A single-season prospective study of respiratory viral infections in lung transplant recipients.

The frequency and complications of respiratory viral infections (RVI) were studied in 50 ambulatory lung transplant patients during a single winter season, using viral antigens, viral cultures and PCR of nasal washes or bronchoalveolar lavages. Patients' survival, episodes of acute rejection and occurrence of bronchiolitis obliterans (BO) or BO syndrome (BOS) were monitored for 1 yr after the study. Overall, 32 (64%) patients had 49 symptomatic episodes. Documented infections included eight due to respiratory syncytial virus (RSV), one due to parainfluenza virus (PIV) and 10 due to influenza (FLU). Four of the FLU infections were serological rises without symptoms. Overall, 17 (34%) patients had documented viral infection; four patients had lower respiratory involvement and two (one RSV, one PIV) were hospitalised for aerosolised ribavirin treatment. After 1 yr there were three (6%) deaths unrelated to RVI. BO or BOS had occurred in one (6%) out of 17 patients with and three (12%) out of 33 without RVI. Respiratory viruses infected one-third of ambulatory lung transplant recipients in a single season. In conclusion, respiratory viral infection was not associated with subsequent graft dysfunction. Larger prospective studies are required to better define the acute and long-term morbidity of these infections.

Risks of drawing inferences about cognitive processes from model fits to individual versus average performance.

With the goal of drawing inferences about underlying processes from fits of theoretical models to cognitive data, we examined the tradeoff of risks of depending on model fits to individual performance versus risks of depending on fits to averaged data with respect to estimation of values of a model's parameters. Comparisons based on several models applied to experiments on recognition and categorization and to artificial, computer-generated data showed that results of using the two types of model fitting are strongly determined by two factors: model complexity and number of subjects. Reasonably accurate information about true parameter values was found only for model fits to individual performance and then only for some of the parameters of a complex model. Suggested guidelines are given for circumventing a variety of obstacles to successful recovery of useful estimates of a model's parameters from applications to cognitive data.

Predicting true patterns of cognitive performance from noisy data.

Starting from the premise that the purpose of cognitive modeling is to gain information about the cognitive processes of individuals, we develop a general theoretical framework for assessment of models on the basis of tests of the models' ability to yield information about the true performance patterns of individual subjects and the processes underlying them. To address the central problem that observed performance is a composite of true performance and error, we present formal derivations concerning inference from noisy data to true performance. Analyses of model fits to simulated data illustrate the usefulness of our approach for coping with difficult issues of model identifiability and testability.

On the processes underlying stimulus-familiarity effects in recognition of words and nonwords.

The authors investigated the recognizability of recently studied word and nonword stimuli in relation to both experimentally controlled prior frequency of occurrence and, for words, normative frequency (assessed by counts of occurrences in printed English). The interaction between these variables was small and nonsignificant across all conditions of 2 experiments. Patterns of recognition measures in relation to controlled prior frequency, but not normative frequency, appeared interpretable in terms of response biases generated by long-term priming. Application of a global memory model and analyses of correlations among item categories yielded evidence for a lexicality dimension underlying normative-frequency effects and an implication that "word-frequency effects" on recognition are better termed lexicality effects.

Traps in the route to models of memory and decision.

It is proposed that the products of investigations of learning, memory, and decision over the last half century that are most likely to endure have resulted from interactions between models and experimental research. In this article, some of the traps that must be coped with to make fruitful interactions possible are examined and illustrated with case studies from research on probability learning, category learning, and recognition memory. Topics addressed include functions of models in research; the logic of model testing; fitting models to signal plus noise; values and hazards of averaging data; and potential contributions of neural science to the development of cognitive models.

Distal short segment fixation of thoracolumbar and lumbar injuries.

