Psychophysics of Reading in Normal and Low Vision

246 Pages·2006·18.252 MB·\246

by  Gordon E. Legge (Author)

Psychophysics of Reading
in Normal and Low Vision

Psychophysics of Reading
in Normal and Low Vision
Gordon E. Legge
University of Minnesota
CRC Press
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To Wend and Alex with love,
-Gordon E. Legge
July, 2005

Contents
Preface and Acknowledgments xiii
1 Vision and Reading 1
Gordon E. Legge
Box 1. 1 Complete Citations for the 20 Articles in the Psychophysics
of Reading Series 5
Box 1.2 Citations to M. A. Tinker's Classic Series of 13 Articles 7
2 Measuring Reading Speed 9
Gordon E. Legge
2. 1 Three Methods for Measuring Reading Speed 9
Drifting Text Method 10
RSVP Method 12
Flashcard Method 13
Clinical Potential of the Flashcard Method 15
2.2 Subtleties in the Measurement of Reading Speed 16
Text Difficulty, Word Length, and Carver's Metric 16
Instructions to Participants 16
Oral and Silent Reading of Short and Long Passages 17
Context Effects 18
2.3 How Fast Do People Read? 20
Reading Speeds of Normally Sighted People 20
Speed Reading 23
vii
Viii CONTENTS
Box 2. 1 Role of the Magnocellular Pathway in Reading
and Dyslexia 24
Effect of Age on Normal Reading Speed 28
Low-Vision Reading Speed 30
Auditory and Tactile Reading Speed 30
Box 2.2 Characteristics of Braille 32
Is Reading Speed Limited by Motor Movements, Sensory
Coding, or Cognition? 35
2.4 Comparison of Reading Speed to Other Measures of Reading
Performance 36
Comprehension 36
Eye Movements 38
Reading Accuracy, Visual Search, and Visual Comfort 39
3 Visual Mechanisms In Reading 43
Gordon E. Legge
3. 1 Two Important Properties of Letters in Text: Contrast
and Size 44
Contrast Definitions 45
Size Definitions 46
3.2 The Effect of Character Size in Normal and Low Vision 48
Normal Vision 48
Low Vision 51
3.3 Contrast Effects in Normal and Low Vision 52
Normal Vision 52
Low Vision 55
3.4 The CSF Model of Reading 56
3.5 The Spatial-Frequency Channel Model of Reading 59
3. 6 Reading with Peripheral Vision 66
3. 7 The Visual Span 67
Box 3. 1 Historical Antecedents of the Visual Span 68
Two Methods for Measuring the Visual Span 72
The Impact of Contrast and Character Size on the Visual
Span 76
Three Determinants of the Size of the Visual Span 79
3.8 Central-Field Loss and Reading Difficulty 83
Macular Degeneration and Central-Field Loss 83
CONTENTS ix
Central-Field Loss Usually Means Slow Reading 84
Why Do People With Central Scotomas Read Slowly? 86
Implications for Rehabilitation 88
3.9 Linking Letter Recognition to Reading Speed 91
A Model Based on Letter Recognition 91
Word Shape 94
Box 3.2 Is There a Visual Word Form Area? 96
Bottom-Up and Top-Down Processes in Word Recognition 98
Box 3.3 Dual-Route Theory 100
3. 10 Summary and Conclusions 103
4 Displaying Text 107
Gordon E. Legge
4.1 Text Legibility 107
Definition 10 7
Box 4. 1 Fonts for Highway Signs 109
Legibility Metric 111
4.2 Font Effects in Normal and Low Vision 112
Influence of Font Design 112
Influence of Spacing 115
Fonts for Low vision 116
4.3 Display Resolution 117
Effects of Sample Density and Spatial-Frequency
Bandwidth 117
Implications for Text Displays 123
Defocused Text 125
Reading and Myopia 127
Sampled Displays and Low Vision 129
Box 4.2 Pixelized Vision as a Prosthetic for Blind People 132
4.4 The Window-Size Effect and Page Navigation 137
Relation to Visual Span 141
4.5 Navigating Through Text 145
Eye Movements in Reading 145
Small Displays 147
4.6 Navigating Through Text with Magnifiers 149
Using Large Print or Short Viewing Distance to Magnify 149