The Retinostriate Pathway Flashcards
How many layers does the striate cortex have?
Contains 6 layers (1, ⅔, 4A, 4B, 4C, 5, 6)
Cortical Magnification
The amount of cortical area that is dedicated to a particular area of the visual field.
Eccentricity
Term referring to the angular distance from the centre of the visual field or from the fovea of the retina
What is one important consequence of cortical magnification?
Visual acuity declines in an orderly fashion with eccentricity
Visual Crowding
Inability to recognize a target object in clutter
What are the receptive fields of striate cortex neurons like? And what do you respond to?
They are not circular like the retina or LGN but rather they are elongated and respond vigorously to bars, lines, edges and gratings than to round spots of light
Orientation Tuning:
Tendency of neurons in the striate cortex to respond optimally to certain orientations and less to others
Individual neuron in the striate cortex responds best when?
The line or edge is at the right orientation
What types of orientation do most cells respond to?
More cells are responsive to horizontal and vertical orientations than to obliques
Cortical cells are much more narrowly ______and respond to smaller range of _______ than retinal ganglion cells
tuned ; spatial frequencies
Cortical cells respond especially well to moving ______, ______, ______ and ______
lines, bars, edges and gratings
Cortical cells respond strongly when a line moves in _____ but not when the same line moves _______
one direction (left to right), right to left
Ocular dominance
Property of receptive fields of striate cortex neurons in which they tend to prefer visual input from one eye over the other
Are cells in striate cortex influenced by input from one or both eyes?
Cells in the striate cortex can be influenced by input from both the right and left eye
Difference in response of complex and simple cells?
A complex cell will respond regardless of where the stripe is presented as long as it is somewhat within the cell’s receptive field whereas the simple cell will respond only if a stripe is presented to the center of its receptive field
End-Stopping:
The process by which a cell in the cortex increases its firing rate as the length of a bar increases until the bar fills up its receptive field,and then it decreases its firing rate as the bar is lengthed further
How does the size of a particular cell’s receptive field appears to vary with target contrast?
Cell might respond to a smaller portion of the visual field when the grating stimulus has a high contrast than it will when the difference between light and dark bars is more subtle
Adaptation
A reduction in response caused by prior or continuing stimulation
What does adaptation result in?
Both a decrease in firing rate and a change in the tuning curve
Gratings at which orientation elicit the strongest response from the 0 degree selective cells?
Gratings orientated at 0 degrees (vertical) will elicits the strongest response from the 0 degree selective cells
Spatial frequency adaptation is ______selective, thus there is little or no effect on sensitivity to ______following adaptation to a ______
orientation ; vertical gratings ; horizontal grating
Selective adaptation causes which type of neurons to become fatigued?
Selective adaptation causes the neurons most sensitive to the adapting stimulus to become fatigue
What type of neurons are not fatigued by the adaptation procedure?
Neurons responsive to much higher or lower spatial frequencies are not fatigued by the adaptation procedure so contrast sensitivity for these spatial frequencies is not affected.
Why would the visual system use spatial frequency filters to analyse images?
Different spatial frequencies emphasize different types of information
- Low frequencies= empahisize broad outlines
- High frequencies- fine details
High frequencies of an image are:
Low frequencies are:
quick abrupt changes from light to dark
large slow changes from light to dark over a large region
Tilt Aftereffect
Perceptual illusion of tilt, produced by adapting to a pattern of a given orientation.
Optic Disck
Represents the beginning of the optic nerve and is the point where the axons of retinal ganglion cells come together
Optic Nerve
Sends visual information from your retina to your brain
Fill in the structures of the visual pathway, from where ganglion cell axons exit the retina at the optic disk to the visual projection areas in the brain.
1) Optic Nerve
2) Optic Chaism
3) LGN (lateral geniculate nucleus
4) Optic Radiation
5) Visual (straied) Cortex
Optic Radiation
Contains axons from the neurons in the lateral geniculate nucleus to the primary visual cortex.
Visual Cortex
This is where images received from your retina begin to get processed and then sent out to other brain regions
Layers that receive signals receive signals from the nasal half of the left retina are
layers 1, 4, and 6 in the right LGN
Layers that receive signals from the retinal ganglion cells of the left eye that respond to colour.
left LGN, layers 3 and 5; and right LGN, layers 4 and 6
Layers that receive signals that pass through the right optic nerve
left LGN: 1, 4, and 6;
Right LGN, layers 2, 3, and 5
