Fig. 4: Predicted effects of surface material on mass estimation.

A Illustration of the experimental objects, which were three cubes of identical size and weight but different surface material. B Contours illustrate possible prior distributions over mass and volume based on past experience of objects made from the three different materials. In the absence of haptic feedback, the expected mass-volume ratio of the three objects will approximately match the density of the surface material (dashed lines). The red disc corresponds to the actual mass and volume of all three objects. C Illustrates estimation of mass for a lifted object with an expected density that is larger (top), equal (middle), or lower (bottom) than its actual density. Discriminability varies in proportion to the conditional probability of object mass, given visual evidence of object volume and object density. For the same haptic feedback (black dashed line), the different gradients of discriminability lead to different likelihood functions (red curves) and different biases (red arrows) in the mean posterior estimates.