use the term selection termination to indicate the action that ends the entire menu
`
`In non-hierarchic case, selection confirmation and selection
`selection process.
`termination are combined in the sameaction.
`
`There are manydifferent types of input events that could be used to signal selection
`confirmation:
`
`¢ Pen-up/pen-down
`
`Item entry meansselection confirmation occurs the moment the pen
`* Item entry:
`enters an item.
`
`* Boundary crossing: Boundary crossing means that sclection confirmation occurs
`whenthe pen crosses the outside border of a menu item.
`
`¢ Dwelling: Dwelling is the act of keeping the pen pressed and not moving for a
`fraction of a second. A user can avoid issuing dwelling events by keeping the pen
`moving.
`Press-and-wait
`is an example of a dwelling event. However, we
`distinguish between these two events because press-and-wait signals the entry into
`menu mode while dwelling signals selection confirmation.
`
`« Events distinct from pen movement: This includes things like a button press or an
`increase in pressure with a pressure sensing pen.
`
`The type of selection confirmation event used affects other design features:
`
`© mimicking drawing a mark: Since selection from a hierarchy of menu items involves
`a series of selection confirmations and we wish to mimic that act of making a mark,
`an event for selection confirmation that does not interrupt dragging must be used.
`
`In some cases, a user maydesire to change the previewed selection.
`* reselection:
`For example, a user may accidentally move into the wrong item then want to move
`to the correct item. We refer to this process as resclection. Most menu systems
`support reselection.
`
`* pairing command and parameters: The command compass allows dragging to
`continue after the final selection confirmation. Dragging is then used to indicate
`additional parameters to the menu commandjust selected.
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`Figure 2.5 shows whichselection confirmation methods support these features. Item
`entry is not feasible because it docs not allow reselection. Boundary crossing,
`dwelling and events distinct from pen movements support both reselection and
`pairing. We discount “events distinct from pen movement” because it requires
`additional input sensors like pen buttons or a pressure sensing pen.
`
`Figure 2.5 indicates that boundary crossing and dwelling are the only applicable
`choices. Boundary crossing is preferable because a visible boundary(i.e., the edge of
`a menu) gives precise information as to whenselection will occur. This information
`is not visible if dwelling is used. Furthermore, waiting for a dwelling to occur slows
`interaction. It is also possible to use pen release as a confirmation method if pairing
`is not required and the item being selected is the last in a series of selections.
`
`We implemented boundary crossing by having selection confirmation occur when
`the user crossed over the outer edge of a menu item.
`Specifically, selection
`previewing occurred as long as the user stayed within the circle of the menu.
`Selection confirmation occurred when the user moved outside the circle. We
`
`discovered, in practice, that boundary crossing created a problem. As a uscr moves
`away from the center of the menu to confirm an item, the item’s sub-menu pops up
`whenthe outer boundary is crossed. Unless a user moves very slowly, oneis still
`moving when the sub-menu appears. This results in one of the items in the sub-
`menu being selected immediately.
`If the user is moving fast, the boundary point for
`the sub-menu may have already been crossed and this results in an erroneous
`selection confirmation.
`Even if
`the boundary point was not crossed,
`this
`overshooting in the sub-menu causes reselection to be the first action to occur each
`time a sub-menu is popped up. This means that users are not rehearsing the
`movement of drawing a mark, but are rather making a movement which involves
`reselection. This approach was therefore unacceptable.
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`To solve this problem, we used a hybrid approach which combines boundary
`crossing and dwelling. The approach works as follows. As long as the pointeris
`within some distance from the center of menu, a dwelling event
`is ignored.
`Selection preview and reselection are therefore possible without the threat of an
`accidental dwelling occurring. Once the boundaryis crossed, selection preview and
`reselection are still possible but, if the user dwells, the selected item is confirmed
`and its sub-menu appears. This allowed users to use coarser movements to make
`selections without fear of overshooting and selecting from sub-menus.
