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Ken HinckleyEdward CutrellSteve BathicheTim Muss

Microsoft Research & Microsoft HardwareApril 23, 2002

Quantitative Analysis of Scrolling Techniques

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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?

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Accelerated Scrolling Wheel

• Scroll further when you roll faster•Extend range of wheel

• But… Is it really any better?• Possible loss of control /

precision?

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Motivating Questions: Research

• How should one experimentally evaluate scrolling performance? Distance & Precision?

• Which is fastest: blue or green (dotted) ?DistanceA B C

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• 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 log2(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

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Scrolling Experimentfounded 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

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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

6 18 306 *

12 *24 * *48 * * *96 * * *

192 * * *384 * * *

Width

Dist

ance

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Note on Practice Effects

• First 2 phases of each trial eliminated due to start-up effects

1 2 3 4 5 6 7 8 9 102

2.2

2.4

2.6

2.8

3

3.2

3.4

Phase

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Results: Average Movement Times• Overall average Movement Time (MT)

• ScrollPoint & Std. Wheel do not differ significantly• But what if we control for D/W ?

ScrollPoint Accel W1 Accel W3 Standard Wheel0

0.5

1

1.5

2

2.5

Device

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• 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)

0

1

2

3

4

5

6 ScrollPoint

Accel W1

Accel W3

Std Wheel

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• Significant crossover interaction by Distance! • Std Wheel faster at small D, ScrollPoint for large D• Accel mappings improve performance

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5 10 100 500

Distance of Target (lines)

Results: By Distance (Scaled)

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• No interesting crossover effects for Device X W• A faster device is faster across all W

Results: By Width

1.5

2

2.5

3

3.5

4

4.5

5 10 50

Width of Target (lines)

ScrollPoint

Accel W1

Accel W3

Std Wheel

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… and Fitts’ Law Describes our Data

• r ≥ 0.90 for all devices

R R2 SlopeIntercept

(s)IP (bps)

ScrollPoint 0.97 0.94 0.84 0.42 1.19

Accel W1 0.90 0.81 1.16 -0.51 0.86

Accel W3 0.97 0.95 0.80 0.18 1.25

Wheel Std 0.94 0.88 1.25 -0.42 0.80

Error Rate

2.2 %

1.3 %

2.9 %

3.7%

0

2

4

6

8

0

2

4

6

8

0 1 2 3 4 5 6 7Index of Difficulty (bits)

0 1 2 3 4 5 6 7

Accel W3

ScrollPoint

Standard Wheel

Accel W1

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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

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Design Insights

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5 10 100 500

Distance of Target (lines)• 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?

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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”

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Naturally Occurring Behaviors with the Wheel

• How do users roll the wheel?• (1) trying to get somewhere fast, or • (2) reading

0

1

2

3

4

5

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Wheel Speed (dt)

Acceleration Gain

Distributionof Wheel Speedreading

fast

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How Acceleration Works

• Roll faster move further• But do not change “reading” experience

• For Δt < 0.1 notch/s

Δy = K1(1 + K2Δt)α

• Otherwise Δy = 1 line

• The user does nothave to learn anything new!

0

1

2

3

4

5

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

Wheel Speed (dt)

Acceleration Gain

Distributionof Wheel Speed

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ProductVersion

• To play with Accel. Scrolling, download IntelliPoint 4.0

• Differs slightly• e.g. no

fractional lines

• http://www.microsoft.com/hardware/mouse/download.asp

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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

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Thank You!

• Questions?

• kenh@microsoft.com

• http://www.microsoft.com/hardware/mouse/download.asp

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Extra slides for questions etc.

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• Gain theoretically does not affect performance

•MT = a + b log2(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

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Principles of Bimanual Action

• Yves Guiard, 1987. 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.

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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.

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Bimanual Scrolling

• No switching between pointing & scrolling

• Overlapped action of the 2 hands

• Maintain visual focus & concentration on work

• Buxton & Myers 1986bimanual scrolling ~25% faster than scroll bar

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Bimanual Controlon 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

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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 Mapping Flicks

Original Wheel (1 line) 35

Accelerated Scrolling 14

+ OVERDRIVE 7