Editing Motion perception (section)

===DS cells in insects===
The first DS cells in invertebrates were found in [[flies]] in a brain structure called the [[lobula plate]]. The lobula plate is one of the three stacks of the [[neuropils]] in the fly's [[optic lobe (arthropods)|optic lobe]]. The "[[tangential cell]]s" of the [[lobula plate]] composed of roughly about 50 neurons, and they arborize extensively in the neuropile.  The tangential cells are known to be directionally selective with distinctive directional preference. One of which is Horizontally Sensitive (HS) cells, such as the [[H1 neuron]], that depolarize most strongly in response to stimulus moving in a horizontal direction (preferred direction). On the other hand, they hyperpolarize when the direction of motion is opposite (null direction). Vertically Sensitive (VS) cells are another group of cells that are most sensitive to vertical motion. They depolarize when a stimulus is moving downward and hyperpolarize when it is moving upward. Both HS and VS cells respond with a fixed preferred direction and a null direction regardless of the color or contrast of the background or the stimulus.