Term
| Where does information processing begin for the visual system? |
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Definition
| Information processing begins in the retina, where visual stimuli are processed to extract information about form and movement. |
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Term
| After the retina where is information then conveyed? |
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Definition
| Information is conveyed in parallel streams back into the cortical portion of the visual system. Analysis of form color and motion continues in parallel streams in primary (striate) visual cortex. |
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Term
| After the primary visual cortex what two streams does information diverge into? |
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Definition
Information diverges into:
-the dorsal stream-which is concerned with motion
-ventral stream- concerned with form and color |
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Term
| Where are optic nerves sorted? |
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Definition
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Term
| Within the eye, where do retinal ganglion cells become myelinated? |
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Definition
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Term
| What are the output cells of the retina? |
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Definition
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Term
| What are the targets of the retinal ganglion cells? |
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Definition
-suprachiasmatic nucleus of the hypothalamus
-pretectal area
-superior colliculus
-lateral geniculate nucleus (LGN) |
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Term
| What is the function of the suprachiasmatic nucleus of the hypothalamus? |
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Definition
| Light entrainment of the internal circadian clock |
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Term
| What is the function of the pretectal area? |
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Definition
| Stimulation of the pupillary light reflex |
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Term
| What is the function of the superior colliculus? |
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Definition
| Contains multiple overlying maps (visual, auditory, somatosensory, and motor) which represent surroundign space and are involved in orienting movements of the head and eyes |
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Term
| What is the function of the lateral geniculate nucleus? |
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Definition
| Relays visual information to primary visual (striage) cortex |
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Term
| What is the name of the neurons that lie between the 6 layers of the lateral geniculate nucleus? |
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Definition
| Intralaminar or koniocellular neurons |
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Term
| T/F. Each LGN receives information from only one eye. |
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Definition
| False. Due to sorting of RGC axons in the optic chiasm each LGN receives input from one half of the visual field. |
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Term
| What do layers 1 and 2 of the LGN receive projections from? |
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Definition
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Term
| Which layers of the LGN receive projections from the P-type RGCs? |
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Definition
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Term
| What projections do intralaminar neurons receive? |
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Definition
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Term
| Tre/False. Each layer of the LGN receives information from both eyes. |
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Definition
| False. Each layer of the LGN receives information from one eye. |
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Term
| Is the LGN mainly involved in processing or relay? |
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Definition
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Term
| True/False On-center and off-center LGN cells are located in layers 1-2 of the LGN? |
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Definition
| False. on-center and off-center LGN cells are intermixed through all 6 layers. |
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Term
| What are the characteristics of the magnocellular LGN neurons and where do they receive input from? |
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Definition
| Magnocellular LGN neurons receive input from M type RGCs. Magnocellular LGN neurons have larger center-surround receptive fields, respond to stiumlation with transient spiking and are insensitive to color. |
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Term
| What are the characteristics of parvocellular LGN neurons and where do they receive input from? |
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Definition
| Parvocellular cells receive input from P-type RGCs. Parvocellular LGN neurons have small center surround |
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Term
| What is the neurotransmitter released by LGN neurons and what is its affect? |
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Definition
| LGN neurons release glutamate which has an excitatory affect on the cells they synapse with. |
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Term
| Where do axons from the LGN neurons synapse? |
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Definition
| The striate cortex (primary visual cortex, V1, area 17) via optic radiations |
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Term
| How is the primary visual cortex divided? |
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Definition
| The primary visual cortex has a neocortex with 6 major layers. Layer 4 is then subdivided into an additional 4 layers A-D. Layer C is then further divided into alpha and beta. |
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Term
| Do the axons of layer 4 c project outside the cortex? |
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Definition
| No, the stellate neurons of layer IVC are local connections and therefore their axons stay within the cortex. The neurons release excitatory glutamate and receive input from LGN neurons. |
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Term
| Which areas of the neocortex of the primary visual cortex contain output neurons and which contain local connections? |
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Definition
| Stellate neurons of layer IVC are local connections and project within the cortex. Pyramidal neurons of layers II/III and V/VI are output neurons. Layers II/III project to other cortical areas, while layer V/VI project to subcortical areas. |
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Term
| Describe the pattern of organization from the LGN to the primary visual cortex. |
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Definition
| The LGN inputs into the primary visual cortex in a topographic manner known as retinotopic organization, where information originating from specific points on the retinas is relayed to specific points on the striate nucleus. |
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Term
| Describe the pattern of organization of layer IVC of the primary visual cortex. |
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Definition
