MONKEYmedia - TECHNOLOGY: Interaction Device Characteristics

TECHNOLOGY : Interaction Device Characteristics: A Functional Anatomy

This article presents an interface brainstorming tool that brings together a number of important characteristics of software user interface devices and interaction techniques. By focusing on individual interactions, one aspect at a time, it's easier to create multiple variants of any particular design.

The accompanying diagram charts the interrelationships and interdependencies between all of the device characteristics defined below. In our design process at MONKEYmedia, we've found this tool useful in showing us options we haven't thought of. It isn't meant to be an exhaustive set of options, but a catalyst for the creative process. To use it, we circle the set of characteristics that define one option for a design we're working on. Then, we change one or more variables and notice the impact on the whole interaction.

This gives us the opportunity to check each alternative for fit with the overall feel of a product -- so the messages we want to communicate via the product can come through equally as strong from the media content, the architecture that holds it, and the interactions employed. It's also a nice way to show a breadth of possibilities to a client. And, once decided on a final technique for any particular interaction, it makes it easy to communicate clear functional specifications to the engineering staff with little room for ambiguity and misunderstanding.

Affordance

An affordance lets the participant know what is possible to do, or where to look to find out. It can be a literally ever present control such as a visually apparent button to press, or it can be ambient audio or video that draws attention to an area of the media space that either can be acted on (such as a page corner), or where a controller pops-up to be used (such as a slider that remains hidden when not in use, to save screen space). Another example is the little sparkle that Human Code uses on its products, indicating that screen elements can be clicked.

Device Activation

A device can be activated by pressing on a specified area, by clicking one or a number of times, or by simply rolling into proximity of it.

Device Use

A device can be used with either the mouse button up or down. Enable a person to continuously browse media over long durations by not requiring them to hold the button down.

Presence

What is the presence of the software controller that the user manipulates via hardware? It can be visible, like a scrollbar; it can be visible as part of the content, such as a character in an animated game; or it can be invisible as in the case of continuously panning a fish-eye image.

Control System Placement

Where are the controller and its associated parts placed? They can live in front of the contents being affected, such as a scrollbar; they can be part of the content, such as a corner of a page that gets flipped; or if they are invisible they don't have a placement at all.

Interaction Perspective

How does the reader relate to the content via the control system? Readers may view the world from their own 'eyes' -- such as the first person view in virtual reality, reaching into the content space; they may interact with the world through second person experiences of a character in the content space -- such as controlling the progress of a game by influencing the actions of a character; or they may interact with the contents via third person controls that are independent of the contents, such as those that float in front of content spaces and are controlled by an autonomous pointer cursor. (The perspective of the control system may or may not be consistent with the point of view of the narrative. The relation between the two perspectives therefore presents interesting authoring choices.)

Control Device Controller

How does the reader control the software device? What kind of control interpreter exists between the hardware device and the software device? 3rd person devices tend to use a cursor. When activated, the cursor may stay present, directing a device sub-part, or disappear so that the reader's physical actions can be mapped onto the coordinate system of the device rather than the coordinate system of the screen (this is useful if the controller is small, yet requires a full range of arm movement). 2nd person devices tend to use characters or actors themselves as both the device and the controller, yet sometimes one might have the character act on devices within the content space. 1st person devices, when invisible, may have either an invisible or visible controller. Choosing to forgo a visible controller keeps the purity of the content's frame, but is more difficult to provide affordances. A visible controller can be used to provide feedback and usage tips beyond the affects apparent in the space, but they tend to 'break the frame'.

