Transcript ClearType Research Update

Viewing Distance &
Visual Discomfort
While
Using Handheld Displays
Yu-Chi Tai,
James Sheedy, John Hayes,
James Kundart, Hannu Laukkanen
Pacific University, Vision Performance Institute,
Vision Ergonomics Laboratory
Background
• Handheld computer devices (e.g., PDAs, Media players,
Palm-size gaming devices, etc.) have very small screens
to keep them portable;
• These handheld devices potentially sacrifice legibility for
portability;
• This has not prevented their widespread use;
• Habitual working distance using handhelds for their
primary purpose has not been studied.
Questions
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Do subjects view handheld displays closer to the eyes
than other reading materials?
Why might they hold such displays closer than other
reading materials?
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Smaller character size?
Poorer legibility?
Highly interactive operations?
Potential importance to health

Shorter viewing distances are more demanding on
accommodation and convergence
Methods
34 subjects
 19 Male & 5 Female, age 18-33 (mean=24.8);
 20/20+ vision in each eye; no eyestrain history;
 ≥ 6 months of HCD-use experiences.
Target measurements
 Viewing distance (sampled 1 frame/min)
 Surface-EMG from right lower eyelid
 Subjective rating of visual/body discomfort symptoms
(Analog Sensation Questionnaire)
Experiment setup
Viewing distance was measured while performing 10 min of…
 Reading hardcopy text of 5 sizes (6, 7, 8, 10, 12 pt)
 5 types of handheld devices
Three Handheld Devices

Apple iPod

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Sony PSP
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2.5” LED backlight color display
320x240 pixels, 163 ppi, weight 4.8 oz
One thumb-scroll wheel for single-hand operation
4.3” TFT LCD widescreen,
480x272 pixels, 10 oz,
Two thumb-operating button area
HP iPAQ HW6945 smartphone
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3” TFT LCD touch screen
w/ LED backlight & stylus, weight 6.33 oz
10 Testing Conditions
Results
Finding 1:
Viewing distances differed significantly among testing
conditions
Finding 1-1:
When reading hardcopy text, viewing distance decreased
for smaller text sizes
While text size explains 92% variance in viewing distance,
it’s NOT everything  Comparison to 3:1 acuity reserve
Hardcopy conditions
Handheld conditions
55
3:1 acuity reserve
50
HC12pt
HC10pt
Viewing distance (cm)
HC8pt
HC7pt
45
HC6pt
iPod Movie
40
iPAQ Reading
iPAQ text
messaging
35
iPAQ database
searching
PSP game
30
25
1
1.2
1.4
1.6
1.8
2
Text size (x-height, mm)
2.2
2.4
2.6
• Maintaining 3:1 reserve requires more accommodation
4.5
Hard copy viewing distance
accomodative demand
4.0
Accommodation (D)
3:1 acuity reserve accommodative
demand
3.5
3.0
2.5
2.0
1.5
1
1.2
1.4
1.6
1.8
x height (mm)
2
2.2
2.4
Finding 1-2
• With handhelds, viewing distance was closer than reading
6-pt font, depending on the nature of the task.
Task Analysis:
Handheld viewing distance determined by task nature.
Factors of Task Analysis
Condition
Font size
(HxW ,mm)
Text
reading
Cognitive
demanding
Visual
scrutinizing
Motor
Intensive
6-pt
1.1 x 1.0
Yes
Yes
No
No
7-pt
1.3 x 1.1
Yes
Yes
No
No
8-pt
1.7 x 1.3
Yes
Yes
No
No
10-pt
1.9 x 1.7
Yes
Yes
No
No
12-pt
2.3 x 2.0
Yes
Yes
No
No
iPAQ
Reading
1.3 x 1.1
Yes
Yes
No
No
Text
messaging
1.3 x 1.1
Yes
Yes
No
Yes
Searching
database
1.7 x 1.3
Yes
Yes
Yes
No
W atching
movies
1.3 x 1.3
(on menu)
No
No
No
No
Playing
jigsaws
2.7 x 1.3
(on menu)
No
Yes
Yes
Yes
Hardcopy
conditions
Handheld
conditions
Finding 2
• Lower blink rate when playing games
• Higher blink rate when watching movies
Finding 3
No significant difference on subjective rating of
Internal Symptoms
Finding 4
No significant difference on subjective rating of External
Symptoms
Finding 4
Higher physical discomfort in most handheld use, except
for watching movies
Conclusions
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When reading hardcopies, viewing distance
primarily determined by text size.
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When using handhelds, viewing distance usually
is closer than reading hardcopies and is affected
by task nature.
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Visual and body stress was observed even with
as short as 10 minutes of handheld use.
Acknowledgement
This study was supported by
Microsoft Advanced Reading Group
to
Pacific University
Vision Ergonomics Laboratory.