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Biomedical subjects

S Ullman

Publications and source records attributed to S Ullman.

At least 91 records · Page 5Linked to original sources
PubMed1986

The optical flow of planar surfaces.

The human visual system can recover the 3-D shape of moving objects on the basis of motion information alone. Computational studies of this capacity have considered primarily non-planar rigid objects. With respect to moving planar surfaces, previous studies have shown that the planar velocity field has in general a two-fold ambiguity: there are two different planes engaged in different motions that can induce the same velocity field. The current analysis extends the analysis of the planar velocity field in four directions: (1) the use of flow parameters of the type suggested by Koenderink and van Doorn (Optica Acta, 1975, 22, 773-791), (2) the exclusion of confusable non-planar solutions, (3) a new proof and a new method for computing the 3-D motion and surface orientation (4) a comparison with the information available in orthographic velocity fields, which is important for determining the stability of the 3-D recovery process.

Algorithms↗
PubMed1985

Antibodies to human T-cell lymphotropic virus type III in promiscuous healthy homosexual men. Relation to immunological and clinical findings.

Antibodies to human T-cell lymphotropic virus type III (HTLV-III Ab) were present in twenty-one out of sixty-four asymptomatic promiscuous homosexual men from Copenhagen. The presence of HTLV-III Ab was associated with lymphadenopathy (P less than 0.0005), cytomegalovirus isolation (P less than 0.01), low skin test reactivity (P less than 0.01) and episodes of fever within the 2 month period prior to investigation (P less than 0.05). No significant differences occurred in the total number of T-cells, T-suppressor cytotoxic cells, T-helper cells or helper to suppressor ratio (H/S ratio) between HTLV-III Ab positive and negative homosexuals. An H/S ratio less than or equal to 1.0 was significantly more frequent in homosexual men who both had HTLV-III Ab and excreted cytomegalovirus (P less than 0.01). The H/S ratio of HTLV-III negative homosexuals were significantly lower than that of the controls suggesting that a non-HTLV-III related immunosuppression occurs among homosexuals. Within 2 years after the investigation AIDS or the AIDS related complex developed in three of the men, who at the first investigation all had HTLV-III Ab, alterations in T-lymphocyte subsets and cutaneous anergy. It is suggested that a combination of T-cell subset determination and determination of HTLV-III Ab may provide more valuable prognostic information than isolated determination of HTLV-III Ab.

Acquired Immunodeficiency Syndrome↗
PubMed1985

AIDS-induced decline of the incidence of syphilis in Denmark.

The incidence rate of acquired syphilis per 100 000 total population in Denmark increased by 70% from 6.8 in 1978 to 11.6 in 1982. In 1984 this incidence had decreased by 61.2% to 4.5. The fluctuation of the number of acquired syphilis predominated in the male population with an increase of 71.8% during the five year period 1978-1982 and a decrease of 63.2% during the years 1983 and 1984. In 1978, the incidence of acquired syphilis in males was 11.3 per 100 000 total population increasing to 19.5 in 1982, decreasing to 7.2 in 1984. The decreasing number of acquired syphilis cases during the past two years are correlated to a lower number of sexual contacts among homosexual men because of fear of AIDS.

Acquired Immunodeficiency Syndrome↗
PubMed1985

Shifts in selective visual attention: towards the underlying neural circuitry.

Psychophysical and physiological evidence indicates that the visual system of primates and humans has evolved a specialized processing focus moving across the visual scene. This study addresses the question of how simple networks of neuron-like elements can account for a variety of phenomena associated with this shift of selective visual attention. Specifically, we propose the following: (1) A number of elementary features, such as color, orientation, direction of movement, disparity etc. are represented in parallel in different topographical maps, called the early representation. (2) There exists a selective mapping from the early topographic representation into a more central non-topographic representation, such that at any instant the central representation contains the properties of only a single location in the visual scene, the selected location. We suggest that this mapping is the principal expression of early selective visual attention. One function of selective attention is to fuse information from different maps into one coherent whole. (3) Certain selection rules determine which locations will be mapped into the central representation. The major rule, using the conspicuity of locations in the early representation, is implemented using a so-called Winner-Take-All network. Inhibiting the selected location in this network causes an automatic shift towards the next most conspicious location. Additional rules are proximity and similarity preferences. We discuss how these rules can be implemented in neuron-like networks and suggest a possible role for the extensive back-projection from the visual cortex to the LGN.

