Definition - What does System Unit mean? A system unit is the part of a computer that houses the primary devices that perform operations and produce results for complex calculations. It includes the motherboard, CPU, RAM and other components, as well as the case in which these devices are housed. This unit performs the majority of the functions that a computer is required to do.
size constancy - the tendency to perceive the veridical size of a familiar object despite differences in their distance (and consequent differences in the size of the pattern projected on the retina of the eye)
Size constancy is the human expectation for familiar things to be the same size in most situations. But in order to truly bring vertebrate bias down to size, Gould will have to show that honeybees have size constancy -- the ability to remember something they first saw close up when they later see it from farther away.