Biomedical subjects

L Welch

Publications and source records attributed to L Welch.

13 recordsLinked to original sources

PubMed1992

Three-dimensional illusory contours and surfaces.

Under general viewing conditions, objects are often partially camouflaged, obscured or occluded, thereby limiting information about their three-dimensional position, orientation and shape to incomplete and variable image cues. When presented with such partial cues, observers report perceiving 'illusory' contours and surfaces (forms) in regions having no physical image contrast. Here we report that three-dimensional illusory forms share three fundamental properties with 'real' forms: (1) the same forms are perceived using either stereo or motion parallax cues (cue invariance); (2) they retain their shape over changes in position and orientation relative to an observer (view stability); and (3) they can take the shape of general contours and surfaces in three dimensions (morphic generality). We hypothesize that illusory contours and surfaces are manifestations of a previously unnoticed visual process which constructs a representation of three-dimensional position, orientation and shape of objects from available image cues.

Form Perception↗

PubMed1992

Neural computing in cancer drug development: predicting mechanism of action.

Described here are neural networks capable of predicting a drug's mechanism of action from its pattern of activity against a panel of 60 malignant cell lines in the National Cancer Institute's drug screening program. Given six possible classes of mechanism, the network misses the correct category for only 12 out of 141 agents (8.5 percent), whereas linear discriminant analysis, a standard statistical technique, misses 20 out of 141 (14.2 percent). The success of the neural net indicates several things. (i) The cell line response patterns are rich in information about mechanism. (ii) Appropriately designed neural networks can make effective use of that information. (iii) Trained networks can be used to classify prospectively the more than 10,000 agents per year tested by the screening program. Related networks, in combination with classical statistical tools, will help in a variety of ways to move new anticancer agents through the pipeline from in vitro studies to clinical application.

Alkylating Agents↗

PubMed1992

The precision of size constancy.

The precision of objective size judgments, made when target disparity changed at random from trial-to-trial, was compared to the precision of angular size judgments made under the same condition. Subjects judged incremental changes in the vertical distance separating a pair of horizontal lines. For the objective judgments (in cm), the angle subtended by the target separation decreased with increasing depth consistent with the natural geometry of physical objects. For the angular judgments (in arc min), the angular separation did not change with disparity. For separations subtending an angle < 10 arc min, objective thresholds were considerably higher than angular thresholds, indicating that size constancy does not function well at small scales. At larger scales (> 20 arc min), the Weber fractions for angular and objective thresholds were nearly equal (approximately 6%) for two of the three subjects. These same two subjects also learned to judge "objective size" when angular subtense systematically increased with increasing depth in an exact inversion of the natural relationship. Although their "anti-constancy" judgments were less precise (approximately 9%) than their constancy judgments, the fact that subjects could learn this task with little practice suggests that constancy itself may be a learned response. Angular thresholds for targets presented only in the fixation plane were significantly lower than the angular thresholds measured with random changes in disparity, showing that observers with normal stereopsis do not have direct access to information about the angle subtended at the retina.

Depth Perception↗

PubMed1992

Engraftment of leukocyte subsets following autologous bone marrow transplantation in acute myeloid leukemia using anti-myeloid (CD14 and CD15) monoclonal antibody-purged bone marrow.

The cell surface phenotype of leukocyte subsets during reconstitution following autologous bone marrow transplantation (ABMT) using bone marrow purged with anti-myeloid monoclonal antibodies (MoAbs) and complement (C') was evaluated in 20 patients with acute myeloid leukemia (AML). Repopulation of B and T lymphocytes, natural killer (NK) cells, and myeloid cells was assessed by phenotypic analysis using two-color cytofluorography of peripheral blood mononuclear cells (PBMNC) at several time points up to 2 years post-transplantation. In spite of removal of the majority of monomyeloid cells of the autograft by purging with anti-CD14 and anti-CD 15, engraftment occurred rapidly. The myeloid cells appeared normal by surface phenotype. An early rise in NK cells, characterized by expression of CD57 and CD 16, was seen. The CD4:CD8 ratio remained low throughout the study period, primarily due to a persistently low CD4 level. ABMT using bone marrow purged with the anti-myeloid MoAbs PM-81 and AML-2-23 and C' resulted in prompt engraftment of neutrophils. Although there was a prolonged time for recovery of lymphocyte subsets, this did not result in an increased risk of early infectious complications. Late infectious complications post-transplantation were limited to herpes zoster infection in one patient 18 months post-transplantation, and bacterial meningitis in that same patient 2 months later. This study demonstrates that ABMT in patients with AML using bone marrow purged with the anti-myeloid MoAbs PM81 (anti-CD15) and AML-2-23 (anti-CD14) and C' results in rapid hematologic engraftment and delayed phenotypic immunologic reconstitution without significant acute or chronic clinical toxicities.

Adolescent↗

PubMed1978