Outline. The eye first reads the words outlines. We do not read by deciphering one letter after the other, but by identifying, at once, already memorized «word images». This point favours the use of lower cases.
Upper part. We usually read the upper part of the letters, which is more significant. In 1843 already, a French solicitor, Mr Leclair, suggested a visual lopping : he thought he could reduce by half the printing costs with this system. His demonstration is relevant, but it only works if the lower part remains blank ; space saving, which effectively reduces printing costs, is then nil.