HCI is a multidisciplinary subject that draws knowledge from both the technological sciences as well as the human science. Like many other technology related disciplines, HCI is being pushed by the rapid developments in technology, at a pace incompatible with the developments in the human sciences. The development of the HCI discipline takes place in evolutionary fashion and actively revisiting the human sciences to acquire knowledge to apply in HCI is needed (and often carried out) to restore the balance.
This thesis investigates the use of the sense of touch in HCI in the context of multimodal interfaces, and it looks at how these findings gain relevance in a multitasking approach. Humans have many strategies to perform multiple tasks at the same time, by time slicing or capacity sharing, and many investigations and empirical findings in behavioural sciences have led to theories described in this thesis. An experiment has been carried out that investigates the haptic channel in a multitasking environment. Using a dual task (visual and tactile stimuli with manual responses), the experiment looked at whether a central processing limitation (bottleneck), as found in many other experiments using other modalities described in the literature, occurs when the sense of touch is involved.
The thesis describes human cognitive processing with regards to multitasking, and it describes the organisation of the human sense of touch (tactual perception). This is the knowledge from human sciences that can be applied, in order to suggest new forms of interaction in HCI. To introduce the terms used properly, a framework of HCI is laid out with an emphasis on physical interaction.
Although the outcome of the experiment shows that there is a central processing bottleneck even when one of the tasks uses the haptic modality, it is still expected that interfaces that facilitate multitasking can be more effective. The chosen test set up and software proved to be reliable and versitile for carrying out psychometric experiments. Suggestions for further studies are made.
With the current state of the art in transducer technology and digital processing capacity, a new marriage of knowledge from the human sciences and the technological sciences is becoming possible. New interaction paradigms can employ multiple modalities and facilitate multitasking which could transform the way humans interact with the computer.

A.J.Bongers, September 1999