Awareness and working memory in strategy adaptivity.

To further the understanding of the mechanisms of strategy choice, in three experiments, we investigate the role of explicit awareness and working memory in strategy adaptivity. Experiment 1 provided correlational evidence that individual differences in strategy adaptivity to changing base rates are related to individual differences in awareness of those changes but appear not to be related to individual differences in working memory capacity. Experiment 2 replicated the role of awareness, and the results suggest that awareness at the time of the base-rate change, rather than afterwards, is related to increased strategy adaptivity. Experiment 3 measured working memory capacity using a different procedure and manipulated working memory load with a dual-task procedure; again, no apparent role of working memory capacity in strategy adaptivity was found. This juxtaposition of findings presents a challenge for existing models of strategy choice.

Another source of individual differences: strategy adaptivity to changing rates of success.

This article explores an alternative approach to the study of individual differences of cognitive function-- that people may have the same strategies but differential ability to adaptively select among them in response to success and failure feedback from the environment. Three studies involving the complex and dynamic Kanfer-Ackerman Air Traffic Control Task (P. L. Ackerman & R. Kanfer, 1994) demonstrate (a) that individuals do differ systematically along this strategy adaptivity dimension, (b) that those differences have important consequences for overall task performance, and (c) that the differences are primarily associated with reasoning ability and working-memory capacity.

Aortic aneurysm size and graft behavior after endovascular stent-grafting: clinical experiences and observations over 3 years.

PURPOSE: To assess the long-term safety and efficacy of aortic endografts in terms of clinical outcome, continuing aneurysm exclusion, and changes of aneurysm size and graft configuration. METHODS: Between August 1994 and July 1997, 190 patients (176 men; mean age 68.7 years, range 40-87) with aortic and aortoiliac aneurysms were treated with endovascular stent-grafts (Stentor, Vanguard, and EGS) in a tertiary care municipal hospital setting. Follow-up involved clinic visits every 3 to 6 months with contrast-enhanced computed tomography (CT), color duplex, and plain abdominal radiographs at regular intervals; angiography was used selectively. All data were collected prospectively and entered into a computerized database. RESULTS: Implantation was possible in 188 (98.9%) patients. Early conversion to open surgical repair was required in 14 (7.4%) patients. Primary endoleaks were detected in 32 (16.8%) patients. Perioperative mortality was 0.53% (1/190). During follow-up, 17 (8.9%) additional patients were converted to open repair over a mean 20.9 months. Thirty-seven secondary procedures to treat endoleaks and pelvic outflow occlusions were performed in 30 (15.8%) patients. Changes in stent configuration suggestive of endograft disintegration were observed in 31 (29.8%) of 104 abdominal radiographs. Intraluminal layering of thrombus was seen on contrast-enhanced CT images in 20 patients. A significant trend (chi(2)4 = 12.34, p < 0.025) toward aneurysm enlargement was seen in patients with persistent endoleaks at a mean 18-month follow-up. CONCLUSIONS: Although endoleaks after aortic stent-graft placement tend to cause ongoing aneurysm growth, we have also observed aneurysm shrinkage despite ongoing endoleak. The presence or absence of an endoleak in itself may be a poor predictor of successful stent-graft therapy. Lifelong surveillance is needed to assure successful aneurysm exclusion and stability or shrinkage of the aneurysm sac. Technical improvements in stent materials and design are necessary to guarantee long-term stability and safety of the device.

A mechanistic account of the mirror effect for word frequency: a computational model of remember-know judgments in a continuous recognition paradigm.

A theoretical account of the mirror effect for word frequency and of dissociations in the pattern of responding Remember vs. Know (R vs. K) for low- and high-frequency words was tested both empirically and computationally by comparing predicted with observed data theory in 3 experiments. The SAC (Source of Activation Confusion) theory of memory makes the novel prediction of more K responses for high- than for low-frequency words, for both old and new items. Two experiments used a continuous presentation and judgment paradigm that presented words up to 10 times. The computer simulation closely modeled the pattern of results, fitting new Know and Remember patterns of responding at each level of experimental presentation and for both levels of word frequency for each participant. Experiment 3 required list discrimination after each R response (Group 1) or after an R or K response (Group 2). List accuracy was better following R responses. All experiments were modeled using the same parameter values.

