1. Effects of Ocular Transverse Chromatic Aberration on Peripheral Letter Recognition
Shun-nan Yang, PhD, Hannu Laukannen, 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 sequences
Effect of neighbor similarity on response accuracy
Individual ability in letter recognition with wider spacing
Transverse chromatic aberration (TCA) smears retinal images of peripheral stimuli. In reading, text information is extracted from the near periphery where TCA is likely significant. This study utilized the color-fringed letters created by the ClearType (CT) technology (Microsoft, 2009) to measure TCA effects on peripheral letter identification.
Figure 2. Experimental paradigm. The figure shows the temporal sequences for trials with the letter string displayed 1˚ to the left or right of fixation point randomly from trial to trial.
RESULTS
Effects of font rendering, spacing, and letter position on response accuracy
MATERIALS & METHODS
Methods. Thirty-one adults with 20/20 monocular visual acuity participated in the study. They briefly viewed a letter string composed of five letters (Consolas font, 11 point) and reported whether the middle letter was identical to a subsequently presented one. Font type, location, spacing, and neighbor similarity were randomly altered across trials.
Figure 7. Choice probability (CP) for different font renderings with wide spacing. A) CP values for letters presented in the left periphery. Same illustration as in Figure 6. B) CP values in the right periphery. C) Mean choice probability (CP) for different font renderings in left (top 4 symbols) and right peripheries (bottom 4 symbols).
Figure 5. Effect of TCA on response accuracy in relation to letter position and neighbor similarity. Same illustration as in Figure 3. It shows that there was no significant difference in the effect of font rendering in the left periphery, but there was a significant difference in the effect between (Black&White, RGB-CT) and (Grayscale, BGR-CT) in the right periphery.
CONCLUSIONS
We investigated whether the TCA effect can be revealed by viewing color-fringed letters in the periphery. Results show that TCA significantly affects the accuracy of periphery letter recognition and the effect depends on the order of the subpixel layout, the horizontal location of the letter string, and the inter-letter spacing. TCA diminishes one’s ability to process text in the near retinal periphery not only by reducing the acuity but also by enhancing lateral interference from adjacent letters.
Individual ability to recognize a narrowly spaced letter independent of guessing
TCA effect, test stimuli and predictions
Figure 3. Effect of TCA on response accuracy in letter recognition in relation to letter position and spacing. Each box represents the 84% interval of the response accuracy. The lack of overlap for any two boxes indicates a statistically significant difference of α < .05 for the corresponding conditions in response accuracy.
Figure 4. Directional bias in TCA effect. The X axis indicates the percentage of change in response accuracy in the right periphery and the Y axis in the left periphery. Positive changes indicate increased accuracy and negative changes decreased accuracy in comparison to the baseline (B&W) accuracy.
ACKNOWLEDGEMENTS
The Advanced Reading Group of Microsoft Corporation supported this research with a grant to James E. Sheedy, O.D., Ph.D.
Figure 6. Choice probability (CP) for different font renderings with narrow spacing. A) CP values for letters presented in the left periphery. Each symbol indicates the corresponding correct choice (Y axis) and false alarm (X axis) for the same subject. B) CP values in the right periphery. C) Mean choice probability (CP) for different font renderings in left (top four symbols) and right peripheries (bottom 4 symbols).
Figure 1. Illustration of TCA, test stimuli, and expected effects. A) TCA effect on the retinal image of peripheral stimuli. B) Letter strings with different types of font rendering and letter spacing. C) Expected TCA effect in left and right periphery on the retinal image of color-fringed letters