Computer/Human InteractionLecture 26Overview:Gulf of Execution: Refining Action PlansGulf of Execution: Executing Action SequencesGulf of ExecutionHow to get from user task goal to the physical movements to accomplish the task.System goal – software-oriented goal to accomplish taskAction plan – steps for accomplishing goalExecution – physical actions that implement action sequenceMulti-taskingNote that humans are good at multi-tasking; consider its effect on interactionUsers must have flexibility and control over multiple interactions, must be able to stop and start “in the middle”Example: multiple windowsEasy to have multiple tasks goingIncreases plan complexity; i.e., how to find thingsOverlapping windows vs. Tiled windowsModal InteractionExample: modal interactionModes generally are to be avoided, since usually they require that task be completed before starting another, but sometimes are necessaryExample: Vi vs. emacsMessage dialog boxes especially annoying, compromise by allowing user to cancelExecuting Action SequencePhysical implementation of plan stepsArticulatory directness is mapping of physical movement with a device to task input requirementDirect – twist a knobIndirect – type in a numberInput DevicesDifferent input devices have different affordances. What are the input characteristics and sample applications the following are used for?Buttons?Keyboard?Mouse?Joystick?Trackball?Speech InterfaceStar Trek future – talk to computerWhat are the input characteristics of a speech interface?What types of applications should a speech interface be good for?What are the current limitations of technology?PragmaticsPragmatics are physical behaviors required by a user interfaceThey should have underlying structure matching the conceptual task being implemented, i.e., match the chunksExample: selecting text chunk – press down on mouse button to specify start of selection, hold down while dragging, release mouse button to specify end pointAnticipate ErrorsCarefully analyze physically challenging actions. Fitts’ Law: time to select a target is function of distance and size of target. Of course not all targets can be large...Overlearned procedures (e.g. from other systems) lead to intrusions (slips, not mistakes). E.g. Ctrl-N in emacs vs. in MS WordSupport Error CorrectionForward/backward delete, click to de-selectOften not a design decision, since built into the UI platform directlyBut what does “Back” do?Providing “undo” is a design problemHard to predict/support the right level of reversibilityIssue with logical vs. physical. Example: MS Word AutoFormat quotesOptimization of SequenceLong or clumsy sequences lead to more errors, longer to type in, frustration for usersTradeoff of expressive power and ease of use. Example: typed command language is much faster physically than point/click GUI.Compromise by mixing: keyboard shortcuts, default actions for frequent choices. But be careful not to violate overall consistency or favor one task over other common/important tasks.CustomizationAllow users to write macros to define their own sequences.Especially good for special needs casesSpecial needs accessibility is an on-going area of research in