SEARCH · PubMed Health

Results for “Learning Curve”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 613 records · Page 34Linked to original sources

PubMed2004

Initial experience with laparoscopic donor nephrectomies.

BACKGROUND: Laparoscopic donor nephrectomy (LDN) is being adopted rapidly by transplant centres around the world as it offers less postoperative pain, quicker convalescence, and better cosmetic result when compared with the open approach. There may, however, be a steep learning curve with this technique. METHOD: A retrospective review was performed to evaluate the donor morbidity and graft outcome of 21 consecutive LDN performed at one centre between May 2002 and August 2003. RESULTS: Eighteen LDN were performed on the left and three on the right side. All left and one right LDN were done transperitoneally while the remaining two right side kidneys were removed by a retroperitoneal approach. The mean (+/-SD) operating time and warm ischemic time were, respectively, 236 minutes (+/- 46) and 4 minutes (+/- 1). The mean time for resuming oral intake was 23 hours (SD +/- 22.7). The median length of hospital stay was 5 days (range 3 to 18). One patient was reoperated for bleeding and required four units of packed cell transfusion. One recipient displayed delayed graft function requiring dialysis for 14 days. There were no graft losses. The mean creatinine of the recipients at the time of discharge was 1.15 mg/dL (+/- 0.21). CONCLUSIONS: There is undoubtedly a learning curve with LDN. Nevertheless, with prior skills in similar procedures such as laparoscopic radical nephrectomies, it is feasible to diminish the learning curve and morbidity of LDN to yield results consistent with those in the published literature.

Graft Survival↗

PubMed2006

Totally robotic laparoscopic Roux-en-Y Gastric bypass: results from 75 patients.

BACKGROUND: A technique for Totally Robotic Laparoscopic Roux-en-y Gastric Bypass (TRL-RYGBP) has been reported previously. In this paper, we report our experience with our first 75 TRLRYGBP operations, including the training of three laparoscopic fellows. We describe changes in technique that have evolved with more experience, lessons learned, and the results from a larger series. METHODS: A retrospective review was conducted of the first 75 TRLRYGBP procedures performed at our institution using the da Vinci surgical robot. We recorded demographics including patient age, gender, preoperative BMI, and numbers of NIH-defined co-morbidities. Data were collected on operative time, length of stay, complications, and postoperative weight loss. Results were compared between the three fellows to examine learning curves. RESULTS: The average patient age was 44 years (23-61), average BMI was 46.1 kg/m(2) (34.3-65.5), and the median number of NIH defined co-morbidities was 1 (0-3). Median operative time was 140 minutes (80-312) with mean operative time per BMI of 3.1 minutes (1.6-5.7). Excess weight loss was 48% at 3 months, 64% at 6 months, and 82% at 1 year. The overall complication rate was 22.6% (5.3% intraoperative, 8.0% major, and 9.3% minor including a 2.9% stricture rate and 0% leak rate). Each fellow demonstrated a learning curve of 10-15 cases. CONCLUSION: The authors' continued experience with the TRLRYGBP has confirmed our early results that the use of the da Vinci robot for laparoscopic gastric bypass is a superior alternative to the standard laparoscopic RYGBP, and that the learning curve is significantly faster.

Adult↗

PubMed1997

Effect of training on endoscopic intracorporeal knot tying.

Training in endoscopic, intracorporeal knot tying, was evaluated in 29 obstetrics and gynaecology trainees who performed 100 consecutive intracorporeal, two turn, flat, square knots. An obvious learning curve was observed. With training the quality of the knots increased, whereas the mean duration to tie a knot decreased from 277 +/- 114 to 67 +/- 27 s for the first 10 and the last 10 knots respectively. The initial and final duration of knot tying were lower in more experienced trainees, as estimated by the year of training or the Royal College of Obstetrics and Gynaecology (RCOG) level of experience. More specifically, duration of knot tying was shorter when more diagnostic laparoscopies, laparoscopic sterilizations or adnexectomies had been performed. This effect of previous experience was however limited compared with the overall effect of training. Previous passive experience, however, as determined by the number of assisted or observed surgical interventions, did not affect the learning curves. Speed of knot tying was slightly higher in trainees who spent more of their leisure time performing handicrafts than in trainees who were more interested in reading, but although significant, these differences were only marginal. In conclusion, the data show an important effect of training on the speed and quality of intracorporeal knot tying and confirm that learning curves improve with previous training.

