Chapter 4: The Visual Cortex and Beyond Flashcards
What is the pathway of visual processing starting at the retina and ending in the visual cortex.
Retina (ganglion cells/optic nerve) –> Optic chiasm –> lateral geniculate nucleus (LGN) in the thalamus –> Striate area (AKA V1, or visual receiving area) of the occipital lobe.
Some information goes from the optic chiasm (10%) to the superior colliculus instead of the LGN, to guide eye movement.
What is the Optic chiasm?
the optic chiasm: an X-shaped bungle of fibres at the bottom of the brain. These fibres carry info from each eye and cross over so that all fibres corresponding with the left visual field (from both eyes) end up in the right hemisphere and all fibres corresponding with the right visual field (from both eyes) end up in the left hemisphere.
What is the Lateral Geniculate Nucleus?
the LGN is in the thalamus. It regulates neural info as it moves from the retina to the cortex. it also receives signals back from the cortex which suggests that it operates as a sort of feed back system and is involved in top-down processing
The LGN organizes information it recieves from the various location by eye, receptor type, and by type of environmental information.
What is the visual receiving area?
It is the first visual area of the cortex, also called V1 or the striate cortex due to it’s striped appearance. It also includes areas of the extrastriate cortex (areas V2-5)
What are the different feature detectors between ganglion cells, cells in the LGN, and cells in the cortex?
Ganglion cells have centre surround receptive fields. They respond best to small spots but can also respond to other types of stimuli
Lateral Geniculate Nucleus Cells have centre surround receptive fields very similar to the ganglion cells.
The Cortex has three different types of cells with different receptive fields
- Simple Cortical cells: excititory and inhibitory areas are arranged side by side. They respond best to bars of a particular orientation
- Complex cortical cells: they respond best to movement of a correctly orientated bar moving in a particular direction
- End-Stop cortical cells: they respond best to corners, angles, or bars of a certain length, moving in a particular direction.
What is Selective adaption?
When a stimulus with a specific property is viewed, neurons tuned to that property fire. This firing causes the neurons to either become fatigued or to adapt.
Adaption leads to the neuron firing rate to decrease and the neuron to fire less when that stimulus is presented again. This is a short term effect but it means that, even if the stimulus is presented at the same strength as it was before, it will illicit a weaker response.
What is experience dependent plasticity?
The idea that the response properties of neurons are shaped by experience. If we are not exposed to a stimuli specific to certain neurons, those neurons will lose their ability to respond to that stimulus. (think about the kitten experiment with the striped walls.)
What are neural maps?
When an image on our retina is transformed into neural signals, the signals follow a “neural map” so that objects that create images near each other on the retina are represented by neural signals that are near each other in the cortex.
What does it mean to say that the spatial representation of the visual field is distorted?
The spatial representation of the visual field is distorted in our cortex because more space is allotted to locations near the fovea than locations near the retinal periphery. For example, the fovea only makes up 0.01% of the fovea but it makes up 8-10% of the retinotopic map in the cortex. This distortion is called cortical magnification.
How is the striate cortex organized?
The cortex is organized in columns. Location columns are perpendicular to the surface of the cortex so that all the neurons within a location column have their receptive field at the same location on the retina.
Orientation columns are columns of neurons that share the same preferred orientation.
Each location column is ~1mm in diameter and contains a full range of orientation columns with the orientation columns organized in an orderly fashion (e.g. the 90degree orientation column is right next to the 85degree orientation column).
A complete location column with a full range of orientation columns is called a hyper-column
What changes in the receptive field as we move from the striate cortex to the extrastriate cortex.
As we move from area V1 through V2, V3, V4, V5, the receptive field increases to that more an more aspects of the visual field get combined to form a complete picture.
What different pathways does visual information follow after leaves the occipital lobe? What is the specialty of each of these streams?
Visual information moves through the ventral pathway and the dorsal pathway.
The Ventral pathway is the “what” pathway; it moves from the occipital lobe to the temporal lobe.
The Dorsal Pathway is the “where” pathway; it moves from the occipital lobe to the parietal lobe.
These two pathways feedback and communicate with each other as well.
Where does visual information go after the dorsal and ventral pathways?
Visual information goes to the inferotemporal cortex which processes whole objects in the visual field.
After the inferotemporal cortex, visual information moves to the medial temporal lobe specifically to memory related areas including:
- the parahippocampal cortex
- the entrohinal cortex
- and the hippocampus
Neurons in this area respond to both visual stimuli AND to memories of that stimuli. (e.g. they would respond to both seeing a cat and thinking about a cat you saw last week).
