Biomedical subjects

A P McLean

Publications and source records attributed to A P McLean.

At least 19 recordsLinked to original sources

PubMed2001

Sensitivity to relative reinforcer rate in concurrent schedules: independence from relative and absolute reinforcer duration.

Twelve pigeons responded on two keys under concurrent variable-interval (VI) schedules. Over several series of conditions, relative and absolute magnitudes of reinforcement were varied. Within each series, relative rate of reinforcement was varied and sensitivity of behavior ratios to reinforcer-rate ratios was assessed. When responding at both alternatives was maintained by equal-sized small reinforcers, sensitivity to variation in reinforcer-rate ratios was the same as when large reinforcers were used. This result was observed when the overall rate of reinforcement was constant over conditions, and also in another series of concurrent schedules in which one schedule was kept constant at VI ached 120 s. Similarly, reinforcer magnitude did not affect the rate at which response allocation approached asymptote within a condition. When reinforcer magnitudes differred between the two responses and reinforcer-rate ratios were varied, sensitivity of behavior allocation was unaffected although response bias favored the schedule that arranged the larger reinforcers. Analysis of absolute response rates ratio sensitivity to reinforcement occurrred on the two keys showed that this invariance of response despite changes in reinforcement interaction that were observed in absolute response rates on the constant VI 120-s schedule. Response rate on the constant VI 120-s schedule was inversely related to reinforcer rate on the varied key and the strength of this relation depended on the relative magnitude of reinforcers arranged on varied key. Independence of sensitivity to reinforcer-rate ratios from relative and absolute reinforcer magnitude is consistent with the relativity and independence assumtions of the matching law.

Animals↗

PubMed2001

Variable-ratio versus variable-interval schedules: response rate, resistance to change, and preference.

Two experiments asked whether resistance to change depended on variable-ratio as opposed to variable-interval contingencies of reinforcement and the different response rates they establish. In Experiment 1, pigeons were trained on multiple random-ratio random-interval schedules with equated reinforcer rates. Baseline response rates were disrupted by intercomponent food, extinction, and prefeeding. Resistance to change relative to baseline was greater in the interval component, and the difference was correlated with the extent to which baseline response rates were higher in the ratio component. In Experiment 2, pigeons were trained on multiple variable-ratio variable-interval schedules in one half of each session and on concurrent chains in the other half in which the terminal links corresponded to the multiple-schedule components. The schedules were varied over six conditions, including two with equated reinforcer rates. In concurrent chains, preference strongly overmatched the ratio of obtained reinforcer rates. In multiple schedules, relative resistance to response-independent food during intercomponent intervals, extinction, and intercomponent food plus extinction depended on the ratio of obtained reinforcer rates but was less sensitive than was preference. When reinforcer rates were similar, both preference and relative resistance were greater for the variable-interval schedule, and the differences were correlated with the extent to which baseline response rates were higher on the variable-ratio schedule, confirming the results of Experiment 1. These results demonstrate that resistance to change and preference depend in part on response rate as well as obtained reinforcer rate, and challenge the independence of resistance to change and preference with respect to response rate proposed by behavioral momentum theory.

Animals↗

PubMed1998

An outbreak of Serratia marcescens infections related to contaminated chlorhexidine.

An outbreak of Serratia marcescens infections occurred in a university tertiary-care hospital. Alcohol-free chlorhexidine solutions were contaminated with S marcescens. The majority of patient and chlorhexidine strains had similar pulsed field-gel electrophoresis banding patterns. Chlorhexidine was recalled, and the rate of S marcescens isolation returned to baseline. Chlorhexidine without alcohol should not be used as an antiseptic.

Anti-Infective Agents, Local↗

PubMed1997

Stomal ulcer after gastric bypass.

