Fig. 1. Illustration of the stimuli.

a Static images show the two different haptic stimulus conditions, with examples of different numerosities. In the equal individual size condition, each sphere was the same size irrespective of the number of spheres. So, the total volume of the spheres increased with increasing numerosity. In the equal total volume condition, the total volume of all spheres was kept constant. So, as numerosity increased the individual sphere size decreased. b Examples of the visual stimulus at different numerosities. The total surface area of the dot pattern remained the same across numerosities. A large, thin, red fixation cross passes diagonally through the center of the display, and through the center of the dot pattern.