`
`Dwelling is also consistent with press-and-wait. In both these activities, keeping the
`pen pressed against the display and holdingit triggers the display of a menu.
`
`A selection can also be confirmed without dwelling by releasing the pen at any point
`in the hierarchy of a menu. This allows any item in the hierarchy to be selected and
`also signals selection termination.
`
`2.5.6.
`
`Mark ambiguities
`
`The current design presents a dilemma if we consider using marks to make
`selections from hierarchies of menus. The idea behind using marks for selection is
`
`Selection confirmation event
`
`allows
`
`allows
`
`mimicking
`
`reselection?
`
`marking?
`
`allows
`
`pairing?
`
`
`
`events distinct from pen
`movement
`
`yes
`
`yes
`
`yes
`
`(* yes in the non-hierarchic case)
`
`( as long as the pointer is kept moving)
`
`Figure 2.5: Different selection confirmation methods characteristics.
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`that selection will be fast and fluid. This implies that we do not desire or expect a
`user to “include” dwellings when making selections using marks. This would be
`unnatural and slow the marking process.
`
`A problem can occur if dwellings are not included when making marks. Consider a
`selection from a hierarchythat is two levels deep. Suppose the user makesa straight
`line mark. Does the mark correspond to a selection from the parent menu or the
`child menu? Figure 2.6 shows the problem. If dwellings no longer occur we cannot
`disambiguate the selection. If we base the interpretation on boundary crossing, then
`the mark is unambiguous. Unfortunately, this makes the size of a mark affect its
`interpretation (i.e., the marks cannotbe scaled).
`
`It is based on the
`One solution to this problem is called no category selections.
`observation that items which have subitems are generally categories of commands,
`not commandsthemselves, and selecting a category is not a meaningful operation.
`For example, when using linear hierarchic menus on the Macintosh, selecting the
`“font” category leads to a menu of commandsthat change the font. Selecting “font”
`by itself (i.c., releasing the mouse button when “font” is sclected) performs no
`operation. Therefore we assumethat there is no needto select a category. Thus, we
`can consider any straight line to be a selection into a submenu (case (b) in Figure
`2.6). Note that this permits selection of certain menu items that are embedded in
`submenus by drawing a short straight mark. We recommend designers put the
`most popular item in a category in this position to promote efficiency.
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`
`Figure 2.6: Ambiguity in selecting from a hierarchy of menu items two levels deep
`using a mark. Overlaid grayed menu show possible interpretations.
`In (a),
`the
`interpretation is the selection of item 1. However,
`(b) is another interpretation
`according to boundary crossing rules (the selection of item 1.1).
`Interpretation by
`boundarycrossing is sensitive to the size ofmarks,
`
`Nocategory selections breaks down when the depth of the hierarchy is greater than
`two. Suppose a user makes a ““” mark as shownin Figure 2.7 (a). The start of the
`mark and the change in direction within the mark indicate two points of menu
`selection. However, what indicates selection from the third level of menu? Figure
`2.7 showsthis problem. Once again, boundary crossing can be applied to derive an
`unambiguous set of menu selections but this results in unscalable marks.
`
`There are several solutions to this problem which preserve scaling. The first
`solution, referred to as the no-oping (from the phrase “no operation”),
`is to simply
`not permit a series of menu selections that result in a straight line. One way of
`doing this involves making the item in the child menu that “lines up” with the
`selection angle of the parent a null operation. This ensures that the beginning of a
`selection of a non-null item from a child menu is indicated by a change in angle.
`Unfortunately, this “wastes” a useful sector in a menu.
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`
`Figure 2.7: Possible interpretations of mark when selecting from hierarchies greater
`that two levels deep. The straight line sections of the mark have no artifacts to indicate
`whetherthe selection at that point is being madefromthe parent orfrom the child.
`
`A second solution is axis-shifting. This involves rotating child menus such that no
`item appears at the same angle as an item in the parent menu. Figure 2.8 shows an
`example of this technique. Axis-shifting involves aligning the boundary between
`two items in the child menu with the selection angle of the parent item. This ensures
`that the beginning of a selection from child menu is indicated by a change in angle.
