Topic 6&7 Cortical organisation Flashcards
How is orientation information represented in cortical area V1?
Cells in orientation columns are tuned to the same orientation and show a progressive change in the preferred orientation across the cortex
What is meant by the term “cortical magnification factor”?
Amount of cortex devoted to visual space decreases with increasing eccentricity.
Neighbouring orientation-tuned columns in V1 have preferred orientations that differ by about 10 degrees. How does the visual system process orientation information so as to be sensitive to changes in orientation of less than 10 degrees?
Through the relative response of overall population activity of all the columns.
If you view a series of lines tilted to the left of vertical for a minute, what will you see when you then immediately view of series of vertical lines? Explain why such a percept occurs.
Perceived orientation will be the right (the tilt aftereffect).
Cells tuned to the left will be greatly adapted, those tuned to vertical slightly adapted, those tuned to the right, not adapted.
In terms of sensitivity to orientation, what is the oblique effect and why might it occur?
The oblique effect refers to
greater sensitivity to vertical and horizontal lines than to oblique ones.
Why?
Greater exposure to vertical and horizontal contours in the environment.
Are the tuning properties of visual cells genetically determined? Discuss experimental evidence that supports your claim.
The initial properties of cells are genetically determined.
Visual deprivation study on newborns or animals deprived of visual input shows the innate tuning properties of the cells.
e.g. monkeys that are mature at birth have essentially the same tuning properties as normal adults.
Does the visual environment affect the tuning properties of visual cells? Discuss experimental evidence.
Yes.
- Selective stimulation experiments related to binocular development and motion development support that abnormal visual experience can change the tuning properties of cells. Visual experience within critical period is necessary for normal development.
- Given the tilt aftereffect, tuning can be changed later in life.
What is the significance of a “critical period” in cortical development?
Visual experience within a critical period is necessary for normal development. With sensitivity to damage in that period, abnormal visual experience can totally change the tuning properties of cells.
