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Chapter 3

Chapter 3 - study notes

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Department
Psychology
Course Code
PSYB51H3
Professor
Matthias Niemeier

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CHAPTER 3 SPATIAL VISION: FROM STARS TO STRIPES
-The retina processes information similar to a computer. Which neurons in which pathways
play a role? Describe some of the functions of the pathways. In which important way does
retinal information processing differ from that of a usual computer?
- retina neuron pathway 2 types: vertical (in retina everything begins with
photoreceptors ie rods and cones then bipolar cells then ganglion cells and then out of retina
) and horizontal/lateral pathway the neurons that are present are the amercrine cells.
Functions of the lateral pathway is lateral inhibition (good for contrast). Function of the
vertical pathway 1)convergence, retinal peripheral, the photoreceptors will project on the
bipolar cells and connect to ganglion cells, info bundles cuz there are way more
photoreceptor than ganglion cells that exit the eyes. 2) divergences happens in foveo,
individual photoreceptor will connect to 2 bipolar cell, one on and one off 3) transport
neuron from eye to brain. Diff from computer in this way: processing and interpreting
VISUAL ACUITY: OH SAY, CAN YOU SEE?
-contrast= diff in luminance /b/ an object and the background or /b/ lighter and darker
parts of the same object
-acuity = smallest spatial detail that can be resolved
-cycle = pair consisting of one dark and one bright bar
-visual angle = angle that would be formed by lines going form top and bottom or left and
right (depends on stripes) of a cycle on the page, through the center of the lens, calculated
by dividing size of cycle by viewing distance at which you can barely make out the
orientation of the gratings, then take the arctangent of this ratio.
One of the limits of spatial vision is the finest high-contrast detail that can be resolved,
limit due to spacing of photoreceptors in retina . show via Sine wave grating =grating
with a sinusoidal luminance profile. If receptors are spaced out we should be able to make
out grating but if cycle falls on single cone, we see nothing but gray, this call aliasing =
misperception of a grating due to under sampling.
DR describe visual acuity not in angles nor cycles but 20/20.20/30 need glasses. 20/10 better
than normal. Visual acuity = distance at which a person can just ID letters/distance at
which a person with normal vision can just ID letters. Eye DRs use letter as a whole that is
5 times as large as the strokes that form the letter
20/20 is designed to subtend an angle of 5 arc min, and each stork of 20/20 letter subtends
an angle of 1 arc min = 0.017 degree, with minimum of 1 arc of visual angle can tell black
and white stripes apart
www.notesolution.com
Spatial frequency # of cycles of grating per unit of visual angle, # of times a pattern, sine
wave, repeats in a given unit of space, 1/degree = cycles per degree = # of dark and bright
bars per degree of visual angle
The wider the stripes, ie lower spatial frequency, is not easier to distinguish the light
stripes from the dark. CSF Contrast Sensitivity Function shaped like inverted U, x-axis
is spatial frequency (cycles/degree) and y-axis is contrast sensitivity (ability to see the
separate black and white), cal by taking reciprocal of contrast threshold ex for a
1cycle/degree grating to be distinguish from uniform gray, dark stripes must be 1% darker
than light stripes. Thus 1/0.01=100 = y-axis. At 60cycle/degree we get the same as
1cycle/degree = 100CFS
RETINAL GANGLION CELLS AND STRIPES
-ganglion cells responds well to certain types of stripes or gratings, when spatial frequency
of grating is low, ganglion cell responds weakly, cuz the bright bar of grating lands in
inhibitory surround. When spatial frequency is too high, ganglion cells responds weakly cuz
both dark and birth stripes fall within receptive field center washing out response. When
spatial frequency is just right, with bright bar filing center and dark bars in surround, cell
responds fast.
-ganglion response depend on phase of grating, it position within receptive field. If it fits
perfectly then respond. If it turns 90 degree, so half receptive field be light and dark as itz
surround, then no response. If 180 degree shift then totally in incorrect place and no
response. If 270degree then it is same as 90degree no response
LATERAL GENICULATE NUCLEUS (LGN)
-LGN structure in thalamus, part of midbrain, that receives input from the retinal ganglion
cells and has input and output connections to visual cortex. It has 2 layers: magnocellular
layers (2 bottom layers of LGN, larger than the top 4, it receives input from M ganglion
cells in retina, responds to large, fast-moving objects), parvocellular layers receives P
ganglion cells, process details of stationary targets
-left LGN receives projections from the left sides of retinas in BOTH eyes and the right
LGN receives projections from the BOTH sides of the retina. Then each layer of LGN
receives input from one or the other eye. Layer 1,4,6 of right LGN listen to the left
(contralateral, referring to the opposite side of the body or brain) eye and layers 2,3,5
receive input from the right (ipsilateral, referring to the same side of the body or brain)
eye
-each layer of LGN contains half of the visual field of an eye
www.notesolution.com
-topographical mapping =orderly mapping of the world in the LGN nucleus and the
visual cortex
-LGN neurons have receptive fields like retinal ganglion cells. If LGN respond to same
pattern as ganglion cells, y dont ganglion cell axons just travel right back to cerebral
cortex? Cuz there are more connections from other parts of brain to LGN than there are
connections from LGN to cortex
STRIATE CORTEX
-primary visual cortex, v1, area 17, or striate cortex = receiving area for LGN inputs
in cerebral Cortex, responsible for processing visual info, it has 6 main layers, like LGN,
striate cortex has a systematic topographical mapping of visual field
-objects imaged on or near the fovea are processed by neurons in a large part of the striate
cortex but objects imaged in the far right or left periphery are allocated only a tiny portion
of striate cortex. This distortion of visual image is called cortical magnification amount
of cortical area devoted to a specific region in the visual field, the cortical representation of
the fovea is greatly magnified compared to the cortical representation of the peripheral
vision . consequence of cortical magnification is that visual acuity declines in an orderly
fashion with eccentricity (distance form fovea). Foveal representation in the cortex is highly
magnified cuz visual system must make a trade off. High resolution requires a great # of
resources: dense array of photoreceptors, one to one lines form photoreceptors to retinal
ganglion cells and a large chunk of striate cortex
RECEPTIVE FIELDS IN STRIATE CORTEX
- map receptive fields of neurons in striate cortex, receptive fields of striate cortex neurons
are not circular like retina and LGN, but are elongated, responding much more vigorously
to bars, lines, edges, and gratings than to round circles of light
-striate cortex responds best when line or edge is at just right orientation, not when line is
tilted more than 30 degree away from optimal orientation = orientation tuning
- circular receptive fields in LGN are transformed into elongated receptive fields in striate
cortex cuz LGN cells tat feed into a cortical cell are in a row. Other evidence suggest that
neural interactions (lateral inhibition) within cortex play a role in orientation tuning
- cortical cells like retinal ganglion cells also respond to gratings (collection of lines), and
like ganglion cells they respond best to grating that have just the right spatial frequency to
fill the receptive-field center, so they too are tuned to a particular spatial frequency which
corresponds to a particular line width, cortical cells are much more narrowly tuned, respond
to a smaller range of spatial frequencies than retinal ganglion cells
www.notesolution.com

