A comparison of two methods of scaling on form perception via a haptic interface

In this fundamental study, we compare two scaling methods by focusing on the subjects' strategies which are using a sensory substitution device. Method 1 consists in a reduction of the sensor size and its displacement speed. Here, speed reduction is obtained by a "human" movement reduction (hand speed reduction). Method 2 consists in a classical increase of the image dimension. The experimental device couples the pen on a graphics tablet with tactile sensory stimulators. These latter are activated when the sensor crosses the figure on the computer screen. This virtual sensor (square matrix composed of 16 elementary fields) is displaced when the pen, guided by a human hand displacements, moves on the graphics tablet. Even if it seems that there is no difference between the two methods, the results show that the recognition rate is closely dependent on the figure size and the strategies used by the subjects are more suitable for method 2 than the method 1. In fact, half of the subjects found that method 1 inhibits their movements and the majority of them don't feel the scaling effect, whereas this is clearly felt in method 2.