Letter case and text legibility in normal and low vision

Abstract

It is thought by cognitive scientists and typographers alike, that lower-case text is more legible than upper-case. Yet lower-case letters are, on average, smaller in height and width than upper-case characters, which suggests an upper-case advantage. Using a single unaltered font and all upper-, all lower-, and mixed-case text, we assessed size thresholds for words and random strings, and reading speeds for text with normal and visually impaired participants. Lower-case thresholds were roughly 0.1 log unit higher than upper. Reading speeds were higher for upper- than for mixed-case text at sizes twice acuity size; at larger sizes, the upper-case advantage disappeared. Results suggest that upper-case is more legible than the other case styles, especially for visually-impaired readers, because smaller letter sizes can be used than with the other case styles, with no diminution of legibility.

Figure 1

Shapes of words in (a), outlined in (b), are more distinctive in mixed-case and lower case than all upper-case text.

Figure 2

Means of normally-sighted participants' (n = 3) log size thresholds (in arc min visual angle) for identification of words and random strings as a function of letter case condition. Error bars indicate +/− 1 s.e.m.

Figure 3

Means of log size threholds of participants with low vision (n = 4) as in Figure 2.

Figure 4

Mean reading speeds for MNREAD sentences presented by RSVP (left) and continuous text (right) for the two case conditions for normally-sighted readers (acuity reserve = 2; n=3).

Figure 5

Average reading speeds for MNREAD sentences presented by RSVP (left) and continuous text (right) for the two case conditions for low vision readers (acuity reserve = 2; n=4).

Figure 6

Average reading speeds for MNREAD sentences presented by RSVP (left) and continuous text (right) for the two case conditions for two normally-sighted readers (acuity reserve = 10; n=2).