Vision Performance Institute Technical Report Effect of Character Spacing on Text Legibility Yu-Chi Tai, Shun-nan Yang, and John Hayes, James Sheedy Vision Performance Institute, Pacific University, Oregon, USA Running title: Font size and optimal inter-letter spacing Correspondence concerning this article should be addressed to Yu-Chi Tai, Vision Performance Institute, Pacific University in Oregon, Forest Grove, OR 97116. Email:
[email protected] Phone: 1.503.352.2289. Abstract This study investigated the effect of inter-letter spacing on letter and word recognition over a range of font sizes, font types, and different levels of text familiarity (word frequency). Inter-letter spacing affects the degree of lateral interference form neighboring letters. For commonly used fonts, character spacing is proportional to font size. Since lateral interference would be expected to operate over a fixed retinal area, we hypothesized that, relative to the default spacing for the common 10- to 12-point fonts, the optimal inter-letter spacing would be larger for smaller font sizes and smaller for larger font sizes. We also hypothesize that optimal spacing will be smaller for familiar words than for unfamiliar words because of top-down enhancement and that sans serif fonts will need wider spacing than serif fonts because of the extra contours. Fifty-four subjects were recruited and tested in two tasks: text (letter and word) recognition and spacing preference. In the text recognition, subjects were asked to read aloud 840 words or the middle letter in each of 420 random-letter strings. Half of the words were high-frequency and the other half low-frequency.