones in the retina Peripheral vision Foveal vision Low spatial frequency High spatial frequency Livingstone (2000)  A https://livingstone.hms.harvard.edu/vision-and-art  B https://livingstone.hms.harvard.edu/vision-and-art The Retina The eye also contains a small number of intrinsically (or directly) light-sensitive retinal ganglion cells. Intrinsically Photosensitive Retinal Ganglion Cells (ipRGC) These cells utilize the photopigment melanopsin which is maximally sensitive to blue light. They have connections through to the superchiasmatic nucleus (SCN) and are critical for entraining circadian rhythms light including SCN Zielinska-Dabkowska (2018) The location of the ‘blind spot’ in the retina The location of the blind spot in the left eye Synaptic transmission  Synaptic vesicles trc.ucdavis.edu/.../synapse1/synapse.html http://wormbook.sanger.ac.uk/chapters/www_synapticfunction/synapticfig1_small.jpg Vesicles fuse with the membrane and release neurotransmitter Watanabe (2015)  Neurotransmitter-gated channels on postsynaptic neuron outside Glutamate synaptic cleft or gap + + + + - - - - Cell membrane inside  Neurotransmitter-gated channels on postsynaptic neuron outside + + + + - - - - Cell membrane inside  Neurotransmitter-gated sodium channels outside + + + + - - - Na+ Cell membrane inside Depolarisation of membrane = Excitatory postsynaptic potential (EPSP  Neurotransmitter-gated potassium channels outside GABA + + - - inside  Neurotransmitter-gated potassium channels outside + + - - K+ inside Hyperpolarisation of membrane = Inhibitory postsynaptic potential (IPSP)  The Retina Release Glutamate Release GABA Simultaneous contrast Simultaneous contrast Simultaneous contrast Lateral inhibition (an opponent process) Mach bands Mach bands Mach bands  Visible light is part of the electromagnetic spectrum 400nm 700 nm 5G 4G Normalised absorbance of the three human cone pigments Snakes, rats, mice Most mammals humans, apes Incl. cats and dogs old world monkeys Monochromatic view Dichromatic view Trichromatic view (no blues, greens, or (only blues and (blues, greens, and reds) greens) reds) Birds, reptiles and many The mantis shrimp fish have 4 receptor types has 12 types of colour receptor. 8 in the visible spectrum, 4 in the ultraviolet  Colour blindness R/G colour blind (approx 5-10% of males 0.1% females) may see numbers in top left and bottom middle only – rest are just spots Colour blindness Original Weak in green (most common) Deuteranomaly No red (second most common) Protanopia http://members.shaw.ca/hidden-talents/vision/color/colorblind1.html How do the three types of cones (in humans) interact with each other? red+green=yellow X X  Colour afterimage due to competition between colour channels Opponent-process theory suggests that colour perception is controlled by the activity of two opponent systems; a blue-yellow stimulus mechanism and a red-green mechanism. Adaptation in particular colour receptors favours the opponent colours afterimage As a result of the opponent process there are some colour combinations that we never see, such as reddish-green or yellowish-blue e.g. Blue yellow  Opponent Processes in homeostasis Homeostasis is any self-regulating process by which an organism tends to maintain stability while adjusting to conditions that are best for its survival e.g. controlling body temperature Too cold just right too hot shiver sweat Risk of occupational heat exposure in the shade Lancet Planetary Health  Opponent Processes in motivation Approach-Avoidance conflict arises from competition between the drives to pursue reward and to avoid harm Decision approach avoid Kurt Lewin What mechanisms underlie all these phenomenon? Opponent processes END