Biomedical subjects

L Welch

Publications and source records attributed to L Welch.

At least 19 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

Hard metal interstitial pulmonary disease associated with a form of welding in a metal parts coating plant.

We describe two cases of hard metal pulmonary disease (one fatal) in workers employed in the same area of a metal coating plant using the detonation gun process for applying a durable metal surface to metal parts. In this form of welding, a mixture of powdered metals, including tungsten carbide and cobalt, is heated by ignition of a flammable gas and propelled from the end of the "gun" at high temperature and velocity to form a welded metal coating. This process is done in an enclosed chamber and with each application, large volumes of fine aerosols are created. Inhalation exposure to hard metal may occur during the mounting and removal of the metal parts between applications, in spite of engineering controls and industrial hygiene surveillance. One of the cases presented with minimal chest x-ray abnormalities and an obstructive pattern on pulmonary function testing, although subsequent open lung biopsy showed diffuse interstitial pulmonary fibrosis. The fact that two cases of hard metal pulmonary interstitial disease occurred where thorough exposure control procedures and a surveillance program for cobalt were in place may indicate the need for revisions of the current technology used when hard metal is applied in the detonation gun process.

Adult↗

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

The treatment of a chronic organic mental disorder with dextromethorphan in a man with severe mental retardation.

Response to dextromethorphan (15 mg b.i.d.), an antitussive agent not usually considered to have psychotropic properties, was seen in a 25-year-old man with severe developmental disabilities, congenital rubella, and an organic mental disorder. Dextromethorphan affects CNS serotonergic systems, and this was the probable therapeutic mechanism. This and other published cases suggest the existence of a distinct organic mental syndrome in developmentally disabled persons which responds to drugs that increase indoleaminergic activity.

Adult↗

PubMed1992

Surveillance of sentinel occupational mortality in the District of Columbia: 1980 to 1987.

Epidemiological surveillance of sentinel occupationally related deaths commonly relies on computerized analyses of mortality data obtained from vital statistics records. A computer search of death records in the District of Columbia for the period 1980 to 1987 identified 15 cases that noted asbestosis, silicosis, coal worker's pneumoconiosis, or primary cancer of the pleura/mesothelioma as the underlying cause of death. A manual review of the death certificates for the same period identified three times as many cases (n = 48) with any mention of these conditions. Problems with performing surveillance of these events using death certificates include the lack of sufficient information to identify mesotheliomas and the failure to code and computerize all contributing causes of death.

Abstracting and Indexing↗

PubMed1992

Increased blood and urine copper after residential exposure to copper naphthenate.

Despite widespread industrial use of copper naphthenate, there are no reports of the relationship of copper naphthenate and copper absorption in humans or animals. We report a family of three individuals who lived in a home where copper naphthenate was sprayed on the inner foundation. Subsequently, these individuals developed non-specific complaints. In two of these individuals, serum copper levels were elevated when first measured months after copper naphthenate was sprayed in the home. A gradual decline over several years in urine and serum copper levels was observed in the individual who maintained follow-up. It is not known if symptoms reflected exposure to naphthenate, the solvent vehicle, volatilized copper, or the stress of exposure to a malodorous compound perceived as toxic. Exposure to copper naphthenate may be another cause of an elevated serum and urine copper level but the interpretation of these levels as "normal" or "toxic" requires additional study for clarification. This report suggests the need for further study of the absorption and relative toxicity of copper naphthenate.

Absorption↗

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↗

PubMed1991

Chronic neuropsychological and neurological impairment following acute exposure to a solvent mixture of toluene and methyl ethyl ketone (MEK).

A 38 year-old laborer experienced solvent intoxication during each of two spray paintings of a dump truck and other heavy equipment in an enclosed, unventilated garage. The paint base consisted primarily of toluene and methyl ethyl ketone. Nausea, headaches, dizziness, respiratory difficulty and other symptoms began after exposures. Over the next several days he developed impaired concentration, memory loss and cerebellar signs including an intention tremor, gait ataxia and dysarthria. MRI of the brain and EGG early in the work-up were normal, although later MRIs demonstrated fluid collection over the left parietal area. Examination by a toxicologist and neurologist revealed likely toxic encephalopathy with dementia and cerebellar ataxia. Three formal neuropsychological assessments over 2 1/2 years quantified cognitive, motor and behavioral changes. Despite similar findings in chronic exposure to these solvents, lasting sequelae following acute exposure have not been widely reported.

