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Interactive Screens
Uniting Depth and Surface

      As computer use becomes more wide-spread, usability becomes an increasing concern. Usability addresses issues such as learnability, intuitiveness, usefulness, efficiency, and cultural appropriateness of computer software. Specific guidelines have been created by individuals such as Jakob Nielsen that define the balance that a designer must negotiate when attempting to satisfy the requirements of usability. These days, the importance of usability can be seen just in the number of names it has: ergonomics, HMI (human-machine interface), HCI (human-computer interaction), CHI (computer-human interaction), UCD (user-centered design), HF (human factors), and UID (user interface design), to name a few. In this article, I will often use the phrase "interface design" interchangeably with "usability."
          Interface design consists primarily of two halves: designing displays, and designing human interactivity. The main objective of display design is typically to create transparent views into the information space being accessed. It is important that the frame--everything that is used to display and contextualize the information--does not distract the user from the information itself. In short, display design is about creating transparent windows into the information space that emphasize the depth of the space, not the surface and frame of the display. The primary goal of designing human-computer interaction, on the other hand, is to create opaque objects that map the information space and afford direct manipulation that guides and constrains human interactions to reduce the memory load on the individual. In this case, the emphasis is on the interactions between the user and the frame and how they can manipulate the information.
          One might notice that these two sides of interface design parallel the dichotomy characterized by the differences between early Italian perspective painting and Dutch modernist art--the opposing forces of transparency vs. opacity, window vs. map, and depth vs. surface. In the genealogy of visual representation, user interface design is breaking new ground by uniting many of the characteristics that are traditionally opposed. Interactive screens are uniting depth and surface.

The Desktop Metaphor

For years, user interface design of computer software has moved to embrace the notion of the Graphical User Interface (GUI). In most cases, GUI's take the form of a windowing environment--one that provides multiple windows or views into the information space that the software accesses. Some common examples are the Macintosh Operating System, Microsoft Windows, and X Windows for UNIX. In all three cases, the metaphor of a desktop is used in which the surface of the screen represents the surface of a desk, upon which may be placed items such as documents, folders, and tools.

[Image: MacOS running Adobe Photoshop]
Figure 1. Overlapping windows atop a blue textured desktop.

          The central component of GUI's, the window, is an element of depth. Each window opens into the potentially infinite universe of the information space. While many applications, such as word processors and spreadsheets, tend to have very flat information spaces, other applications like 3D modelers can literally have almost infinite depth. Windows primarily serve the display aspect of interface design, providing transparent views into the depths of the information space.
          The desktop itself, however, is primarily surface oriented. It serves the interaction aspect of interface design in that it provides a way of manipulating and organizing the collection of windows. Relative to the desktop, the windows themselves become the information space. The frames around the windows are the opaque objects that can be seized and dragged about. The desktop has only a limited sense of depth in that the windows may overlap and are sometimes adorned with bevelled edges. But all of this is done to augment the sense of surface--surface that can be grabbed and manipulated.
          When viewing this standard kind of graphical interface, one merely needs to change one's focus to switch from a depth-oriented to a surface-oriented visual representation. With a simple change of mental context, the windows can become merely objects scattered across the surface of the screen. Switch back, and one is peering into the deep void of another information space. And all along, nothing on the screen has changed.

Layers of Interactivity

Early GUI interfaces tended to be very flat, like the example windows shown in Figure 1. The sense of depth was derived almost solely from the overlap of the windows. Except in a few applications whose specific purpose was to display 3D representations, a majority of the tools and controls within a window tended to have no overlapping areas, lighting effects, or drop shadows. More recent GUI designs, however, have begun to incorporate layers of depth within the window, which correspond to the levels of interactivity they provide. The Netscape web browser shown below, for example, demonstrates this sort of design.

[Image: Netscape Web Browser]
Figure 2. Netscape web browser.

