Haptic recognition of shapes at different scales: A comparison of two methods of interaction

In order to design a “haptic zoom”, in this fundamental study, we compare two scaling methods by focusing on the strategies adopted by subjects who are using a sensory substitution device. Method 1 consists of a reduction of the sensor size and of its displacement speed. Speed reduction is obtained by a “human” movement adjustment (hand speed reduction). Method 2 consists of a straightforward increase in the dimensions of the image. The experimental device used couples a pen on a graphics tablet with tactile sensory stimulators. These are activated when the sensor impinges on the outline of the figure on the computer screen. This virtual sensor (a square matrix composed of 16 elementary fields) moves when the pen, guided by human hand movements, moves on the graphics tablet. The results show that the recognition rate is closely dependent on the size of the figure, and that the strategies used by the subjects are more suitable for method 2 than for method 1. In fact, half of the subjects found that method 1 inhibited their movements, and the majority of them did not feel the scaling effect, whereas this was clearly felt in method 2.