Fifteen patients with thoracolumbar and lumbar spine injuries were treated between November, 1993, and April, 1996, using a posterior approach that involved short segment distal fixation at or one level below the level of injury. Medical records and radiographs were reviewed for complications, maintenance of correction, repeat surgeries and functional status. Indications for this technique included fractures and ligamentous injuries that did not require direct canal decompression and were without severe comminution. The level of injury was T12 in two patients, L1 in seven patients, L2 in two patients, L3 in three patients, and L4 in one patient. Average age at injury was 29.1 years (range 18-70). The average length of follow-up was 18 months (range 12-32). There were 11 males and four females. One patient presented with incomplete paraplegia; all others were intact to neurologic testing. Posterior instrumentation and fusion were performed in all patients with no attempt at direct decompression. Supplementary infralaminar hooks were used at the distal end in 12 of 15 patients. Mean sagittal plane correction of preoperative deformity was 7.0 degrees (range 1-24). Mean loss of correction on most recent follow-up was 4.4 degrees (range 0-11). There was one deep infection and two known cases of pseudoarthrosis. Four patients underwent hardware removal and one had loss of fixation at the superior end of the construct. No patients lost neurologic function. There were no mechanical complications at the distal end of the fixation. Three patients returned to relatively normal preinjury status, five suffered partial disability, six suffered full disability and one was lost to follow-up. From our review of this relatively small group of patients, short segment fixation distally for selected thoracolumbar and lumbar injuries appears to be a reasonable option.

Shoulder hemiarthroplasty for proximal humeral fractures.

Shoulder hemiarthroplasty is a well-accepted surgical procedure for the treatment of specific subtypes of proximal humeral fractures, including four-part fractures, three-part fractures associated with severe osteopenia, head-splitting and severe articular impression fractures. Careful patient assessment and meticulous surgical technique are essential to prevent complications. The results are satisfactory in approximately 80% of cases. The results are better in younger patients and in acute versus chronic fractures. There are a significant number of complications that are related to technical details of the procedure. Careful placement of the prosthesis and secure reattachment of the tuberosities to the shaft reduce the chance of complication following surgery. Good to excellent results in terms of range of motion and pain relief can be expected in most patients.

Models of human memory and their implications for research on aging and psychopathology.

Because nearly all human behavior depends to some degree on functioning of the memory system, progress in understanding the diverse psychopathological effects of trauma must be expected to reflect the state of research and theory on human memory. An informal survey of literature on research in psychopathology reveals increasing attention to processes of memory and cognition but an absence of citations of the models of memory that subsume research results and mediate their applications. In this article, a series of steps is taken with the aim of redressing this situation. The first is an overview of contemporary models of memory. From these a set of widely supported assumptions about basic processes and structures is abstracted to form a composite model, which is illustrated in application to several major research paradigms. Finally, consideration is given to implications of the composite model for effects of psychopathological trauma and for some aspects of the maturation and decline of memory functions throughout the life span.

Direct and indirect stimulus-frequency effects in recognition.

Subsequent recognition of stimuli perceived in a given situation was studied in relation to stimulus familiarity as determined by frequency in observers' prior experience. To distinguish direct and indirect frequency effects, on the basis of selective memory retrieval and selective attention during learning, respectively, rigorous controls were imposed on stimulus rehearsability and learning conditions. As predicted by a global memory model, both hits and false alarms on recognition tests increased as a function of prior frequency in a concordant pattern that indicates a direct effect, in contrast with the usual indirect effect of varying normative word frequency. Understanding the role of experiential stimulus frequency in recognition may further the interpretation of research in such paradigms as eyewitness testimony.

Processes of memory loss, recovery, and distortion.

The author proposes that many forms of memory distortion, including the progressive changes in recollection of a learning experience often observed over successive tests, are due to the same processes that yield veridical recollection in some circumstances and memory loss and recovery in others. In a framework for interpreting all of these aspects of memory, the author assumes that the objects and events of a learning experience are encoded in parallel in traces of their perceptual attributes, which are basic to recognition, and in traces of reactions made to the events during or following learning, which are basic to recall. Random perturbation of remembered attribute values in both types of traces over retention intervals is a pervasive cause of both loss and distortions of memory.

Interactions of stimulus attributes, base rates, and feedback in recognition.

Continuous old-new recognition was studied in relation to 3 factors that have been relatively neglected in previous research-stimulus attributes, old-new base rates, and informative feedback following responses. Under all conditions, both hits and false alarms increased over trials and all measures of recognition depended strongly on stimulus properties, notably interitem similarity. In contrast to expectations based on earlier results, both hit and false-alarm levels proved independent of old-new base rate when tests were given without feedback; with feedback added, false-alarm rates tended to approach true old-stimulus base rates with some types of stimuli, though not with words. The findings are compatible, in general, with current composite-memory models and were predicted in detail by an array-similarity model deriving from categorization theory.