Adult↗

PubMed1990

Finding the common bond: stereoacuity and the other hyperacuities.

Hyperacuity thresholds for disparity, motion displacement and relative width (widths less than 10 min arc) were measured as a function of the separation between test and reference targets for separations ranging from 18-288 min arc. All three thresholds were similar in magnitude, and showed a nearly identical rise with increasing separation. Nevertheless, eccentricity, not separation, is the variable limiting all of these thresholds. This point is underscored by the fact that relative width judgments, made by comparing the narrow widths separating two pairs of lines (test and reference widths), are equally good without the reference pair. The most precise foveal judgments of stereo and motion do require a visible reference target because the observer cannot otherwise distinguish between oculomotor "jitter" and target-driven changes in disparity or motion. At eccentricities greater than 2 deg, stereo and motion thresholds for a single unreferenced line (150 msec duration) were equal to the referenced thresholds, presumably because the oculomotor noise is less than the positional uncertainty associated with these peripheral loci.

Depth Perception↗

PubMed1990

Coherence determines speed discrimination.

The visual system must determine which elements in a scene to regard as parts of a single object and which to regard as different objects. We can create stimuli that are ambiguous, ie consistent with more than one interpretation, and ask in what situations the stimulus elements are interpreted as part of a single object and when they are interpreted as multiple objects. The ambiguous stimuli in this study were moving plaid patterns--the sum of two drifting gratings with different orientations. Observers may see a rigid coherent plaid object moving in one direction, or may see two gratings moving in different directions sliding over one another. When the gratings have similar contrasts they appear to cohere and only the plaid speed is perceptually available; when the gratings have different contrasts they appear to slide and only the speeds of the gratings are perceived. Coherence thus determines what speed information is passed to higher stages of motion processing. A two-stage model of plaid motion perception is presented which agrees with the model proposed by Adelson and Movshon and extends it, detailing the relationship between coherence and speed discrimination.

Acceleration↗

PubMed1989

The perception of moving plaids reveals two motion-processing stages.

When viewed through a small aperture, the perceived motion exhibited by a long moving line or grating is ambiguous. This situation prevails because even a perfect machine could only detect motion perpendicular to a moving contour, so motion parallel to a contour is undetectable. The human visual system views the world through an aperture array--the neural receptive fields. Therefore a moving object is viewed through many small apertures and the motion within many of those apertures is ambiguous. This ambiguity may be resolved by monitoring the motion of a distinctive feature, such as a line-end or corner, and attributing to the larger object the motion of the feature. Alternatively, Adelson and Movshon have suggested that moving images are processed in two stages, that is, they are first decomposed into one-dimensional components which are later recombined to generate perceived object motion. For a moving plaid, defined as the sum of two drifting gratings, these alternative models generate different predictions concerning the resolution of the plaid's motion ambiguity. A feature monitor would respond to the motion of the intersections between gratings, whereas the two-stage motion processor would first decompose the plaid into its constituent gratings and subsequently recombine them to generate the perception of a moving plaid. Using speed discrimination to distinguish between the two models, I find that discrimination thresholds reflect the speed of a plaid's component gratings, rather than the speed of the plaid itself. This result supports the two-stage model. Although speed discrimination is limited by component processing, observers cannot directly access component speed. The only perceptually accessible velocity signal is generated by the second-stage pattern processing.

Humans↗

PubMed1989

Is there a constancy for velocity?

Human observers are unable to use disparity information to transform the angular velocity signal into a precise object-based code. The Weber fraction for discriminating changes in objective velocity (cm/sec) is about twice the Weber fraction for discriminating changes in angular velocity (deg/sec), and is substantially higher than predicted from a combination of the errors in judging disparity and angular velocity. By comparison, judgments of the distance traversed by the moving target show excellent size constancy. The discrimination of changes in objective size (cm) is as precise as the discrimination of changes in angular size (deg). The angular velocity signal is useful without transformation into an object-centered signal; it guides eye and body movements, and is the basis of motion parallax judgments. The need to retain this angular signal may explain why there is no efficient mechanism for velocity constancy.