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Description
CHAPTER 3 SPATIAL VISION: FROM STARS TO STRIPES -The retina processes information similar to a computer. Which neurons in which pathways play a role? Describe some of the functions of the pathways. In which important way does retinal information processing differ from that of a usual computer? - retina neuron pathway 2 types: vertical (in retina everything begins with photoreceptors ie rods and cones then bipolar cells then ganglion cells and then out of retina ) and horizontallateral pathway the neurons that are present are the amercrine cells. Functions of the lateral pathway is lateral inhibition (good for contrast). Function of the vertical pathway 1)convergence, retinal peripheral, the photoreceptors will project on the bipolar cells and connect to ganglion cells, info bundles cuz there are way more photoreceptor than ganglion cells that exit the eyes. 2) divergences happens in foveo, individual photoreceptor will connect to 2 bipolar cell, one on and one off 3) transport neuron from eye to brain. Diff from computer in this way: processing and interpreting VISUAL ACUITY: OH SAY, CAN YOU SEE? -contrast= diff in luminance b an object and the background or b lighter and darker parts of the same object -acuity = smallest spatial detail that can be resolved -cycle = pair consisting of one dark and one bright bar -visual angle = angle that would be formed by lines going form top and bottom or left and right (depends on stripes) of a cycle on the page, through the center of the lens, calculated by dividing size of cycle by viewing distance at which you can barely make out the orientation of the gratings, then take the arctangent of this ratio. One of the limits of spatial vision is the finest high-contrast detail that can be resolved, limit due to spacing of photoreceptors in retina . show via Sine wave grating =grating with a sinusoidal luminance profile. If receptors are spaced out we should be able to make out grating but if cycle falls on single cone, we see nothing but gray, this call aliasing = misperception of a grating due to under sampling. DR describe visual acuity not in angles nor cycles but 2020.2030 need glasses. 2010 better than normal. Visual acuity = distance at which a person can just ID lettersdistance at which a person with normal vision can just ID letters. Eye DRs use letter as a whole that is 5 times as large as the strokes that form the letter 2020 is designed to subtend an angle of 5 arc min, and each stork of 2020 letter subtends an angle of 1 arc min = 0.017 degree, with minimum of 1 arc of visual angle can tell black and white stripes apart www.notesolution.com
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