Image-based models of letter recognition in reading, such as template matching, predict a strong dependence on letter orientation.
Models based on viewpoint-invariant features of letters predict little or no effect of orientation.
Figure 1 Procedure. The subjects were instructed to read the text passages as quickly as possible without skipping words. They answered 3 multiple-choice questions after each passage to test for comprehension. 12 normally sighted, native English speakers read 5 passages in each of the 8 orientation conditions. The effect of letter rotation on reading speed.