1 Ken Hinckley Edward Cutrell Steve Bathiche Tim Muss Microsoft Research & Microsoft Hardware April 23, 2002 Quantitative Analysis of Scrolling Techniques

2 Motivating Questions: Product Multi-Channel scrolling devices (1) save time to grab scrollbar (2) maintain visual focus on primary task Can performance of the scrolling wheel be improved? How does it compare? How to evaluate & test our new scrolling products in general?

3 Accelerated Scrolling Wheel Scroll further when you roll faster Extend range of wheel But… Is it really any better? Possible loss of control / precision?

4 Motivating Questions: Research How should one experimentally evaluate scrolling performance? Distance & Precision? Which is fastest: blue or green (dotted) ?

5 Widely used to study rapid, aimed movements (Fitts 1954) Used in pointing device studies since 1978 Task: Point at a target W wide at distance D The Law: MT = a + b log 2 (D/W + 1) a, b fit by linear regression using observed MT Never applied to scrolling D W Fitts’ Law: Cough Syrup for Input Devices

6 Scrolling Experiment founded in Fitts’ Law Frame Target line Scroll back & forth between 2 lines in a doc Ex: comparing paragraphs Each Trial had at least 10 Phases of individual scrolling movements

7 Experimental Design Device X D X W ScrollPoint Standard Wheel 3 lines/notch Accel. W1 1 line/notch Accel. W3 3 lines/notch nonsensical D X W’s e.g. D=6, W=18

8 Note on Practice Effects First 2 phases of each trial eliminated due to start-up effects

9 Results: Average Movement Times Overall average Movement Time (MT) ScrollPoint & Std. Wheel do not differ significantly But what if we control for D/W ?

10 Hard to see what’s going on in raw MT data D: 3.5 cm to 2.25 meters; So MT also has wide range Results: By Distance (Raw Data)

11 Significant crossover interaction by Distance! Std Wheel faster at small D, ScrollPoint for large D Accel mappings improve performance Results: By Distance (Scaled)

12 No interesting crossover effects for Device X W A faster device is faster across all W Results: By Width

13 … and Fitts’ Law Describes our Data r ≥ 0.90 for all devices Error Rate 2.2 % 1.3 % 2.9 % 3.7%

14 Representative Tasks for Scrolling We experimented with several tasks: Scrolling while proofreading text for misspellings Searching for highlighted line in document [and following the link – Zhai] Searching for highlighted target word in document, in presence of highlighted distracter words Fitts’ task sensitive to subtle device diffs Cognitive & visual search issues ignored

15 Design Insights No one device or acceleration setting is “best” Accel W1 vs. Std Wheel: faster + better resolution Is it possible to combine Accel W1 / Accel W3 mappings to have optimal performance?

16 Qualitative Results ScrollPoint: Most Ss preferred for long D But in practice many would “just grab scrollbar” “very ineffective in targeting lines” “my hand didn’t get tired” Standard Wheel: moved predictably Fatigue / comfort frequent negative comment Accel W3: “very easy to scroll long distances”, but most Ss disliked larger notches Accel W1: liked finer notches, but still “tedious to scroll long distances”

17 Naturally Occurring Behaviors with the Wheel How do users roll the wheel? (1) trying to get somewhere fast, or (2) reading reading fast

18 How Acceleration Works Roll faster  move further But do not change “reading” experience For Δt < 0.1 notch/s Δy = K 1 ( 1 + K 2 Δt) α Otherwise Δy = 1 line The user does not have to learn anything new!

19 Product Version To play with Accel. Scrolling, download IntelliPoint 4.0 Differs slightly e.g. no fractional lines hardware/mouse/download.asp

20 Future Work Apply Fitts approach to a scroll/select task Scroll, then click on object of varying W Two-handed scrolling: Current experiment can compare right- vs. left-handed devices, but not higher level benefits of 2h scrolling, e.g. Anticipatory cursor motion Avoid fatigue from single hand doing everything Scrollbar: cost of moving mouse back and forth to scrollbar needs to be considered More scrolling expt’s needed with Fitts’ Law

21 Thank You! Questions? hardware/mouse/download.asp

22

23 Extra slides for questions etc.

24 Gain theoretically does not affect performance MT = a + b log 2 (D/W + 1); gD/gW = D/W Observed MT almost unchanged for g = 1  10 g Reduces footprint of device & reclutching On Wheel, reduced footprint = faster MT Jellinek & Card 1991

25 Principles of Bimanual Action Yves Guiard, For right-handers: Right-to-left reference: Action of the right hand occurs within the frame-of-reference defined by the left. Scale Asymmetry: Movements of the right hand occur at higher spatial and temporal frequencies than the left Left-hand Precedence: Action starts with the left hand.

26 Principles of (Bimanual) Scrolling Right-to-left reference: Movement of mouse cursor is within current document view. Scale Asymmetry: Scrolling is a coarse task, cursor movement & selection are high-precision Left-hand Precedence: Scrolling precedes detailed activity in the document. (MacKenzie 1998) Scrolling is a background task that should be assigned to the nonpreferred hand.

27 Bimanual Scrolling No switching between pointing & scrolling Overlapped action of the 2 hands Maintain visual focus & concentration on work Buxton & Myers 1986 bimanual scrolling ~25% faster than scroll bar

28 Bimanual Control on Office Kbd Navigation controls on left Scrolling [wide wheel] Web [Forward / Back] Windows [AppToggle] Cut, Copy, Paste also well suited to left side Compound selection [or placement of IP] + articulation of command

29  OVERDRIVE “Automatic transmission” for the wheel (+accel.) Evaluating… Informally, seems to work great! in a ~10 pg doc: IntelliPoint 4.0!  IP 5.0 (?)  All of these have 1 line/notch precision Wheel MappingFlicks Original Wheel (1 line) 35 Accelerated Scrolling14 + OVERDRIVE 7