`Axis-shifting avoids the wasted sectors that occur with no-oping.
`
`This discussion has presented four solutions to hierarchic menu design which are
`intended to produce an unambiguous vocabulary of marks. The four solutions are:
`boundary crossing, no categoryselections, no-oping, and axis-shifting. The aspects
`of the design that are affected by these solutions are: the ability to select any item
`within the hierarchy, the ability to have mark interpretation independentof the size
`of a mark, the ability to select leaf items with a single straight line, and the ability to
`have all items in a menu active. These aspects may also vary relative to the depth of
`the menu. Figure 2.9 summarizes this design space.
`
`A solution can be chosen based on the demandsof the menu. If menus are only one
`or two levels deep and menucategories do not need to be selected, then no category
`selections will work. Boundary crossing and axis-shifting are suitable when
`hierarchies are more than two levels deep and category menu items need to be
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`selected. Boundary crossing is also an acceptable solution if category items need to
`be selected and markscaling is not an issuc.
`
`Figure 2.8: Axis shifting rotates a child menu such that child menu items do not appear
`on the same angle as the parent menu item. This results in a mark language where
`selection confirmations are indicated by changes in angle.
`With this scheme marks can
`be drawn at anysize.
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`
`
`
`
`
`
`
`
`Policy no depth|select any marks allows all items
`
`
`
`
`
`
`
`limit? scalable?|“straightitem? active?
`
`
`
`lining”
`
`
`
`no category
`
`selections
`
`No (except
`
`in 1 deep
`
`case)
`
`Figure 2.9: Policies that avoid ambiguous interpretation ofmarking menu marks.
`
`2.5.7.
`
`Display methods
`
`There are several design options which concern how menusare displayed:
`
`* Menu trail refers to leaving parent menus displayed as a user descends a hicrarchy
`of menu items.
`
`¢ Menu overlap refers to displaying child menus overthe top of parent menus.
`
`These methods become important when backing up in a hicrarchy of menus.
`
`2.5.8.
`
`Backing-up the hierarchy
`
`The ability to back-up in a hierarchy of menus is useful for browsing menu items
`and correcting mistakes. Backing-up can be one of three types: back-up onlyto the
`parent menu, back-up to any ancestor menu, back-up to any ancestor menu item.
`Backing-up can be accomplished in several ways. Pointing to an item cantrigger a
`back-up to the item, or an explicit action can trigger a back-up (i.e., tapping the pen
`triggers a back-up to the parent menu). A combination of these two methods can be
`used (i.e., tapping on an item to back-up to it). Lifting the pen is already used to
`indicate selection termination, so the back-up technique is restricted to pointing
`while the pen is being dragged.
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`Backing-up brings the roles of menu trail and menu overlap into play. Pointing to
`the item in order to back-up to it requires that item be displayed on the screen.
`Therefore a menutrail must be provided. However, child menu items may cover up
`parent items making it impossible to point to “covered” items. The design must
`ensure that parent items are not covered up.
`
`Design requirements dictate that backing-up in marking menus operates like
`backing-up in traditional drag-through hierarchical menus: to back-up to a parent
`menu item, a user points to it; the system then closes the currently displayed child
`menu and displays the child menu of the parent item. We can adopt this scheme for
`marking menusbut it reduces the advantage of radial menu selection. Figure 2.10
`shows the problem that occurs. A selection from a child menu may result in
`pointing to a parent menu item andthis causes an unintended back-up. A prototype
`implementation of marking menus revealed this to be a real problem. The problem
`could be avoidedif a user is “careful”, but this tends to slow users down.
`
`
`
`Figure 2.10: A problem with the backing up by pointing to a parent item. Is the user
`selecting item a.c or backing up to item b?
`
`To solve this problem, we could restrict marking menusto operate like linear menus
`where selection occurs only if the user is pointing inside a menu item. This has two
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`major disadvantages. First, it selection sensitive to the length of strokes, and second,
`it massively reduces item size from a sector of the entire screen to the small sector of
`the menu.
