Lecture 12 Flashcards
What is retinotopic mapping?
Retinotopic mapping is the point-to-point mapping of external world onto retina, lateral geniculate nucleus, and V1. After V1 there is no retinotopic mapping (starts becoming not 1 to 1), before and during V1 there is retinotopic mapping. It is done through cells in particular locations which only respond to specific stimuli in specific locations. As cells look for more complex shapes they look at more of the world and hence are no longer 1 to 1.
What is the receptive field and why do retinal ganglion cells like dots?
The receptive FIeld: the area of the retina which when stimulated by light causes a change in the neural activity of the cell. Retinal ganglion cells like “dots” because of positives in the center and negatives on the outside, if there is only light or only darkness they cancel out so no signal, this process is due to center-surround architecture.
What is lateral inhibition and what does it do? Why is this relevant to centre Surround architecture?
Lateral inhibition refers to how cells transmit information as well as inhibiting its neighbour, this is relative to the power of the signal of the cell. This means that contrast is enhanced as colours become darker or lighter based on relative surroundings. The centre surround architecture relys on this, a centre cluster of cells surrounded by surrounding cells, if a dot falls on the centre cells or some degree of cells the signal will increase, if there is all darkness or all light they will cancel out and no change in signal will occur.
How can our receptive field be smaller in a particular area?
cells are more densely packed at the fovea and hence our receptive fields are smaller when we foveat something.
How do we go from dots to lines?
By combining retinal ganglion cells together onto a V1 cell we essentially create a line, still a centre-surround architecture.
How does vision swap sides?
Nasal retinal fibers cross to the other side, temporal retinal fibers go to the same side. Nasal retina of the eye projects out, temporal projects in. The right hemisphere looks at the left visual field, the left hemisphere looks at the right visual field.
What are some blindness examples?
Monocular blindness is when youre blind in one eye. Bitemoral hemianopia is when you have half vision (nasal retinal fibers damaged in one eye, nasal in the other, hence both hemispheres are missing the opposite half, so full vision is available but no peripheral). Homoymous hemianopia is when there is damage to the nasal retinal fibers of one eye and temporal retinal fibers of the other (typically damage after optic chiasm). Homonymous hemianopia with macular sparing occurs with damage to V1 and is the same, but they can still point to objects in their blind field (can’t tell what it is), can also sense it if moving.
