Effect of Tablet Tilt and Display Conditions on User Posture, Performance and Preferences 10th Applied Ergonomics Conference March 15, 2007 Tom Albin Auburn Engineers Hugh McLoone Microsoft 2007 1
A Report of Two Studies Tablet Tilt Display Conditions 2007 2
Tablet PC Tilt and Glare Glare is the specular reflection of a light source on the surface of the screen 2007 3
The Geometry of the Law of Reflection Determines Whether or Not Glare is Apparent 2007 4
Users Avoid Glare by Changing the Geometry By changing the light source s location Not always feasible By changing the eye s location May result in postural discomfort By changing the screens position Move or tilt the screen 2007 5
Flat Screen - 0º A flat screen will reflect light sources that are forward of the screen 2007 6
Tilted Screen - 30 º At 30 º the source is above the screen 2007 7
Conclusion Tilting the screen is an effective means of avoiding specular glare 0 to 50 may be sufficient range of tilt to control specular glare 2007 8
Tilting the Screen is an Effective Control for Glare What is the effect of tilt on users: performance posture preferences opinions 2007 9
Effect of Tilt Angle on Performance, Posture and Preferences
Part 1. Tilt Angles 10 participants, all college students (9 m, 1 f) Two performance tasks (reading and target tapping) Postural Data (wrist F/E, wrist UD/RD, forearm P/S, Neck Bend) Subjective impressions (Likert scale, comments Four pre-determined angles (counterbalanced for order), one selected by participant (always last) 2007 11
Four Pre-determined Tilt Angles Used, Plus One More Chosen by Participants 0 45 30 60 2007 12
Performance Tasks Reading Test - Participant reads a paragraph, identifies the inconsistent word, then taps it. Multi-Direction Target Tapping Test - Participant taps a circular target which varies in size and location on the screen 2007 13
Performance Results Target tapping significantly faster for freely chosen tilt angle Likely due to practice effect (always last) No effect of tilt on reading performance 2007 14
Posture Results Significantly less neck-bending between 0 and 60 degree conditions No significant differences between tilt conditions for wrist and forearm postures Postures while using tablet appear similar to those observed while using standard keyboards and mice 2007 15
Ad Lib Tilt Angles (Mean = 33.7, sd = 19 ) 2007 16
Preference for Tilt Angles For each tilt angle Participants ranked the tilt angle Stated whether it would be acceptable to them 2007 17
Opinions and Comments on Tilt Angles - Likert Scaling Reading Participants agreed with statements that tilted screens were easier to read; the more tilt the more the agreement The freely chosen tilt angle was highly favored Tapping Participant responses were slightly favorable to indifferent with regard to tilt The freely chosen tilt angle was highly favored 2007 18
Summary of Comments on Tilt Angles The extreme angles (0 and 60 ) received the most negative comments 60 harder or more uncomfortable to tap 0 harder to read 0 (flat) tilt angle 2 participants described this condition as familiar due to similarity to paper or book 3 participants said they could tap or write better in this position 4 participants said they had difficulty reading the screen due to glare in this tilt position 2007 19
Summary of Comments on Tilt 30 tilt angle Angles (continued) Two rated this position as comfortable Two rated it as easy to read Two rated it as difficult to tap 45 tilt angle One rated it as best compromise 60 tilt angle Six rated it as uncomfortable for the hands and wrists 2007 20
Part 1 Conclusions A self-chosen tilt angle has a positive effect on target tapping performance Likely due to practice effect Increasing tilt angles have a positive effect on neck posture Participants perceive that differences in tilt angle affect their ability to read the screen Participants tilt angle preferences vary, most commonly between 20 and 50 degrees 2007 21
Effect of Display Conditions on Performance, Posture and Preferences
Part 2. Display Conditions 10 participants, all college students (9 m, 1 f) Two performance tasks (reading and target tapping) Postural Data (wrist F/E, wrist UD/RD, forearm P/S, Neck Bend) Subjective impressions (Likert scale, comments All combinations of H/L Ambient Light, H/L Reflectivity, W/N Field of View 2007 23
Display Conditions High Ambient Light /Low Ambient Light 30 foot candles vs. 110 foot candles Highly Reflective /Low Reflective Surface Glass plate vs. no glass plate Wide Field of View/ Narrow Field of View 2007 24
Glass vs. No Glass 2007 25
Wide & Narrow Fields of View 2007 26
Display Conditions Affect Glare on Tablet Screens For all combinations of the three screen conditions, what is the effect of those conditions on users : performance posture preferences opinions 2007 27
Performance Effects No significant differences were seen for reading or target tapping tasks as a function of any of the display conditions 2007 28
Postural Effects No significant effects of display conditions on user head/neck, arm or wrist posture were observed 2007 29
Opinions and Comments on Display Conditions - Dichotomous Comparisons Low Ambient Light was significantly preferred to High Ambient Light A Low Reflective Surface was significantly preferred to a High Reflective Surface A Wide Field of View (FOV) surface was preferred to a Narrow FOV Surface 2007 30
Opinions on Display Conditions - Preferences and Acceptability 2007 31
Opinions and Comments on Display Conditions - Likert Scales For all lighting conditions The combination of Low Reflective and Wide FOV surfaces was most preferred Low Reflective Surface preferred to Wide FOV 2007 32
Open-Ended Comments Regarding Display Conditions Participants favored low ambient light levels, low reflectivity and wide Field of View (FOV) Four participants noted that the narrow FOV conditions limited head/neck movement Three participants noted that the narrow FOV screens had dark spots, were dark at the edges, or had distorted colors Seven of the participants noted higher glare when the glass plate was added to the display One noted the glare but said would be concerned about scratches to the screen without it. 2007 33
Conclusions Regarding Display Conditions Display Conditions did not affect performance or posture Low ambient lighting, Low reflective surfaces and Wide FOV were favored Low reflective surface with wide FOV was most favored condition However, nearly all participants said that either reflectivity or FOV condition would be acceptable 2007 34