The effect of inter-letter spacing on reading Yu-Chi Tai, John Hayes, James Sheedy College of Optometry Pacific University, Forest Grove, Oregon ABSTRACT Reading is a complex task where linguistic codes are picked up through the visual system for cognitive processing. The typical reading pattern includes a repetitive pattern of saccadic eye movements and intervening fixations on the text. The saccadic eye movements typically span 7-9 characters and have duration of approximately 35 ms during which no visual information is processed but cognitive processing may continue. During the fixations of approximately ms, text information is acquired during the first 100 ms and cognitively interpreted during the remainder of the fixation. Efficient reading requires the ability to quickly extract information during the short pause of an eye fixation; presumably more legible text enhances visual acquisition. We investigated the effects of inter-letter spacing upon threshold word legibility as well as eye movements and speed during reading. MATERIALS & METHODS RESULTSRESULTS (cont’d) Figure 2. Relative legibility of individual letters and words with various spacing levels. Error bars are SEM. “#” indicates significant difference (p < 0.05) from the letter legibility; “*” indicates significant difference (p < 0.05) from the legibility in the setting of default character spacing. CONCLUSIONS CONTACT INFORMATION In Experiment 1, the threshold legibility of lower case letters and words was measured using a distance visual acuity method derived from standardized clinical testing of visual acuity (ISO, 1994) and as used in previous legibility studies. Thirty subjects (age 18 to 35 years) were recruited and screened to meet the following inclusion criteria: best-corrected visual acuity of 20/20 or better, no ocular pathology and no binocular vision anomalies. Experiment 2 explored the effects of spacing and legibility upon reading by measuring eye movement patterns and reading speed when reading text with different inter-letter spacings. Forty-one subjects (11 male and 30 female), years of age, were screened to have corrected or uncorrected visual acuity of 20/20 or better in both eyes. ACKNOWLEDGEMENTS This study was supported by a grant from Microsoft Corporation to James E. Sheedy. Word legibility improves with spacing, but does not surpass individual letter legibility – the “letter superiority effect.” Spacing Samples The visual system “adapts” to spacing changes by altering fixation duration and eye movement size However, words/fixation does not change …nor does the reading speed Principal Investigator Yu-Chi Tai T: E: As inter-letter spacing increases, threshold word legibility significantly improves until it reaches asymptote at single letter legibility, suggesting the existence of crowding effect on word recognition and letter recognition as the fundamention for word identification. However, inter-letter spacing does not affect reading speed; rather, the effect is compensated by changes in eye movement patterns. Although text legibility decreases with condensed spacing, the visual system adapts with smaller saccade amplitudes and increased fixation duration; and vice versa with expanded spacing. The number of words processed per fixation is largely unchanged, indicating that cognitive processing regulates eye movement and ultimately limits reading speed for normally sighted individuals. Measuring eye movements