Lecture 4: Parallel Processing Flashcards
1
Q
- Midget cells to what layer of LGN?
- Parasol to what layer?
- Bistratified to what layer?
A
- Parvocellular (Dorsal 4 layers)
- Magnocellular (Ventral 2 layers)
- Interlaminar Regions
2
Q
- Parvo are sensitive to what?
- Magno?
- Konio respond best to what?
A
- Red-Green color contrast; No fast movement
- Monochromatic, and respond to FAST MOVEMENT
- respond well to Blue-Yellow Chromatic Contrast
3
Q
- Parallel Processing: Define
A
- Specific parts of Visual Info are Processed along specialized Visual Pathways (channels)
4
Q
X and Y Cells
- Came up during the study of cat ganglion cells
1. What did X-Cells refer to?
2. Y-cells?
A
- Linear Cells
- Non-linear cells
* This was first studied in 1966.
5
Q
X-Cell
- A Spatial Grating can be positioned w/in the Cell’s receptive field so that what happens?
a. What is this position referred to?
b. Why is it called this?
A
- so that NO response is elicited.
a. The NULL POSITION
b. Because here, Excitation and INhibition are LINEARLY SUMMED and CANCEL each other. So, Excitation is equal to Inhibition.
6
Q
Y-Cell: nonlinear
- Can a null position be found?
a. What does this indicate?
A
- No. There is always a response from the cell
a. Cell doesn’t sum spatial info in a linear fashion. tells us X and Y cells play different roles in vision. (Parallel visual pathways)
7
Q
Photoreceptors
- When exposed to light what do they do?
a. This is related to what?
A
- Hyperpolarize
a. Intensity of the stimulus
8
Q
Horizontal Cells
- 2 Classes of Horizontal cells
A
- H1 and H2
9
Q
Horizontal:
- H1 Receive input from what?
- H2 from where?
A
- Primarily from M and L cones; Little input from S cones
2. Strong S-Cone input and input from L and M cones
10
Q
Horizontal
- What do they sum up?
a. High degree of spatial summation, what happens?
A
- Input from Photoreceptors distributed over a LARGE AREA of the RETINA
a. due to this HIGH level of SPATIAL SUMMATION, an ANNULUS Elicits a STRONG response from a HORIZONTAL CELL, causing it to Hyperpolarize
11
Q
Bipolar
- On-Center bipolar Cells characterized by what?
A
- By an INVAGINATING Synapse that they make w/Photoreceptors in the OPL
12
Q
Bipolar
- Both on and off center bipolar cells synapse with what?
- In Dark conditions, photoreceptors continuously release what?
a. Light stimulation will do what? - For on Center Bipolar Cells: What molecule is inhibitory?
a. A Reduction in its release causes what?
A
- in the IPL
- Neurotransmitter
a. Causes Hyperpolarization of the Photoreceptors and a reduction of the neurotransmitter release - Glutamate
a. Causes DEPOLARIZATION of the Bipolar Cell
13
Q
Bipolar Cells
- Off Center: Glutamate has what effect?
- Receptive field centers of the MIDGET BIPOLAR Cells are formed by what 2 things?
a. What else? - Midget bipolar cells manifest what 2 things?
A
- Opposite: Excitatory, and a reduction in its release, secondary to hyperpolarization of a photoreceptor, causes relative inhibition (hyperpolarization) of the Bipolar Cell
- by L or M Cones
a. S cone communicate w/a specific class of Bipolar Cells, referred to as S-CONE BIPOLAR CELLS - Both HIGH Spatial Resolution and Color Opponency
14
Q
On-center midget bipolar cell: Receptive field is made of what?
A
- center made of a Single cone and the Surround by a mixture of L and M cones.
15
Q
On-center diffuse cell is made of what?
A
A mixture of L and M cones as well as the surround
16
Q
Amacrine cells
- What do they show?
- First Retinal Neurons to display what?
- Tend to respond how?
a. Though to play a critical role in what?
A
- A Center-surround organization like bipolar cells
- APs
- Briefly, transiently, at the stimulus onset and offset.
a. in Coding Movement
17
Q
- As the diameter of a spot of light is increased, the ganglion cell manifests SPATIAL SUMMATION up to what?
a. Results in what happening?
b. Beyond this, what happens?
A
- up to the PERIMETER of its receptive field center (On Center)
a. Increase in frequency of APs
b. Light falls onto the Antagonistic surround, causing a decrease in the Frequency of APs
18
Q
Strong stimulus for a Ganglion cell?
- What are they selective for?
