Tilted letters and tilted words: a possible role for principal axes in visual word recognition.

Subjects made lexical decisions to columnar letter strings in which every letter was either upright or tilted 90 degrees clockwise as if the whole letter string had been rotated from the horizontal. Lexical decisions were faster in the latter case. The advantage for the tilted format was also found when all strings were presented in aLtErNaTiNg CaSe or in uppercase, so this advantage cannot be due to preservation of the tilted words' global shape. The cost for the upright-letter format increased with the number of letters in the columnar strings. These data suggest that words recognition may involve shape description or position coding relative to a reference frame based on the principal axis of the letter string.