On interactive surfaces such as touch screens, tabletops or interactive walls, the addition of active tactile feedback has been shown to greatly improve user performance and subjective evaluation of the interaction. However, common electromechanical solutions to enable tactile stimuli on flat touch displays entail the use of costly, complex and cumbersome actuator technology. This especially holds true for solutions which try to address the full complexity of our sense of touch, i.e. our ability to experience warmth, coolness, pressure, stickiness or smoothness. In this paper, we propose the use of liquid as a medium for versatile tactile feedback.

Tangible user interfaces utilize our ability to interact with everyday objects in order to manipulate virtual data. Designers and engineers usually follow the rule "form follows function", they support an existing interaction with a purpose-built interface. Still, we do not fully exploit the expressiveness of forms, materials and shapes of the nondigital objects we interact with. Therefore, we propose to invert the design process: we empower materiality to inspire the implementation of tangible interactions. Glass objects were chosen as an example of culturally and structurally rich objects: in a three-month workshop, these glass objects were transformed into interactive artefacts. In the paper, we present three resulting contributions: First, we describe our inverted design process as a tool for the stimulation of multidisciplinary development. Second, we derive a list of material-induced interactions. Third, we suggest form-related interactions as a means of designing future tangible interfaces.

In our everyday life, the perception of thermal cues plays a crucial role for the identification and discrimination of materials. When touching an object, the change of temperature in the skin of our fingertips is characteristic for the touched material and can help to discriminate objects with the same texture or hardness. However, this useful perceptual channel is disregarded for interactive elements on standard touchscreens. In this paper, we present a study in which we compared the rate of object discrimination for stand-alone thermal stimuli as well as supplemental thermal stimuli characterizing virtual materials on a touchscreen. Our results show that five materials could be discriminated at a stable rate using either stand-alone or supplemental thermal stimuli. They suggest that thermal cues can enable material discrimination on touch surfaces, which gives way for expanded use of thermal stimuli on interactive surfaces.

Multi-touch screens and surfaces for manipulating digital content play a crucial role in mobile and ubiquitous computing. Augmenting these interactive surfaces with tactile feedback has been found to increase interaction speed, reduce operating errors and minimize visual and cognitive load. Communicating detailed tactile characteristics of virtual elements, however, requires complex electromechanical or electrostatic actuator setups. This increase in complexity makes tactile interfaces intricate, costly or poorly scalable. In order to provide sophisticated tactile sensations with simple actuator technology, we exploit a haptic psychophysical phenomenon called Phantom Sensation. We present a comparison of three standard tactile actuator technologies to see which one can recreate the Phantom Sensation with maximum effect. Our results show the way to a simple and scalable implementation of illusion-based tactile feedback for interactive surfaces. We explore the notion of the Phantom Sensation and its possible applications within a ubicomp scenario.

Haptic feedback on touch-sensitive displays provides significant benefits in terms of reducing error rates, increasing interaction speed and minimizing visual distraction. This particularly holds true for multitasking situations such as the interaction with mobile devices or touch-based in-vehicle systems. In this paper, we explore how the interaction with tactile touchscreens can be modeled and enriched using a 2+1 state transition model. The model expands an approach presented by Buxton. We present HapTouch -- a force-sensitive touchscreen device with haptic feedback that allows the user to explore and manipulate interactive elements using the sense of touch. We describe the results of a preliminary quantitative study to investigate the effects of tactile feedback on the driver's visual attention, driving performance and operating error rate. In particular, we focus on how active tactile feedback allows the accurate interaction with small on-screen elements during driving. Our results show significantly reduced error rates and input time when haptic feedback is given.

In this paper we investigate tangible interaction on interactive tabletops. These afford the support and integration of physical artefacts for the manipulation of digital media. To inform the design of interfaces for interactive surfaces we think it is necessary to deeply understand the benefits of employing such physical handles, i.e., the benefits of employing a third spatial dimension at the point of interaction.To this end we conducted an experimental study by designing and comparing two versions of an interactive tool on a tabletop display, one with a physical 3D handle, and one purely graphical (but direct touch enabled). Whilst hypothesizing that the 3D version would provide a number of benefits, our observations revealed that users developed diverse interaction approaches and attitudes about hybrid and direct touch interaction.

Collaborative creativity is traditionally supported by formal techniques, such as brainstorming. These techniques improve the idea-generation process by creating group synergies, but also suffer from a number of negative effects. Current electronic tools to support collaborative creativity overcome some of these problems, but introduce new ones, by either losing the benefits of face-to-face communication or the immediacy of simultaneous contribution. Using an interactive environment as a test bed, we are investigating how collaborative creativity can be supported electronically while maintaining face-to-face communication. What are the design-factors influencing such a system? We have designed a brainstorming application that uses an interactive table and a large wall display, and compared the results of using it to traditional paper-based brainstorming in a user study with 30 participants. From the considerations that went into the design and the observations during the study we derive a number of design guidelines for collaborative systems in interactive environments.