A
- SPATIAL CONTRAST, but not Diffuse illumination. Contrast info is extracted form the visual scene very early in the visual system, w/in the retina itself
19
Q
Ganglion Cells
- The Center-Surround organization found in ganglion cells has its origin in what cells?
a. On-Center Midget Ganglion Cells synapse with what? - Midget Ganglion cells are referred to as what?
a. Constitute what % of FOVEAL and NON-FOVEAL GANGLION CELLS? - On-Center diffuse Bipolar Cells synapse with what?
A
- in Bipolar cells
a. with On-center Midget bipolar cells (Off with off, on with on) - Retinal Parvo Cells
a. 70% - On-center Parasol Ganglion cells. (off with off)
20
Q
- S-Cone bipolar cells synapse onto what?
a. % of ganglion cells? - The center of the ganglion cell is influenced by what?
a. The surround is influenced by what?
A
- Small Bistratified Cells
a. 8% - Bipolar Cells
a. Lateral Inhibition arising from Horizontal Cells
21
Q
- Key feature of Central and Midperipheral Midget bipolar cells is the contribution of what to the Formation of the RECEPTIVE FIELD CENTER?
a. This holds true for what else? - In peripheral retina: What happens?
a. Each cone bipolar makes contact with what?
A
- only 1 Cone
a. For Midget Ganglion Cells located in the Fovea - More than 1 Bipolar Cell feeds into a Midget Ganglion Cell CENTER, resulting in LARGER RECEPTIVE FIELD CENTERS, increased Spatial SUMMATION and DECREASED SPATIAL RESOLUTION
a. with B/w 1 and 10 cone photoreceptors, and rod bipolars contact 30-50 rods
22
Q
- Parasol Ganglion cels (10%) respond how to a flash of light?
- Midget ganglion cells will respond how to a flash of light?
- Why the difference?
A
- Transiently
- Sustained response
- may be due to the nature of the Amacrine Cell input, with parasol ganglion cells presumably receiving substantial input from transient amacrine cells and midgets receiving a large input from sustained amacrine cells.
23
Q
Biplexiform Cells
- The only type of ganglion cell that connects to what?
a. Role in vision?
A
- That connects DIRECTLY to PHOTORECEPTORS
a. Unclear
24
Q
LGN
- Each layer of LGN gets input from what?
- Ipsilateral Eye
- Contralateral Eye
A
- ONLY ONE EYE
- Layers 2,3 and 5
- Layers 1, 4, and 6
25
Q
- Ganglion cells adjacent in the retina will project to cells where?
A
- ADJACENT in the LGN, forming an orderly map (RETINOTOPIC MAPPING)
26
Q
- Parvo and Magno neurons account for what % of the Retinogeniculate Pathway
- Konio cells what %
- What neurons are characterized by color opponency?
A
- 80% (70% parvo; 10% magno)
- 10%
- Parvo and Konio Neurons. This means they’re excited by certain wavelengths and inhibited by others.
27
Q
- Parvo: Smaller receptive fields: Support what better?
2. Magno: Larger: support what?
A
- Spatial Resolution (Better VA): Mostly connected to FOVEAL GANGLION CELLS
- Greater Spatial Summation and Better Sensitivity in Low Light
28
Q
- Parvo cells show what?
- Parvocellular layers manifest what?
- Konio cells exhibit what?
A
- Inhibition (decreased AP frequency) for short wavelengths and excitation (increased rate) for long wavelengths: Color Opponency
- Red-Green Opponency
- Blue-Yellow Opponency
* R-G and B-Y project to separate layers of the striate cortex
29
Q
- What do magno neurons show?
A
- Same spectral sensitivity in their Center surround, manifesting spatial Antagonism, but not color opponency
30
Q
- Parvo cellular axon diameters are what?
- Magno cellular neurons have what?
- Large diameter cables transmit what?
A
- smaller and they transmit electrical signals slower
- Have larger diameter axons
- transmit electrical signal faster. This would contribute to faster motion perception
31
Q
- Transient responses to rapid changes in illumination gives what?
- Parvo neurons manifest sustained responses when?
A
- gives magno neurons the capability to resolve high temporal frequency stimuli
- when presented with a long-duration stimulus: they respond to the stimulus for a relatively long period of time.
32
Q
- Damage in Layers 3-6 (parvo cells) causes what?
- Sensitivity to High-frequency flick is what?
- Lesions in LGN Layers 1-2 (Magno cells) cause poor what?
A
- reduced color perception and poorer visual acuity.
- is preserved
- poor detection of High-frequency flicker and greater difficulty in detecting large objects. Color perception and high spatial resolution are unaffected
33
Q
*Study slide 31
A
Study slide 31