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 Do subjects view handheld displays closer to the eyes than other reading materials? Why might they hold such displays closer than other reading materials? 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 2.5” LED backlight color display 320x240 pixels, 163 ppi, weight 4.8 oz One thumb-scroll wheel for single-hand operation Sony PSP 4.3” TFT LCD widescreen, 480x272 pixels, 10 oz, Two thumb-operating button area HP iPAQ HW6945 smartphone 3” TFT LCD touch screen w/ LED backlight & stylus, weight 6.33 oz 6

10 Testing Conditions 7

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

Maintaining 3:1 reserve requires more accommodation

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.

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 When reading hardcopies, viewing distance primarily determined by text size. When using handhelds, viewing distance usually is closer than reading hardcopies and is affected by task nature. 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.