Endoscopy↗

PubMed2001

[Duration of surgery in osteosynthesis of fractures of the trochanter].

PURPOSE OF THE WORK: To analyze duration of surgery in individual types of internal fixation of fractures of the trochanteric massif and identify factors which have an impact on it. MATERIAL: Analysis covered a group of 137 patients treated with Ender nailing (EN), 314 patients by means of Dynamic Hip Screw (DHS), 74 patients by means of Gamma nail, 37 patients by means of Proximal Femoral Nail (PFN) and 13 patients by means of 130 degrees angled blade plate. The groups of patients included basicervical femoral neck fractures (29 cases), peritrochanteric and subtrochanteric fractures. Peritrochanteric fractures were evaluated according to Kyle classification, types I and II as stable (174 cases), type III unstable (159 cases) similarly as type IV (peri/subtrochanteric fractures or comminuted fractures of the whole trochanteric massif--35 cases). High subtrochanteric fractures (55 cases) were evaluated after Seinsheimer. From the viewpoint of AO/ASIF classification they were 31A1, 31A2, 31A3 fractures. EN was indicated mainly in Kyle I through IV fractures, DHS for basicervical fractures and Kyle I through III fractures, Gamma nail for Kyle I through IV fractures and high subtrochanteric fractures, PFN mainly for high subtrochanteric fractures and Kyle III fractures, 130 degrees angled blade plate was indicated only for stable peritrochanteric Kyle I fractures. RESULTS: The average duration of surgery, i.e. starting from the skin incision until the suture of the wound, was in DHS 47 min., in EN 52 min., in 130 degrees angled blade plate 54 min., in PFN 58 min. and in Gamma nail 70 min. The shortest time intervals were achieved in stable peritrochanteric fractures of Kyle I and II (EN, DHS, Gamma), the longest ones in high subtrochanteric fractures (Gamma, PFN). The impact of the learning curve was analyzed in DHS. In 1995 the average duration was 70 min. (35 patients/year), in 2000 already only 39 min. (123 patients/year). DISCUSSION: If we wish to make a serious evaluation of the duration of surgery of any method we must not forget that apart from it there is a whole number of other factors by which it is influenced. In case of proximal femur it is the type of fracture, the number and experience of surgeons, mastering the learning curve, annual frequency of surgeries at the respective Department as well as variation within the surgical technique (e.g. in DHS the number of distal locking and the number of locking screws, etc.) A significant role in this study was also played by the development of internal fixation at the Department of the authors. For instance, considerably shorter duration of surgery as well as minimum of complications in PFN were achieved thanks to mastering of the learning curve on the Gamma nail which we had started to use 3 years before. An objective evaluation requires also a sufficient number of cases in order to eliminate errors caused by low numbers and other variable factors. CONCLUSION: Surgery duration data which we present are comparable with the values included in the world literature. It applies not only to the duration of surgery in individual implants but also in individual types of proximal femur fractures. At present at our Department the average duration of surgery ranges in dependence on the applied implant, type of fracture and skills of the surgeon between 30 and 60 minutes. Relatively shortest duration can be achieved in DHS, in Gamma nail and PFN the duration is slightly longer. However, the duration of surgery is only a supporting factor. Of much greater importance for the patient is the quality of the surgery. Thus favouring any method only on the basis of the duration of surgery is absolutely irrelevant.

Bone Nails↗

PubMed2003

Current controversies in sentinel lymph node biopsy for breast cancer.

