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Biomedical subjects

A Slater

Publications and source records attributed to A Slater.

At least 19 recordsLinked to original sources
PubMed1991

Form perception at birth: Cohen and Younger (1984) revisited.

Cohen (1988; Cohen & Younger, 1984) has suggested that there is a shift in the perception of form sometime after 6 weeks of age. Prior to this age infants can remember the specific orientations of line segments, but cannot process and remember the angular relations that line segments can make. Experiment 1 used simple line stimuli with newborn infants to test this suggestion. Following habituation to a simple two-line angle the newborns dishabituated to a change of orientation but not to a change in angle, confirming Cohen and Younger's suggestion that orientation is a powerful cue in early shape perception. In Experiments 2 and 3 newborns were familiarized either to an acute or to an obtuse angle that changed its orientation over trials. On subsequent test trials the babies gave strong novelty preferences to a different angle. Alternative interpretations of the results are discussed, but these experimental findings are compatible with the suggestion that newborns can quickly learn to process angular relations, and that rudimentary form perception may not be dependent on a lengthy period of learning and/or maturation for its development.

Attention↗
PubMed1991

Visual processing of stimulus compounds in newborn infants.

An experiment is described in which newborn infants' processing of stimulus compounds was investigated. After familiarization to two alternately presented stimuli which differed in colour and orientation, the newborns showed significant preferences for a stimulus which had a novel colour/orientation combination: the novel stimulus was produced by recombining features of the stimuli used for familiarization. This finding argues against the view that infants initially process separate components, or parts, of visual stimuli and are only able to attend to the correlations between them after about 3 months of age. Rather, the ability to process and remember stimulus compounds is present at birth.

Attention↗
PubMed1990

Size constancy at birth: newborn infants' responses to retinal and real size.

Two experiments are described whose aim was to investigate whether perception of size at birth is determined solely by proximal (retinal) stimulation, or whether newborn babies have the ability to perceive an object's real size across changes in distance. In Experiment 1, preferential looking between pairs of stimuli which varied in real size and viewing distance was found to be solely determined by retinal size, suggesting that changes to proximal stimulation can have profound effects on newborns' looking behavior. However, in Experiment 2 newborns were desensitized to changes in distance (and retinal size) during familiarization trials, and subsequently strongly preferred a different sized object to the familiar one, suggesting that the real size had been perceived as constant across the familiarization trials. These results confirm Granrud's (1987) findings that size constancy is present at birth.

Attention↗
PubMed1989

The effects of small plate osteosynthesis on postoperative radiotherapy.

Small plate osteosynthesis is becoming increasingly popular in reconstruction following ablative surgery for oral malignancies. In those cases where postoperative radiotherapy is to be included in the treatment it has been suggested that these plates may cause problems such as dose enhancement and tumour shielding and should therefore be removed prior to the radiotherapy. A physical method is described to assess the anticipated radiation dose changes at the tissue/plate interface both behind and in front of the plate. As a result of this assessment certain recommendations are made.

Bone Plates↗
PubMed1988

Orientation discrimination and cortical function in the human newborn.

There is some controversy concerning whether or not the visual abilities of the newborn are mediated entirely through subcortical pathways or whether the visual cortex is functioning at birth. A critical test of cortical functioning is discrimination of orientation: orientation-selective neurons are found in the visual cortex but not in subcortical parts of the visual system. An experiment is described in which newborn infants were habituated to a square-wave grating oriented 45 degrees from vertical. After habituation, significant preferences for the novel, mirror-image, grating were found, a result which argues for some degree of visual cortical functioning at birth.

Arousal↗
PubMed1987

Whole-body protein turnover in adult hemodialysis patients as measured by 13C-leucine.

Muscle wasting may occur in patients with chronic renal failure (CRF). To determine whether this is due to a decrease in the synthesis or an increase in the breakdown of muscle protein, we evaluated postabsorptive whole-body protein breakdown, oxidation, and synthesis rates at steady state during a primed, continuous infusion of 13C-leucine. This was done in seven subjects on chronic maintenance hemodialysis (MHD) and in seven normal control subjects. The protein breakdown rate in MHD was not different from that in controls (103 +/- 19 and 106 +/- 19 mumol leucine.kg-1.h-1, respectively). In MHD, however, the protein oxidation rate was 43% greater than that in controls (20 +/- 6 and 14 +/- 4 mumol leucine.kg-1.h-1, p less than 0.05), whereas net protein synthesis was less (p less than 0.05). Reduced net synthesis and increased oxidation rates of protein in the postabsorptive state may therefore contribute to the muscle-wasting syndrome in patients with CRF.

Adult↗
PubMed1985

Pattern preferences at birth and their interaction with habituation-induced novelty preferences.