| Layer IVC is organized in ocular dominance columns or stripes with LGN axons relaying information specifically from either the left or right eye to the cortical neurons in the one column. |
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Term
| Where in the primary visual cortex does information from both eyes converge? |
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Definition
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Term
| Where in the primary visual cortex does information from the p channel and m channel converge? |
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Definition
| It does not, p and m channel information remains segregated. |
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Term
| How can blob channels be histologically identified? |
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Definition
| By cytochrome oxidase, a mitochondrial enzyme. |
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Term
| Are blob monocular or binocular? |
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Definition
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Term
| What information is detected by p-type retinal ganglion cells and what is its path from the retina to the primary visual cortex? |
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Definition
| P-type retinal ganglion cells detect information concerning detail, shape, form and some are wavelength sensitive. When stimulated the P-type retinal ganglion cells release excitatory glutamate on parvocellular LGN neurons. Stellate Parvocellular LGN neurons then release excitatory glutamate on pyramidal primary visual cortex neurons in layer IVC beta. If the information involves wavelength then it is projected to blob layer III. If the information does not involve wavelength it projects to layer III IB. |
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Term
| Trace the M channel path. |
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Definition
| M-type RGC detect information about movement. This information is then relayed to the magnocellular neurons of the LGN which then relays the information to neurons of layer IVC alpha of the primary visual cortex. These neurons then relay the information on to layer IVB. |
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Term
| Describe the characteristics of layer IVC alpha cells. |
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Definition
IVC alpha cells are elongated receptive fields
-oval on and off zones
-originally called simple cells
-orientation specific
-cells perpendicular to pial surface have the same orientation preference
-cells parallel to the pial surface have systematically shifting orientation preference |
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Term
| Describe the characteristics of IVB cells. |
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Definition
-Orientation selective
-many are binocular
-many are orientation and directionally sensitive
-allow for analysis of movement |
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Term
| Describe the size of the receptive field of PIB layer III neurons. |
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Definition
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Term
| Are PIB channels directionally sensitive? |
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Definition
| No, they are orientation selective though. |
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Term
| T/F. Retinotopic organization is continued in the visual cortical areas past the primary visual cortex. |
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Definition
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Term
| What is a hypercolumn composed of? |
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Definition
Complete set of orientation columns
-input from both eyes (complete set of ocular dominance columns)
All three info processing channels |
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Term
| What is the dorsal stream responsible for analyzing? |
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Definition
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Term
| What is the ventral stream responsible for analyzing? |
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Definition
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Term
| Trace the path of the ventral stream. |
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Definition
| V1 to V2 to V3 to V4 to MT to MST to other dorsal areas. |
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Term
| Trace the path of the ventral stream. |
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Definition
| V1 to V2 to V3 to V4 to IT to other ventral areas. |
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Term
| What are the characteristics for neurons withing the MT area |
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Definition
-detect motion
-directionally sensitive
-large receptive field
-organized into direction of motion columns rather than stationary orientation columns
-respond preferentially to complex motions such as linear motion, radial motion, or circular motion |
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Term
| A patient reports that when pouring coffee the coffee appears frozen until the cup is full and then suddenly it is overflowing. Where might this patient have a lesion? |
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Definition
| Somewhere in the dorsal stream. |
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Term
| What is the size of the receptive field for the nuerons of V4? |
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Definition
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Term
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Definition
| condition caused by lesion to V4 area of the ventral stream. There is partial or complete loss of color visions, despite normally functioning cones in the retina. |
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Term
| What is the grandmother cell theory? |
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Definition
| It is one theory on how the response of individual neurons can lead to the perception of visual objects. States that perception occurs when a single cell, or small group of cells, fire in response to a very specific stimulus. |
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Term
| Other than the grandmother cell theory, what other theory is thought to account for how responses from individual neurons can lead to perception of visual objects. |
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Definition
| The parallel activation theory states that visual information is processed simulataneously in multiple parallel areas of the visual system. |
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Term
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Definition
| Strabismus is the misalignment of the two eyes. |
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Term
| If strabismus is not addressed prior to the critical period what is the result? |
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Definition
| The LGN axon terminals of the deprived eye fail to properly innervate layer VI. |
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Term
| What is the mechanism for near field depth perception? |
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Definition
| Retinal disparity. Uses neurons that receive binocular input. |
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Term
| What are the mechanisms for far field depth perception? |
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Definition
-Size
-Interposition
-Linear perspective
-Light and shadow
-motion parallax |
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