Despite the widespread use of sentinel lymph node biopsy (SLNBx) in the surgical management of breast cancer patients, several areas remain controversial. The following controversies are reviewed: Learning curves and validation studies. There clearly is a learning curve, and a completion ALND should be done until adequate proficiency is exhibited, both in terms of identification and false-negative rates. Location of injection. Intradermal injection offers superior identification rates compared with peritumoral injection, with comparable false-negative rates. Subareolar injection is as accurate as peritumoral injection. The value of scintigraphy. Routine scintigraphy does not enhance identification or false-negative rates. Mapping agents. Blue dye and radioactive tracer combined to provide a higher identification rate than either used alone.SLNBx in DCIS. In patients with a high risk of microinvasion, such as large tumors, a mass or high-grade DCIS-SLNBx is justified.SLNBx following neoadjuvant chemotherapy. Although there is evidence that SLNBx after neoadjuvant chemotherapy may be accurate, these data should be applied cautiously. Implications of non axillary SLN, especially internal mammary nodes. Data do not support routine resection of internal mammary sentinel lymph nodes outside a clinical trial. Implications of micrometastases in the sentinel lymph node seen only on immunohistochemistry. Since the significance of such metastases is unclear, decisions regarding treatment of these patients should be individualized. The value of completion axillary lymph node dissection. Is being addressed in clinical trials. Until those studies mature, completion ALND should be performed for patients with SLN metastases, but may be abandoned for patients with a negative SLN.

Breast Neoplasms↗

PubMed2004

Evolution of donor morbidity in living related liver transplantation: a single-center analysis of 165 cases.

OBJECTIVE: During the last 14 years, living donor liver transplantation (LDLT) has evolved to an indispensable surgical strategy to minimize mortality of adult and pediatric patients awaiting transplantation. The crucial prerequisite to performing this procedure is a minimal morbidity and mortality risk to the healthy living donor. Little is known about the learning curve involved with this type of surgery. PATIENTS AND METHODS: From January 1991 to August 2003, a total of 165 LDLTs were performed in our center. Of these, 135 were donations of the left-lateral lobe (LL, segments II and III), 3 were of the left lobe (L, segments II-IV), 3 were full-left lobes (FL, segments I-IV), and 24 were of the full-right lobe (FR, segments V-VIII). We divided the procedures into 3 periods: period 1 included the years 1991 to 1995 (LL, n = 49; L, n = 2; FR, n = 1), period 2 covered 1996 to 2000 (LL, n = 47), and period 3 covered 2001 to August 2003 (LL, n = 39; FR, n = 23; FL, n = 3; L, n = 1). Perioperative mortality and morbidity were assessed using a standardized classification. Length of stay in intensive care unit, postoperative hospital stay, laboratory results (bilirubin, INR, and LFTs), morbidity, and the different types of grafts in the 3 different periods were compared. RESULTS: One early donor death was observed in period 1 (03/07/93, case 30; total mortality, 0.61.%). Since 1991, the perioperative morbidity has continually declined (53.8% vs. 23.4% vs. 9.2%). In period 1, 28 patients had 40 complications. In period 2, 11 patients had 12 complications, and in period 3, 6 patients had 9 complications. Within the first period, 1 donor underwent relaparotomy because of bile leakage. Postoperative hospital stay was 10 days, 7 days, and 6 days, respectively. Donation of the full right lobe, in comparison with that of the left lateral lobe, resulted in a significantly diminished liver function (bilirubin and INR) during the first 5 days after donation but did not increase morbidity. One donor from period 1 experienced late death caused by amyotrophic lateral sclerosis. CONCLUSIONS: In a single center, morbidity after living liver donation strongly correlates to center experience. Despite the additional risks associated with temporary reduction of liver function, this experience enabled the team to bypass part of the learning curve when starting right lobe donation. Specific training of the surgical team and coaching by an experienced center should be implemented for centers offering this procedure to avoid the learning curve.

Adult↗

PubMed2002

Abdominal wall recurrences after colorectal resection for cancer: results of the Italian registry of laparoscopic colorectal surgery.