`
`The solution is to reduce the size of the back-up targets. This is done byrestricting
`the back-up targets to the center hole of the parent menus. This drastically reduces
`the probability of accidentally pointing to a back-up target.
`Furthermore, we
`constrain the user to dwell on a center before back-up takes place. This allows the
`user to “pass through” centers without backup occurring. Figure 2.11 showsthis
`back-up scheme.
`
`This approach has the restriction of only allowing back-up to parent menus.
`Backing up to a parent menu and displaying another one of the child menus cannot
`be combined in the same operation. Some hierarchic linear menus allow this.
`However, this restriction permits fast and unconstrained selection when moving
`forwardin the hierarchy, while still allowing back-up.
`
`This back-up scheme has several more advantages. First, onc can back-up to any
`parent menu, grandparent menu, etc. Second, menu overlap can occur just as long
`as menu centers do not get covered. Finally, because backing-up actually returns
`the cursor to parent menus, rather than redisplaying parent menu at the cursor
`location, this reduces the chances of menus “walking off” the screen (this problem is
`further discussed in Section 6.2.3).
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`
`
`In (1) the user moves into
`Figure 2.11: Backing-up in hierarchic marking menus.
`the center of a parent menu and dwells momentarily.
`In (2) the system senses the
`dwelling and backs-up to the parent menu by removing the child of item a. Selection
`may then continue from the parent.
`
`2.5.9.
`
`Aborting selection
`
`Most menu systems have a way of specifying a null selection. Generally this is
`accomplished byselecting outside a menu item. As explained previously, marking
`menus allow selection to occur outside the item to make selection easier. To
`
`circumvent this problem, the center hole of a menu is used to indicate no selection.
`Lifting the pen within the center hole results in the menu selection being aborted.
`
`A mark may be also be aborted. This involveseither lifting the pen before the mark
`is complete or turning the mark into an uninterpretable scrawl while drawing it.
`
`2.5.10.
`
`Graphic designs and layout
`
`During everyday use of marking menus we observed some problems witha “pie”
`graphical representation. First, as the numbcr of items in the menu increases and
`the length of labels increases, the size of the pie grows rapidly. This creates several
`problems. First, having large areas of the screen display and undisplay is visually
`annoying.
`Second, a large menu occludes too much of the screen.
`In many
`situations, a menu associated with a graphical object must be popped up over the
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`object. The problem is that displaying the menu completely hides the object. This
`results in the context of the selection being lost. Third, large menus take time to
`display and undisplay.
`In most systems, the image “underneath “ a menuis saved
`before a menu is displayed, and restored when a menu is undisplayed. When a
`menu is very large, these operations take considerable amounts of time because
`large sections of memoryare being copied to and from the display. Also, algorithms
`for sizing and laying out labels within the pie of the menu can be quite complex.
`This makes the implementation of menu layout procedures complex. Complex
`computations may also delay the display of menus.
`
`To solve these problems we designed an alternate graphic layout for marking menus
`called “label”!°. Figure 2.12 shows an example. This alternate design has several
`advantages over a pic representation. First, it reduces the amount of screen that
`changes when a marking menu is displayed and undisplayed, and therefore,
`it
`reduces visual annoyance.
`Second,
`it occludes less of
`the screen than a pie
`representation because only the menu center and labels are opaque. Thus more of
`the context underneath a menu can be seen. This design also reduces the amount of
`memory that must be copied to and from the display, and hence it reduces the
`amount of time neededto display a menu.
`
`Another issue of graphical layout is the problem of displaying menus near an edge
`or comer of the screen. Pie menu systems deal with this issue by using a technique
`called “cursor warping”. Unfortunately, cursor warping is not suitable for pen-
`based systems.
`In Chapter 6, we further discuss this issue and describe an
`alternative to cursor warping.
