The Effects of Feedback The Effects of Feedback on Targeting with on Targeting with

Multiple Moving TargetsMultiple Moving Targets

David Mould and Carl GutwinDavid Mould and Carl Gutwin

OverviewOverview

► Introduction / MotivationIntroduction / Motivation►Research QuestionResearch Question►Experimental DesignExperimental Design►ResultsResults►ConclusionsConclusions

TargetingTargeting

►The user sees a target (a window, a The user sees a target (a window, a menu item), moves the cursor to it, menu item), moves the cursor to it, and selects itand selects it

►An extremely common task in modern An extremely common task in modern mouse-based user interfacesmouse-based user interfaces

Targeting is easyTargeting is easy

► In typical applications, targets are In typical applications, targets are highly visible and stationary.highly visible and stationary.

►Feedback has been suggested as a Feedback has been suggested as a method of improving targeting method of improving targeting performance – but Akamatsu et al. ran performance – but Akamatsu et al. ran a study finding that feedback doesn't a study finding that feedback doesn't help under these conditionshelp under these conditions

Virtual World applicationsVirtual World applications

Xu, Stewart, and FiumeGI 2002

Computer Game applicationsComputer Game applications

Warcraft 3 (Blizzard Entertainment)

Targeting can be hardTargeting can be hard

► In other applications, targeting can be more In other applications, targeting can be more difficult:difficult:

► targets might movetargets might move► in a cluttered environment, targets might be in a cluttered environment, targets might be

hidden or the user might be distractedhidden or the user might be distracted

► Does feedback improve targeting when the Does feedback improve targeting when the task is more difficult?task is more difficult?

► (It can, per Fraser & Gutwin – is this the kind (It can, per Fraser & Gutwin – is this the kind of task where feedback will help?)of task where feedback will help?)

The Role of FeedbackThe Role of Feedback

►Feedback is used in many applications Feedback is used in many applications where targeting might seem difficult.where targeting might seem difficult.

►Games use sevral kinds of visual Games use sevral kinds of visual feedback:feedback:

► highlighting the targethighlighting the target► haloing the targethaloing the target► writing text in a sidebarwriting text in a sidebar► many othersmany others

Our study: Does feedback Our study: Does feedback help?help?

►Maybe feedback helps in difficult Maybe feedback helps in difficult tasks.tasks.

►Pilot: a few graduate students Pilot: a few graduate students performed targeting tasks with moving performed targeting tasks with moving targets and cluttertargets and clutter

►Pilot results: no effect on completion Pilot results: no effect on completion time, maybe some effect on error ratetime, maybe some effect on error rate

Targeting EnvironmentTargeting Environment

ConditionsConditions

►Different conditions: speed, occluder Different conditions: speed, occluder count, feedback conditioncount, feedback condition

►Each participant saw all conditionsEach participant saw all conditions

►Feedback condition order varied, but Feedback condition order varied, but other conditions were fixed in order of other conditions were fixed in order of increasing difficultyincreasing difficulty

Speed conditionSpeed condition

►Three different speeds: "slow", Three different speeds: "slow", "medium", "fast""medium", "fast"

►Slow: 45 pixels/second (~1.3 cm/s)Slow: 45 pixels/second (~1.3 cm/s)►Medium: 220 pixels/second (~6.4 cm/s)Medium: 220 pixels/second (~6.4 cm/s)►Fast: 400 pixels/second (~11.7 cm/s)Fast: 400 pixels/second (~11.7 cm/s)

►Entire window: 600 pixels across, square.Entire window: 600 pixels across, square.

Occluder count conditionOccluder count condition

►We varied the number of occluders:We varied the number of occluders:►None (no occluders)None (no occluders)►Few (22 occluders)Few (22 occluders)►Medium (44 occluders)Medium (44 occluders)►Many (88 occluders)Many (88 occluders)

►We always showed the home base as We always showed the home base as well.well.

Increasing Occluder CountIncreasing Occluder Count

Feedback conditionFeedback condition

►All feedback was visualAll feedback was visual

►Three feedback conditions:Three feedback conditions:►NoneNone►Target-only (target lit on mouse-over)Target-only (target lit on mouse-over)►All objects (all objects lit on mouse-All objects (all objects lit on mouse-

over)over)

Summary of conditionsSummary of conditions

►All participants exposed to all All participants exposed to all conditions: all combinations of 3x4x3 conditions: all combinations of 3x4x3 factorsfactors

►Feedback type was fully Feedback type was fully counterbalanced, while occluder count counterbalanced, while occluder count and speed were presented in and speed were presented in increasing order of difficultyincreasing order of difficulty