PURPOSE: The purpose of the present study was to evaluate prospectively the abdominal wall recurrence rate after laparoscopic resection for colorectal cancer, to analyze the impact of the learning curve on abdominal wall recurrence, and to assess the outcome of those patients. METHODS: The Italian Registry of Laparoscopic Colorectal Surgery database was analyzed to obtain data on cancer patients with abdominal wall recurrence, concomitant local or distant metastases, and interval between initial surgery and diagnosis of trocar site or minilaparotomy recurrences. The records of the initial procedures and the technique of specimen removal were reviewed. RESULTS: From January 1992 to July 2000, 2,583 patients (1,753 cases of carcinomas and 830 cases of benign diseases) were recorded. The malignant lesions were located on the right colon in 19 percent, the left colon in 48.8 percent, and rectum in 32.2 percent. Sixteen patients with histologic evidence of colorectal adenocarcinoma recurrences at the abdominal wall were observed (0.9 percent). Ten patients presented an advanced stage (III for 7 patients and IV for 3 patients). Eleven cases occurred during the learning curve period (the first 50 consecutive cases). The median survival time after abdominal wall recurrence diagnosis was 16 (range, 12-60) months. By July 2000 only two patients were alive. CONCLUSIONS: The results of the Italian prospective Registry of Laparoscopic Colorectal Surgery confirm that the incidence of abdominal wall recurrences is similar to that reported in open studies (<1 percent). Most abdominal wall recurrences occurred in the learning curve period, suggesting that surgical experience may play a role in the development of this outcome. The prognosis of these patients is very poor.

Abdominal Muscles↗

PubMed1993

Speed and accuracy of aimed hand movements in left-handed human subjects: sex-related differences in motor control.

Speed and accuracy in hand speed in relation to sex-related differences were studied in left-handed normal subjects. Hand skill was assessed by a peg moving task. Hand speed increased linearly with successive trials (motor learning). Left-hand speed exhibited a higher learning capacity than right-hand speed. Right-hand speed and right-hand learning were equivalent in males and females. Left-hand speed was higher in females than males; left-hand learning was equivalent in males and females. Left minus right (L-R) hand speed decreased linearly with right-hand speed; left-hand speed did not influence L-R hand speed. Learning curves were constructed for each subject. Standard error of a learning curve was considered as accuracy of hand skill. In females, accuracy of hand movement decreased as hand speed increased. In males, only accuracy of right-hand speed decreased as right-hand speed increased; left-hand accuracy did not depend on left-hand speed. It was concluded that right brain controlling left hand in left-handers has a higher capacity than left brain for motor learning; L-R hand speed was largely determined by left brain; accuracy in hand skill depends on both brains in females, and on only left brain in males; the female brain is more bilaterally organized than male brain in fine motor control.

Adult↗

PubMed2004

Dynamical trajectories in category learning.

Category learning has traditionally been studied by examining how percentage correct changes with experience (i.e., in the form of learning curves). An alternative and more powerful approach is to examine dynamical learning trajectories--that is, to examine how the parameters that describe the current state of the model change with experience. We describe results from a new experimental paradigm in which empirical-learning trajectories are directly observable. In these experiments, participants learned two categories of spatial position, and they were constrained to identify and use a linear decision bound on every trial. The dependent variables of principal interest were the slope and the intercept of the bound used on each trial. Data from two experiments supported the following conclusions. (1) Gradient descent provided a poor description of the empirical trajectories. (2) The magnitude of changes in decision strategy decreased with experience at a rate that was faster than that predicted by gradient descent. (3) Learning curves suffered from substantial identifiability problems.

Cues↗

PubMed2001

Bile duct injury during laparoscopic cholecystectomy: results of a national survey.

