In Figures 4D–4F, we simulated 200 identical motion detectors homogeneously covering one period of the moving sine wave grating (wavelength λ = 20°). The amplitude of the stimuli ranged from 0.1 (OFF; sine grating minimum value) to 0.5 (ON; sine grating maximum value), with an intermediate luminance of 0.3. We thank Mark Huebener for critically reading the manuscript, Juergen Haag and Franz Weber for discussions, and Renate Gleich, Christian Theile, BMS-354825 order and Wolfgang Essbauer for technical assistance. “
“Many animals, including insects, turn in response to wide-field visual motion cues, providing a behavioral readout

of the motion percept (Götz, 1964, Götz et al., 1973, Hassenstein, 1951, Hassenstein and Reichardt, 1956, Hecht and Wald, 1934 and Kalmus, 1949). A rich theoretical and experimental framework relates the spatiotemporal patterns of visual stimuli to the firing patterns of direction-selective

neurons and to optomotor behaviors (Buchner, 1976, Egelhaaf and Borst, 1989, Egelhaaf et al., 1989, Götz et al., 1973, Haag and Borst, 1997, Hassenstein and Reichardt, 1956, Hausen and Wehrhahn, Ceritinib nmr 1989, Reichardt, 1961, Reichardt and Poggio, 1976 and Rodrigues and Buchner, 1984). These relationships can be compactly described by the spatial summation of local multiplication operations that compare local visual contrast changes over space and time in a model known as the Hassenstein-Reichardt correlator (HRC) (Hassenstein and Reichardt, 1956). Although neurons both upstream and downstream of the HRC have been studied in detail (Eckert, 1981, Haag and Borst, 1997, Hausen, 1976, Joesch et al., 2008, Juusola et al., 1995, Katsov and

Clandinin, 2008, Laughlin and Osorio, 1989, Rister et al., 2007, van Hateren, 1992, van Hateren et al., 2005 and Zhu et al., 2009), the neural implementation of the HRC itself remains elusive. Sitaxentan The HRC correlates light intensities between two points in space and time; an intensity deviation at one point is multiplied by an intensity deviation at a neighboring point at a later time (Figures S1A and S1B, available online). By performing this operation twice in antisymmetric fashion the signed output of the HRC provides information about the direction and speed of motion. This model was originally inferred from experiments with minimal motion signals comprising sequential changes in the brightness of two neighboring points in space that guided the turning behavior of a beetle, Chlorophanus ( Hassenstein and Reichardt, 1956). In these experiments, each point in space could be made either brighter or darker than the background, producing four contrast combinations. Two of these combinations, in which the two points change contrast in the same direction with both becoming sequentially brighter or darker, can be referred to as “phi” stimuli.