week 3 - lateral inhibition

Question 1

neural processing

Answer 1

the interaction of signals in many neurons

Question 2

lateral inhibition

Answer 2

a neuron’s response to a stimulus is inhibited by the excitation of a neighboring neuron

Question 3

Limulus eye experiment

Answer 3

• ommatidia (units of the eye) allow recordings from a single receptor (able to target specific receptor)
• light shown into a single receptor leads to rapid firing rate of nerve fiber
• adding light into neighboring receptors leads to reduced firing rate of initial nerve fiber

Question 4

horizontal cells

Answer 4

• local (inhibitory) cells
• no action potentials
• no axons
• responsible for lateral inhibition

Question 5

action potential with horizontal cells

Answer 5

1. horizontal cells activated by photoreceptors
2. act on the initial bipolar cell (inhibition is small, does not make much of a difference)
3. horizontal cells also send inhibitory information to adjacent bipolar cells

Question 6

Hermann grid

Answer 6

illusion of gray images in the intersection of white areas

Question 7

What is responsible for the Hermann grid illusion?

Answer 7

• signals from bipolar cells cause effect
• receptors responding to white corridors send inhibiting signals to receptor at intersection
• the lateral inhibition causes a reduced response which leads to the perception of gray at the intersections

Question 8

In regards to the Hermann grid, would the brain respond stronger to dark or light color?

Answer 8

light color

Question 9

mach bands

Answer 9

• people see an illusion of enhanced lightness and darkness at borders of light and dark areas
• actual physical intensities indicate that this is not the stimulus itself

Question 10

How does our brain react to mach bands?

Answer 10

• receptors responding to low intensity (dark) area have smallest output
• receptors responding to high intensity (light) area have largest output

Question 11

What is the reasoning behind the mach bands illusion?

Answer 11

• all receptors are receiving lateral inhibition from neighbors
• in low and high intensity areas amount of inhibition is equal for all receptors
• receptors on the border receive differential inhibition

Question 12

edge detection

Answer 12

Our brain acts as an information processing machine with the help of contour lines, shape perception, shape recognition, and light intensity.