Human-computer interaction (= HCI) is a discipline concerned with the design, evaluation and implementation of interactive computing systems for human use and includes the study of the major phenomena surrounding this theme. Human-computer interaction pertains to the joint performance of tasks by humans and machines; the structure of communication between humans and machines; human capabilities to use machines (including the learnability of interfaces); algorithms and programming of the interface itself; engineering concerns that arise in designing and building interfaces; the process of specification, design, and implementation of interfaces; and design trade-offs. Human-computer interaction thus has science, engineering and design aspects. Because human-computer interaction studies a human and a machine in communication, it draws on underpinning knowledge both from the side of the machine and of the human. On the machine side, techniques in computer graphics, operating systems, programming languages and development environments are relevant. On the human side, communication theory, graphic and industrial design, linguistics, social sciences, cognitive psychology and human performance are relevant. And, of course, human aspects such as emotions and feelings become relevant as well.

2. Emotional and Metaphoric Interfaces
Artists and designers have always been skilled in applying metaphors when designing systems, objects or works of art. Metaphors can evoke certain sensations or emotions in the spectators, feelings that can often not be described with words alone. The power of metaphors is in the fact that they tap into cultural, historic and emotional knowledge that we humans have built up in the course of our lives. Touching for example an object that looks like a cat (even if it is in fabric or plastic) will evoke a nice, warm and cozy feeling, or emotions of personal attachment and care might be triggered. Through our daily interactions with objects or even beings that we touch, manipulate, look at, perceive or interact with, we have developed a rich intuitive knowledge of how these things work and what kind of emotions and sensations are being attached to them. Using this immanent, intuitive and emotional knowledge, in 1991 we became interested in exploring the power of emotional and metaphoric interfaces. The first emotional and metaphoric interface we designed in 1992 was a living plant. In this system real plants are the interfaces, and users touch these plants to create artificial plants on a computer screen. When users touch a real plant and see the effect of this touch translated into a graphical form on a screen, they are suddenly reminded of that immanent intuition they already had about plants. It is for this reason that we must increase our awareness of the ways that the interface carries these beliefs as hidden content.

3. Natural and Intuitive Interfaces
Closely linked to designing emotional and metaphoric interfaces is the concept of natural and intuitive interfaces. By this we mean interfaces that feel very easy and natural in their use, without that the user has to go through a lengthy learning process when he or she wants to interact with this system. Natural interfaces are, for example, gesture-, speech-, touch-, vision- and smell-based interactions or basically actions and sensations that refer to our daily life experiences. Using, for example, living plants as an interface not only provides a new, emotionally charged and unusual connection between computers and living beings but it also poses the questions of what a plant is, how we perceive it and how we interact with it when we touch it or approach it. Natural interfaces also circumvent the annoyance of wearing unpleasant devices before entering virtual space (= unencumbered interaction). As the user moves about in the interaction space, he or she starts to learn how to use his or her body for triggering and playing sounds and music.

4. Non-linear, Multilayered and Multimodal Interaction
We also believe that interaction in interactive systems should not be linear but instead feel like a journey. The more one engages in interaction, the more one should learn about it and the more one should be able to explore it. We call this non-linear interaction as it is not pre-scripted and predictable but instead develops as users interact with the system. The interaction path in our systems should also be multilayered, meaning that the interaction feedback should be simpler at the beginning and become increasingly complex when users further interact with the system, continuously discovering new levels of interaction experiences. And finally, a last cornerstone in designing our systems is the design of multimodal interaction experiences that combine several senses, such as vision, sound, touch and smell. Over the past years multimodal interaction has in fact become a mainstream research trend in HCI, and it defines multimodality as the combination of multiple input modalities to provide the user with a richer set of interactions compared to traditional unimodal interfaces. The combination of input modalities can be divided into six basic types: complementarity, redundancy, equivalence, specialization, concurrency, and transfer.

5. Interface Cultures: Creating Innovative Interaction Experiences
In 2004 the University of Art and Industrial Design in Linz established a new master study program called “Interface Cultures”. The title of this program was coined by the university based on the book “Interface Culture” by Steven Johnson. He predicted that new types of interfaces will alter the style of our conversations, prose and thoughts in the future and he rightfully predicted that interface designs would be strongly linked to artistic innovation as they reach out into applications in our daily lives. By designing interactive systems that bridge social, entertaining and artistic elements thr prototypes and installations of artists and designers have often reached out in the wider field of media products and entertainment applications. Being situated at an art university, we foremost concentrated on the development of artistic prototypes and projects that bridge the gap between art, design, entertainment and product development. One of our main goals is to create an environment where artistic exploration can be combined with technical and scientific research.