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Biomedical subjects

M J Morgan

Publications and source records attributed to M J Morgan.

At least 127 records · Page 7Linked to original sources
PubMed1990

Spatial filtering and spatial primitives in early vision: an explanation of the Zöllner-Judd class of geometrical illusion.

The apparent length and orientation of short lines is altered when they abut against oblique lines (the Zöllner and Judd illusions). Here we present evidence that the length and orientation biases are geometrically related and probably depend upon the same underlying mechanism. Measurements were done with an 'H' figure, in which the apparent length and orientation of the cross-bar was assessed by the method of adjustment while the orientation of the outer flanking lines was varied. When the flanking lines are oblique the apparent length of the central line is reduced and its orientation is shifted so that it appears more nearly at right-angles to the obliques than is in fact the case. Measurements of the orientation and length effects were made in three observers, over a range of flanking-line angles (90, 63, 45, 34 and 27 deg) and central line lengths (9, 17, 33 and 67 arc min). The biases increased with the tilt of the flanking-lines, and decreased with central line length. The extent of the length bias could be accurately predicted from the angular shift by simple trigonometry. We describe physiological and computational models to account for the relation between the orientation and length biases.

Humans↗
PubMed1990

6-Hydroxydopamine lesions of the ventral tegmentum abolish D-amphetamine and morphine analgesia in the formalin test but not in the tail flick test.

The effect of bilateral 6-hydroxdopamine (with desipramine) lesions of the ventral tegmental area-substantia nigra region on analgesia produced by morphine and D-amphetamine was examined with the formalin and tail flick tests in rats. These lesions depleted dopamine, but not noradrenaline, in the ventral and anterior striatum. Morphine and D-amphetamine produced analgesia in the formalin test in sham lesioned rats but not in lesioned rats. In contrast, morphine produced the same degree of analgesia in the tail flick test in sham lesioned and lesioned rats while D-amphetamine did not produce analgesia in this test. These data suggest that morphine and D-amphetamine analgesia in the formalin test involves dopamine, whereas morphine analgesia in the tail flick test does not.

Analgesia↗
PubMed1990

Biases and sensitivities in geometrical illusions.

Psychometric functions were collected to measure biases and sensitivities in certain classical illusory configurations, such as the Müller-Lyer. We found that sensitivities (thresholds or just noticeable differences) were generally not affected by the introduction of illusory biases, and the implications of this for theories of the illusions are discussed. Experiments on the Müller-Lyer figure showed that the effect depends upon mis-location of the ends of the figure, rather than upon a global expansion as demanded by the size-constancy theory. A new illusion is described in which the perceived position of a dot is displaced towards the centre of a surrounding cluster of dots, even though it is clearly discriminable from other members of the cluster by their colour. We argue that illusions illustrate powerful constraints upon visual processing: they arise when subjects are instructed to carry out a task to which the visual system is not adapted.

Distance Perception↗
PubMed1990

Characterization of the 5' end of the gene for human glucose phosphate isomerase (GPI).

We have isolated the gene coding for human glucose phosphate isomerase, and here we report the characterization of its 5' end including the first two exons. The gene is greater than 50 kb in size and contains a minimum of eight exons. We have no evidence that this gene is part of a multigene family or that there are any pseudogenes. The potential transcription start site has been determined by primer extension analysis and is 52 bp upstream from the translation initiation site of the protein. Sequences 5' to the transcription initiation site and within the first intron are extremely GC rich and form part of a CpG island. Five potential Sp1 sites (GGGCGG) have been located at positions -57, -61, -95, +183, and +575. The most 5' of these (GGGGCGGGGG) is likely to be the main Sp1 binding site, as it conforms precisely to a 10-bp consensus sequence. At position -44 there is a putative TATA box (CATAAA). Thus in common with an increasing number of genes, the putative promoter region of glucose phosphate isomerase shows structural similarities to both housekeeping and facultative gene promoters.

Amino Acid Sequence↗
PubMed1990

Future funding policies from non-government sources: the Wellcome Trust.

As we enter the 1990s, the Trust is taking on a new and unsought role as a mainstay of University biomedical research. It is to be hoped that recent statements from Government, which appear to recognize the harm being wreaked on the Universities, will prove to be more than pious platitudes.

Biochemistry↗
PubMed1990

Evidence for positional coding in hyperacuity.

Observers performed simple pattern discriminations [tests of orientation (vernier) acuity and spatial-interval acuity] with targets consisting of spatially separated squares. We investigated the effects on acuity of supernumerary squares placed at various mean positions between the two squares constituting the target configuration. The exact position of the supernumerary squares relative to the target squares changed randomly from trial to trial, so that their spatial relationship to the targets could not serve as a cue. Observers attempted to ignore these supernumerary squares and to base their judgments on the outer target squares alone. The supernumerary squares raised thresholds if they were sufficiently close (4.4-arcmin separation) to the target squares but not if they were at a greater distance (21.0 arcmin). The results therefore show that the observers could ignore the supernumerary squares, even when they fell into the space between the target squares. This finding suggests that observers can select a class of length- and orientation-tuned filter that is suited exactly to the requirements of a particular psychophysical task. We argue that filter models of hyperacuity are insufficient unless they address this critical issue of filter selection and that a complete model requires an explicit spatial representation of target feature position.

Humans↗
PubMed1989

Work overload induced changes in fast and slow skeletal muscle myosin heavy chain gene expression.

