ch 6: the visual system pt 2
DESCRIPTION
Ch 6: The Visual System pt 2. The Retina. After light passes through the pupil & lens, it hits the retina & is converted to a neural signal Has 5 layers of different types of neurons Receptors Horizontal cells Bipolar cells Amacrine cells Retinal ganglion cells. The Retina. - PowerPoint PPT PresentationTRANSCRIPT
Ch 6: The Visual System pt 2
The RetinaAfter light passes through the pupil & lens, it
hits the retina & is converted to a neural signal
Has 5 layers of different types of neurons1. Receptors2. Horizontal cells3. Bipolar cells4. Amacrine cells5. Retinal ganglion cells
The RetinaThe layers of the retina are considered
inside-outLight must pass through the top 4 layers
before reaching the receptor layerOnce the receptors are
activated, the neural signal goes back through the layers
to the retinal ganglion cells (which then exits the eyeball)
The RetinaThere is a blind spot where the ganglion cell
axons leave the eyeFovea: an indentation at the center of the
retina specialized for high acuity vision (fine details)
CompletionYour visual system fills in the gaps in your
retinal image (created by the blind spot) by completionUses info from nearby receptors to “assume”
what receptors in the blind spot would be “seeing” if they were there
Completion used in other scenariosEx: key info will be gathered about edges & the
rest of the object will be filled in
Rods & Cones2 types of retinal
receptorsRods
Scotopic vision More sensitive to light Lacks detail & color 100s of rods converge on
each retinal ganglion cell Brain can’t “be sure”
where the light is coming from
None in the fovea
Cones Photopic vision Dominant in good lighting Provides hi-def color
vision A few cones converge on
each retinal ganglion cell Brain “knows” exactly
where the light is coming from
Animal Vision
Eye MovementEven though your cones are concentrated in
the fovea, you can see a whole view of colorDue to constant scanning of the eyes &
summation of that visual input informationTemporal integration
Essentially allows you to not notice when you blinkYour eyes continuously move and fixate on
one point to the next (fixational eye movements)Saccades
Eye MovementVisual neurons respond to changeIf your eyes were to stop moving, your vision
would fade out & stop working!!
Visual TransductionTransduction: the conversion of energy from
one form to anotherVisual transduction: conversion of light to
neural signals by the visual receptorsRhodopsin: the red pigment in rods that
absorb lightA G-protein coupled receptor that responds to
light (not NTs)Movement of Na+ ions & glutamate NTs allow
for transduction in rods
Retina to the BrainMain pathway is the retina-geniculate-
striate pathwaySends neural signals from each retina to the
primary visual cortex (AKA striate cortex) via the lateral geniculate nuclei (LGN) of the thalamusCalled striate cortex because the cortex is
layered; with stripes/striations
Retina to the BrainTerminology:
Ipsilateral: same sideContralateral: opposite side
All signals from the visual field of one side go to the primary visual cortex of the contralateral hemisphere
Seeing EdgesEdges are the most informative features of
visual stimuliSo our brains have become excellent at
detecting edgesEdges are just where 2 different areas of an
image meetSo our perception of an edge is a contrast
between 2 adjacent areas of the visual fieldMach bands: our brains enhance the contrast
at edges to make them easier to see(we see edges as more
highlighted than they are in the real world)