Search PubMed⌕ Search

Biomedical subjects

C L Baker

Publications and source records attributed to C L Baker.

At least 91 records · Page 5Linked to original sources
PubMed1982

Does segregation of differently moving areas depend on relative or absolute displacement?

We have examined the occurrence of segregation in random dot kinematograms in which a central patch of dots, and the surrounding area, were each coherently displaced, either in the same or opposite directions (Fig. 1), by varying amounts. The limiting displacement for segregation to occur is determined primarily by the displacement of each region alone, rather than the relative displacement of neighbouring regions (Fig 2). We conclude that the "correspondence problem" is solved by means of a short range motion detection process acting on each region separately; segregation is achieved by comparing the results of this process for adjacent regions.

Form Perception↗
PubMed1980

The release of 40S hnRNP particles by brief digestion of HeLa nuclei with micrococcal nuclease.

Brief digestion of HeLa nuclei with mirococcal nuclease releases monomer hnRNP particles as well as monomer and polynucleosomes. Sucrose gradient analysis of the nuclease released material reveals a series of small A260 peaks overlapping a more predominant peak in the 40S region of the gradient. Analysis of the proteins, DNa, and RNA in successive gradient fractions has confirmed that the smaller peaks are monomer and polynucleosomes, and that the larger peak is 40S hnRNP. Like 40S particles isolated by low salt extraction or by sonication, the nuclease released particles are composed of rapidly labeled RNA associated with a group of non-histone proteins the most predominant of which are the 32,000-44,000 MW proteins previously identified as core hnRNP proteins. These results provide further evidence that 40S hnRNP particles exist as discrete structural components of larger in vivo ribonucleoprotein complexes.

Cell Nucleus↗
PubMed1979

Relationship of inappropriate drug prescribing to increased length of hospital stay.

The relationship of inappropriate drug prescribing to increased length of hospital stay was studied. The medical records of 77 cases of pyelonephritis were reviewed retrospectively. Appropriateness of antimicrobial drug therapy was judged by three types of explicit screening criteria: drug-specific, patient-specific, and match of drug to infecting organism. Patients whose therapy passed all the criteria were hospitalized, on the average, two days less than those whose therapy failed one or more of the criteria. This was a significant difference (p less than 0.05). Age, seriousness of the pyelonephritis, or method of payment appeared to have no significant moderating effect on this result. However, the increased length of stay may not have been associated with only inappropriate prescribing, because the inappropriately prescribing physicians kept their patients hospitalized longer beyond the point of symptom remission than did the appropriately prescribing physicians. The study suggest that successful interventions for improving drug therapy could result in large cost savings.

Anti-Bacterial Agents↗
PubMed1978

Proximal femoral focal deficiency: Treatment and classification in forty-two cases.

A review of the surgical experiences in 42 patients with proximal femoral focal deficiency has led us to propose a new classification system. This simplified system consists of 4 definite classes based on the roentgenographic appearance of the proximal shaft, and includes distinct prognosis and treatment groups. Early and accurate prognostication facilitates rational prosthetic design and appropriate surgical treatment in all degrees of involvement. In the less severely involved classes, emphasis is placed on the utilization of the proximal shaft signs of Fixsen and Lloyd-Roberts to identify those hips with an unfavorable prognosis.

Adolescent↗
PubMedDate not supplied

A sustained input to the direction-selective mechanism in cat striate cortex neurons.

Direction-selective neurons in cat striate cortex were tested with bar-shaped stimuli, sequentially flashed at spatially displaced positions chosen to elicit maximal direction selectivity. Temporally overlapping flash exposures of prolonged duration (400-1000 ms) were employed at a series of onset asynchronies to explore the nature of temporal tuning of the direction-selective mechanism. In most neurons studied, direction selectivity was found to be supported by a surprisingly broad range of stimulus onset asynchronies, which was greater for longer exposure durations. These findings imply the existence of a sustained input to the direction-selective mechanism, in spite of the relatively transient nature of most cortical neurons' step responses. A model is described to illustrate how different front-end temporal filters can affect the dependence of two-flash direction selectivity on stimulus onset asynchrony. The versions of the model which successfully predict the form of the observed responses are those which combine inputs from sustained and transient filters.

Animals↗
PubMedDate not supplied

Linear filtering and nonlinear interactions in direction-selective visual cortex neurons: a noise correlation analysis.

