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Fig. 1. e-vector tuning and visual field properties of POL1-neurones. (A) e-vectors eliciting maximal spike frequency ({Phi}max) in 142 POL1-neurones stimulated with a zenithal stimulus. In this circular histogram, {Phi}max is given with respect to the long axis of the head (the straight line connecting 0° and 180°). The radial scale indicates the number of POL1-neurones found for any particular {Phi}max. Note that there are three types of POL1-neurone tuned to approximately 10°, 60° and 130°. (B–D) Data are mapped on zenith projections of the upper visual hemisphere, i.e. the centre of each graph gives the zenith and the concentric circles represent parallels of latitude. (B) {Phi}max orientation as a function of stimulus position in the three tuning types of POL1-neurone (upper, middle and lower graphs). The orientation of the bars indicates mean {Phi}max values at their respective positions on the upper visual hemisphere. The width of the bars shows the number of measurements: thin, N=1; medium, N=2–5; thick, N>5. The numbers of POL1-neurones represented by each graph are 50, 48 and 44 (top to bottom). The {Phi}max values are plotted with respect to the tangent to the parallel of latitude at the indicated positions (compare Fig.2a in) (Schwind and Horváth, 1993). Thus, {Phi}max can be read directly from the graphs; specifically, {Phi}max orientations that are parallel within the visual field appear also parallel in the graph. Note that, for each e-vector type of POL1-neurone, {Phi}max is quite independent of stimulus position. (C) Sensitivity as a function of stimulus position in the three tuning types of POL1-neurone. The diameter of the filled circles indicates mean relative sensitivity at their respective positions on the upper visual hemisphere (reference sensitivity of 1.0 at position 60°/right). Numbers of measurements at each position range from 1 to 9 (for details, see Petzold, 2001). The numbers of POL1-neurones represented by each graph are 5, 8 and 9 (top to bottom). Data in A-C are from POL1-neurones in the left optic lobe receiving input from the cricket’s left eye. (D) Position and size of the visual fields of POL1-neurones. The visual fields (approximate range of >=25% sensitivity; see text) are indicated by the grey areas for the POL1-neurones of both the right and the left optic lobe. r, right; l, left; a, anterior; p, posterior. Compiled from data in Petzold, 2001.