BACKGROUND: Stomal ulcer is a serious complication of gastrogastric fistula following Roux-en-Y gastric bypass for obesity. STUDY DESIGN: A 1-8 year continuous followup of 499 patients with gastric bypass in continuity (GB) and isolated gastric bypass (IGB) documented the incidence of fistula formation, development of stomal ulcer, stimulation of acid production within the gastric pouch, and response to treatment. RESULTS: In 123 GB patients, staple line disruption occurred in 36 (29%) and stomal ulcer occurred in 20 (16%). Gastrogastric fistula with stomal ulcer was significantly lower in 376 patients who underwent IGB, (ie, 11 patients [3%]). Significantly larger amounts of acid, a lower pH, and a greater time with a pH less than 2 were found in the gastric pouches of patients who developed stomal ulcer after Roux-en-Y gastric bypass. All patients had a perforated staple line. Successful closure of the staple line significantly decreased acid production and pH in the gastric pouch when tested before and after remedial operation with healing of stomal ulcers. CONCLUSIONS: Stomal ulcer after gastric bypass is the result of acid production in the bypassed stomach in the presence of a gastrogastric fistula. Separation of the gastric pouch from the main stomach decreases the incidence of fistula formation and stomal ulcer but does not eliminate it. Interposition of a well vascularized organ, the jejunum between the pouch and main stomach, is an attractive solution for patients who require remedial operations on the stomach and possibly for primary operations as well.

Follow-Up Studies↗

PubMed1996

Control of construction-associated nosocomial aspergillosis in an antiquated hematology unit.

OBJECTIVE: To determine the incidence of aspergillosis in patients with leukemia or bone marrow transplants during a construction-associated outbreak, and the effect of an environmental control program for Aspergillus. DESIGN: Clinical, microbiological, and pathological records were reviewed retrospectively once the outbreak was appreciated, and prospectively thereafter, to determine the presence or absence of aspergillosis and duration of neutropenia. SETTING: A university tertiary-care center with a single designated hematology-oncology unit. PATIENTS: From January 1988 to September 1993, there were 141 patients with leukemia or bone marrow transplants identified as being neutropenic during 231 admissions to this specialized unit. INTERVENTIONS: Installation of wall-mounted portable high-efficiency particulate air (HEPA)-filter air purifiers, application of copper-8-quinolinolate-formulated paint, replacement of perforated ceiling tiles with nonperforated type, sealing of all windows, replacement of horizontal, dust-accumulating blinds with vinyl, opaque, roller shades, and systematic and regular cleaning of surfaces. RESULTS: Thirty-six cases of nosocomial aspergillosis were diagnosed during this period. The incidence density (ID) in the preconstruction period was 3.18 per 1,000 days at risk. During construction activity-before the implementation of a control strategy-the ID increased dramatically to 9.88 per 1,000 days at risk. With infection control measures implemented and continued construction work, the ID decreased to 2.91 per 1,000 days at risk, comparable to the preconstruction baseline rate. CONCLUSIONS: An environmental control strategy incorporating widely available technology may have played an important role in controlling this outbreak of construction-associated invasive aspergillosis.

Air Pollution, Indoor↗

PubMed1995

Training general practitioners in surgical and obstetrical emergencies in Ethiopia.

A 6-month course for training general practitioners (GPs) in surgical emergencies was developed and piloted in Ethiopia. The course was designed after an assessment of the surgical manpower needs in Ethiopia. Seven GPs were selected by the Ministry of Health (MOH) from rural hospitals that had no surgical specialists but had operating facilities. The course consisted of 1 week of lectures followed by 11 weeks each in obstetrics/gynaecology and general surgery. The GPs trained in district hospitals under the supervision of surgical specialists. Emphasis was placed on practical experience in managing a limited number of previously identified surgical emergencies. Follow up 9 months after completion of the course showed that five of the seven GPs had completed significant numbers of life saving procedures. Complications occurred largely in advanced disease. Difficulties remain with the recognition of the GPs' training and their supervision. We conclude that GPs can be trained to provide life saving surgery in a short training programme at a modest cost, but mechanisms for ensuring ongoing support need to be established.

Emergency Medical Services↗

PubMed1995

Resistance to reinforcement change in multiple and concurrent schedules assessed in transition and at steady state.

