Example of an orientation-selective neuron.

<p><b>A</b>. The polar plot in A shows the mean response (black dots) in response to the moving gratings (n = 3) with the standard deviation being shown by the grey shaded area. The neuron was selective for motion in almost horizontal directions (e.g., moving gratings with vertically oriented stripes). The red dotted ellipse shows the fit to the raw data with the major and minor axis of the ellipse depicted by the red and green line. Note that the centre of the ellipse (red dot) is only shifted slightly off origin (black dot), which indicates very weak direction selectivity at most. In contrast, the major and minor axes differ markedly in their length, indicating a strong orientation preference of this cell. Direction selectivity was quantified by the DSI, defined as the metric distance of the centre of the ellipse from the centre of the coordinate system, relative to the radius of the major axis of the ellipse (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0062846#s2" target="_blank">Methods</a> and inset in <b>C</b>). Orientation selectivity was quantified by the OSI = 1−(minor axis/major axis) (see <b>A</b> and inset in <b>B</b>). <b>B, C</b>. A Monte-Carlo approach was applied to test the robustness of the calculated OSI and DSI values. In each case the distribution of the indices obtained for 10.000 repetitions is shown, with the experimentally determined OSI and DSI values being superimposed by solid lines. Note that orientation preference was highly significant, whereas no directional preference was present. Rayleigh statistics confirmed the lack of directionality tuning of this neuron.