Device Sensitivity

Software devices can be either position-sensing, force-sensing, or motion-sensing. Position-sensing devices respond to the position of the controller on the device, in terms of screen x and y axes. An example is a pull-down menu. Force-sensing devices respond to movement within the hardware device, independent of screen position. They respond only to change in hardware x and y. An example is a continuous video controller: when the mouse is still, the video plays at 1x speed, but when it is rolled to the right speeds up the video, and when still again slows to 1x speed. This works well with homogeneous physical devices, like trackballs, because they can roll forever. It doesn't work as well with physically unbounded translation devices like mice, because the reader would repeatedly have to lift the mouse and replace it on the table whenever they reach the edge. Motion-sensing devices fall somewhere in-between position-sensing and force-sensing devices. They attend to change in screen x, y. An example is a hand pointer that grabs & pans an image when rolled. In this case, the motion of the pointer on the screen, not a particular location on the screen, matters.

Interpretation

This relates to how physical device movement translates into software device movement. Both factors (acceleration & inertia) can be evaluated in terms of the effect on the controller or the effect on the contents. Is there a linear 1-to-1 relationship between movement and output, or is output multiplied by an increasing factor or calculated to fit a curve as the participant moves the device? For example, mice, desktop trackballs and portable computer trackballs all have different acceleration curves designed around different ways the hand and fingers are likely to move and express fatigue. It is efficient to use acceleration to give the participant wide breadth of control within a small control size. It is important, however, to not simultaneously neglect fine resolution of control in intermediate areas of the device. Inertia relates to what happens to the content when the reader lets go of the controller. Does it stop immediately at the place released or does it keep moving? Does it continue for a preset distance or does it decelerate smoothly? This is good for tossing objects across a media space: get the gesture going, then let go...

Device State (Upon Disengagement)

What happens to the device when the reader lets go? Does it spring return to a resting position (like a physical joystick), or remain in position (like a checkbox or radio button). Spring return is useful when the position of the device is not related to the position of the content, and the device can be used over and over again from a resting position (as can an audio scrubbing tool).

Device Output Value Stability

Spring return devices are always volatile; they lose their output value when released. Remain in position devices, however, can be both volatile and non-volatile. Non-volatile devices are useful in establishing a consistent mapping relationship between positions of the device and particular states of, or positions in the content space (as scrollbar thumbs do within scrollbars - showing position in the document being scrolled).

Device Texture & Perception

Devices can have discrete states, as do check-boxes and play/pause toggle buttons. They can also have a range of distinguished positions, where a particular position always refers to a particular state or position in the content. The top of the scrollbar always refers to the beginning of a document. Distinguished position controls can also be notched, in that they snap to notches along the length of the device. A continuous controller for video makes use of a notch-point for 1x speed so that the reader can easily play the video at the correct speed. However, they can continuously drag the control thumb beyond that position for speeding-up and slowing down.

Device Boundaries

Bounded interactions have effective limits of motion (as scrollbars do: the thumb can only move within the bar); while unbounded interactions are without limit (as invisible controllers can be). Some devices, such as a 1st person panning hand, fall in-between the two definitions: they are basically unbounded, in that they can move all over the screen, but are also literally bound by the edges of the window/screen frame -- since the hand is grabbing a particular place of the picture, auto-scroll upon hitting the edge of the window would break the kinesthetically consistent feel.

Device Disengagement

A device can be disengaged by releasing the mouse button, by clicking one or a number of times, by pressing and holding the mouse button, by rolling out of proximity of it, or by waiting for a specified period of time.

Number of Control Axes

How many dimensions does the device move in? 1D, like a scrollbar (x or y) or a button (z); 2D, like a panning hand; or 3D, like QuickDraw 3D's object rotation interactions.

Axis Independence

Free devices have more than one axis, and are easy to move in any direction. They are good to use when there is no special significance to motion along a single axis. In contrast, sticky devices have a barrier (light or strong) that prevents inadvertent activation of one axis when another is being used.

Axes Relationship

Orthogonal devices have axes fixed in a frame of reference, while nested devices move along axes that change because they are nested within other axes. QuickDraw 3D's object rotation interactions provide an example of axis nesting: as the user changes the orientation in one axis, the possibilities of rotation in the other axes change. It is reversible though, because the interdependent movements can be unwound, letting the user rely on kinesthetic memory to quickly return the object to a remembered orientation.