The effect of fonts boldness on different point sizes
An experiment by Beier and Oderkerk (2019) demonstrated that at both small and large point sizes, light and ultra-black fonts were inferior to all the fonts in the middle of the weight scale. Further, the bolder weights in the middle of the scale enhanced recognition in the small font size, while failing to do so in large font size.

These findings provide evidence that under reading situations involving small font sizes and signs read form great reading distances, bolder weights will improve letter recognition. They also showed that both light and ultra-black font weights should be avoided in any case where letter recognition is a priority.

For more see:
Beier, S. & Oderkerk, C.A.T. (2019). ‘Smaller Visual Angles Show Greater Benefit of Letter Boldness than Larger Visual Angles’. Acta Psychologica 199 (August): 102904. 1–8.

Typography for elderly people
By testing participants of all ages, researchers have found that reading speed stabilizes around the age of 40, after which it gradually continues to decrease over the lifespan; that the point size that one can read at a relative good speed slowly decreases from the age of 23, with a rapid decline from the age of 68; and, finally, that reading acuity (clarity at small point sizes) tends to worsen from the age of 16 (Calabrese et al., 2016).

Older participants are also more affected by added ‘noise’ or blurring of the test fonts in lexical decision tasks of identifying words or non-words: they tend to retain less visual information from the peripheral visual field (which is important for reading longer paragraphs of text); they are more easily distracted by irrelevant elements in the text; and they have greater difficulty tuning into a specific font style, than younger participants. Our data further indicates that compared to younger readers, older readers are more easily distracted by the negative influence of letter crowding (letters appearing to merge with their neighbors) and lighter font weights.

In short, when designing for this reader group, keep in mind to create simple layouts, with high contrast between background and foreground, and never use light font weights, or unusual font designs.

For more see:
Beier, S. & Oderkerk, C.A.T. (2019) ‘The effect of age and font on reading ability’, Visible Language, 53.3, 51–69.

Character complexity
Research shows that the simpler the character skeleton, the more legible the character.

This rule of thumb only applies when the shape of the character does not increase the rate of misreadings. In an investigation of the legibility of digits in a short exposure of three-digit strings at the peripheral visual field, research by Beier and Bernard (2018) showed that digits and letters benefit from having the simplest shapes. In other words, the shorter the morphological skeleton, the more legible the character.

These results somewhat contradict the approach applied by several renowned type designers whose focus on ensuring differentiation between characters may result in added features, such as cross bars and tails.

For the London Underground typeface, for example, Edward Johnston created a loop in the lowercase ‘l’ to differentiate it from the capital ‘I’. This resulted in a more complex letter skeleton, which in theory would lower legibility.

An earlier investigation, also by Sofie Beier (Beier & Larson 2010), showed that at greater reading distances, a tail on the ‘l’ results in fewer errors, that a cross bar on the letter ‘i’ can improve legibility, and that the letter ‘a’ should have a two-storey design.

Following this, we conclude that the advantage of the shorter morphological skeleton only applies in situations where the simple character skeleton will not result in a greater number of misreadings.

For more see:
Beier, S., Bernard, J.B. & Castet, E. (2018) ‘Numeral legibility and visual complexity’, Proceedings of DRS2018, Design Research Society, vol. 5, 1841-1854, Limerick, 25th-28th June.

Beier, S. & Larson, K. (2010) ‘Design Improvements for Frequently Misrecognized Letters’, Information Design Journal, 18(2), 118-137.