Attention↗
PubMed1984

Visual routines.

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Evoked Potentials, Visual↗
PubMed1984

Maximizing rigidity: the incremental recovery of 3-D structure from rigid and nonrigid motion.

The human visual system can extract 3-D shape information of unfamiliar moving objects from their projected transformations. Computational studies of this capacity have established that 3-D shape can be extracted correctly from a brief presentation, provided the moving objects are rigid. The human visual system requires a longer temporal extension, but it can cope with considerable deviations from rigidity. It is shown how the 3-D structure of rigid as well as nonrigid objects can be recovered by maintaining an internal model of the viewed object and modifying it at each instant by the minimal nonrigid change that is sufficient to account for the observed transformation. The results of applying this incremental rigidity scheme to rigid and nonrigid objects in motion are described and compared with human perception.

Computers↗
PubMed1984

T lymphocyte subsets in homosexual men from Copenhagen.

Screening of sixty-six asymptomatic homosexual men from Copenhagen revealed significantly lower Leu-3a/Leu-2a ratios as compared to controls. Ten (15%) of the homosexuals had a ratio less than or equal to 1.0. The low Leu-3a/Leu-2a ratios were the result of an increase in the absolute number of Leu-2a cells. Homosexuals with many partners and those who had been sexual partners of patients with the acquired immuno-deficiency syndrome (AIDS) had significantly lower ratios than those without these features. Cytomegalovirus was isolated from urine and/or sputum of 15% and this was associated with a Leu-3a/Leu-2a ratio less than or equal to 1.0. The observed immunological abnormalities could either represent latent infection with the putative AIDS agent or alternatively be caused by repeated infections and/or exposure to allogenic spermatocytes or lymphocytes.

Acquired Immunodeficiency Syndrome↗
PubMed1984

The prognosis of asymptomatic homosexual men with decreased T-helper to T-suppressor ratio.

Screening of 70 asymptomatic homosexual men in Copenhagen revealed that 13 (19%) had T-helper to T-suppressor (H/S) ratios less than or equal to 1.0. Clinical and immunological follow-up examinations for 2-7 months (mean, 5.2 months) disclosed that none of the 13 men developed the acquired immunodeficiency syndrome (AIDS) or AIDS-like symptoms. An increase in H/S ratios to greater than 1.0 was observed in 11 of the 13 men during the time of observation. The decreased H/S ratios were due to an increase in the T-suppressor population. The T-helper population did not at any time differ from that found in 31 male control subjects. The biological relevance of the observed decrease in H/S ratios was supported by the demonstration of a positive correlation to a decrease in the proliferative response of the lymphocytes. Serological studies did not reveal any specific infectious background for the low H/S ratio found in the 13 men, and the reason for the 'spontaneous' increase during the time of observation remains unknown. The present results indicate that most asymptomatic homosexual men with a decreased H/S ratio will experience normalization of the immunological variables.

Acquired Immunodeficiency Syndrome↗
PubMed1984

Plasma separation in patients with bronchial asthma, atopic dermatitis and hyperimmunoglobulinaemia E.

