GYTE – BİL763 – Human- Computer Interaction TERM PAPER PRESENTATION. Fitts ’ Law and Expanding Targets : Experimental Studies and Designs for User Interfaces Authors : Michael J. McGuffin , Ravin Balakrishnan. Student Name: Orkun AKİLE Student Id : 131041028. INTRODUCTION.
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GYTE – BİL763 – Human-ComputerInteraction
TERM PAPER PRESENTATION
Fitts’ LawandExpandingTargets : ExperimentalStudiesandDesignsfor User InterfacesAuthors : Michael J. McGuffin, RavinBalakrishnan
Student Name: Orkun AKİLE
StudentId : 131041028
A : Amplitude of themotion
W : Width of thetargetmeasuredalongtheaxis of motion
K : K is a constantwhosevalue is proposedto be 0, ½ or1
ID : Thelogarithm is referredto as index of difficulty.
a, b : Constants a and b varywithfactorssuch as pointingdevice, musclesusedforinput, control-displayratio (C:D). Todetermine a and b typically an experiment is performed. Fitting a straightlinetothemeasureMT valuesyields a and b as theinterceptandslope of theline.
Lower-Level Models of Motor Control
Instruments: A workstationrunning Linux, with a 21-inch, 1280x1024 colordisplay. A puck on 12x18 inchdigitizing tablet wasused as inputdevice.
Discretetargetselectiontask is studiedwherethetarget’swidthexpandsdynamicallyafterthestart of movement.
Participants : Twelvevounteers(9 male, 3 female) between 20 and 35 years.
× 2 conditionsperparticipant
× 5 blockspercondition
× 13 A, W combinations per block
× 5 trials per A, W combination
= 7800 trials in total
1 -performance is significantly enhanced by expandingtargets even when expansion occurs after 90% of the distance towards thetarget has been traversed,
2 - the task of acquiring an isolated expanding targetcan be accurately modeled by Fitts’ law,
3 -for sufficiently high ID values,performance is approximately as good as, or better than, the best that couldbe expected, given our rationale for the lower bound on movement time. Thislast point means that users benefited fully from expansion for sufficiently highID, suggesting that the final expanded target size is much more important fordetermining performance than the initial target size.
Although the tiled expanding targets just considered arenot expanded in motor space (at least, not along the tiled dimension), the visualexpansion of targets can be used to display more data or more detailed previewsassociated with targets, while still allowing targetsto be efficiently packed into a small screen space when not in use. Furthermore,if targets are only tiled along one dimension, they can be expanded in motorspace along the other dimension to aid selection along that direction.Figures 9 and 10 illustrate two designs that are equivalent in terms of motorspace but that differ critically in the feedback given in visual space.
Considerations for visual feedback reveal a tension between allowing occlusionof neighbors, which can interfere with the visibility of a desired target, versusshifting of neighbors, which creates moving targets during sideways cursormotion. We feel the design in Figure 10 is a good hybrid in that it allows for anadjustable trade-off between these two effects and might be further improvedusingtransparency.
Thisapproachofferspotentiallygreatestadvantages but has not yet beendemonstratedto be workableand is not readyto be applied in realinterfacedesignwork. Accordingto a mathematical model which is set up in thispaperindicatesthat a nerreduction in selection time withtiledexpandingtargetsmay be possible. However, in practice, thebenefitmay be negligiblysmall.