Fig. 2. Generation of traction vector maps using the gelatin traction force assay. (A) A vector map of the experimental bead displacements generated by the optical flow algorithm (Marganski and Dembo, 2003) with an outline of the cell edge and cell body superimposed upon it. The direction and size of the vectors indicate the direction and magnitude of bead displacements occurring in the plane of the substratum, generated by a moving keratocyte. (B) A vector map of traction stress computed from the bead displacements in panel A. Arrows indicate the size and direction of traction stresses. (C) A contour map showing areas of similar traction magnitude. Regions of low and high traction stress are represented by cool (blue-light green) and warm (yellow-purple) colors, respectively.