Show for the various types of retinal cell how their interconnections with sign-inverting or sign-conserving synapses account for the polarity (hyperpolarization vs. depolarization, or increased vs. decreased firing) of each cell’s response to a small spot centered in the cell’s receptive field.
List and explain some the visual phenomena thought to result from center-surround antagonism in the receptive fields of visual cells.
Lateral antagonism serves to
a. enhance contrast
b. accentuate temporal changes
c. help in detection of motion
d. inhibit selectivity to orientation
Consider an on-center X-cell whose receptive field center is 1o in diameter. Which of the following stimuli should cause the largest burst of spikes at onset? (All stimuli are at the same "intensity" - that is, the same number of photons per unit area per second, and are concentric with the middle of the field).
a. a spot 1/2o in diameter
b. a spot 1o in diameter
c. a spot 2o in diameter
d. an annulus with an inner diameter of 1o and an outer diameter of 2o
Increased firing of an "off" center ganglion cell signifies
a. there is light everywhere in this vicinity
b. there is no light anywhere in this vicinity
c. the local area just became dimmer than that nearby
d. the local area just became lighter than that nearby
Consider an on-center X-cell with its receptive field exactly bisected by a black/white border, as shown below. The left half field is white; the right half field is black. Suddenly, there is an instantaneous contrast reversal: the left half becomes black, the right half becomes white. What is the cell's response to that switcheroo?
a. firing increases when the fields reverse
b. firing decreases when the fields reverse
c. there is no change from the ongoing rate of firing
d. the cell transiently behaves like a Y cell
Show how lateral inhibition allows a single cell to be selectively sensitive, responding only if its particular “trigger feature”, perhaps the image of a small bug, is present in its receptive field, and explain the significance of the “trigger feature” concept for our understanding of perception.
Currently several labs are working to replace diseased retinas with implanted light-sensitive chips that can stimulate the optic nerve electrically. Discuss the successes and the difficulties in these efforts.