Figure 8

Determining whether, and, if so, when, to close the wings. The plot shows the expected rate of expansion of the image of a gap as it is approached, as a function of the instantaneous visual angle subtended by the gap, with the physical width of the gap as a parameter. The vertical dashed line represents an angular width of 90deg. These curves are plotted assuming an approach speed of 4m/s, based on analysis of video sequences (Vo, Schiffner and Srinivasan, unpublished data).