Work induced hypertrophy of the slow postural soleus and the fast phasic plantaris muscles was produced by tenotomy of the synergistic gastrocnemius muscle. Increases in weight of both muscles were associated with proportionately even larger increases in total RNA and mRNA levels. Alterations in levels of specific myosin heavy chain (MHC) isoform mRNAs were measured using the slot blot procedure with radioactively labelled oligonucleotides as probes. Type 1 MHC gene expression was unaffected in both muscles by work overload, whereas type 2a was deinduced in the soleus and type 2b was deinduced in the plantaris. The neonatal MHC gene was transiently reinduced in the plantaris.

Animals↗
PubMed1989

Motion-deblurring in human vision.

If photographs are taken of moving objects at slow shutter speeds the images of the objects are blurred. In human vision, however, we are not normally conscious of blur from moving objects despite the fact that the temporal response of the photoreceptors is sluggish. It has been suggested that there are motion-deblurring mechanisms specifically to aid the visual system in the analysis of the shape of retinally moving targets. Models of motion deblurring have been influenced by the finding that certain very precise spatial pattern discriminations are unaffected by motion. An example is vernier hyperacuity, in which the observer must detect the direction of offset between two lines with abutting ends. With a stationary stimulus, observers can detect a vernier cue of less than 10 arcsec and acuity is unaffected by retinal-image motion of up to 3 deg s-1 We confirm this finding, but provide evidence against any general deblurring mechanism by showing that another kind of hyperacuity, discrimination of the distance between two parallel lines (spatial interval acuity), is interfered with by motion. This argues against a general deblurring mechanism, such as a neural network 'shifter circuit', and we point out that the high level of vernier acuity for moving stimuli is susceptible to an alternative explanation.

Humans↗
PubMed1989

Perceived diagonals in grids and lattices.

Diagonal lines are seen running between the intersections in repetitive grid patterns, but not in lattices of dots. We show that these lines, which are of reverse contrast to the grid, cannot be explained by global Fourier components in the pattern, or by low-pass orientation-specific filtering. The lines depend upon local diagonal components at the intersection, and we suggest that the output of local detectors are combined by collector units receiving their input from different visual field positions. Relevant neurophysiological evidence is discussed, and the model is extended to subjective contours and the Fraser twisted cord.

Form Perception↗
PubMed1989

The Weber relation for position is not an artefact of eccentricity.

We have measured the spatial threshold for discriminating the length of arcs falling on isoeccentric circles in the periphery out to 4 deg. The just-noticeable-difference rises with the arc length in the range 10-500 arc min, repeating the usual finding with foveally presented straight-line stimuli. Our results do not support a recent suggestion that the Weber relation is mainly due to greater positional uncertainty in the peripheral retina.

Humans↗
PubMed1989

Spatial properties of mechanisms for detection of moving dot targets in dynamic visual noise.

The maximum displacement threshold for direction discrimination (dmax) was determined for single or paired dot targets moving discretely against a background of dynamic visual noise. dmax rose as the spatial density of noise was reduced, or when the interframe interval was decreased. dmax was greater for dot pairs than for single dots, and rose progressively as the distance between the dots was reduced. dmax was also greater if the orientation of the target dot pairs differed from the orientation of paired dots in the background noise. Dichoptic presentation of the target and background noise allowed the target to be detected with an accuracy that did not depend on displacement.

Female↗
PubMed1988

Mouse glucose-6-phosphate isomerase and neuroleukin have identical 3' sequences.

Neuroleukin is a neurotrophic factor of relative molecular mass (Mr) 56,000 (56K) found in skeletal muscle, brain, heart and kidneys which supports the survival of embryonic spinal neurones, skeletal motor neurones and sensory neurones. Neuroleukin is also a lymphokine product of lectin-stimulated T cells and induces immunoglobulin secretion by cultured human peripheral blood mononuclear cells. Mouse neuroleukin has been cloned, the complete nucleotide sequence has been determined and its complementary DNA has been transiently expressed in monkey COS-1 cells. The serum-free supernatant of the transfected, but not of control mock-transfected, cells was shown to mimic the properties of neuroleukin isolated from mouse salivary glands. In our work on the molecular genetics of carbohydrate metabolism we have recently isolated a mouse glucose-6-phosphate isomerase (or phosphoglucose isomerase, PGI) cDNA clone using the yeast PGI gene (PGI 1) as a probe. We report here that there is complete sequence identity between the 759 nucleotides at the 3' end of this clone (coding and non-coding) and the sequence of mouse neuroleukin.

Amino Acid Sequence↗
PubMed1988

Complementation of metabolic defect in phosphoglycerate kinase (PGK)-deficient line of Chinese hamster ovary cells by introduction of human PGK cDNA.

A full-length copy of the coding sequence of the human phosphoglycerate kinase (PGK) gene was introduced into a glycolysis-negative, PGK-deficient line of Chinese hamster ovary (CHO-K1) cells by gene transfer. Transformants were isolated either by cotransfer of the bacterial aminoglycoside phosphotransferase (AGPT) gene, or by direct selection for expression of the PGK gene. Integration of the human PGK gene has been demonstrated by Southern blot analysis and its expression by starch gel electrophoresis. PGK transformants behaved phenotypically as predicted by the properties of their wild type parent: mannose was no longer toxic, but instead was metabolized via glycolysis to lactic acid, and cell growth was no longer dependent on glutamine oxidation. Thus a complex phenotypic change has been mediated by gene transfer. The combination of R1.1.7 cells and the PGK plasmid provides another system to facilitate the study of mammalian gene expression.

Animals↗