The effect of intensive plasma separation performed eight times within 5 weeks in four patients with atopic dermatitis, bronchial asthma and hyperimmunoglobulinaemia E was followed as regards clinical symptoms and changes in the concentrations of serum (S) IgE, S IgG, S IgA, S IgM, plasma complement C3 split products, S transferrin, blood eosinophils, chemotaxis of neutrophil cells and histamine metabolites in urine in samples obtained consecutively during the period of observation. The occurrence of circulating immune complexes (IC) was analysed by a polyclonal rheumatoid factor (pRF) agglutination inhibition assay and an IgE IC specific technique. IgE IC were demonstrated in three of the patients prior to plasma separation, complexed IgE was 2-3% of the total concentration of S IgE. In one patient complexes were detected by the pRF agglutination inhibition assay, also. In the three patients with IgE IC, the complexes disappeared during treatment, but recurred in two of the patients shortly after the last plasma separation. Shortly after eight separations the S IgE was reduced in all patients to a mean level of 46% of the pre-exchange concentrations. During the following 3 weeks the relative increase of S IgE in three of the patients was similar to the values obtained for S IgG. Serum IgG was subnormal in all patients during the period of treatment. Increasing numbers of eosinophils were observed in three of the patients after the fifth separation procedure. The histamine metabolite 1,4-methylimidazoleacetic (1,4- MIAA ) in urine was increased in all patients, but no significant changes were observed during the treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1983

A randomized trial of etretinate (Tigason) in palmoplantar pustulosis.

5 patients with palmoplantar pustulosis (PPP) were randomized to 8 weeks of daily treatment with either oral etretinate, 1 mg/kg b.w. or placebo. Good or moderate effect was obtained in 18 or 20 patients on etretinate compared o 6 of 21 patients on placebo (p less than 0.001). Etretinate proved to be significantly superior to placebo with regard to influence on the individual symptoms and signs of pustulosis. All patients on etretinate experienced some side effects from the mucous membranes, but they were generally mild. Treatment was discontinued after 4 weeks in 3 patients for reasons unrelated to treatment, in 4 for lack of effect (all on placebo) and in 2 for side effects (both or etretinate). Etretinate is a good alternative to other systemic treatments of PPP.

Adult↗
PubMed1983

Cutaneous sarcoidosis: an immunofluorescence study.

Biopsy specimens from granulomatous skin lesions of 14 patients with active sarcoidosis were examined by immunofluorescence microscopy. In seven lesions, deposits of IgM, IgA or complement C3 were demonstrated in the dermal vessel walls and/or at the dermal-epidermal junction. Similar deposits were found in three of twelve biopsy specimens from clinically normal skin from a buttock of the same patients. The results support the hypothesis that deposition of circulating immune complexes in the vessel walls may be of importance for the development of granulomatous lesions in sarcoidosis.

Female↗
PubMed1982

Adaptation and gain normalization.

It has been suggested in the past that adaptation effects may serve a useful role in perception. This paper shows that if the adaptation process follows a simple scheme, called proportional gain adjustment, then it can fulfil two useful functions: correction of errors and recalibration. The proposed scheme controls the gain of the system. Although it is memoryless, it ensures a setting of the gain at such a level that the average of the measured signal in the environment is always mapped onto a fixed internal representation. The proportional gain adjustment scheme is discussed in the context of single-band multi-channel models, and is shown to exhibit various phenomena associated with visual adaptation.

Adaptation, Physiological↗
PubMed1982

A model for the temporal organization of X- and Y-type receptive fields in the primate retina.

A model is proposed for the temporal characteristics of X- and Y-type responses of ganglion cells in the primate retina. The main suggestions of the model are: (I) The X-type temporal response is determined primarily by the delay between center and surround contributions. (II) The Y-type response is generated in the inner plexiform layer by a derivative-like operation on the bipolar cell's input, followed by a rectification in the convergence of these inputs onto the Y-ganglion-cell. (III) The derivative-like operation is obtained by recurrent inhibition in the dyad synaptic structure. The X- and Y-type responses predicted by the model, for a variety of stimuli, were examined and compared with available electrophysiological recordings. Finally, certain predictions derived from the model are discussed.

Animals↗