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98 Cards in this Set

  • Front
  • Back
What 3 cells make up the vertical pathway?
Photoreceptors, bipolar cells and ganglion cells
What do Bipolar cells mainly do?
They used for convergence and divergence of information
What are the 3 types of bipolar cells and what do each of them do?
Diffuse bipolar cells - for sensitivity

Midget Bipolar cells - for acuity

On and off-bipolar cells - for changes in illumination
What are ganglion cells for??
On and Off center receptive fields
what is an eye disease that affects the scotoma?
Retinitis pigmentosa
Defintion of contrast
The difference in illumination between a figure and its background
Definition of acuity
The smallest spatial detail that can be resolved
How do vision scientists measure visual acuity?
They use the smallest visual angle of a cycle of grating
How do eye doctors measure visual acuity?
They use distance, say 20/20
Herman Snellen invented...
A method for designation visual acuity

He had the "stroke" equal ro 1/5 of the letter size
Spatial Frequency
The number of cycles of a grating per unit of visual angle - usually in degrees
Cycles per degree
The number of dark and bright bars per degree of visual angle
What are the 3 basics rules of sine gratings
They are...

- Patterns of stripes with fuzzy boundaries are quite common

- The edge of any object produces a single stripe, often blurred by a shadow, in the retinal image

- The visual system appears to break down images into vast number of components, each is a sine wave grating with particular spatial frequency
What pattern of retinal ganglion cells elicits the strongest response?
Medium Frequency
What is the order of the Visual pathway? Involving the Superior Colliculus
Goes to the Pulvinar nucleus, and then to the secondary visual cortex and then to higher order visual cortical areas
What is the order of the visual pathway? Involving the LGN
The lateral Geniculate nucleus goes to the primary visual cortex. From here it goes to the second visual cortex, and then to higher order visual cortical areas
What signals are send to EITHER the superior colliculus or the lateral geniculate nucleus


2 Cells
Contralateral Nasal Retional Ganglion cell Axons, and Ipsilateral Temporal Retinal cell Ganglion cell axons
What is the LGN?
Lateral Geniculate Nucleus

The axons of retinal ganglion cells synapse in the LGN
What are two cell types that are in the LGN?
Parvocellular (small) and Magnocellular (large)
Where does the parvocullular neurons receive their input?
From midget Cells
What is another name for striate cortex?
Primary visual cortex or V1
How many cells are in the striate cortex?
200 million!
What are two important features of striate cortex??
Topographical mapping - which is cortical topography, and

the dramatic scaling of information from different parts of visual field

This is cortical magnification
Visual acuity declines in an orderly fashion with...
Eccentricity
Selective Responsiveness

Orientation tuning
The tendency of neurons in striate cortex to respond optimally to certain orientations and less to others
Many cortical cells respond espeically well to these 4...
Bars, edges, gratings, direction
Each LGN cell responds to one eye or the other, but

BUT.. second point
Never to both


But, each striate cortex cell can respond to input from both eyes

Ocular Dominance Columns
End stopping
The process by which cells in the cortex first increase their firing rate as the bar lenght increases to fill up its receptive field, and then decreases their firing rate as the bar is lenghtened further
Adaptation
A reduction in responce caused by prior or continuing stimulation
What 3 theories did Oliver Selfridge come up with?
- Simple model of letter recognition
- Perception by committee
- The Pandemonium Model of Letter recognition
Good continuation
Group elements to form smootly continuing lines
Common Fate
Group elements moving in the same direction together
Synchrony
Group elements changing at the same time together
Common Region
Elements perceived to be part of a large region are grouped together
Connectedness
Elements that are connected to each other are grouped together
What are the Gestalt figure-ground assignment principles

4
Surroundedness, size, symmetry, parallelism
Object recognition starts _______ figure-ground assignment ______
Object recognition starts before figure-ground assignment finishes
Where/how system
Object localization manipulation - Parietal Cortex

Dorsal Stream
What system
Object identification

IT cortex

Ventral Stream
What is the range of visible light?
400 nm to 700 nm
problem of univariance
A set of different wavelenght-intensity combinations can elicit exactly the same response from a single type of photoreceptor
Scotopic
Dim light levels at or below the level of bright moonlight

Rods are sensitive to scotopic light levels
What is photopigment in rods?
Rhodopsin
ALl rods have same sensitivity to wavelenght, making______
it impossible to discriminate light
What are the 3 varieties of cone photoreceptors?
S-cones (short wavelenghts)

M-Cones (middle)

L-cones (long)
Trichromatic Theory of color processing
The color of any light is defined in our visual system by the relationships between a set of three numbers, the outputs of three receptor types now known to be the three cones

