Abstract: While there are well established guidelines for interaction via mouse and keyboard, new forms of interaction being devised for small handheld devices have yet to be standardised. There is a case for re-visiting basic principles for user interface design such as how to signal mode. Two ways of signalling case mode when editing text into a small handheld device such as a mobile phone are considered in this paper. One is through the system prompt, e.g. ‘Entry:’, the other is through the case of the last letter displayed in response to a button push. Two unsupervised web-based experiments are described which show that users are sensitive to both these signals for case mode. The first experiment manipulated the prompt in a text entry task using a web simulation of a novel mobile device. The results showed that users’ expectations were influenced by the case of the letters in the prompt. Users took many more trials to learn to expect a case inconsistent with the model provided by the prompt. The second experiment manipulated both the case of the letters in the prompt and the case of the last letter displayed. The results replicated the findings above and demonstrated a strong effect of the case of the last letter displayed. Guidelines for signalling case mode and a notation (Interaction Units) are suggested that might be used to reason about low level interaction design with handheld devices. |
