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Effect of Display and Text Parameters on Reading

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Effect of Display and Text Parameters on Reading EFFECT OF DISPLAY AND TEXT PARAMETERS ON READING PERFORMANCE DISSERTATION Presented in Partial Fulfillment of the Requirements for the Degree Doctor of Philosophy in the Graduate School of The Ohio State University By Venkiteshwar M. Subbaram, B.S. Optom, M.S. ***** The Ohio State University 2004 Dissertation Committee: Approved by Dr. Mark A. Bullimore, Advisor Dr. James E. Sheedy _________________________ Advisor Dr. Angela M. Brown Vision Science Graduate Program ii ABSTRACT Delivering text on electronic displays offers significant advantages to the user in terms of information access from a single device. It is important to make the display readable with the same level of comprehension and comfort as paper. The purpose of this research was to investigate various parameters that affect reading performance at increasing levels of cognition: legibility, visual search, and reading tasks. A series of studies were conducted to identify and analyze the major parameters affecting legibility, which is defined as the recognition of letters and words. Another study investigated the relationship between legibility and reading performance of text based tasks: letter counting, word search, and reading speed. Following each task, subjects rated their discomfort: eyestrain, blurred vision, dry eyes, headache, and neck or backache, on a questionnaire. The major parameters identified were letter case, pixel density, font type, and stroke width. Significant interactions were observed between display type and font smoothing. Legibility of upper case and lower case letters were not significantly different when letters were matched for size. Letters were more legible, by at least 10%, than words. Legibility increased ii with increase in pixel density up to 9 pixels (10-pt font) indicating that 10-pt characters contain sufficient detail for their identification. Sans serif fonts were more legible than the serif fonts, with Verdana being the most legible font tested. The use of bold letters enhanced legibility, whereas italic letters were less legible. The combination of Verdana and ClearType offered the best legibility among conditions tested. For words, increase in character spacing improved word legibility considerably to the extent that word legibility matched letter legibility. This indicates that the reduced legibility observed at default character spacing is due to the crowding of the constituent letters. The implications of the results with respect to word perception are discussed. Reading speed, however, is significantly faster under default spacing than with altered character spacing. Legibility was significantly related to readability. The results suggest testing of both letter and word legibility when investigating this relationship. No difference in legibility or reading speed was observed between computer displays and paper under optimized display and text parameters settings. iii Dedicated to my Parents Thank you for your encouragement, support and understanding iv ACKNOWLEDGMENTS I wish to thank my co-advisers, Mark Bullimore and James Sheedy, for intellectual support, encouragement which made this possible, and for their time and patience in correcting my scientific and stylistic errors. Working with them has been both privilege and pleasure. I am grateful to Angela Brown, for her help with the Fourier Analysis and her guidance. Special thanks to Kevin Larson for his expert guidance and to John Hayes for his help with statistics. I thank my parents for their sacrifices and encouragement; my friends Farzan, Anu, and Neville for their continued support without which this dissertation would not have been possible. This research was supported by Microsoft, USA and the Office Ergonomic Research Committee (OERC). v VITA July 27, 1977 …….. Born – Palghat, India 1999……………………. B.S. Optometry, Elite School of Optometry, Chennai, India 2001……………………. M.S. Vision Science, The Ohio State University, Columbus, Ohio 1998-1999………….. Volunteer Optometrist, Public Health Center, Chennai, India 1998-1999………….. Intern Optometrist, Sankara Nethralaya, Medical Research Foundation, Chennai, India 1999-2003………….. Graduate Teaching Associate, The Ohio State University, Columbus, Ohio 2002-present………. Graduate Research Associate, The Ohio State University, Columbus, Ohio PUBLICATIONS Research Publications 1. Subbaram MV, Bullimore MA (2002). Visual Acuity and the Accuracy of the Accommodative Response. Ophthalmic Physiol Opt 22:312-318. vi 2. Sheedy JE, Subbaram MV, Hayes JR (2003) Filters on Computer Displays – Effects on Legibility, Performance and Comfort. Behaviour and Information Technology 22:427-433. FIELDS OF STUDY Major Field: Vision Science vii TABLE OF CONTENTS Page Abstract……………………………………………………………………………………………………ii Dedication……………………………………………………………………………………………….iv Acknowledgments ………………………………………………………………………………….v Vita ……………………………………………….