This is the first level of processing
Hue
Chromatic aspect of a color
Saturation
Chromatic strenght of a hue
Brightness
Distance from black in color space
Lateral Geniculate nucleus has cells that are
maximally stimulated by spots of light
Some cells in the LGN are...
excited by L-cone onset in center and inhibited by M-cone onsets in their curround
Opponet color theory
The perception of color is based on the output of three mechanisns
what are the three color opponency in the opponent color theory
Red-Green

Blue-Yellow

Black-White
Negative Afterimage, and what does it show us?
A visual image seen after the stimulus has been removed

This is a way to see opponent colors in action
What are the 2 binocular cues?
Convergnce and retinal disparity
7 monocular cues
Light and Shadow

Occlusion

Motion parallax

Relative Size and Familiar Size

Relative Clarity

Texture gradient

Linear perspective
Diffuse Bipolar Cells
Detecting low light sensitivity
midget bipolar cells
At the fovea

Cones in a one to one relationship

Cones -> Midget bipolar cells -> Retinal Ganglion cells
Temporal information is...
ipsalateral
Nasal informaton travels
Contralaterally
Superior Colluculus responds to
movement
Lateral Geniculate Nucleus is responsible for
Perceptual experience
Motion Parallax
closer objects seem to be moving faster than distant objects
Linear perspective
Linear lines appear to converge as they approach the horizon
Visual acuity
The distance at which a person can just identity the letters divided bythe distance at which a person with normal vision can just identify the letters
20/20 vision explained
If you have to be 20 feet to discern detail that someone at 20 feet can discern, you have 20/40 vision
- Visual acuity is much poorer in the periphery than the
Fovea
- Spatial frequency
The number of cycles of a grating per unit of visual angel
- Retinal ganglion cells are “tuned” to
Spatial frequency
Retinal Ganglion cells each respond best
to a specific spatial frequency that matches its receptive-field size
- Lateral Geniculate nucleus
a structure in the thalamus, part of the midbrain, that receives input from the retinal ganglion cells and has input and output connections to the visual cortex
- Magnocellular layers
the neurons in the bottom two layers of the lateral geniculate nuclea, which are physically larger than those in the top four layers. Receives input from M ganglion cells
- Parvocellular layer
The neurons in the top 4 layers of the LGN which are physically smaller than those in the bottom 2 layers. Receives input from P ganglion cells
- In the LGN 1,4,6 layers receives info _______

and 2,3,5 ________
- In the LGN 1,4,6 layers receives info conralateral, and 2,3,5 receive ipsilateral
- V1, Striate cortex, primary visual cortex
receives direct inputs from the lateral geniculate nucleus as well as feedback from other brain areas and is responsible for processing visual information
- Cortical magnification
the amount of cortical area devoted to a specific regin in the visual field
Neurons in Striate cortex are
elongated and respond to stripes
o Oreintation tuning
the tendency of neurons in striate cortex to respond optimally to certain orientations and less to others
o Ocular dominance
the property of the receptive fields of striate cortex neurons by which they demonstate a preference responding somewhat more rapidly when a stimulus is presented in one eye than when it is presented in the other
o Simple cells
clearly defined excitatory and inhibitory regions – phase sensitive
o Complex cells
a neuron whose receptive field characteristics cannot be easily predicted my mapping with spots of light
o Hypercolumn
a 1-millimeter block of striate cortex containing two sets of columns, each covering every possible orientation which one set preferring input from the left eye and one set preferring input from the right eye
- Middle (midlevel) vision
a loosely defined stage of visual processing that comes after basic features have been extracted from the image and before object recognition and scene understanding
- Illusory contour
a contour that is perceived even though nothing changes from one side of the contour to the other in the image – the arrow
- Good continuation
two elements will tend to group together if they seem to lie on the same contour
- Similarity
the tendency of 2 features to group together will increase as the similarity of them increases
- Common region
two features will tend to group together if they appear to be part of the same large region
- Necker cube
an outline that is perceptually bi-stable. Unlike the situation with most stimuli, two interpretations continually battle for perceptual dominance
o Relateability
the degree to which two line segments appear to be part of the same contour
- Recognition by components
object recognition model which holds that objects are recognized the identities and relationships of their component parts
- Prosopagnosia
an inability to recognize faces
- Agnosia
a failure to recognize objects in spite of the ability to see them
- Phototropic
light intensities that are bright enough to stimulate the cone receptors and bright enough to saturate the rod receptors
- S – cone
short wavelengths – 440 nm peak
- M-cone –
middle wavelengths – 535nm peak
- L-cone
long wavelenght peaks 565
- Metamers
different mixtures of wavelengths that look identical. More generally, any pair of stimuli that are perceived as identical in spite of physical differences
Saturation, which color is most, which is least?
white has 0, red is fully saturated