`
`Although not shown in Figure 2.12, marking menus have many standard features
`found in traditional menus. For example, marking menus allow grayed-out and
`checked items. Also, if an item has a submenu, a small circle appears to the right of
`the label. The intention is that this circle represents the center hole of the submenu.
`Wealso found it valuable to hide the labels of parent menus, thus reducing screen
`clutter. The only portion of a parent menuthat is displayed is the center hole (so a
`user can point to it to back-up). We havealso experimented with transparent menus
`
`19 We acknowledge Mark Tapia for his assistance in designing and implementing the alternate graphical layout
`for marking menus
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`
`
`
`(a)
`
`(b)
`
`Figure 2.12: An alternate graphic representation for a radial menu “label”. Rather
`than displaying “pie” shapes (a), only the labels and center are displayed (b). The
`menu then occludes less ofdisplay and can be displayedfaster.
`
`and graying out parent menusbuta full discussion of these experiments is beyond
`the scopeof this dissertation.
`
`2.5.11.
`
`Summary of design
`
`The previous sections described and discussed various design features and options
`of marking menus. We now summarize the features and indicate which design
`options weelected to use.
`
`Marking menus use discrimination by angle. Selection previewing in menu modeis
`supported by dragging the pen into an item, and the item being highlighted.
`Selection confirmation is indicated by a combination of boundary crossing and
`dwelling. Selection termination is indicated by pen up.
`
`To avoid mark ambiguities, we recommend three possible strategies: no-oping, no
`category selections and axis-shifting.
`If menus require only a few items, no-oping
`may be a suitable solution. If menus are only two levels deep and category selection
`is not required, no category selection is a suitable solution.
`If menus require many
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`menu items, and are more than two levels deep, axis-shifting must be used.
`practice, we used no category sclection in many situations.
`
`In
`
`Making a selection in menu mode leaves a menu trail but only the center of parent
`menu is displayed. We foundin practice this reduces the visual clutter the would be
`caused by the display of inactive parent menu items. Menusare allowed to overlap,
`but because only the center of parent menu is displayed, this generally does not
`cause visual confusion.
`
`In menu mode, selection can be aborted by terminating the selection while pointing
`to the center hole of a menu. In mark mode,selection can be aborted by turning the
`mark into a “scribble”.
`
`If a user dwells while drawing a mark, the system indicates the menu items that
`would be selected by the mark by displaying the menus “along” the mark. The
`system then goes into menu mode. This process, called mark confirmation, can be
`used to verify the items that are about to be selected by a mark or a portion of a
`mark.
`
`Marking menus can be displayed in either a “pie” representation or a “label”
`representation. A “label” representation is suitable when there is a need to
`minimize the amount of screen occluded by the display of the menu.
`
`2.6.
`
`SUMMARY
`
`The success of an interaction technique dependsnot only on its acceptance by uscrs
`but also on its acceptance byinterface designers and implementors. An “industrial
`strength” interaction technique must not only be effective for a user, but also have
`the ability to co-exist with other interaction techniques, other paradigms, and
`differing features of the software and hardware. Because of these demands, as in
`many other interaction techniques, our motivation and design behind marking
`menus is complex. What appears on the surface as a simple interaction technique is
`actually based on many different motivations and has many design subtleties and
`details.
`
`In this chapter we defined marking menus and described the various motivations
`for developing and evaluating them. These included providing marks for functions
`which have no intuitive mark,
`supporting unfolding interface paradigms,
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`simplifying mark recognition, maintaining compatibility with existing interfaces,
`and supporting both novice and expert users. We are also motivated to study
`marking menusas a wayto evaluate the design principles they are based on.
`
`Wethen outlined the issues involved in evaluating marking menus and proposed an
`initial design. The major parameters to be evaluated concern the question of how
`much functionality can be loaded on a marking menu. Essentially our research
`focus is on establishing the limitations of marking menus sointerface designers who
`are utilizing marking menus can design accordingly. The remaining chapters
`explore the limitations and characteristics of the design.