OBJECTIVE: To determine whether surgical residency training has influenced the occurrence of common bile duct injuries during laparoscopic cholecystectomy, and to asses the anatomic and technical details of bile duct injuries from the practices of surgeons trained in laparoscopic cholecystectomy after residency versus surgeons trained in laparoscopic cholecystectomy during residency. SUMMARY BACKGROUND DATA: Shortly after the introduction of laparoscopic cholecystectomy, the rate of injury to the common bile duct increased to 0.5%, and injuries were more commonly reported early in each surgeon's experience. It is not known whether learning laparoscopic cholecystectomy during surgery residency influences this pattern. METHODS: An anonymous questionnaire was mailed to 3,657 surgeons across the United States who completed an Accreditation Council for Graduate Medical Education (ACGME)-approved residency between 1980 and 1990 (group A) or 1992 and 1998 (group B). All surgeons in group A learned laparoscopic cholecystectomy after residency, and all those in group B learned laparoscopic cholecystectomy during residency. Information obtained included practice description, number of laparoscopic cholecystectomies completed since residency, postgraduate training in laparoscopy, and annual volume of laparoscopic cholecystectomy in the surgeon's hospital. In addition, technical details queried included the completion of a cholangiogram, the interval between injury and identification, the method of repair, and the site of definitive treatment. The primary endpoint was the occurrence of a major bile duct injury during laparoscopic cholecystectomy (bile leaks without a major bile duct injury were not tabulated). RESULTS: Forty-five percent (n = 1,661) of the questionnaires were completed and returned. Mean practice experience was 13.6 years for group A and 5.4 years for group B. At least one injury occurrence was reported by 422 surgeons (37.6%) in group A and 143 surgeons (26.5%) in group B. Forty percent of the injuries in group A occurred during the first 50 cases compared with 22% in group B. Thirty percent of bile duct injuries in group A and 32.9% of all injuries in group B occurred after a surgeon had performed more than 200 laparoscopic cholecystectomies. Independent of the number of laparoscopic cholecystectomies completed since residency, group A surgeons were 39% more likely to report one or more biliary injuries and 58% more likely to report two or more injuries than their counterparts in group B. Bile duct injuries were more likely to be discovered during surgery if a cholangiogram was completed than if cholangiography was omitted (80.9% vs. 45.1%). Sixty-four percent of all major bile duct injuries required biliary reconstruction, and most injuries were definitively treated at the hospital where the injury occurred. Only 14.7% of injuries were referred to another center for repair. CONCLUSIONS: Accepting that the survey bias underestimates the true frequency of bile duct injuries, residency training decreases the likelihood of injuring a bile duct, but only by decreasing the frequency of early "learning curve" injuries. If one accepts a liberal definition of the learning curve (200 cases), it appears that at least one third of injuries are not related to inexperience but may reflect fundamental errors in the technique of laparoscopic cholecystectomy as practiced by a broad population of surgeons in the United States. Intraoperative cholangiography is helpful for intraoperative discovery of injuries when they occur. Most injuries are repaired in the hospital where they occur and are not universally referred to tertiary care centers.

Adult↗

PubMed2006

The impact of introducing laparoscopic radical prostatectomy on surgical wait times for prostate cancer.

Wait times for radical prostatectomy are increasing in Canada. However, the impact of adopting a new surgical technique, such as laparoscopic radical prostatectomy (LRP), is not known. We outline the determinants of surgical wait time, the potential impact of adopting LRP and ways to minimize the impact. Surgical wait time is determined by surgical demand (number of people wanting surgery) relative to supply (number of surgeries a centre is able to offer). The introduction of any new technique will at first prolong operative times, but the degree to which it does is dependent on the learning curve of the surgeon and perioperative team. The influence of this learning curve on wait times depends on surgeon-level factors including case selection, triaging and scheduling tendencies, as well as hospital-level factors such as the amount and flexibility of operating room and hospital resources. The impact of adopting new technology may be minimized by the following: one surgeon per group initially learns the new procedure; the group and learning surgeon continue to offer the conventional procedure; early procedural experiences with the new technique are made as homogenous as possible; and a constant, dedicated team is created. Thus, the potential benefits of new techniques like LRP may be realized when adopted in a way that minimizes a negative impact on surgical wait times.

Appointments and Schedules↗

PubMed2001

Urologic laparoscopy.

Urologic laparoscopy initially was confined to a diagnostic role or the treatment of benign conditions. Many of these initial procedures, however, have been abandoned because they offered no significant benefit over open surgery. The treatment of urologic malignancies, however, recently has emerged as the most common indication for laparoscopic urologic surgery. Maturing data for laparoscopic radical nephrectomy, nephroureterectomy and partial nephrectomy demonstrate equivalent oncologic results. Newer applications such as laparoscopic radical prostatectomy are evolving. Despite these data demonstrating many advantages as compared with open techniques, urologists have been slow to include laparoscopy in their practice. This reluctance has been seen in other disciplines and is no doubt, at least in part, caused by the steep learning curve. Laparoscopic management of urologic malignancies is complicated and difficult to learn. In a multi-institutional review of laparoscopic complications, 71% of the complications occurred in the first 20 cases. The risk of complications and operative time significantly declines with experience, however. Higashihara et al reported a decline in laparoscopic operative time to levels comparable to open radical nephrectomy. The learning curve seems to be approximately 30 to 40 cases. The scope and practice of urology does not provide a common procedure of relatively low complexity such as the general surgical cholecystectomy or gynecologic tubal ligation to facilitate the adoption of laparoscopy by urologists. Nevertheless, evolving techniques and equipment coupled with the incorporation of laparoscopic training in residency and fellowship programs will help secure laparoscopy a prominent place in the treatment of urologic malignancy.