Spatial and temporal properties related to direction selectivity of both simple and complex type visual cortex neurons were assessed by cross-correlation analysis of their responses to random ternary white noise. This stimulus consisted of multiple randomly placed bars, each colored white, black, or gray with equal probability, which were rerandomized every 5-10 ms. A first-order cross-correlation analysis of a neuron's spike train with the spatiotemporal history of the stimulus provided an estimate of the neuron's linear spatiotemporal filtering properties. A nonlinear correlation analysis measured the amount of interaction for pair-wise combinations of bars as a function of their relative spatial and temporal separations. The spatiotemporal orientation of each of these functions was quantified using a "motion energy index" (MEI), which was compared to the neurons' direction selectivity measured with drifting sinewave gratings. Both first-order and nonlinear correlation plots usually showed s-t orientation whose sign was consistent with the neuron's direction preference; however, in many cases the MEI for first-order analysis was weak compared to that seen in the nonlinear interactions. The structures of the nonlinear interaction functions were also compared with predictions from a conventional model of direction selectivity based on a simple spatiotemporally oriented linear filter, followed by an intensive nonlinearity ("LN model"). These comparisons showed that some neurons' data agreed reasonably well with such a model, while others agreed poorly or not at all. Simulations of an alternative model which combines signals from idealized lagged and nonlagged front-end linear filters produce noise correlation results more like those seen in the neurophysiological data.

Animals↗
PubMedDate not supplied

Cortical processing of second-order motion.

Neurons in the mammalian visual cortex have been found to respond to second-order features which are not defined by changes in luminance over the retina (Albright, 1992; Zhou & Baker, 1993, 1994, 1996; Mareschal & Baker, 1998a,b). The detection of these stimuli is most often accounted for by a separate nonlinear processing stream, acting in parallel to the linear stream in the visual system. Here we examine the two-dimensional spatial properties of these nonlinear neurons in area 18 using envelope stimuli, which consist of a high spatial-frequency carrier whose contrast is modulated by a low spatial-frequency envelope. These stimuli would fail to elicit a response in a conventional linear neuron because they are designed to contain no spatial-frequency components overlapping the neuron's luminance defined passband. We measured neurons' responses to these stimuli as a function of both the relative spatial frequencies and relative orientations of the carrier and envelope. Neurons' responses to envelope stimuli were narrowband to the carrier spatial frequency, with optimal values ranging from 8- to 30-fold higher than the envelope spatial frequencies. Neurons' responses to the envelope stimuli were strongly dependent on the orientation of the envelope and less so on the orientation of the carrier. Although the selectivity to the carrier orientation was broader, neurons' responses were clearly tuned, suggesting that the source of nonlinear input is cortical. There was no fixed relationship between the optimal carrier and envelope spatial frequencies or orientations, such that nonlinear neurons responding to these stimuli could perhaps respond to a variety of stimuli defined by changes in scale or orientation.

Animals↗
PubMedDate not supplied

Arthroscopic classification and treatment of lateral epicondylitis: two-year clinical results.

We assessed the clinical utility of 42 arthroscopic releases for lateral epicondylitis in 40 patients (average age, 43 years) with an average of 14 months of symptomatic history before surgery. At arthroscopy, we found 15 type I lesions (intact capsule), 15 type II lesions (linear capsular tear), and 12 type III lesions (complete capsular tear), and associated disorders were found in 69% of the patients. At an average follow-up of 2.8 years, patients were asked to report on elbow pain and function. Subjectively, the patients rated their pain at rest as an average of 0.9 (0 = no pain; 10 = severe pain). They rated their pain with activities of daily living as 1.4 and their pain with sports and work as 1.9. Functionally, they averaged 11.1 of 12 possible points. Of the 39 elbows in the 37 patients who were available for follow-up, 37 were rated "better" or "much better." Patients returned to work in an average of 2.2 weeks. Grip strength averaged 96% of the strength of the unaffected limb. Arthroscopic tennis elbow release is a reliable treatment that allows patients an expedited return to work and may result in greater postsurgical grip strength.

Activities of Daily Living↗
PubMedDate not supplied

Acute combined posterior cruciate and posterolateral instability of the knee.

