Fig. 2. The receptive field organisation and morphology of the V1 neurone [receptive field modified from Krapp et al. (Krapp et al., 2001)]. The orientation and length of each arrow in the vector map indicates the local directional motion preference and sensitivity, respectively. The map resembles the optic flow pattern generated by a rotation of the head about an axis approximately midway between pitch and roll (nodes at 45° and -135° azimuth). The grey box shows the approximate area and position of the display monitor we used for stimulating the compound eye. Inset: A schematic drawing of the fly brain, with a camera lucida drawing of a stained V1 neurone on the right-hand side (courtesy of Klaus Hausen). The approximate electrode position is indicated by the open arrowhead. Scale bar, 200 µm.