Experimental procedureExperimental procedure

►Six groups, for six different feedback Six groups, for six different feedback ordersorders

►Eighteen participants in totalEighteen participants in total►Participants were asked to click as quickly Participants were asked to click as quickly

and accurately as possibleand accurately as possible►After a short learning period, participants After a short learning period, participants

completed 16 targeting tasks in each of completed 16 targeting tasks in each of 36 condition combinations36 condition combinations

►Following the study, participants Following the study, participants completed a questionnairecompleted a questionnaire

ResultsResults

►TimingTiming►Error rateError rate►Target occlusion at moment of Target occlusion at moment of

selectionselection►PreferencesPreferences

Results (timing)Results (timing)

0

0.2

0.4

0.6

0.8

1

1.2

1.4

0 22 44 66 88

Number of objects

Co

mp

letio

n ti

me

pe

r ta

rge

t (se

c)

none

target

all

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

0 22 44 66 88

Number of objectsC

om

ple

tion

tim

e p

er

targ

et (

sec)

s low

medium

fast

feedback had no effect on timing completion time became longerwith higher speeds and with moreoccluders

Results (error rate)Results (error rate)

0

0.05

0.1

0.15

0.2

0.25

0.3

none target all

Feedback type

Err

ors

per

targ

et

Overall error rate went down with increasing feedback

Results (error rate)Results (error rate)

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0 100 200 300 400 500

Object velocity (pixels/sec)

Err

ors

pe

r ta

rge

t

none

target

all0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

0 22 44 66 88

Number of objectsE

rro

rs p

er

targ

et

none

target

all

errors were reduced withmore feedback

errors increased with speed errors increased with occluder count

Results (occlusion)Results (occlusion)

0

5

10

15

20

25

30

35

40

45

50

0 22 44 66 88

Number of objects

Perc

ent

occlu

sio

n o

f ta

rget

none

target

all

Average target occlusion increasedwith occluder count

Results (preferences)Results (preferences)

0

2

4

6

8

10

12

14

16

18

Fastest Most Accurate OverallPreference

Which interface was...

Num

ber

of

part

icip

ants

No feedback

Target only

All objects

Everyone liked target-only feedback best

Results SummaryResults Summary

►Both completion time and errors Both completion time and errors increase with occluder count and with increase with occluder count and with speedspeed

►Target feedback had no effect on Target feedback had no effect on completion timecompletion time

►Target feedback reduced error ratesTarget feedback reduced error rates►All-object feedback helped more than All-object feedback helped more than

target-only feedbacktarget-only feedback►Users preferred target-only feedbackUsers preferred target-only feedback

Possible Explanations -- timePossible Explanations -- time

►We know that increased target speed We know that increased target speed increases targeting difficulty increases targeting difficulty (Jagacinski et al. 1980)(Jagacinski et al. 1980)

►Not surprised to find that increasing Not surprised to find that increasing occluder count increases targeting occluder count increases targeting difficultydifficulty

Possible Explanations -- errorPossible Explanations -- error

► Increase in error rate with speed: Increase in error rate with speed: targets can escapetargets can escape

► Increase with occluder count: Increase with occluder count: occluders more likely to intercept a occluders more likely to intercept a clickclick

►Feedback reducing error rate: signal Feedback reducing error rate: signal whether or not a click will succeedwhether or not a click will succeed

►All-object feedback: a strong signalAll-object feedback: a strong signal

Possible explanations -- Possible explanations -- preferencepreference

►Users liked target-only feedback the bestUsers liked target-only feedback the best►Six of eighteen participants complained Six of eighteen participants complained

of distraction in all-object feedbackof distraction in all-object feedback

►Target-only feedback only positiveTarget-only feedback only positive►All-object feedback highlights mistakesAll-object feedback highlights mistakes►Positive advice welcome, but all advice Positive advice welcome, but all advice

usefuluseful

ImplicationsImplications

►Despite user's preferences, we cannot Despite user's preferences, we cannot provide target-only feedback in a real provide target-only feedback in a real applicationapplication

►But, all-object feedback is good too: it But, all-object feedback is good too: it does not reduce completion time, and does not reduce completion time, and it does reduce error rateit does reduce error rate

Future WorkFuture Work

►A less intrusive all-object feedback?A less intrusive all-object feedback?►By what mechanism was error By what mechanism was error

reduced?reduced?►Traditionally, feedback helps only the Traditionally, feedback helps only the

final stage of tracking. Can we devise final stage of tracking. Can we devise feedback which is helpful at earlier feedback which is helpful at earlier stages?stages?

Questions?Questions?