Adrenalectomy↗

PubMed2001

Novice construction of chess memory.

Novice acquisition of skilled recall of chess positions was studied in an experiment in which two novices studied a series of five hundred chess positions during a period of several months. They spent fifteen minutes to half an hour a day teaching themselves these positions. As a result their skill in recalling chess positions rose from sixteen percent to somewhere between forty to fifty percent. The learning curve proved to have a shape which indicates that in the beginning learning is very fast but after some 100-150 studied positions the speed of learning decreases substantially. A computer simulation was used to model the results and analyse alternative explanations. Two alternative ways of thinking were tested. In the first, chunk construction was assumed to be based on the neighbourhood of associated pieces. The second model assumed a frequency-based correlative association process. Although the learning curves of the two models are very similar in shape to those of the subjects, the frequency-based associative model gave a better explanation for the data. This is why it is natural to suggest that common co-occurrence in addition to easily recognizable chess-specific characteristics, like colour and type of pieces, guide associative processes during chess players' learning of chess-specific chunks.

Association Learning↗

PubMed2003

The interaction between cost-management and learning for major surgical procedures - lessons from asymmetric information.

The theory of the learning curve states that learning effects are of particular importance in industries, where human skills play an important role. Consequently, one would expect to find large learning effects for surgical procedures because the physician's experience is quite important for this type of work. For hospitals, there exists indeed a well-documented effect that shows a positive relationship between the number of a certain type of surgery being performed and its resulting quality (volume-outcome relationship). Empirical analyses of the impact of learning on the average cost of a procedure, however, have noted a conspicuous absence of learning effects. Using a mechanism design approach, the paper analyzes a model of quality and cost-management for a hospital, where learning effects are included into the cost function and asymmetric information exists between management and physician. It seeks to answer the question, whether recommendations from a symmetric information scenario with respect to learning carry over to a health care setting, where informational problems tend to be pronounced and severe. If surgery volume interacts with physicians' informational rents, an optimal management reaction to the presence of learning may result in a policy, which is the exact opposite of the one under symmetric information.

Clinical Competence↗

PubMed2002

Measuring cervical length with ultrasound: evaluation of the procedures and duration of a learning method.

OBJECTIVE: To evaluate the learning curve and principal learning steps for a novice ultrasound operator to master the technique for measuring cervical length by transvaginal ultrasound. SUBJECTS AND METHODS: The study involved asymptomatic patients with a singleton pregnancy between 21 and 38 weeks attending for a routine ultrasound scan. Two operators new to cervical ultrasound including one with experience in transvaginal gynecological ultrasound were assessed during their training. After an initial lecture session on the technique of cervical measurement, the trainees had one or two supervised practice sessions, validated by two interobserver agreement studies with 30 patients at a time; these compared the level of agreement between trainer and trainee throughout. Five examinations were performed in the first practice session; a second session was planned if the trainee could not perform all five examinations alone satisfactorily, in agreement with four quality criteria predefined for good cervical measurements. The second session lasted until five consecutive examinations could be performed adequately without the trainer's aid. Agreement between the two operators was assessed by intraclass correlation coefficient (ICC). The ICCs were compared with Fisher's Z transformation. RESULTS: Of the 150 patients included, 2.7% gave birth before term. The trainee with no experience in transvaginal ultrasound required two practice sessions; none of the five ultrasound scans performed in the first session was correct. In the second session, 18 consecutive ultrasound examinations were necessary to obtain five consecutive adequate results. During interobserver studies with the trainer, the ICC progressed from 0.43 in the first study to 0.64 in the second and 0.77 in the third (P = 0.049 between the first and third studies). The trainee with experience in transvaginal ultrasound required only one practice session. The ICC increased from 0.73 to 0.85 in the two interobserver studies with the trainer. CONCLUSIONS: Measurement of cervical length by transvaginal ultrasound examination is a technique that can be learnt rapidly. While roughly 23 supervised ultrasound scans appear necessary for an operator with no experience in transvaginal ultrasound, substantially fewer are required for an operator already familiar with this approach for other indications.