Behavioral momentum theory relates resistance to change of responding in a multiple-schedule component to the total reinforcement obtained in that component, regardless of how the reinforcers are produced. Four pigeons responded in a series of multiple-schedule conditions in which a variable-interval 40-s schedule arranged reinforcers for pecking in one component and a variable-interval 360-s schedule arranged them in the other. In addition, responses on a second key were reinforced according to variable-interval schedules that were equal in the two components. In different parts of the experiment, responding was disrupted by changing the rate of reinforcement on the second key or by delivering response-independent food during a blackout separating the two components. Consistent with momentum theory, responding on the first key in Part 1 changed more in the component with the lower reinforcement total when it was disrupted by changes in the rate of reinforcement on the second key. However, responding on the second key changed more in the component with the higher reinforcement total. In Parts 2 and 3, responding was disrupted with free food presented during intercomponent blackouts, with extinction (Part 2) or variable-interval 80-s reinforcement (Part 3) arranged on the second key. Here, resistance to change was greater for the component with greater overall reinforcement. Failures of momentum theory to predict short-term differences in resistance to change occurred with disruptors that caused greater change between steady states for the richer component. Consistency of effects across disruptors may yet be found if short-term effects of disruptors are assessed relative to the extent of change observed after prolonged exposure.

Journal Article↗

PubMed1995

Contrast and reallocation of extraneous reinforcers as a function of component duration and baseline rate of reinforcement.

Four pigeons responded on multiple schedules arranged on a "main" key in a two-key experimental chamber. A constant schedule component was alternated with another component that was varied over conditions. On an extra response key, conjoint schedules of reinforcement that operated in both components were arranged concurrently with the multiple schedule on the main key. On the main key, changes in reinforcement rate in the varied component were inversely related to changes in response rates in the constant component (behavioral contrast). On the extra key, some reinforcers were reallocated between components, depending on the schedules in effect on the main key in the varied component. In the varied component, the obtained rates of reinforcement on the extra key were inversely related to main-key reinforcement rate. In the constant component, extra-key reinforcer rates were positively related to main-key reinforcer rates obtained in the varied component, and were not a function of response rates on the extra key. In two comparisons, the rate at which components alternated and the value of the main-key schedule in the constant component were varied. Consistent with earlier work, long components reduced the extent of contrast. Reductions in contrast as a function of component duration were accompanied by similar reductions in the extent of reinforcer reallocation on the extra key. In the second comparison, lowering the rate of reinforcement in the constant component increased the rate at which extra-key reinforcers were obtained, reduced the extent of reinforcer reallocation, and reduced contrast. Overall, the results are consistent with the suggestion that some contrast effects are due to the changes in extraneous reinforcement during the constant component, and that manipulations of component duration, and manipulations of the rate of reinforcement in the constant component, affect contrast because they influence the extent of extraneous reinforcer real-location.

Journal Article↗

PubMed1994

Forgetting in rats following medial septum or mammillary body damage.

This study examined the effects of medial septal (MS) and mammillary body (MB) radio-frequency lesions in an automated delayed-matching-to-sample (DMTS) procedure using lever-position stimuli and rats. Memory performance pre- and postsurgery was assessed with a negative exponential decay function fitted to bias-free measures of recognition. Part 1 showed that MS, but not MB or sham-control surgery, impaired DMTS performance. This impairment in the MS group was best characterized as an increase in the rate of forgetting. Part 2 examined the interaction between MS and MB lesion effects and proactive interference arising from responses made on the previous DMTS trial. The results indicated that proactive interference effects were similar for all groups. These results provide further support for the critical role of the MS region in memory function but indicate that damage to this brain region does not disrupt memory function through a heightened sensitivity to proactive interference.

Animals↗

PubMed1994

Contrast and undermatching with regular or irregular alternation of components.

Behavioral contrast and response-ratio sensitivity to reinforcement were compared in multiple schedules in which components alternated strictly or according to a pseudorandom sequence. Average component durations in the two regimes were always 60 s, and order of presentation of component alternation regimes was counterbalanced across subjects. In Part 1, the reinforcer rate in one component was reduced from 60 per hour to zero, while that in the other component was unchanged. Positive behavioral contrast occurred in the constant component in that response rates increased, but neither the reliability nor the magnitude of contrast was affected by the manner in which components alternated. Part 2 was similar, except that a number of different reinforcer rates were used in the varied component. Neither contrast nor sensitivity of response ratios to changes in reinforcer ratios depended on the regime of component alternation. Thus, the predictability in time of future reinforcement conditions, which is a feature of regular multiple scheduling, does not appear to be a determinant of multiple-schedule performance.

