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Lecture 3

10 Pages
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Department
Psychology
Course Code
PSYB51H3
Professor
Matthias Niemeier

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Lecture 3: Spatial Vision
Short Answer Question (Sample) – on info learned from last lecture
-Pathway: In the retina there are 2 types of pathways
1)Lateral pathway – [neurons that a play a role in this pathway in the retina]
horizontal cells followed by amacrine cells
2)Vertical pathway – [neurons that a play a role in this pathway in the retina] so
they’ve photoreceptors (rods and cones), followed by bipolar cells and the ganglion
cells [then it goes out of the retina]
Functions of these 2 pathways:
1)Lateral pathway: its serving for lateral inhibition
Lateral inhibition increases the contrast and sharpness in visual response.
This phenomenon occurs in the mammalian retina, for example.
In the dark, a small light stimulus will be enhanced by the different photoreceptors
(rod cells). The rods in the center of the stimulus will transduce the "light" signal to
the brain, whereas different rods on the outside of the stimulus will send a "dark"
signal to the brain. This contrast between the light and dark creates a sharper
image. This mechanism also creates the Mach band visual effect.
So thats what the visual system deals with mostly differences
in luminance not really absolute levels of luminance [not much
info. in that]
2)Vertical pathway: 2 functions
www.notesolution.com
a)Convergence: so multiple photoreceptors will project onto bipolar cells and
multiple of those will project onto ganglion cells = so information is bundled as there
are way more photoreceptors in the retina than there are ganglion cells that exit the
eye [ so you dont want an optic nerve thick[er] so that you cant move your eyes]
b)Divergence: happens in the fovea = so an individual photoreceptor will connect to 2
bipolar cells [one ON and one OFF bipolar cell]
c)Transmission of neural signals: transports the neural info. Out of the eye into
the brain
Q) In which imp. way does the retinal info. processing differ from that of a
usual computer?
-the retina does a whole bunch of processes at the same time
-While the computer processes one thing at a time [although it does it fast]
[Check with text]
Natural Scene Statistics
-there are certain statistical describable regularities in the outside world
Printing press metaphor
So with the invention of the printing press = the # of books just exploded and with that literacy
came about in Europe!
BUT
Its to do with the alphabets!
-For English: so for movable types - there are 26 uppercase and 25 lowercase alphabets!
-But for Chinese text: youve would have to create 1000 moveable types!
So all these alphabets are based on a small set of letters [some kind of a symbol]
as opposed to Chinese text
you cant reduce it to less than 1000 of these
symbols!
www.notesolution.com
So Gutenbergs advantage was = it was WAY MORE EFFICIENT! [For
English] just by the nature of diff. Alphabets or ways to write!
Its about efficiency!
So western alphabet more efficient
Just like letters are building bricks/elements of language:
= in a similar way the visual images can be described/represented as compositions of simple
elements
-So we dont use alphabets to describe images but we’ll use gratings! These gratings are
just like the letters of the alphabet!
-So in the early stages of visual processing: the visual system filters out these elements =
these gratings! [so its like finding all the “letters that are all there in the visual images]
Types of Gratings
-Rectangular grating = its called that b/c when you present this grating in terms of
light/intensity on the y-axis along some horizontal axis dimension = then the distribution
of luminance is some kind of a rectangle
[White which is up and black which is down & is pretty much rectangular so hence the name]
-Sine Wave (sinusoidal) grating = has smooth transitions
-One specific sub-category of sine wave gratings = Gabor
Characteristics of gratings
-Cycle = grating repeats itself
www.notesolution.com

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Description
Lecture 3: Spatial Vision Short Answer Question (Sample) on info learned from last lecture - Pathway: In the retina there are 2 types of pathways 1) Lateral pathway [neurons that a play a role in this pathway in the retina] horizontal cells followed by amacrine cells 2) Vertical pathway [neurons that a play a role in this pathway in the retina] so theyve photoreceptors (rods and cones), followed by bipolar cells and the ganglion cells [then it goes out of the retina] Functions of these 2 pathways: 1) Lateral pathway: its serving for lateral inhibition Lateral inhibition increases the contrast and sharpness in visual response. This phenomenon occurs in the mammalian retina, for example. In the dark, a small light stimulus will be enhanced by the different photoreceptors (rod cells). The rods in the center of the stimulus will transduce the light signal to the brain, whereas different rods on the outside of the stimulus will send a dark signal to the brain. This contrast between the light and dark creates a sharper image. This mechanism also creates the Mach band visual effect. So thats what the visual system deals with mostly differences in luminance not really absolute levels of luminance [not much info. in that] 2) Vertical pathway: 2 functions www.notesolution.com
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