Ch. 5.2 How the Brain Processes Visual Information Flashcards
Where does the optic nerve start and where does it end?
- It starts with the ganglion cells in the retina.
- Most of its axons go to the lateral geniculate nucleus of the thalamus
- some go to the hypothalamus and superior colliculus.
When light strikes a receptor, does the receptor excite or
inhibit the bipolar cells?
What is the effect on horizontal cells?
What effect does the horizontal cell have on bipolar cells?
The receptor excites both the bipolar cells and the horizontal cell.
The horizontal cell inhibits the same bipolar cell that was excited plus additional bipolar cells in the surround.
If light strikes only one receptor, what is the net effect (excit- atory or inhibitory) on the nearest bipolar cell that is directly connected to that receptor? What is the effect on bipolar cells to the sides? What causes that effect?
It produces more excitation than inhibition for the nearest bipolar cell. For surrounding bipolar cells, it produces only inhibition. The reason is that the recep-tor excites a horizontal cell, which inhibits all bipolar cells in the area
What is the effect of lateral inhibition?
Lateral inhibition heightens contrast and is important for many functions in the nervous system.
- vision, when light hit a surface, the bipolars just inside the border are most excited, and those outside the border respond the least.
- olfaction, a strong stimulus can suppress the response to another one that follows slightly after it, because of inhibition in the olfactory bulb
- In touch, stimulation of one spot on the skin weakens the response to stimulation of a neighboring spot, again by lateral inhibition
- In hearing, inhibition makes it possible to understand speech amid irrelevant noise
As we progress from bipolar cells to ganglion cells to later cells in the visual system, are receptive fields ordinarily larger, smaller, or the same size? Why?
They become larger because each cell’s receptive field is made by inputs converging at an earlier level.
What are the differences between the parvocellular and magnocellular systems?
Neurons of the parvocellular system have small cell
bodies with small receptive fields, are located mostly in and near the fovea, and are specialized for detailed and color vision.
Neurons of the magnocellular system have large cell bodies with large receptive fields, are located in all parts of the retina, and are specialized for perception of large patterns and movement.
If you were in a darkened room and researchers wanted to “read your mind” just enough to know whether you were having visual fantasies, what could they do?
They could use fMRI, EEG, or other recording methods to see whether activity increased in your primary visual cortex (V1).
What (disorder?) is an example of an unconscious response to visual information?
In blindsight, someone can point toward an object or move the eyes toward the object, despite insisting that he or she sees nothing.
What is a simple cell in the visual cortex?
A simple cell has a receptive field with fixed excitatory and inhibitory zones. The more light shines in the excitatory zone, the more the cell responds. The more light shines in the inhibitory zone, the less the cell responds.
WHat is a complex cells in the visual cortex? And how to test if a cell is simple og complex?
complex cells, located in areas V1 and V2, do not respond to the exact location of a stimulus. A complex cell responds to a pattern of light in a particular orientation (e.g., a vertical bar) anywhere within its large receptive field.
Most of them respond most strongly to a stimulus moving in a particular directio.
The best way to classify a cell as simple or complex is to present the stimulus in several locations. A cell that responds to a stimulus in only one location is a simple cell. One that responds equally throughout a large area is a complex cell.
What do cells within a column of the visual cortex have in
common?
They respond best to lines in the same orientation. Also, they are similar in their preference for one eye or the other, or both equally.
What is a feature detector?
It is a neuron that detects the presence of a particular aspect of an object, such as
a shape or a direction of movement.
What is the effect of closing one eye early in life? What is the
effect of closing both eyes?
If one eye is closed during early development, the cortex becomes unresponsive to it.
If both eyes are closed, cortical cells remain somewhat responsive for several weeks and then gradually become sluggish and unselective in their responses.
What early experience would cause a kitten or human child
to lose stereoscopic depth perception?
- Strabisimus (lazy eye).
If the eye muscles cannot keep both eyes focused in the same direction, the developing brain loses the ability for any neuron in the visual cortex to respond to input from both eyes.
Instead, each neuron responds
to one eye or the other. Stereoscopic depth perception requires cells that compare the input from the two eyes.
What causes astigmatism?
Astigmatism results when the eyeball is not quite spherical. As a result, the person sees one direction of lines more clearly than the other
