1. Effects of transverse chromatic aberration on peripheral word identification
Shun-nan Yang, PhD, Hannu Laukkanen, OD, Yu-Chi Tai, PhD, James E. Sheedy, OD, PhD
College of Optometry | Pacific University | 2043 College Way | Forest Grove | Oregon 97116
ABSTRACT
EXPERIMENTAL DESIGN
RESULTS (cont’d)
RESULTS (cont’d)
Trial sequence
Effects of font rendering, position, and word frequency on response time
Transverse chromatic aberration (TCA) degrades peripheral retinal images, and significantly affects single letter recognition. It is unclear whether TCA affects the ability to identify word stimuli. This study utilized color-fringed words to measure the effects of TCA on identifying words with different familiarity and eccentricities.
Subject preference for different font rendering A A B
Figure 2. Experimental paradigm for word identification. The figure shows the temporal schematic of a trial, with a target word displayed to the left of fixation point. The actual target position randomized from trial to trial.
MATERIALS & METHODS
Subjects: Thirty-three adults with 20/20 or better visual acuity participated in the study.
Equipments: RGB subpixeled LCD screen was used to displayed RGB-rendered images.
Tasks: They briefly viewed a 6- to 7-letter word (Consolas font, 11 point) of high- or low-frequency words with different font rendering (black&white, weak CT, strong CT) and location (1, 2, 4, and 6 degree to the left or right of fixation).
Measurement: Subjective preference was measured and by comparing paragraphs with different font rendering and size displayed side-by-side, and quantified using logit analysis. B
RESULTS
Effects of font rendering, position, and word frequency on response accuracy
Figure 6. Subjective preference of font rendering upon comparing side-by-side displayed paragraphs. A) An example with larger high CT text (left, 12-point 100% CT) vs. small B&W font (right, 9-point B&W). B) Results of logit analysis on font preference. Positive values indicate greater preference to higher CT paragraph. The ends of box indicates the inter-quartile interval (IQI, difference between the 1st and 3rd quartile), and the whisks indicate 1.5 IQI. The Circles and asterisks indicate outliers. A
Figure 4. Effect of font rendering and word position on response time in word identification in relation to word frequency. A) High frequency. B) Low frequency.
CONCLUSIONS
Our results show that proper color fringe reduced TCA in the right periphery by shortening the time required for word identification there, when the word is less familiar to the readers. It did not impede word identification in the left, but increased the influence of word frequency there.
Weaker CT resulted in greater improvement in response time, but this was not predicted by subjective preference. Our finding suggest a objective benefit but not subjective preference to the use of CT text in reading.
Effects of word frequency on individual TCA effect
TCA effect, test stimuli and predictions B
Figure 3. Effect of font rendering and word position on the accuracy in word identification in relation to word frequency. The lack of overlap for any two intervals indicates a statistically significant difference of α < .05 for the corresponding conditions in response accuracy. A) High frequency target word. B) Low frequency target words.
ACKNOWLEDGEMENTS
The Advanced Reading Group of Microsoft Corporation supported this research with a grant to the Vision Performance Institute.
Figure 1. Illustration of TCA, test stimuli, and expected effects. A) TCA effect on the retinal image of peripheral stimuli. B) Letter strings with B&W, weak CT, and strong CT rendering. C) Expected effect of color fringed letters in the left and right periphery.
Figure 5. Effect of word frequency on the changes in response time relative to font rendering. The figure shows the normalized change in response time, (RTl - RTh) / RTl, for all subjects.