**8. Conclusion**

In this chapter we reviewed basic knowledge concerning spatial biases in the perception of slant and then presented novel experimental results. Our experiments tested whether the perceived 3D orientation bias function for surfaces explored by dynamic touch was similar to that for visually perceived slant and static haptic touch. We found evidence that supports the view that the spatial bias for the perceived 3D orientation of surfaces in manual reaching space is similar across visual and haptic modalities whether measured numerically with respect to vertical or with respect to horizontal or even when measured non-verbally using a horizontal-vertical bisection task. We have further suggested that the orientation bias function in manual reaching space resembles the first quarter cycle of a sine function.
