V. Hayward proposed the following apparatus to easily demonstrate the approximate conditions experienced by subjects when exploring illusory haptic objects.Get two finger-sized, low quality magnets (high quality ones are too strong for this demo) that have two parallel, flat faces. Sandwich one magnet in between two pieces of cardboard or plastic (Fig 1).

Place the second magnet on top of the sandwich and move it sideways with a fingertip (Fig. 2). 

The magnetic field forces you experience resemble the forces that were used to create illusory haptic objects. If the magnets' poles attract each other, you will experience forces that resemble those of an illusory hole. Now flip the sliding magnet so that the magnets repel each other. You will experience forces that resemble those of a virtual bump. However, there are major differences between the forces in this demo and those of the illusory objects. The demo has forces in many different directions, compared to only horizontal forces in a virtual object. As a result, when the magnets repel each other the magnet you slide may move vertically, unlike what happens with the tool in our experiments. The tool always moved following the geometry of the plastic object on which the tool rolled. Also, the demo's forces do not depend on the contact force you apply. There is also substantial friction in the demo, which was greatly minimized in the experiments.

Design by NisiSama
© Gabriel Robles-De-La-Torre
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