Editing Motion perception (section)

===The Hassenstein-Reichardt model===
[[File:Reichardt model.jpg|thumb|Reichardt model]]
It is now known that motion detection in vision is based on the Hassenstein-Reichardt detector model.<ref>{{Cite journal| vauthors = Hassenstein B, Reichardt W |date=1956-10-01|title=Systemtheoretische Analyse der Zeit-, Reihenfolgen- und Vorzeichenauswertung bei der Bewegungsperzeption des Rüsselkäfers Chlorophanus|journal=Zeitschrift für Naturforschung B|volume=11|issue=9–10|pages=513–524|doi=10.1515/znb-1956-9-1004|issn=1865-7117|hdl=11858/00-001M-0000-0013-F2EA-6|s2cid=98709700|hdl-access=free}}</ref> This is a model used to detect correlation between the two adjacent points. It consists of two symmetrical subunits. Both subunits have a receptor that can be stimulated by an input (light in the case of visual system). In each subunit, when an input is received, a signal is sent to the other subunit. At the same time, the signal is delayed in time within the subunit, and after the temporal filter, is then multiplied by the signal received from the other subunit. Thus, within each subunit, the two brightness values, one received directly from its receptor with a time delay and the other received from the adjacent receptor, are multiplied. The multiplied values from the two subunits are then subtracted to produce an output.  The direction of selectivity or preferred direction is determined by whether the difference is positive or negative. The direction which produces a positive outcome is the preferred direction.

In order to confirm that the Reichardt-Hassenstein model accurately describes the directional selectivity in the retina, the study was conducted using optical recordings of free cytosolic calcium levels after loading a fluorescent indicator dye into the fly tangential cells. The fly was presented uniformly moving gratings while the calcium concentration in the dendritic tips of the tangential cells was measured. The tangential cells showed modulations that matched the temporal frequency of the gratings, and the velocity of the moving gratings at which the neurons respond most strongly showed a close dependency on the pattern wavelength. This confirmed the accuracy of the model both at the cellular and the behavioral level.<ref>{{cite journal | vauthors = Haag J, Denk W, Borst A | title = Fly motion vision is based on Reichardt detectors regardless of the signal-to-noise ratio | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 101 | issue = 46 | pages = 16333–8 | date = November 2004 | pmid = 15534201 | pmc = 526200 | doi = 10.1073/pnas.0407368101 | bibcode = 2004PNAS..10116333H | doi-access = free }}</ref>

Although the details of the Hassenstein-Reichardt model have not been confirmed at an anatomical and physiological level, the site of subtraction in the model is now being localized to the tangential cells. When depolarizing current is injected into the tangential cell while presenting a visual stimulus, the response to the preferred direction of motion decreased, and the response to the null direction increased. The opposite was observed with hyperpolarizing current. The T4 and T5 cells, which have been selected as a strong candidate for providing input to the tangential cells, have four subtypes that each project into one of the four strata of the lobula plate that differ in the preferred orientation.<ref name=boreul/>