Journal Article↗

PubMed1993

List item memory in rats: effects of delay and delay task.

The Serial Position Effect (SPE) was studied in rats using 2 manipulations analogous to those that have been shown to decrease the recency effect but leave the primacy effect intact in human Ss. In Part 1, delays (5 s to 60 s) were imposed between exposure to a sequence of arms presented in a 12-arm radial maze and a subsequent test phase. In Part 2, the effect of free access to food in a short (10-s) delay was examined. The results from Parts 1 and 2 showed that the primacy and recency effects were differentially sensitive to the delay and events within it. In particular the recency effect was found to be more sensitive to disruption from these sources. The present demonstration of a reduction in recency with procedures analogous to those used with humans extends the evidence, suggesting that the SPE obtained in rats and humans is a similar phenomenon.

Animals↗

PubMed1992

Production of a serial position effect in rats using a 12-arm radial maze.

The effects of item position (the serial position effect: SPE) on the recognition of a list of arms presented in an 8-arm radial maze have not been shown to be robust across studies which differ in numbers of subjects, amount of training and task difficulty. The present study examined whether more robust SPEs could be obtained in rats with a 12-arm radial maze using a matching-to-sample serial probe recognition (SPR) procedure. In Part 1, 23 rats received extensive training on recognition of list of arms from a 5-arm list and, in Part 2, 20 rats received training with a 7-arm list. Both Parts 1 and 2 showed that a reliable and persistent SPE emerged due to superior recognition of items at the first and last serial positions compared with the middle positions. However, the SPE was more pronounced with the 7-arm than 5-arm list. It is argued that adequate task difficulty along with sufficient subject and trial numbers is necessary to produce a clear SPE. In Part 3, an alternative means of assessing accuracy derived from signal-detection theory is examined, and the procedural requirements for its use are identified. Although this measure did not alter the conclusions reached using percent correct, it is proposed that the bias-free measure, log d, is superior to traditional indices of memory performance which may obscure the presence of, or changes in, the SPE. The procedures used here provide a valuable means to produce clear, reliable and persistent SPEs. Such procedures are essential if researchers are to be confident about the effects of lesions or drugs upon list memory in their attempts to explore the neurological bases of memory and model human neurological disorders.

Animals↗

PubMed1992

Resistance to change and the law of effect.

Three experiments using multiple schedules of reinforcement explored the implications of resistance-to-change findings for the response-reinforcer relation described by the law of effect, using both steady-state responding and responding recorded in the first few sessions of conditions. In Experiment 1, when response-independent reinforcement was increased during a third component, response rate in Components 1 and 2 decreased. This response-rate reduction was proportionately greater in a component in which reinforcer magnitude was small (2-s access to wheat) than in the component in which it was large (6-s access to wheat). However, when reinforcer rates in the two components were varied together in Experiments 2 and 3, response-rate change was the same regardless of the magnitude of reinforcers used in the two components, so that sensitivity of response rates to reinforcer rates (Experiment 2) and of response-rate ratios to reinforcer-rate ratios (Experiment 3) was unaffected by the magnitude of the reinforcers. Therefore, the principles determining resistance to change, described by behavioral momentum theory, seem not to apply when the source of behavior change is the variation of reinforcement contingencies that maintain the behavior. The use of extinction as a manipulation to study resistance to change is questioned.

Journal Article↗

PubMed1992

Successive independence and behavioral contrast in a closed economy.

Two pigeons had access to multiple concurrent schedules of reinforcement for 24 hours per day in their home cages. The variable-interval schedules comprising the multiple concurrent schedules were varied across 16 conditions. In three sets of conditions, one schedule was varied while its concurrent alternative and the concurrent schedules in the other component were held constant. Behavioral contrast was observed; that is, as the rate of reinforcement arranged by the varied schedule decreased, response rates on the constant schedules typically increased. These conditions formed part of two larger sets of conditions in which the concurrent schedules in one multiple-schedule component remained constant while the concurrent schedules in the other component were varied. Successive independence was found, in that behavior allocation during the constant component did not vary as a function of the reinforcer ratios in the varied component. Successive independence between components in multiple concurrent schedules is a robust result that occurs in closed economies and under conditions that promote behavioral contrast.

