Exam 5 Flashcards
Rhodopsin
is the light-absorbing pigment in rods. Absorption of light by rhodopsin triggers a cascade of reactions involving over 12 chemicals
What kind of damage would “artificial eyes” offer little hope for?
People born with cataracts or blind since birth
What is the problem with using rhodopsin for these artificial eyes?
Sensitive only to blue light and people would see the world in shades of grey (aka no color vision). It likely would require a “boost” when used with humans–something like glasses to tune the lightwaves.
What are the advantages and disadvantages of inserting the replacement pigment into ganglion cells? Into bipolar cells?
Ganglion cells are easily accessible and have more staying power. They also are the last to die-off in degenerative diseases. However, they may differ on the effects on vision and there is no binding package that can discriminate the types (20). Bipolar cells are difficult to access and injection risks detaching the retina from its support surface.
What have been the results with mice using the replacement pigments?
We have used both bipolar and ganglion cells–in cases the cells do become light sensitive and fire an action potential in response to light. Mice are able to “pass” some simple behavioral tests like navigating a water maze, but their acuity measures ½ the acuity of normal mice.
How Do We Get Channelrhodopsin into Bipolar/Ganglion Cells?
Gene therapy: The protein gene is inserted into a virus and the virus is injected into the eye. The binding package of the gene is modified so that it will bind with only certain cells.
How is the retina mapped onto the striate cortex?
Parts of the retina that are closest together are also close together on the cortex.
What is the cortical magnification factor, and what function does it serve?
The cortical magnification factor is the idea that visual stimulation of the small fovea relates to a large part of the cortex and peripherary vision relates to a small part of the cortex. This means that objects we look at are more clear/detailed.
Brain imaging
Brain imaging can be done by injecting a liquid that attaches to oxygen in the blood of the brain and can then be viewed as active areas fill with blood, or by using magnetic fields in order to “line up” elements in high-concentrated, bloody areas of the brain.
How has brain imaging been used to determine the retinotipic map in humans?
This is used by stimulating parts of the eye and then determining the active parts in the brain.
Location columns and Orientation columns
Location columns are perpendicular to the surface of the cortex and contain all receptive fields from a location on the retina. Each of these location columns contains a complete set of orientation columns that visually helps determine the orientation of an object.
How do feature detectors respond to a scene?
We look at a scene and it is split into location columns on your cortex corresponding to the location of the stimulus on our retina. Each location column contains a complete set of orientation columns and the one orientation column needed is stimulated within the location column. Signals are then sent to other parts of the brain as necessary.
What does it mean that the cortical representation of a scene does not have to resemble the scene, but just has to contain information that represents the scene?
While our retina is actually stimulated in a way that reflects a proper image of the real world. The cortex (or neural map/signal) of the vision does not represent an image, but instead contains the necessary details (color, location, orientation, placement) in order to “describe” the image being seen.
Action Pathway (Dorsal Pathway, How Pathway, Where Pathway)
Pathway that conducts signals from the striate cortex to the parietal lobe. Is involved in determining where an object is and how to act upon that object.
Binding Problem
The problem of how neural activity in many separated areas in the brain is combined to create a perception of a coherent object.
Contralateral eye
The eye on the opposite side of the body
Feature detectors
A neuron that responds selectively to a specific feature of the stimulus such as orientation or direction of motion.
Fusiform gyrus (fusiform face area/FFA)
An area in the human inferotemporal (IT) cortex that contains neurons that are specialized to respond to faces.
Ipsilateral eye
The eye on the same side of the body
Landmark discrimination task
The behavioral task used in Ungerleider and Mishkin’s experiment in which they provided evidence for the dorsal, or where, visual processing stream. Monkeys were required to respond to a previously indicated location.
Lateral geniculate nucleus (LGN)
The nucleus in the thalamus that receives inputs from the optic nerve and, in turn, communicates with the cortical receiving area for vision.
Location pathway/column
a column in the visual cortex that contains neurons with the same receptive fields locations on the retina.
Object discrimination task
The behavioral task used in Ungerleider and Mishkin;s experiments in which they provided evidence for the ventral, or what, visual processing streams. Monkeys were required to respond to an object with particular shape.
Optic chiasma
Split: Right visual field goes to left brain. Left visual field goes to right brain.
Primary visual receiving area
occipital cortex– the area of the cerebral cortex that first receive most of the signals initiated by a sense’s receptors.
Prosopagnosia
A form of visual agnosia in which the person can’t recognize faces.
Rod and frame illusion
?
Selective adaptation
A procedure in which a person or animal is selectively exposed to one stimulus, and then the effect of the exposure is assessed by testing with a wide range of stimuli. Typically, sensitivity to the exposed stimulus is decreased.
Superior colliculus
An area in the brain that is involved in controlling eye movements and other visual behaviors. The area receives about 10 percent of the ganglion cell fibers that leave the eye in the optic nerve.
Ventral pathway (What pathway)
Pathway that conducts signals from the striate cortex to the temporal lobe. It is involved in recognizing objects.
What part of the visual pathways from the eye to the brain cross over from the left eye to the right brain and vice versa? Where do they cross over? What is the effect of the crossover in terms of what parts of space are represented in what half of the brain?
They cross over at the optic chiasma. ??
What is the superior colliculus involved with?
It is responsible for the control of eye movements.
How are the layers in the lateral geninculate nucleus organized (with respect to both the what and where pathways and with respect to the two eyes)? (You need to know the general principle, not specifically which layer of the LGN is getting exactly which input.)
10% of ganglion cells go to superior colliculus which controls eye movements, while the other 90% go to LGN. Bilateral structure - One in left hemisphere (right VF) and one in right hemisphere (left VF) The receptive field is also center-surround just like those in the retina.
What is a single disassociation and what it implies about function? What is a double disassociation and what it implies about function?
Single disassociation means one function is absent while the other is present. And double disassociation is like Case 1: Function A intact, B impaired and Case 2: Function A impaired, B intact (meaning that the construction of one element is not reliant on the construction of the other).
What information does the dorsal pathway carry? Which type of retinal cells does it begin with and where in the brain does it terminate. You also need to know that it goes through the Medio-temporal lobe.
The dorsal pathway (also known as the where or how pathway) carries information about where the object is and how to act upon it. It is located near the top back section of the brain, layer one is made up of Magnocellular cells and receives input from contralateral eye while layer two receives input from ipsilateral eye.
