Editing Motion perception (section)

===Direction selective (DS) cells===
Direction selective (DS) cells in the retina are defined as neurons that respond differentially to the direction of a visual stimulus. According to Barlow and Levick (1965), the term is used to describe a group of neurons that "gives a vigorous discharge of impulses when a stimulus object is moved through its receptive field in one direction."<ref name=barlev/> This direction in which a set of neurons respond most strongly to is their "preferred direction". In contrast, they do not respond at all to the opposite direction, "null direction". The preferred direction is not dependent on the stimulus—that is, regardless of the stimulus' size, shape, or color, the neurons respond when it is moving in their preferred direction, and do not respond if it is moving in the null direction. There are three known types of DS cells in the vertebrate retina of the mouse, ON/OFF DS ganglion cells, ON DS ganglion cells, and OFF DS ganglion cells. Each has a distinctive physiology and anatomy. Analogous directionally selective cells are not thought to exist in the primate retina.<ref>{{cite journal | vauthors = Dhande OS, Stafford BK, Franke K, El-Danaf R, Percival KA, Phan AH, Li P, Hansen BJ, Nguyen PL, Berens P, Taylor WR, Callaway E, Euler T, Huberman AD | display-authors = 6 | title = Molecular Fingerprinting of On-Off Direction-Selective Retinal Ganglion Cells Across Species and Relevance to Primate Visual Circuits | journal = The Journal of Neuroscience | volume = 39 | issue = 1 | pages = 78–95 | date = January 2019 | pmid = 30377226 | pmc = 6325260 | doi = 10.1523/JNEUROSCI.1784-18.2018 }}</ref>

====ON/OFF DS ganglion cells====
ON/OFF DS ganglion cells act as local motion detectors. They fire at the onset and offset of a stimulus (a light source). If a stimulus is moving in the direction of the cell's preference, it will fire at the leading and the trailing edge. Their firing pattern is time-dependent and is supported by the [[Werner E. Reichardt|Reichardt]]-[[Bernhard Hassenstein|Hassenstain]] model, which detects spatiotemporal correlation between the two adjacent points. The detailed explanation of the Reichardt-Hassenstain model will be provided later in the section. 
The anatomy of ON/OFF cells is such that the dendrites extend to two sublaminae of the inner plexiform layer and make synapses with bipolar and amacrine cells. They have four subtypes, each with its own preference for direction.

====ON DS ganglion cells====
Unlike ON/OFF DS ganglion cells that respond both to the leading and the trailing edge of a stimulus, ON DS ganglion cells are responsive only to a leading edge. The dendrites of ON DS ganglion cells are monostratified and extend into the inner sublamina of the inner plexiform layer. They have three subtypes with different directional preferences.

====OFF DS ganglion cells====
OFF DS ganglion cells act as a centripetal motion detector, and they respond only to the trailing edge of a stimulus. They are tuned to upward motion of a stimulus. The dendrites are asymmetrical and arbor in to the direction of their preference.<ref name=boreul/>