Activity anorexia: An interplay between basic and applied behavior analysis.

The relationship between basic research with nonhumans and applied behavior analysis is illustrated by our work on activity anorexia. When rats are fed one meal a day and allowed to run on an activity wheel, they run excessively, stop eating, and die of starvation. Convergent evidence, from several different research areas, indicates that the behavior of these animals and humans who self-starve is functionally similar. A biobehavioral theory of activity anorexia is presented that details the cultural contingencies, behavioral processes, and physiology of anorexia. Diagnostic criteria and a three-stage treatment program for activity-based anorexia are outlined. The animal model permits basic research on anorexia that for practical and ethical reasons cannot be conducted with humans. Thus, basic research can have applied importance.

Base-rate effects in category learning: a comparison of parallel network and memory storage-retrieval models.

Exemplar-memory and adaptive network models were compared in application to category learning data, with special attention to base rate effects on learning and transfer performance. Subjects classified symptom charts of hypothetical patients into disease categories, with informative feedback on learning trials and with the feedback either given or withheld on test trials that followed each fourth of the learning series. The network model proved notably accurate and uniformly superior to the exemplar model in accounting for the detailed course of learning; both the parallel, interactive aspect of the network model and its particular learning algorithm contribute to this superiority. During learning, subjects' performance reflected both category base rates and feature (symptom) probabilities in a nearly optimal manner, a result predicted by both models, though more accurately by the network model. However, under some test conditions, the data showed substantial base-rate neglect, in agreement with Gluck and Bower (1988b).

Implementation of a total parenteral nutrition program in the skilled nursing facility: role of the nursing director.

Nursing directors of 24 skilled nursing facilities in North Carolina were questioned about implementation of total parenteral nutrition (TPN) therapy in the SNF. Issues addressed were job satisfaction, increased work load for staff nurses and directors, as well as staff development. It was concluded from the results of the study that while 81 percent of the nursing administrators enjoyed TPN therapy, only 50 percent were interested in such a program.

Application of a cognitive-distance model to learning in a simulated travel task.

A cognitive-distance model for choice, obtained by specializing a general class of models for categorization, was tested in a situation simulating the task of controlling speed of a vehicle in tasks defined by different relations between speed and probability of delay. Subjects exhibited significant learning whenever delay schedules permitted greater-than-chance performance, but on the average they did not approach optimal performance in the sense of choosing speeds so as to maximize distance attained in allowed time. Evidence was obtained that subjects encoded information about probabilities of delay and distributions of distance attained at different speeds quite accurately in memory and that suboptimal performance was due primarily to imperfect discrimination among representations of choice alternatives on a cognitive scale of expected distance.

Memory storage and retrieval processes in category learning.

The detailed course of learning is studied for categorization tasks defined by independent or contingent probability distributions over the features of category exemplars. College-age subjects viewed sequences of bar charts that simulated symptom patterns and responded to each chart with a recognition and a categorization judgment. Fuzzy, probabilistically defined categories were learned relatively rapidly when individual features were correlated with category assignment, more slowly when only patterns carried category information. Limits of performance were suboptimal, evidently because of capacity limitations on judgmental processes as well as limitations on memory. Categorization proved systematically related to feature and exemplar probabilities, under different circumstances, and to similarity among exemplars of categories. Unique retrieval cues for exemplar patterns facilitated recognition but entered into categorization only at retention intervals within the range of short-term memory. The findings are interpreted within the framework of a general array model that yields both exemplar-similarity and feature-frequency models as special cases and provides quantitative accounts of the course of learning in each of the categorization tasks studied.

Levels of association theory.

Three levels of association theory are distinguished: (a) empirical laws relating operationally definable units; (b) theoretical concepts of association, supported by converging lines of evidence; and (c) theories assimilating concepts of association into more elaborate structures. These levels correspond roughly to stages in the evolution of association theory from the mid-19th century to the present. Ebbinghaus's major contribution as a theorist was to accomplish the transition from the first level to the second. The analysis of serial learning in terms of his conception of multiple types of associations may prove to have greater generality than has yet been realized. However, to account for many phenomena of practical and theoretical interest, this model requires augmentation by a control concept that provides a basis for organization beyond serial linkages of units.