Identifying optimum performance trade-offs using a cognitively bounded rational analysis model of discretionary task interleaving.

We report the results of a dual-task study in which participants performed a tracking and typing task under various experimental conditions. An objective payoff function was used to provide explicit feedback on how participants should trade off performance between the tasks. Results show that participants' dual-task interleaving strategy was sensitive to changes in the difficulty of the tracking task and resulted in differences in overall task performance. To test the hypothesis that people select strategies that maximize payoff, a Cognitively Bounded Rational Analysis model was developed. This analysis evaluated a variety of dual-task interleaving strategies to identify the optimal strategy for maximizing payoff in each condition. The model predicts that the region of optimum performance is different between experimental conditions. The correspondence between human data and the prediction of the optimal strategy is found to be remarkably high across a number of performance measures. This suggests that participants were honing their behavior to maximize payoff. Limitations are discussed.

Blending speech output and visual text in the multimodal interface.

OBJECTIVE: Simultaneous reading and listening with a redundant display of visual text with speech output was investigated to determine how variations in verbal working memory capacity and content complexity affected comprehension. BACKGROUND: Previous work has found some evidence of a benefit for displays that blend speech and visual text; content complexity and verbal working memory capacity are likely to significantly determine this benefit. METHOD: In the experiment reported here, a multimodal display of e-mail messages was compared with speech output alone and with a purely visual display. Comprehension of the messages was examined in relation to verbal working memory capacity and the complexity of the messages. Thirty-two users participated in the study, which used a repeated measures design. RESULTS: The data show that the multimodal interface did not affect comprehension relative to a purely visual interface, even when the content was more complex, although it did improve the comprehension of complex information relative to a purely auditory interface. Lower-capacity participants were neither especially advantaged nor disadvantaged by the multimodal interface. Participants expressed a marked preference for the multimodal display of the more complex sentences. CONCLUSION: The experiment suggests that a redundant multimodal display will neither assist nor disrupt understanding when compared with a purely visual display, but it will assist understanding of complex content when compared with speech output alone. APPLICATION: Redundant displays of visual text and speech have potential application in multitask situations, in multimedia presentations, and for devices with small screens.

Configuration of anchorage holes affects cemented fixation of the acetabular component in total hip replacement: an in vitro study.

Although surgical fixation techniques are major contributing factors to the survivorship of total hip replacements, they vary considerably among orthopaedic surgeons. We investigated the effect of the following configuration of anchorage holes on the stability of acetabular component fixation: 3 x 12 mm, 3 x 6 mm, 6 x 6 mm, and 12 x 6 mm. The reconstructed acetabulae were tested to torque failure, whilst being subjected to a compressive load of 2.1 KN. Higher torque to failure values were obtained for specimens with three 12 mm anchorage holes, compared with six or more 6 mm anchorage holes and were in line with our computer simulation results. We propose that the longevity of cemented total hip replacements could be improved by drilling a few large anchorage holes.

Thirty-year results of a prospective study of Charnley total hip arthroplasty by the posterior approach.

We present the results of 228 consecutive Charnley low friction hip arthroplasties, performed in 193 patients, between July 1972 and December 1976. Unusually for this time, all hips were inserted by the posterior approach without a trochanteric osteotomy. All patients were enrolled into a prospective study; both preoperative and postoperative clinical and radiologic findings were recorded. This series was independently reviewed in 1985 (Atrah SGK. Long-term follow-up of Charnley total hip replacement through posterior approach. MSc thesis, University of London, 1987) and again in 2002. The preoperative and perioperative findings were similar to contemporary series. Implant positioning was also assessed. Because of our stable population, only 2 patients were lost to follow-up. Our survivorship results show a 10-year survival of 93% deteriorating to a 30-year survival of 73% (+/-6.1). The survivors were assessed radiologically and scored clinically using the Merle d'Aubigné-Postel score with a mean value of 12. The reason for revision was also recorded. These results are comparable to other studies and justify the use of the posterior approach.

Towards a conception for an engineering discipline of human factors.

This paper concerns one possible response of human factors to the need for better user interactions of computer-based systems. The paper is in two parts. Part I examines the potential for human factors to formulate engineering principles. A basic prerequisite for realizing that potential is a conception of the general design problem addressed by human factors. The problem is expressed informally as: 'to design human interactions with computers for effective working'. A conception would provide the set of related concepts which both expressed the general design problem more formally, and which might be embodied in engineering principles. Part II of the paper proposes such a conception and illustrates its concepts. It is offered as an initial and speculative step towards a conception for an engineering discipline of Human Factors.