Adult↗

PubMed2006

Bayesian analysis of interleaved learning and response bias in behavioral experiments.

Accurate characterizations of behavior during learning experiments are essential for understanding the neural bases of learning. Whereas learning experiments often give subjects multiple tasks to learn simultaneously, most analyze subject performance separately on each individual task. This analysis strategy ignores the true interleaved presentation order of the tasks and cannot distinguish learning behavior from response preferences that may represent a subject's biases or strategies. We present a Bayesian analysis of a state-space model for characterizing simultaneous learning of multiple tasks and for assessing behavioral biases in learning experiments with interleaved task presentations. Under the Bayesian analysis the posterior probability densities of the model parameters and the learning state are computed using Monte Carlo Markov Chain methods. Measures of learning, including the learning curve, the ideal observer curve, and the learning trial translate directly from our previous likelihood-based state-space model analyses. We compare the Bayesian and current likelihood-based approaches in the analysis of a simulated conditioned T-maze task and of an actual object-place association task. Modeling the interleaved learning feature of the experiments along with the animal's response sequences allows us to disambiguate actual learning from response biases. The implementation of the Bayesian analysis using the WinBUGS software provides an efficient way to test different models without developing a new algorithm for each model. The new state-space model and the Bayesian estimation procedure suggest an improved, computationally efficient approach for accurately characterizing learning in behavioral experiments.

Bayes Theorem↗

PubMed2004

Functional characteristics of the associative areas of the cortex involved in visual information discrimination learning processes in monkeys.

Experiments on three groups of rhesus macaques (intact and with bilateral removal of field 7 and the sulcus principalis) were performed to study the functional characteristics of the associative areas of the cortex while the monkeys learned visual discrimination. Significant differences in learning processes associated with removal of structures and the properties of the stimuli were seen in all animals, in the form of different types of learning curves. As compared with intact monkeys, removal of field 7 had no effect on learning processes for images with properties such as spatial frequency, color, and animal images, though there was a significant worsening in the characteristics of learning during visual discrimination of spatial relationships between objects. Learning processes became unstable, the number of peaks and troughs on learning curves increased, and as a result the training periods were significantly lengthened and 85% of the animals were unable to achieve the learning criterion. Removal of the sulcus principalis significantly worsened the characteristics of discrimination of the sizes of geometric objects, the spatial relationships between them, and stimuli of different colors. The stable reaction time and the probability of refusal in most cases also increased for monkeys of both these groups. Cluster analysis based on the quantitative characteristics of learning processes, despite individual differences between the monkeys, demonstrated a tendency for stimuli to be separated into classes corresponding to different types of information. These data show that the result of sensory processing is that several (at least three) functional visual information flows are generated and that different areas of the cortex deal with these different flows.

Animals↗

PubMedDate not supplied

Relationship between learning characteristics and the properties of visual objects in rhesus macaques with bilateral removal of parietal cortex field 7.

Behavioral experiments were used in rhesus macaques with bilateral excision of field 7 of the lower parietal cortex to study the relationship between visual differentiation learning processes and a variety of stimulus properties. All animals showed significant differences associated with stimulus properties, which produced different types of learning curves. For each monkey, visual stimuli were divided into compact groups in terms of the "similarity" of their learning characteristics. Removal of field 7 had no effect on the process of learning visual image discrimination when this was based on properties such as color and geometrical shape, but worsened the learning characteristics when visual differentiation was based on spatial information, when the learning process became unstable, with increases in the numbers of peaks and troughs on the learning curve and a significant increase in the duration of the learning period. The time to a stable motor response also became significantly greater than for visual images distinguished by shape and color. It is suggested that during the process of learning visual discrimination, processing and extraction of image signs by the visual system for objects characterized by spatial relationships is accompanied by the formation of spatial distinguishing signs, this process involving neuronal structures in field 7 of the lower parietal cortex, which appears to be the main area determining visual-vestibular interactions. Increases in oscillations and in the difficulty of the learning process for differentiation on the basis of spatial information after removal of field 7 might be due to a transfer from one strategy to another, resulting from disruption of the mechanisms which evaluate body image and egocentric orientation on the basis of visual-vestibular interactions.

Animals↗