………………………………………………………. vi List of Tables ………………………………………………………………………………..……... xiii List of Figures………………………………………………………………………………………… xv Chapters: 1. General Introduction……………………………………………………………………….. 1 1.1 Reading Performance on Computer Displays…………..……………… 3 1.2 Legibility of Characters on Computer Displays……………………….. 4 1.3 Character Spacing and Word Legibility ….……………………………….. 5 1.4 Legibility and Reading Speed ……………..…………….……………………… 5 2. Reading Performance…………………………………………………….………………… 7 2.1 Introduction……………………………………………………………………….………. 7 2.2 Defining Legibility……………………………………………………………….……… 8 2.3 Methods / Techniques………………………………………………………….……. 9 2.3.1 Visibility Method……………………………………….………………………. 9 2.3.2 Distance Method……………………………………….………………………. 10 2.3.3 Short-Exposure Method………………………….………………………… 11 2.3.4 Defocus Method……………………………….……………………………….. 12 2.3.5 Blink Rate Method…………………………………………………………….. 12 2.3.6 Speed of Reading Method…………………………………………………. 13 2.3.7 Eye Movements…………………………………………………………………. 14 2.4 Typographical Factors affecting Reading Performance…………….. 16 2.4.1 Letter Case………………………………………………………………………… 16 2.4.2 Letter Size…………………………………………………………………………. 18 viii 2.4.3 Font Type…………………………………………………………………………… 20 2.4.4 Letter Stroke Width…………………………………………………………… 22 2.5 Words…………………………………………………………………………………………. 23 2.5.1 Word Shape Model……………………………………………………………. 24 2.5.2 Constituent Letter Recognition Model………………………………. 26 2.5.3 Character Spacing……………………………………………………………… 27 2.6 Reading from Paper versus Computer Displays……………………….. 28 2.6.1 Reading from paper…………………………………………………………… 28 2.6.2 Reading from Computer Displays……………………………………… 29 2.6.2.1 Display Type………………………………………………………… 30 2.6.2.2 Display Size…………………………………………………………. 32 2.6.2.3 Luminance and Contrast…………………………………….. 34 2.6.2.4 Resolution…………………………………………………………….. 36 2.6.2.4.1 Font Smoothing……………………………………… 37 2.6.2.5 Viewing Parameters…………………………………………….. 39 2.6.3 Previous Studies………………………………………………………………… 41 2.7 Summary……………………………………………………………………………………. 47 3. General Methodology…………………………………………………………………………. 58 3.1 Introduction………………………………………………………………………………… 58 3.2 Subjects……………………………………………………………………………………… 59 3.3 Display Instrumentation…………………………………………………………….. 59 3.4 Study Tasks………………………………………………………………………………… 61 3.4.1 Legibility……………………………………………………………………….……. 61 3.4.1.1 Technique…………………………………………………………….. 61 3.4.1.2 Design………………………………………………………………….. 62 3.4.1.3 Test Distance Calibration…………………………………….. 62 3.4.1.4 Procedure…………………………………………………………….. 63 3.4.2 Letter Counting Task…………………………………………………………. 64 3.4.2.1 Technique…………………………………………………………….. 64 3.4.2.2 Design………………………………………………………………….. 64 3.4.2.3 Procedure…………………………………………………………….. 65 3.4.3 Word Search Task…………………………………………………………….. 65 3.4.3.1 Technique…………………………………………………………….. 65 3.4.3.2 Design………………………………………………………………….. 65 3.4.3.3 Procedure…………………………………………………………….. 66 3.4.4 Reading Task…………………………………………………………………….. 66 3.4.4.1 Technique…………………………………………………………….. 66 3.4.4.2 Design………………………………………………………………….. 67 3.4.4.3 Procedure…………………………………………………………….. 67 3.4.5 Discomfort Rating………………………………………………………………. 68 3.4.5.1 Technique…………………………………………………………….. 68 3.4.5.2 Design………………………………………………………………….. 68 3.4.5.3 Procedure…………………………………………………………….. 68 ix 3.5 Viewing Parameters…………………………………………………………………… 69 3.5.1 Text Size……………………………………………….………………………….. 69 3.5.2 Illumination………………………………………………………………………… 69 3.5.3 Display Luminance and Contrast………………………………………. 69 3.5.4 Viewing Distance and Orientation…………………………………….. 70 3.6 Overall Study Design…………………………………………………………………. 70 4. Computer Displays – Performance and Comfort Comparison…………. 74 4.1 Introduction ……………………………………………………………………………….. 74 4.2 Methods………………………………………………………………………………………. 75 4.3 Results………………………………………………………………………………………... 75 4.3.1 Legibility…………………………………………………………………………….. 76 4.3.2 Letter Counting Speed………………………………………………………. 76 4.3.3 Reading Speed…………………………………………………………………… 77 4.3.4 Symptoms…………………………………………………………………………………….. 77 4.4 Discussion………………………………………………………………………………….. 77 4.5 Conclusions ……………………………………………………………………………….. 79 5. Primary Factors Affecting Legibility of Letters and Words………………. 87 5.1 Introduction……………………………………………………………………………….. 87 5.2 Methods………………………………………………………………………………………. 88 5.3 Results……………………………………………………………………………………….. 88 5.3.1 Font Size……………………………………………………………………………. 89 5.3.2 Font Type…………………………………………………………………………… 89 5.3.3 Stroke Width………………………………………………………………………. 90 5.3.4 Interaction between Font Size and Type………………………….. 90 5.3.5 Interaction between Stroke Width and Display Type………. 90 5.3.6 Interaction between Font Smoothing and Display
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