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`Chapter 3: An empirical evaluation of
`non-hierarchic marking menus
`
`This chapter addresses basic questions about marking menu design variables: how
`many items can marking menus contain; what kinds of input devices can be used in
`conjunction with marking menus; how quickly can users learn the associations
`between items and marks; how muchis performance degraded by not using the
`menu;
`and whether there is any advantage in using an ink-trail. This chapter
`describes an experiment which addresses these questions. The approachis to pose
`specific hypotheses about the relationship between important design variables and
`performance, and then to test these hypotheses in the context of a controlled
`experiment. The results of the experiment are then interpreted to provide answers
`to the basic questions posed above.
`
`In this experiment we limit our investigation to non-hierarchic marking menus. We
`do this for several reasons. First, this experimentserves as a feasibility test of non-
`hierarchic marking menus. If non-hierarchic marking menus prove feasible, then an
`investigation of hierarchic marking menus is warranted. Second, we feel that the
`characteristics of non-hierarchic marking menus must be understood before we can
`begin to investigate hierarchic marking menus. Our findings on non-hierarchic
`marking menus can then be used to refine our design and evaluation of hierarchic
`marking menus. Third, this experiment addresses many factors. To include the
`additional factor of hicrarchic structuring would make the experiment too large and
`impractical.
`
`To date there is little research applicable to our investigation. Callahan, Hopkins,
`Weiser, and Shneiderman (1988) investigated target seek time and error rates for 8-
`item pie menus, but concentrated on comparing them to linear menus. In particular
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`they were interested in what kind of information is best represented in pie menu
`format. Section 2.3.1 described their results.
`
`Our experiment focuses on selecting from marking menus using marks. To address
`the questions posed at the start of this chapter, the experiment examines the effect
`that the number of items in a menu, choice of input device, amount of practice, and
`presence or absence of an ink-trail or menu, has on responsetime and errorrate.
`
`3.1.
`
`THE EXPERIMENT
`
`3.1.1.
`
`Design
`
`In this experiment, we varied the numberof items per menu and input device for
`three groups of subjects and asked them to select target items as quickly as possible
`from a series of simple pie menus. One group selected target items from fully
`visible or “exposed” menus (Exposed group). Since there is little cognitive load
`involved in finding the target item from menus which are alwayspresent, wefelt
`that this group would reveal differences in articulation performance due to input
`device and numberof items in a menu.
`
`Two other groups sclected items from menus which were not visible (“hidden”
`menus). In one group, the cursor left an ink-trail during selection (Marking group),
`and in the other, it did not (Hidden group). The two hidden menu groups were
`intended to uncover cognitive aspects of performance. Hiding the menus would
`require the added cognitive load of either remembering the location of the target
`item by remembering or mentally constructing the menu, or by remembering the
`association between marks and the commands they invoke through repeated
`practice. Comparing use of an ink-trail with no ink-trail was intended to reveal the
`extent to which supporting the metaphor of marking and providing additional
`visual feedback affects performance. The Exposed group provided a baseline to
`measure the amount
`that performance degraded when selecting from hidden
`menus.
`
`3.1.2.
`
`Hypotheses
`
`We formed the following specific hypotheses to address the questions posed at the
`start of this chapter:
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`How much is performance degraded by not using the menu?
`
`Hypothesis 1. Exposed menus will yield faster response times and lowererror rates
`than the two hidden menu groups. However, performance for the two hidden
`groups will be similar to the Exposed group when the numberof items per menuis
`small. When the number of items is large, there will be greater differences in
`performance for hidden versus exposed menus. This prediction is based on the
`assumption that the association between marks and items is acquired quickly when
`there are very few items. As the number of menu items increases, the association
`between marks and items takes longer to acquire, and mentally reconstructing
`menusin order to infer the correct mark becomes moredifficult.
`
`How many items can marking menus contain?
`
`For exposed menus, response time and number of errors will
`Hypothesis 2.
