The Effects of Feedback on Targeting with Multiple Moving Targets David Mould and Carl Gutwin

Overview ► Introduction / Motivation ► Research Question ► Experimental Design ► Results ► Conclusions

Targeting ► The user sees a target (a window, a menu item), moves the cursor to it, and selects it ► An extremely common task in modern mouse-based user interfaces

Targeting is easy ► In typical applications, targets are highly visible and stationary. ► Feedback has been suggested as a method of improving targeting performance – but Akamatsu et al. ran a study finding that feedback doesn't help under these conditions

Virtual World applications Xu, Stewart, and Fiume GI 2002

Computer Game applications Warcraft 3 (Blizzard Entertainment)

Targeting can be hard ► In other applications, targeting can be more difficult: ► targets might move ► in a cluttered environment, targets might be hidden or the user might be distracted ► Does feedback improve targeting when the task is more difficult? ► (It can, per Fraser & Gutwin – is this the kind of task where feedback will help?)

The Role of Feedback ► Feedback is used in many applications where targeting might seem difficult. ► Games use sevral kinds of visual feedback: ► highlighting the target ► haloing the target ► writing text in a sidebar ► many others

Our study: Does feedback help? ► Maybe feedback helps in difficult tasks. ► Pilot: a few graduate students performed targeting tasks with moving targets and clutter ► Pilot results: no effect on completion time, maybe some effect on error rate

Targeting Environment

Conditions ► Different conditions: speed, occluder count, feedback condition ► Each participant saw all conditions ► Feedback condition order varied, but other conditions were fixed in order of increasing difficulty

Speed condition ► Three different speeds: "slow", "medium", "fast" ► Slow: 45 pixels/second (~1.3 cm/s) ► Medium: 220 pixels/second (~6.4 cm/s) ► Fast: 400 pixels/second (~11.7 cm/s) ► Entire window: 600 pixels across, square.

Occluder count condition ► We varied the number of occluders: ► None (no occluders) ► Few (22 occluders) ► Medium (44 occluders) ► Many (88 occluders) ► We always showed the home base as well.

Increasing Occluder Count

Feedback condition ► All feedback was visual ► Three feedback conditions: ► None ► Target-only (target lit on mouse-over) ► All objects (all objects lit on mouse-over)

Summary of conditions ► All participants exposed to all conditions: all combinations of 3x4x3 factors ► Feedback type was fully counterbalanced, while occluder count and speed were presented in increasing order of difficulty

Experimental procedure ► Six groups, for six different feedback orders ► Eighteen participants in total ► Participants were asked to click as quickly and accurately as possible ► After a short learning period, participants completed 16 targeting tasks in each of 36 condition combinations ► Following the study, participants completed a questionnaire

Results ► Timing ► Error rate ► Target occlusion at moment of selection ► Preferences

Results (timing) feedback had no effect on timingcompletion time became longer with higher speeds and with more occluders

Results (error rate) Overall error rate went down with increasing feedback

Results (error rate) errors were reduced with more feedback errors increased with speederrors increased with occluder count

Results (occlusion) Average target occlusion increased with occluder count

Results (preferences) Everyone liked target-only feedback best

Results Summary ► Both completion time and errors increase with occluder count and with speed ► Target feedback had no effect on completion time ► Target feedback reduced error rates ► All-object feedback helped more than target-only feedback ► Users preferred target-only feedback

Possible Explanations -- time ► We know that increased target speed increases targeting difficulty (Jagacinski et al. 1980) ► Not surprised to find that increasing occluder count increases targeting difficulty

Possible Explanations -- error ► Increase in error rate with speed: targets can escape ► Increase with occluder count: occluders more likely to intercept a click ► Feedback reducing error rate: signal whether or not a click will succeed ► All-object feedback: a strong signal

Possible explanations -- preference ► Users liked target-only feedback the best ► Six of eighteen participants complained of distraction in all-object feedback ► Target-only feedback only positive ► All-object feedback highlights mistakes ► Positive advice welcome, but all advice useful

Implications ► Despite user's preferences, we cannot provide target-only feedback in a real application ► But, all-object feedback is good too: it does not reduce completion time, and it does reduce error rate

Future Work ► A less intrusive all-object feedback? ► By what mechanism was error reduced? ► Traditionally, feedback helps only the final stage of tracking. Can we devise feedback which is helpful at earlier stages?

Questions?