Attention-aware systems (AAS) are systems capable of adapting to, and supporting, human attentional processes especially in situations of multi-tasking, frequent interactions with other users, and highly dynamic environments. In this paper we discuss the rationale for AASs and their role within current HCI research, we review current research and applications of AASs, and we highlight the issues that will need to be addressed in the future for their design. KEYWORDS Attention aware systems,

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... tive systems, notification systems, attentive user interfaces, transparent systems, visual attention, tracking. INTRODUCTION Much information science research has focussed on the design of systems enabling users to access, communicate, and use information quickly and efficiently. However the users' ability to exploit this information is seriously limited by finite human cognitive resources. In cognitive psychology the role of attentional processes in allocating cognitive resources has been demonstrated to be crucial. Attention is often defined as the set of processes guiding the selection of the environmental stimuli to be attended. Access to information therefore is not only regulated by its availability but also by the users' choice to attend the information -this choice being governed by attentional processes. Recently several researchers and practitioners in Human Computer Interaction (HCI) have concentrated on the design of systems capable of adapting to, and supporting, human attentional processes. These systems, that often rely on very different technologies and theories, and that are designed for a range of applications, are called attention-aware systems (AAS). In the literature these systems have also been referred to as Attentive User Interfaces (Vertegaal, 2003). However, we prefer using the former name as it stresses the fact that issues related to attention are relevant to the design of the system as a whole rather than limited to the interface. In this section we analyze the rationale for AASs and we discuss their role in HCI research. Why attention-aware systems Information overload is one of the most often mentioned problems of working, studying, playing, and generally living in a networked society. One of the consequences of information overload is the fast shift of attention from one subject to another or one activity to another. In certain situations the ability to quickly access several information sources, to switch activities, or to change context is advantageous. In other situations it would be more fruitful to create and maintain a focus whilst offering the possibility to switch attention to other contents or activities only as a background low-noise open choice. System awareness about the cost/benefits of attentional shifts with respect to the user's goals is essential in environments where (1) attentional switches are very often solicited, or (2) where the users' lack of experience with the environment makes it harder for them to select the appropriate attentional focus, or (3) where an inappropriate selection of attentional focus may cause serious damage to the system, its users, or third parties. Systems relying highly on multi-user interaction, such as virtual communities and certain systems supporting cooperative work, are examples of environments where attentional switches are often solicited. Online educational systems are example of environments where the lack of knowledge and experience of users with the subject at hand makes it harder for them to select the appropriate attentional focus and may easily cause a loss of focus. Life critical systems are examples of environments where an inappropriate selection of attentional focus may cause serious damage. The need for AASs is quite widespread especially if one considers that assessing, supporting, and maintaining users' attention may be desirable in other environments such as entertainment and e-commerce. Attention-aware systems in HCI research A large portion of research on human attention in digital environments is based on the findings of cognitive psychology. For example Raskin (2000) analyses how single locus of attention, and habit formation have important consequences on human ability to interact with computers. He proposes that habit creation is a mechanism that can be used to shift the focus of users from the interface to the specific target task. The study above follows the classic "direct manipulation" school (Shneiderman, 1992; Shneiderman, 1997) which aims at supporting the attentional choices of the user by making the device "transparent" so that the user can focus on the task rather than on the interface. The wide range of systems designed with this aim is often referred to as transparent systems, a term also employed in ubiquitous computing (Abowd, 1999; Weiser, 1991). Another area of research focuses instead on designing interfaces and systems capable of guiding the users in the choice of attentional focus. The system is seen as proactive, visible, and capable of supporting the users in their choices. This type of systems are often designed as artificial agents (Bradshaw, 1997; Huhns & Singh, 1997) acting as proactive helpers for the user (Maes, 1994; Negroponte, 1997) and they are frequently referred to as proactive/adaptive systems. TERMS AND THEIR DEFINITION Locus of attention Amongst all sensory input, the locus of attention is the input to which one allocates mental resources. Input that falls outside the locus of attention may go absolutely unnoticed. An example of locus of attention is a specific section of a computer screen. Direct manipulation user interfaces Interfaces that aim at making objects and actions in the systems visible by [graphical] representation. They were originally proposed as an alternative to command line interfaces. The system's objects and actions are often represented by metaphorical icons on screen (e.g. dragging a file to the recycle bin for deleting a file). Designers of direct manipulation user interface strive to provide incremental reversible operations and visible effects. Endogenous attentional processes Refers to the set of processes of voluntary (conscious) control of attention. These processes are also referred to as top-down, or goal-driven. An example of endogenous attentional mechanism is the attention you are paying at this page as you are reading. Endogenous attention is voluntary, it requires explicit effort, and it is normally meant to last. Exogenous attentional processes Refers to the set of processes by which attention is captured by some external event. These processes are also referred to as bottom-up, or stimulus-driven. An example of this mechanism would be the attention shift from your reading due to a sudden noise. Exogenous attention is triggered automatically and it normally lasts a short time before it is either shifted or becomes controlled by endogenous processes. Visual attention Visual attention is the process by which we select the visual information most relevant to our current behaviour. In general, of all the visual stimuli we receive, we only attend to a few, this determines what we "see". Visual attention controls the selection of appropriate visual stimuli both by pruning irrelevant ones and by guiding the seeking of relevant ones. Research in visual attention aims at understanding the mechanisms by which human sensory and cognitive systems regulate what we see. Gaze tracking