Week 3 Flashcards
Convergence can be either excitatory or inhibitory. True or false
True
Which receptors excite ESPS the neuron at point B?
3, 4, 5
Which receptors converge on inhibitory neurons ISPS that reduce activity at B.
1,2, 6, 7
Presenting light to the center of an Excitatory center, inhibitory-surround receptive field:
More action potentials in the ganglion cell.
Presenting light to the center of an inhibitory center, excitatory surround receptive field:
Fewer action potentials in the ganglion cell.
Summation of excitatory and inhibitory connections in the retina creates _______ for ganglion cells and other visual system neurons.
Receptive fields
Edge enhancement
An increase of perceived intensity of borders in visual field
What happens in Chevreul Illusion?
People tend to see, enhance lightness, and darkness at the borders between light and dark areas.
Why does edge enhancement happen?
- Center-surround cells near the border get different input than those in the middle.
- Because of the effect of lateral inhibition in center-surround receptive fields.
When an image is focused on the retina, in which part of the retina should you have the greatest amount of lateral inhibition?
A. Macula.
B. Fovea.
C. Blindspot.
D. Periphery.
E. All areas with receptors should be roughly equal.
D. There should be greater convergence in the rods of the periphery.
Lateral inhibition alone fails to explain the Chevreul illusion in some situation. What does that suggest?
The effect goes beyond local lateral inhibition. It is only part of the story we need to look further on in the brain for more answers.
Where do retinal signals go?
Approximately 1 million ganglion cells, send axons out of each retina. These axons formed the optic nerve.
Approximately 10% of these go to the superior colliculus , to eat with orienting and multi sensory responses.
About 90% go to the lateral geniculate nucleus (LGN) of the thalamus.
About how many ganglion axons go to each LGN? how many axons go to the visual cortex?
900,000
360,000
Items in the visual fiend go to the _____ side of both retina.
Opposite
Signals from each hemiretina go to the LGN on the _____ side.
Same (ipsilateral)
Each LGN has ___ layers
6
Which LGN layers receive signal from the same eye?
2,3,5
Which LGN layers receive signals from the opposite eye.
1,4,6
Magnocellular Pathway (M-cells)
which layers? What do they do?
Layers 1 and 2
Transmit info of motion and depth.
Parvocellular pathway (P-cells)
Which layers, what do they do?
Levels 3 - 6
Contain info about detail and color
koniocellular pathway
Which layers, what do they do?
In-between layers
involved with color vision
Signals received in the right LGN must have come form:
A. The right eye
B. The left eye
C. The right visual field
D. the left visual field
D The left visual field
Spatial Maps
Both the retina and the LGN organize activity by spatial maps
Retinotopic Map
Each place on the retina corresponds to a place in the LGN
Use single-cell recordings to determine the location of the corresponding neuron in the LGN
How do we get from LGN to the Visual Cortex (V1)?
- the optic radiation leads from LGN to V1.
- The receptive fields in V1 is the smallest but also more complex. Information across visual fields and eyes is now integrated for the first time in V1.
T or F: cells in visual cortex respond differently than cells in the retina and LGN (center-surround)
True
Simple cells
Made by the convergence of LGN cells, best activated by the correctly oriented bar
Complex cells in V1 and V2
Made by the converging simple cells(May be convergence of motion sensitive cells from retina, alternatively. Respond to movement of bars of light in a specific direction ( not the stationary lights).
End-Stopping Cells
respond to moving lines of specific length or moving centers or angles
feature detectors
cells in the V1 are called that because there able to capture simple spatial features of objects.
Hierarchical processing.
Representations are built from simple receptive fields and become more complex as you go higher in the cortex
Cortical magnification
Describes how many neurons in an area of the visual cortex are ‘responsible’ for processing a stimulus of a given size, as a function of visual field location.
cortical magnification factor
The size of the magnification
Selective adaptation
The tendency for a cell to become fatigued, when faced with sustain stimuli
Fatigue or adaptation to a stimulus result in two main effects:
- a decrease in neural firing rate
- a reduction in firing rate when a similar stimulus is presented again immediately.
experience dependent plasticity
In animals reared in environments that contain only certain types of stimuli, neurons that respond to those stimuli become more predominate due to neural plasticity
Benefits of color vision
- helps us classify and identify things
- facilitates perceptual organization; makes some objects ‘pop-out’
- evolutionary psychology behind this; foraging for food
Physical Basis of color
- Associated with our sensitivity to particular wavelengths
- However, colors are not a property of light waves. Our experience of color is a result of an interaction between wave of lights and sensory system.
Chromatic colors / hues
They are perceived when particular wavelengths reach to eyes
Achromatic colors
if all wavelengths are transmitted equally (black/white/grey)
Selective reflection
selective reflection of one object specifies its chromatic color
Selective transmission
for clear objects
we can distinguish ___ colors if depending on wavelength only
200
in total we can do 2.3 mil
Subtractive color
Mixing paints with different pigments.
Adding pigments will result in a chance of selective reflectance.
Adding blue and yellow
Additive color
Mixing lights of different specific wavelengths
Direct combination of wavelengths - all wavelengths are available for the observer to see
Reflectance of all wavelengths