          The browser shows three distinct layers of interactivity. The top layer, emphasized in Figure 3 below, corresponds to buttons. No other controls appear at this level. As the highest controls on the window, they naturally encourage direct manipulation--interaction focused directly on the object itself.

[Image: Netscape Web Browser with buttons highlighted]
Figure 3. Top layer of interactivity: buttons.

On the middle layer (shown in Figure 4) appear labels and other non-interactive components. This layer, sandwiched between the higher and lower levels is intuitively the most neutral, the most inert. It does not encourage interactivity as do the other two layers, but does serve a mapping function by labelling and categorizing the information spaces.

[Image: Netscape Web Browser with labels highlighted]
Figure 4. Middle layer: labels and non-interactive components.

On the bottom layer appear all of the interactive components that are not buttons. For example, in the figure below, the Location text field and the web page itself appear on this third layer. The bottom layer, one could argue, would tend to discourage any sort of direct manipulation such as with the pointing device. However, it can also be argued that the depressions in the window serve as wells or pools, attracting information content. And in fact, it is often in these information pools that you find the bulk of the content of the window.

[Image: Netscape Web Browser with text fields highlighted]
Figure 5. Bottom layer of interactivity: text fields and interactive screens.

          What is particularly interesting about these layers of interactivity is that the top two layers, those of buttons and labels, form a sort of frame within the frame of the window. The bottom layer, containing the information pools, tends less to provide frames and more to provide views. In other words, the higher layers provide the direct manipulation and maps for manipulating, organizing, and conceptualizing the information, while the lowest level provides the transparent views into the information spaces, paralleling the relationship between windows and the desktop.

3D Consoles

In games and multimedia software, where there is less emphasis on rigid user interface standards, thus providing greater freedom to work with the aesthetics of a piece, there is a strong movement toward 3D console-type interfaces. These interfaces are continuing to blur the lines between window and frame.
          For example, in Figure 6 below, the application recreates the likeness of a computer screen within its own frame. Although this technique still parallels the window-desktop relationship, it draws more attention to the console screen as a surface as well as a window.

[Image: Faith multimedia project]
Figure 6. Faith multimedia project incorporating a 3D console.

          The various interface components of the Multimedia Music application shown in Figure 7, are still divided in a relatively traditional manner between window and frame. However, it is far more difficult to distinguish one from the other. In fact, much of the "frame" in this case (everything surrounding the curled sheet of paper), is itself a window onto another broader information space that contextualizes the information that appears on the paper.

[Image: Multimedia Music CD-Audio page]
Figure 7. Multimedia Music "CD-Audio" page with several layers of depth.

          In the third example, below, the distinction between window and frame has been all but removed. The object and the information are united, mapped and displayed simultaneously. The display itself is the object to be manipulated.

[Image: Marathon console screen]
Figure 8. Marathon video game utilizing a 3D console.

          While some of the most advanced work in breaking down the dichotomy between window and frame is taking place in multimedia and game development, that is not to say that these new united ways of representing and interacting with visual information spaces will not begin to trickle into the standard applications market. In fact, the Kai Power Tools 3.0 MetaToys device shown in Figure 9 demonstrates one of the most advanced user interface designs in which the object that is manipulated and the view that it affords are entirely united. In the image below, both the traditional windows and desktop are literally left in the shadow of the future of user interface design.

[Image: Kai Power Tools 3.0 MetaToys device]
Figure 9. Kai Power Tools 3.0 "MetaToys" device.

Conclusion

Computer use brings one very important characteristic to the genealogy of visual representation--interactivity. Few media have relied so heavily upon the action of the user or viewer as do digital media. As a result, interactivity has become a driving force behind the movement toward new forms of visual representation that attempt to balance transparent displays of information with opaque objects that facilitate the mapping and manipulation of these information spaces. In essence, the requirements of usability are driving interactive screens to unite depth and surface.

    [Return to Top] Copyright 1997, Mark R. Johnson.
Last modified 4/26/97.