`monotonically increase as the number of items per menu increases. This is because
`we assume that performance on exposed menus is mainly limited by the ease of
`articulation of menu sclection, as opposed to case of remembering or inferring the
`menu layout. We know that performance time and errors monotonically increase as
`target size decreases, all else being equal(Fitts, 1954).
`
`Hypothesis 3. For hidden menus (Marking and Hidden groups), response time will
`not solely be a function of number of items per menu.
`Instead, menu layouts that
`are easily inferred or that are familiar will tend tofacilitate the cognitive processes
`involved. We predict that menus containing eight items can be more easily mentally
`represented than those containing seven items, for example. Similarly, a menu
`containing twelve items is familiar since it is similar to a clock face, and thus we
`predict it is more easily mentally represented than a menu containing eleven items.
`
`What kinds of input devices can be used in conjunction with marking menus?
`
`Hypothesis 4. The stylus will outperform the mouse both in terms of response time
`and errors. The mouse will outperform the trackball. This prediction is based on
`previous work (Mackenzic, Sellen, & Buxton, 1991) comparing these devices in a
`Fitts' law task (i.e., a task involving fast, repeated movement between twotargets in
`one dimension).
`
`Hypothesis 5. Device differences will not interact with hidden or exposed menus,
`or the presence or absence of marks. Differences in performance due to device will
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`not depend on whether the menus are hidden or exposed, or whether or not marks
`are used. Therationale for this is that we assume performance differences stemming
`from different devices are mostly a function of articulation rather than cognition.
`Wealso assumethatthe articulatory requirements of the task are relatively constant
`
`across groups.
`
`Is there any advantage in using an ink-trail?
`
`Hypothesis 6. Users will make straighter strokes in the Marking group. We based
`this prediction on the assumption that visual feedback is provided in the Marking
`group and also that hidden menus support the “marking” metaphor as opposed to
`the “menu selection” metaphor.
`
`How quickly can users learn the associations between items and marks?
`
`Hypothesis 7. Performance on hidden menus (Marking and Hidden groups) will
`improve steadily across trials. Performance with exposed menus will remain fairly
`constant across trials. This prediction is based on belief that articulation of selection
`(or simply executing the response) will not dramatically increase with practice since
`it is a very simple action. Performance on hidden menus, however, involves the
`additional cognitive process of recalling the location of menu items. We believe this
`process will be subject to more dramatic learning effects over time.
`
`3.1.3.
`
`Method
`
`Subjects. Thirty-six right-handed subjects were randomly assigned to one of three
`groups (Exposed, Hidden, and Marking groups). AII but one had considerable
`experience using a mouse. Only one subject had experience using a trackball. None
`of the subjects had experience with a stylus.
`
`Equipment. The task was performed on a Macintosh IIX computer. The standard
`Macintosh mouse wasused andset to the smallest C:D ratio. The trackball used was
`
`a Kensington TurboMouse, also set to the smallest C:D ratio. The stylus was a Wacom
`tablet and pressure-sensitive stylus (an absolute device). The C:D ratio used was
`approximately one-to-one.
`
`Task. Subjects used each of three input devices to select target “slices” from a series
`of pie menus as quickly and as accurately as possible. The pies contained either 4,5,
`7,8, 11, or 12 slices. All pic menus contained numbered segments, always beginning
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`witha “1” immediately adjacent and to the right of the top segment. The otherslices
`were labeled in clockwise order with the maximum numbcrat the top (sec Figure
`3.1 (a)). The diameter of all pie menus was 6.5 cm., and Geneva 14 point bold font
`wasused to labelthe slices.
`
` ©)
`
`(a)
`
`(b)
`
`(c)
`
`Figure 3.1: Selecting item 5 from an eight-item pie menu (a) in the Exposed group,
`(b) in the Hidden group, and (c) in the Marking group.
`
`In designing this experiment, a great deal of time was spent discussing what kind of
`items should be displayed in the pie menus. Menus in real computer applications
`usually contain meaningful items, but the order in which they appear is not casily
`inferred.
`The numbered menus we used, on the other hand, used ordered,
`meaningless labels. We wanted to approxi