PSY2061 Lecture 5: PSY2061 – Lecture – Week 5 – Sensory Systems
5 Jun 2018
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PSY2061 – Lecture – Week 5 – Sensory Systems
• Overlapping systems governing other non-traditional senses, ability to
detect: • temperature thermoception • kinaesthetic sense
proprioception • pain nociception • balance equilibrioception •
vibration (mechanoreception)
• principles of sensory system organisation
•
o Primary sensory cortex: input mainly from thalamic relay nuclei
Secondary sensory cortex: input mainly from primary and
secondary cortices within the sensory system Association cortex:
input from more than one sensory system, usually from the
secondary sensory cortex
o hierarchical organisation
o
▪ specificity and complexity increases with each level
▪ sensation - detecting a stimulus
▪ perception - understanding the stimulus
o functional segregation - distinct functional areas within a level
o parallel processing - simultaneous analysis of signals along
different pathways
• the visual system
•
o structure of the eye
• light passes through the cornea - refracts the incoming light and
creates an upside down imagine in the retina
• retina contains photoreceptor cells that transform light into
electrical signals - transmitted from the retina to the brain via the
optic nerve
• photoreceptors
•
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o 120 million rods, 6 million cones
o rods and cones contain different pigments
o rods - rhodopsin - saturated in daylight - sensitive to low
amounts of light -
o cones take over
o
▪ sensitive to different wavelengths
▪ blue - short
▪ green - medium
▪ red - long
o cone and rod division
o
▪ photooptic - cone-mediated
▪
▪ high acuity in good lighting
▪ scotopic - rod mediated
▪
▪ low acuity in dim lighting
▪ lack detail and colour
• colour vision
•
o based on electromagnetic wavelengths
• ganglion cells
•
o midget cell - m cell
o
▪ course patterns
▪ rapid movement
o parasol cells - p cell
o
▪ colour
▪ coded by cone system
• tectopulvinar pathway
•
o retina - superior colliculus - pulvinar -V2 - other cortical areas
o 10% of neurons in the optic nerve
o rapid reorientation, attentional capture
o most input from M cells - sensitive to motion
o superior colliculus also projects directly to eye muscles
o
▪ realigns focus into fovea
▪ detailed analysis via geniculostriate pathway
• geniculostriate pathway
•
o runs from the retina - geniculate nuclei - primary visual
cortex
o
• lateral geniculate nucleus
•
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o magnoceullar m layers
o
▪ big cell bodies
▪ bottom two layers of LGN
▪ particularly responsive to movement
▪ input primarily rods
o parvocellular p layers
o
▪ small cell bodies
▪ top four layers of LGN
▪ colour, detail
▪ still or slow objects
▪ input primarily cones
• primary visual (striate) cortex - v1
•
o located in occipital lobe
• receptive fields
•
o similarities seen at all levels:
o
▪ receptive fields of foveal areas are smaller than those
in periphery
▪ neurons’ receptive fields are circular in shape
▪ neurons are monocular
▪ many neurons at each level have receptive fields with
excitatory and inhibitory areas
▪ responses have either an on or off centre
o cortical cells
o
▪ most neurons in V1 are either
▪
▪ simple
▪
▪ rectangular
▪ on/off regions like cells in layer IV
▪ all monocular
▪ complex
▪
▪ rectangular
▪ larger receptive fields
▪ do not have static on/off regions
▪ not location sensitive
▪ motion sensitive in particular direction
▪ many binocular
• organisation of primary visual cortex
•
o functional vertical columns
o
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