Alternatively, effortless reading may simply require that letter orientation is consistent with the word's frame of reference. We have investigated these alternatives. In the WORD condition, reading time was independent of orientation range a . This invariance is not achieved via orientation-invariant letter recognition. Instread orientation invariance requires that letters in a word have a consistent orientation even if this orientation is different from the word orientation.
Effortless reading is possible provided adjacent letters share the same letter-centered coordinates.