A BRIEF REVIEW OF HCI AND GRAPIDCAL PRESENTATION 22 Marcus ( 1983) is of the view that visual communication between computers and

people ta kes place in three different phases that represent the three "faces" of the computer : outerfaces, inter faces and innerfaces. "Outerfaces are the displa ys of information that are the final products of computation. Interfaces are the frames of command/control and documentation that computer system users encounter . Innerfaces are the frames of command/control and documentation that computer experts confront, specifically the builders and maintainers of computer systems." He argues that computer graphics should be exploited to support the design of each of these three faces.

Windows

The desktop metaphor was introduced in the Star and Macintosh Lisa systems, and with it the popularity of WIMP interfaces increased. In windows systems, the user's screen is divided into a number of possibly overlapping rectangular areas, each of which handles a specific function or is itself a "virtual terminal". Windows allow the user to interact with more than one source of information at the same time. It is this plethora of contexts, coupled with the graphical nature of the displays and the use of interactive input devices, which give this typ e of interface its power . Card, Pavey and Farrell (1984) classify windows systems into four major categories (1) the familiar TTY text windows, (2) time multiplexed windows, (3) space multiplexed windows and (4) non-homogeneous wind ows. Research interest in windows has been focused on the differences between systems based on the overlapping window paradigm and those based on the tiled window paradigm .

As the complexity of the windows systems increases, windows mana gers are used to help the user monitor and control differ ent contexts by separating them physically into different parts of one or more display screens. These windows managers are often implemented as part of a computer's operating systems. Indeed, the increasing popularity of windows has also attributed to the standardisation of the interfaces of windows mana ger systems such as the Microsoft Windows, the Macintosh, the X

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Windows (Scheifler & Gettys, 1 986) and Motif. "This high level interface can also ma k e application code more portable from one machine to another, since the same window manager procedural interface can be provided on different machines." (Myers,

1988)

Icons

Despite its relatively short history, iconic interfacing is now widespread a nd it represents a fundamental aspect of the new generation of interfaces. Rogers (1989) suggests that, since we live in a strongly visual and spatially organised environment,

CHAPTER 2: A BRIEF REVIEW OF HCI AND GRAPHICAL PRESENTATION 23

interfaces that also use visual spatial information are more conducive to learning. Lodding ( 1982), an early proponent of the use of icons at the interface, classifies them into three categories: representational, abstract and arbitrary. He further argues that icons can reduce the complexity of a system and hence make it easier to learn (Lodding, 1983). This is achieved by giving an immediate impression to the user that the system is easy to use and in doing so has a positive effect on the first time user. There is quite a selection of guidelines from a variety of fields, ranging from graphics arts to computer science, available to the icons designers (Gittens, Winder & Bez, 1984; Gittens, 1 986; Marcus, 1 984; Marchant, 1985)

Fairchild, Meredith & Wexeblat (1989) present a formal structure for describing icons and their relations to objects, and an extension which they called automatic icons. Icons are mappings from icon space, which deals with representational properties, to object space, which deals with computational objects. Automatic icons serve as icon generators, generating icons based on the properties of the object and the mapping between the object and the image. This provides the system designers with more power and flexibility in the construction.

There appears to be quite consistent empirical evidence to support the use of icons at the user interface. Guastello, Traut & Korienek ( 1989) reported that mixed modality (textual and pictorial) metaphors are rated as more meaningful than icons that utilise verbal or pictorial elements only. In their experiment to compare the usability of menu items constructed of text alone, icons alone, and text and icons together, Kacmar and Carey (1991) also concluded that menus constructed of a mixed format (text and icons) result in smallest number of incorrect choices by users without any significant difference in the time they take to make a selection. In their study of videotex choice pages, Muter and Mayson (1986) reported that whilst icon-like graphics had no effect on the users' response time, their error rate in the graphics condition was half that measured in the text only condition.

In his study of the memorability of icons in an information retrieval task, Lansdale ( 1988) reports no exceptional levels of recall. He suggests, however, that icons may be useful in enhancing and supporting the search process by rapidly limiting the number of documents through which a user is asked to search. Lansdale, Simpson & Stroud (1990) compared the use of words and icons as external memory aids in an information retrieval task. Their results indicated strongly that recall was higher when subjects made their own selection of enriching attributes as opposed to having them selected for them. When comparing words and icons, they found no evidence that the modalities of the enrichers were a significant factor in recall. Recall performance seems

CHAPTER 2: A BRIEF REVIEW OF HCI AND GRAPHICAL PRESENTATION 24