The importance of frameworks for directing empirical questions: reply to Goodie and Fantino (2000).

A. S. Goodie and E. Fantino (2000) make two main criticisms of the predictions of M. C. Lovett and C. D. Schunn's (1999) RCCL model. (RCCL is pronounced "ReCyCLe"; it stands for Represent the task, Construct a set of action strategies, Choose from among those strategies according to success rate, Learn new success rates.) In both cases, the authors believe the criticisms reflect a failure to appreciate the difference between broad frameworks and specific mathematical/computational models. In this article, the value of a broad framework, such as RCCL, in directing new empirical analyses and guiding theoretical development is shown. In particular, RCCL expands on existing work to reveal how variability and change in mental representations influence base-rate sensitivity. The authors also address several other issues raised by A. S. Goodie and E. Fantino (2000) and show that qualitative shifts in individuals' choice behavior are present in their original data--a key prediction of RCCL that does not appear in previous accounts.

Epidural versus general anesthesia: does anesthetic management influence early infrainguinal graft thrombosis?

A few contemporary reports have suggested that the use of epidural anesthesia may favorably influence early graft patency in patients undergoing infrainguinal revascularization. In order to test this hypothesis, we have retrospectively reviewed our experience with 303 primary femoropopliteal-tibial bypass procedures in 294 patients from January 1989 through June 1994. A total of 145 of these operations were done under epidural anesthesia (EA) and 158 under general anesthesia (GA); the demographic profiles for the patients in both of these groups were nearly identical. Thirteen patients (4.2%) died during the perioperative period (EA 3.4%, GA 5.0%; p = 0.48). Early graft thrombosis occurred in 35 patients (12%) during the same hospital admission (EA 14%, GA 9.4%; p = 0.28). There were no significant differences in the graft thrombosis rates for EA and GA with respect to surgical indications (claudication versus limb salvage), graft materials (vein versus synthetic), or the extent of revascularization (popliteal versus crural). Most graft failures appeared to be related to such conventional factors as disadvantaged outflow vessels and/or specific technical complications. Therefore, we conclude that the choice between EA and GA should continue to be made selectively on the basis of traditional anesthetic considerations.

Priming, analogy, and awareness in complex reasoning.

The mechanisms by which a concept used in solving one complex task can influence performance on another complex task were investigated. We tested the hypothesis that even when subjects do not spontaneously make an analogy between two domains, knowledge of one domain can still spontaneously influence reasoning about the other domain via the mechanism of priming. Four groups of subjects (two experimental and two control) were given a simulated biochemistry problem on Day 1 and a simulated molecular genetics problem on Day 2. For the two experimental groups, the solution to the biochemistry problem involved inhibition. For the two control groups, the solution did not involve inhibition. On Day 2, all subjects received the same version of the molecular genetics problem in which the solution involved the concept of inhibition. Subjects in the experimental conditions were more likely to attain the correct answer, to propose inhibition, and to propose inhibition early in the problem-solving session than were subjects in the control conditions. However, subjects in the experimental conditions made no reference to the biochemistry problem either in their verbal protocols or in a post-task questionnaire. The results are interpreted as demonstrating that an implicit process--priming--can make old knowledge available for current problem solving.

Small bowel necrosis associated with postoperative jejunal tube feeding.

BACKGROUND: Postoperative enteral nutrition using jejunal tube feeding is widely practiced and usually well tolerated. Functional intestinal complaints occur frequently but generally respond to alteration of the infusion rate or tube feeding formula. Occasionally, however, nonspecific signs of intestinal disturbance progress to a syndrome of abdominal distention, hypotension, and hypovolemic shock resulting in extensive small bowel necrosis. STUDY DESIGN: During a six-year period, four patients have been identified retrospectively who had this complication among 1,359 patients receiving jejunal tube feeding. Their clinical course was evaluated critically and compared with 11 cases described in the literature. RESULTS: Small bowel necrosis is a rare but highly morbid complication associated with postoperative jejunal tube feeding. Of 14 patients who had small bowel necrosis develop, 12 succumbed to this complication. The causative mechanism remains unclear, but is most likely the result of several factors. CONCLUSIONS: Tube feeding should be discontinued immediately and total parenteral nutrition should be considered in patients who have abdominal pain, abdominal distention, increased nasogastric drainage, and signs of intestinal ileus.