Fig. 1.

Approaches to a feeder defined by a luminance edge. (A) Two sample paths. (B and C) Plots of feeder-angle and angular speed during the course of these paths. Horizontal dashed line in C shows threshold for measuring turns at 2 SD above the mean angular speed (mean speed with feeder at edge is 120° per s⁻¹ ± 75° per s⁻¹ SD; mean with feeder inset is 107° per s⁻¹ ± 45° per s⁻¹ SD). Note that the onset of the rapid turn often occurs after the feeder-angle has peaked. Arrows show the onset of turns and the boxes their end. Filled diamonds show peaks that did not correspond to identifiable turns (see Materials and Methods). (A–C) (Left) Data from routes with the feeder at the base of the edge; (Right) Routes with feeder inset. (D) Distribution of absolute values of feeder-angles before a turn. Data come from 495 approaches. (E) Plots of turns at high resolution. The start of a turn is specified by the sudden increase in angular velocity and its end by at least three frames over which the ant's body orientation changes by <1°. Boxes and arrows defined as above.