*2.2. Stimuli*

The stimuli were the figures, illustrated in the next sections, mainly based on a cross geometrically composed of five adjacent squares or a cross made up of two-centered and intersected orthogonal rectangles of equal size. Further stimuli were juxtaposed, overlapped, and isolated polygons. The stimuli were displayed on a 33-cm color CRT monitor (Sony GDM-F520 1600 × 1200 pixels, refresh rate 100 Hz, Sony, Tokyo, Japan) driven by a MacBook computer with an NVIDIA GeForce 8600 M GT in ambient illumination provided by a Osram Daylight fluorescent light (250 lx, 5600 K). The overall sizes of the figures were approximately 5 degrees. The luminance of the white elements was 122.3 cd m<sup>−</sup>2. Black components had a luminance value of 2.6 cd m<sup>−</sup>2. The gray background luminancewas62.5cdm<sup>−</sup>2,abouthalfwaybetweenthewhiteandblacklinecomponents.

Viewing was binocular in the frontoparallel plane at a distance of 60 cm from the monitor.