Animals↗

PubMed1992

Contrast and reallocation of extraneous reinforcers between multiple-schedule components.

Four pigeons responded in components of multiple schedules in which two responses were available and reinforced with food. Pecks on the left key ("main" key) were reinforced at a constant rate in one component and at a rate that varied over conditions in the other component. When reinforcer rate was varied, behavioral contrast occurred in the constant component. On the right key ("extra" key), five variable-interval schedules and one variable-ratio schedule, presented conjointly, arranged reinforcers for responses in all conditions. These conjoint schedules were common to both multiple-schedule components-rather than unique to particular components-and reinforcers from these schedules could therefore be arranged in one component and obtained during the other component. In this way, the additional reinforcers were analogous to the "extraneous" reinforcers thought to maintain behavior other than pecking in conventional multiple schedules. Response rate on the extra key did not change systematically over conditions in the constant component, and in the varied component extra responding was inversely related to main-key reinforcement. All subjects obtained more extra-key reinforcers in whichever component arranged fewer main-key reinforcers. Consistent with the theory that reallocation of extraneous reinforcers may cause behavioral contrast, absolute reinforcer rate for the extra key in the constant component was low in conditions that produced positive contrast on the main key and high in those that produced negative contrast. Also consistent with this theory, behavioral contrast was reduced in two conditions that canceled extra-key reinforcers that had been arranged but not obtained at the end of components. Thus, a constraint on reallocation markedly reduced the extent of contrast.

Journal Article↗

PubMed1992

Another view to blood and body substance precaution: 1988-91.

Occupational transmission of human immunodeficiency virus (HIV) in hospitals can be prevented with the use of 'blood and body substance precaution'. At the Royal Victoria Hospital, an infection control objective is to get employees automatically to use blood and body substance precaution with all patients--without relying on isolation signs. The concept of blood and body substance precaution was introduced in 1988 and simultaneously used with disease-specific signs. It was observed that disease-specific signs were mostly used to identify HIV-positive patients; this was verified under documented surveillance from July 7 to August 8, 1990, when 60 patients (14 HIV-positive and 46 whose HIV etiology was unknown) were observed. All 14 known HIV-positive patients were isolated with signs, while only four of 46 unknown HIV-positive patients (8.6%) had signs. The views of individual employees were subsequently studied via a questionnaire and results from this survey showed there was preference for isolating HIV-positive patients and identifying them with a sign.

Attitude of Health Personnel↗

PubMed1991

Clostridium difficile disease in a department of surgery. The significance of prophylactic antibiotics.

A clustering of Clostridium difficile-associated disease in a department of surgery prompted a program of infection control and the evaluation of contributing factors. Fifty patients had diarrhea and positive assays for C difficile cytotoxin during the study period. Twenty-one of the 36 cases that developed among patients admitted to the surgical services occurred on two adjacent general surgery wards that shared attending surgeons and house staff. Perioperative prophylactic antibiotics predated C difficile-associated disease in 20 patients, 12 of whom had short courses (less than 24 hours). Symptoms were typically nonspecific and early diagnosis may be difficult. Incidence remained high, despite infection control measures, until the coincidental closure of two surgical wards. Clostridium difficile-associated disease is a nosocomial infection that can be associated with short courses of prophylactic antibiotics. Recommendations regarding the use of perioperative prophylaxis should recognize C difficile-associated disease as a significant potential complication.

Adult↗

PubMed1991

Genetic studies on a major merozoite surface antigen of the malaria parasite of rodents, Plasmodium chabaudi.

Diversity in a major merozoite surface antigen (MSA-1) of Plasmodium chabaudi has been examined using a panel of monoclonal antibodies (MoAbs). The antigen was found to be different in each of twelve cloned isolates, as shown by its reactivity with the MoAbs in immunofluorescence tests. In genetic crossing experiments, the diverse forms of this antigen were shown to be determined by allelic variation of a single gene. Recombination occurred between the MSA-1 gene, a second blood stage antigen and enzyme markers.

Animals↗