This report concerns 13 consecutive patients (13 knees) who underwent operative treatment for acute combined posterior cruciate and posterolateral instability due to combined injury to the posterior cruciate ligament and the arcuate ligament complex. Our purpose was to examine the method of diagnosis and the results in these patients. There were 12 males and 1 female (average age, 26 years). Five patients were injured in a motor vehicle accident, four in sports activities, and four in nonsports activities. The mechanism of injury was an anteromedial blow to the flexed knee in six patients, a fall onto the knee in two, and unknown in five patients. Eleven patients were available for follow-up evaluation (average, 56 months), and in each the result was rated as good, fair, or poor. In 10 patients (90%) the results were rated as good subjectively, in 11 (100%) as good functionally, and in 8 (73%) as good objectively. Injury to both the posterior cruciate ligament and the arcuate ligament complex can result from rotational force that can be due to a blow to the anteromedial aspect of the knee. Diagnosis can be made by a combined positive response to the posterior drawer test, the anterior drawer test performed with the tibia in internal rotation, the abduction and adduction stress tests performed with the knee in full extension, the posterolateral drawer test, and the external rotation-recurvatum test. In a knee with concomitant injury to the posterior cruciate ligament and the arcuate ligament complex that requires surgical repair, all injured structures should be explored and repaired to ensure a subjectively, objectively, and functionally good result.

Accidents, Traffic↗
PubMedDate not supplied

Operative ankle arthroscopy. Long-term followup.

Ankle arthroscopy has become an accepted procedure for the treatment of various intraarticular disorders. More than 100 ankle arthroscopies have been performed at our institution since 1983. To better define the role of arthroscopic surgery in the treatment of ankle disorders, we evaluated the preoperative examination and indications, operative data, and radiographs of those patients with a minimum of 1 year of followup. Fifty-eight ankles in 57 patients were identified; their average follow-up period was 25 months (range, 12 to 49 months). Preoperative diagnoses were synovitis (26), transchondral defects of the talus (17), degenerative joint disease (8), and osteophytes or loose bodies (7). Subjective results were good or excellent in 64% of cases. The best overall results were achieved in patients with synovitis (77%) and transchondral defects of the talus (71%). Degenerative joint disease patients did not do well. They had only 12% good or excellent results and a 43% rate of subsequent fusion. Complications included superficial and deep infections, temporary and permanent paresthesias, and hemarthroses; the overall complication rate was 15%. In conclusion, operative ankle arthroscopy can be useful in selected patients. It is an effective surgical procedure in patients with synovitis and transchondral defects of the talus. The benefits and long-term results are less predictable with loose bodies and impinging osteophytes; the results are poor with degenerative joint disease. There appears to be a significant risk of complication with ankle arthroscopy; however, with proper indications, a thorough knowledge of anatomical landmarks, and meticulous technique, good results can be obtained.

Adolescent↗
PubMedDate not supplied

Arthroscopic evaluation of acute initial anterior shoulder dislocations.

Arthroscopic evaluation of patients with an acute anterior shoulder dislocation was done to identify and classify the intraarticular lesions that might predict recurrent dislocations. Forty-five shoulders fit the following criteria for inclusion in our study: initial dislocation with no prior history of shoulder problems; confirmation of the dislocation radiographically or reduction by a physician; and arthroscopy within 10 days. The 42 men and 3 women had an average age of 21.2 years (range, 14 to 28 years). Mechanism of injury was a twisting of the arm into forced abduction and external rotation, a fall on the outstretched arm, or a direct blow to the shoulder. Based on this preliminary study of 45 shoulders, we present a classification of the lesions found in the acute shoulder dislocation. Group 1 (six shoulders) had capsular tears with no labral lesions: these shoulders were stable under anesthesia and had no or minimal hemarthrosis. Group 2 (11 shoulders) had capsular tears and partial labral detachments: these shoulders were mildly unstable and had mild to moderate hemarthrosis. Group 3 (28 shoulders) had capsular tears with labral detachments: these shoulders were grossly unstable and had large hemarthrosis. They had complete capsular/labral detachments. In the past, redislocation rates have been primarily related to age at the time of initial dislocation and, to a lesser degree, the period of immobilization. We have identified the intraarticular lesions in 45 patients with an initial anterior glenohumeral dislocation and classified these shoulders into three groups based on the lesions found. By doing so, we can develop a more accurate method of determining which shoulders are prone to recurrent dislocation.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