User-interruption in human-computer interaction (HCI) is an increasingly important problem. Many of the useful advances in intelligent and multitasking computer systems have the significant side effect of greatly increasing user-interruption. This previously innocuous HCI problem has become critical to the successful function of many kinds of modern computer systems. Unfortunately, no HCI design guidelines exist for solving this problem. In fact, theoretical tools do not yet exist for investigating the HCI problem of user-interruption in a comprehensive and generalizable way. This report asserts that a single unifying definition of user-interruption and the accompanying practical taxonomy would be useful theoretical tools for driving effective investigation of this crucial HCI problem. These theoretical tools are constructed here. A comprehensive analysis is conducted through the existing literature. Theoretical constructs from several relevant but diverse fields are identified and discussed. A unifying definition of user-interruption is synthesized. This new definition is supported with an array of postulates, assertions, and a taxonomy of human interruption to facilitate its practical application.

We describe research on the effects of instant messaging (IM) on ongoing computing tasks. We present a study that builds on earlier work exploring the influence of sending notifications at different times and the kinds of tasks that are particularly susceptible to interruption. This work investigates alternative hypotheses about the nature of disruption for a list evaluation task, an activity we had identified as being particularly costly to interrupt. Our findings replicate earlier work, showing the generally harmful effects of IM, and further show that notifications are more disruptive for fast, stimulus-driven search tasks than for slower, more effortful semantic-based search tasks. 1. Introduction Instant messaging systems, including America Online's Instant Messenger, Microsoft Network's Messenger, and Yahoo!'s Messenger service claim over 70 million users and research shows that the number of users of these services is growing rapidly (MediaMetrix, December, 1999). The benefits...

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To decide how to respond to an utterance, a speaker must interpret what others have said and why they have said it. Speakers rely on their expectations to decide whether they have understood each other. Misunderstandings occur when speakers differ in their beliefs about what has been said or why. If a listener hears something that seems inconsistent, he may reinterpret an earlier utterance and respond to it anew. Otherwise, he assumes that the conversation is proceeding smoothly. Recognizing an inconsistency as a misunderstanding and generating a new reply together accomplish what is known as a fourth-position repair. To model the repair of misunderstandings, this thesis combines both intentional and social accounts of discourse, unifying theories of speech act production, interpretation, and repair. In intentional accounts, speakers use their beliefs, goals, and expectations to decide what to say; when they interpret an utterance, speakers identify goals that might account for it. In...

which is/are unaval able. 12-1-84 CENTER FOR THE STUDY OF READING Technical Report No. 43

Humans have a massive capacity to store detailed information in visual long-term memory. The present studies explored the fidelity of these visual long-term memory representations and examined how conceptual and perceptual features of object categories support this capacity. Observers viewed 2,800 object images with a different number of exemplars presented from each category. At test, observers indicated which of 2 exemplars they had previously studied. Memory performance was high and remained quite high (82 % accuracy) with 16 exemplars from a category in memory, demonstrating a large memory capacity for object exemplars. However, memory performance decreased as more exemplars were held in memory, implying systematic categorical interference. Object categories with conceptually distinctive exemplars showed less interference in memory as the number of exemplars increased. Interference in memory was not predicted by the perceptual distinctiveness of exemplars from an object category, though these perceptual measures predicted visual search rates for an object target among exemplars. These data provide evidence that observers ’ capacity to remember visual information in long-term memory depends more on conceptual structure than perceptual distinctiveness.

Funded by the

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of Education under Contract No. MS-NIE-C-400-76-0116.