A series of nine experiments studied the disrupting effect of a secondary task on retrieval from long-term memory. The first five experiments studied the influence of concurrent card sorting or digit span on free recall or paired-associate learning of word lists. When performance was measured in terms of recall probability, the concurrent tasks produced a clear impairment of learning but a much smaller and less consistent impairment of retrieval. This result contrasts with earlier studies by other investigators who used performance on the secondary task as their measure. These tended to show greater disruption at retrieval. Such studies typically use latency measures, and Experiment 6 explored this by using a recognition paradigm in which both accuracy and latency could be measured simultaneously. Concurrent digit load had no significant effect on recognition probability but did produce a clear increase in response latency.Experiment 7 explored the latency effect further, using a semantic memory paradigm. Subjects were required to verify sentences while retaining sequences ranging from zero to nine random digits. Decision latency increased monotonically with digit load, whereas accuracy did not decline significantly until the load exceeded six digits. Experiment 8 required subjects to make semantic category judgments while retaining sequences of six digits. Response latency was increased by concurrent digit load, but the magnitude of this effect was substantially the same for easy and difficult decisions. Concurrent load had no statistically reliable effect on errors. Finally, Experiment 9 examined the effect of concurrent digit load on the rate of generating items from semantic categories. There was a clear and consistent effect.Conclusions are as follows: (a) A demanding concurrent task does not substantially reduce the probability of retrieving an item from either episodic or semantic memory. This suggests the possibility that the process of memory search may be largely automatic, (b) In contrast, concurrent load during learning has a substantial effect on recall performance. This is interpreted in terms of the total time hypothesis; a task that distracts attention from learning will reduce the amount learned, (c) A concurrent task during retrieval does have a clear effect on latency. It is suggested that this reflects response competition at output, (d) The contrast between the pattern shown by errors and that shown by latencies suggests a general methodological conclusion: Attempts to estimate the attentional demands of any task should be interpreted with considerable caution when based on a single measure, be it performance errors, performance latency, or response to a probe reaction time signal. General conclusions demand converging operations, not single paradigms.518

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In the last few years, teenagers have been on the forefront of adopting short message service (SMS), a mobile phone-based text messaging system, and instant messaging (IM), a computer-based text chat system. However, while teenage adoption of SMS had led to a series of studies examining the reasons for its popularity, IM use in the teenage population remains understudied. This omission becomes significant given the increasing interest in domestic computing among human-computer interaction (HCI) and computer-supported cooperative work (CSCW) researchers. Further, because of the dearth of empirical work on teenage use of IM, we find that IM and SMS are sometimes incorrectly assumed to share the same features of use. To address these concerns, we revisit our own studies of SMS and IM use and reexamine them in tandem with other published studies on teenage chat. We consider similarities and differences in styles of SMS and IM use and how chat technologies enable the pursuit of teenage independence. We examine how differences are born out of technological differences and financial cost structures. We discuss how SMS and IM are used in concert to provide increased awareness and to coordinate inter-household communications, and how privacy is regulated within the individual household as a means of maintaining these communications.