Discrimination, Psychological↗

PubMed1989

The role of occupational health clinics in surveillance of occupational disease.

Academic occupational health centers can support state-based occupational disease surveillance by playing a role in case identification and management, physician education, workplace investigation, and surveillance case criteria development. The existing centers can also serve as models for developing new clinics. As plans for developing surveillance continue, the role of these centers should be explicitly defined, and they should be included in helping to develop mechanisms for reporting. In all these ways, the centers can significantly enhance the development of a national surveillance system for occupational disease.

Education, Medical↗

PubMed1986

Contribution of vision variables to mobility in age-related maculopathy patients.

Can mobility performance be predicted from measures of vision function? This study addressed this question by measuring a series of vision variables including visual acuity, visual fields, and differential motion sensitivity in a group of patients with age-related maculopathy (ARM) and a group of age-matched normals. Mobility performance at three adaptation levels was determined objectively on an indoor course. The results indicate that for the patients with ARM, mobility variables can be predicted from measures of vision function, including differential velocity sensitivity, and that simple variables such as time taken to complete the course and average speed are those which relate best to vision.

Aging↗

PubMed1985

Characterization of morphologic and mechanical properties of surgical mesh fabrics.

The objective of this study is to use standard testing methods to characterize the currently available synthetic mesh fabrics in terms of their chemical, physical, mechanical, and morphologic properties. Three commonly used surgical mesh fabrics, Mersilene (Ethicon), Marlex (Davol), and Teflon (USCI), were used, and the tests reveal that they differ from one another chemically as well as configurationally. The experiment included an identification of the structure of the yarn and fabrics; a measurement of the porosity, pore size and shape; and a determination of tensile and bursting strength, flexural rigidity, and wrinkle recovery. A wide variation in structure and performance was observed among the three mesh fabrics. Mersilene mesh fabrics have the highest relative porosity, while Marlex and Teflon meshes have an equivalent, but lower value. Marlex meshes have the highest tensile and bursting strength followed by Teflon and Mersilene meshes. All three meshes have one common strength characteristic--a distinctive difference in tensile strength between the wale and course directions. Marlex mesh fabrics exhibit an immense flexural rigidity and poor wrinkle recovery, due mainly to the monofilament structure of the yarn. Mersilene and Teflon mesh fabrics have similar but considerably lower, flexural rigidity than Marlex. Thus, it is evident that the chemical nature of the constituent fibers, as well as the yarn and fabric structure, have a great effect on the performance of the resulting mesh fabrics. The availability of this characterization data can serve as the basis for a surgeon's selection of the most appropriate commercial surgical mesh fabric for each case, as well as to provide a foundation for the subsequent comparison of their in vivo performance.

Materials Testing↗

PubMed1985

Colliding targets: evidence for spatial localization within the motion system.

The ability to judge the relative location of moving targets is seriously degraded if the targets move in different directions. The vernier acuity for a target in which the two components move in the same direction is not impaired until target velocity exceeds about 4 deg/sec. If the components are moving along trajectories which differ in direction by more than 15 deg, vernier thresholds rise significantly at target speeds greater than 1 deg/sec. The conditions which affect stationary vernier acuity, i.e. separation of target components, duration, and orientation, do not account for the loss in acuity. Our results suggest that localization for moving targets depends on directionally-selective motion detectors.

Female↗

PubMed1985

Sequential recruitment in the discrimination of velocity.

Human observers can discriminate a 5% difference in velocity for a wide range of velocities. Using an apparent-motion stimulus, we demonstrated that velocity discrimination depends on the detection of small changes in asynchrony, changes of the order of 1 msec or less. The simplest component of an apparent-motion stimulus is a pair of spatially separate lines presented asynchronously. Generally the incremental asynchrony threshold for a single pair of lines is much too large to account for velocity discrimination. A sequence of five to eight asynchronously presented targets, equivalent to continuous motion viewed for a duration of 80-100 msec is required to reach asymptotic velocity discrimination. Our experiments rule out probability summation as the explanation for the enhanced temporal sensitivity observed with the sequential presentation of multiple asynchronous targets. Sequential recruitment, a descriptive term for this enhanced temporal sensitivity, depends on the summation of a velocity-specific signal within the physiological network responding to motion.

Adolescent↗