Lack of regularity between letters impacts word recognition performance

Physical inter-letter dissimilarity has been suggested as a solution to increase perceptual differences between letter shapes and hence a solution to improve reading performance. However, the deleterious effects of font tuning suggest that low inter-letter regularity (due to the enhancement of specific letter features to make them more differentiable) may impair word recognition performance. The aim of the present investigation was 1) to validate our hypothesis that reducing inter-letter regularity impairs reading performance, as suggested by font tuning, and 2) to test whether some forms of non-regularities could impair visual word recognition more. To do so, we designed four new fonts. For each font we induced one type of increased perceptual difference: for the first font, the letters have longer extender length; for the second font, the letters have different slants; and for the third font, the letters have different font cases. We also designed a fourth font where letters differ on all three aspects (worst regularity across letters). Word recognition performance was measured for each of the four fonts in comparison to a traditional sans serif font (best regularity across letters) through a lexical decision task. Results showed a significant decrease in word recognition performance only for the fonts with mixed-case letters, suggesting that fonts with low regularity, such as mixed-case letters, should be avoided in the definition of new \"optimal\" fonts. Letter recognition performance measured for the five different fonts through a trigram recognition task showed that this effect is not consistently due to poor letter identification.