Figure 5.

The relative gradient is invariant to object size, shape, and material. A, B, The effect of object properties on the sensory input (RMS amplitude; see Eq. 3) was modeled based on a linear trajectory with a constant sampling density. Thus, differences in the data solely depend on object properties. We simulated an approach toward objects that differed in size (d = 1, 2, or 3 cm) and shape (sphere or cube) (A) or conductivity (B). C, D, Relative gradient for the data of A, B. Although the amplitude functions differ with size and shape (A) or material (B), the relative gradient overlaps, indicating that it is invariant to these object parameters. A–D, Solid lines indicate data for cubes. Dashed lines indicate spheres. B, D, Data are based on a cube of fixed size (d = 1 cm) and different conductivity (see color code). The water conductivity in all cases was 100 μS, and conductive versus nonconductive objects are shown in red and blue, respectively.