Three experiments are described which relate to models of infant visual preferences, and to the ways in which preferences can be modified or created by habituation. In all experiments newborn babies were used as subjects. In Experiments equated 1 and 2 infants were presented with pairs of stimuli that were equated for contour density but which differed in spatial frequency components. The preferences obtained give support to Banks and Salapatek's (1981, Journal of Experimental Child Psychology, 31, 1-45) model of infant preferences which predicts that the maximally preferred stimulus will be that which contains high amplitude spatial frequency components falling within the age group's peak contrast sensitivity. In Experiment 3 an infant-controlled habituation procedure was used. The results obtained suggest that strong natural preferences based on the infants' peak contrast sensitivity cannot be changed by habituating infants either to the preferred or to the nonpreferred member of a stimulus pair. However, where no prior preference exists between two stimuli that are perceptually highly discriminable, very strong novelty preferences are found after habituating newborns to either stimulus. The results suggest that the contrast sensitivity model can be a powerful predictor of preferential looking in newborns, and in addition are further evidence that preferences based on experience can be found from birth.

Exploratory Behavior↗
PubMed1985

Shape constancy and slant perception at birth.

Two experiments are described the object of which was to investigate whether perception of shape at birth is determined solely by proximal (retinal) stimulation, or whether newborn babies have the ability to perceive objective, real shape across changes in slant. In experiment 1 looking at (ie preference for) one stimulus, a square, when paired with either of two trapeziums, was found to change in a consistent manner with changes in slant, indicating that these changes in stimulation are detected and can cause considerable changes in looking behaviour. In experiment 2 newborns were desensitized to changes in slant during familiarization trials, and subsequently strongly preferred a different shape to the familiarized shape in a new orientation. This suggests that the real shape had been perceived as invariant across the retinal changes caused by the changes in slant, and further suggests that shape constancy is an organizing feature of perception which is present at birth.

Attention↗
PubMed1985

Contrast and spatial frequency components in visual preferences of newborns.

A preferential-looking procedure was used to investigate newborns' responses to square-wave gratings varying in spatial frequency and contrast. A preliminary study confirmed that the gratings used in the experiment were suprathreshold. In the experiment newborns' preference for a grating of 0.1 cycle deg-1 within the peak contrast sensitivity range was examined. Reduction in the contrast of this grating led to a transfer of the preference to a high-contrast grating of the same space-averaged luminance with a spatial frequency outside this range (0.42 cycle deg-1). The findings are discussed with reference to the role of the contrast sensitivity function in pattern preferences of newborns: it is suggested that contrast and spatial frequency interact in determining pattern preferences.

Female↗
PubMed1983

Locus of habituation in the human newborn.

There is some controversy concerning the youngest age at which an infant will habituate to a visual stimulus or will prefer a novel to a familiar pattern. One suggestion has been that apparently successful reports of habituation and dishabituation in the newborn baby are attributable to retinal adaptation. This interpretation was tested in two experiments. In both experiments monocular conditions of viewing were used: newborns were habituated with one eye as the 'seeing' eye, and posthabituation novelty preferences investigated with the other eye. Significant preferences were found both for a novel colour (experiment 1) and for a novel shape (experiment 2), which implies that a retinal-adaptation model can be ruled out. It is suggested that the habituation effects and the subsequent novelty preferences found in the experiments are most reasonably interpreted as a function of memory formation, and evidence is presented for the storage of visual experience from birth. The results also demonstrate some form of binocular interaction in the newborn.

Adaptation, Ocular↗
PubMed1982

Hyperthermia and the heat-shock proteins of HeLa cells.

When HeLa cells are subject to hyperthermia, the synthesis of specific heat-shock proteins (HSP) is induced under a variety of thermal conditions. HSP synthesis does not occur at temperatures above 43 degrees C but requires return to a culture temperature of 37 degrees C. Maximal induction appears to be achieved if a brief hyperthermia treatment (10 min, 45 degrees -46 degrees C) is followed by 2 h "development" at 37 degrees C. The induction process requires transcription but not DNA replication, and general cell metabolism is probably also required, as induction does not occur if the heat-treated cells are returned to 4 degrees (rather than 37 degrees C) for development. A small proportion of the HSPs of 72-74 Kd are found in nuclei, but do not appear to bind to DNA. The bulk of these proteins, as well as those at 100 Kd, are cytoplasmic, but none are preferentially associated with mitochondria. Increased synthesis of the 100Kd and 72-74 Kd HSPs was also triggered by pretreatment of the cells with 5 x 10(-5) M sodium arsenite.

Amino Acids↗
PubMed1981

Polypeptides encoded by polyadenylated and non-polyadenylated messenger RNAs from normal and heat shocked HeLa cells.

There is an increased synthesis of proteins in the molecular weight region of 100,000 72,000-74,000 and 37,000 two hours after treatment of HeLa cells for 10 min at 45 degrees C. In vitro translation, using a rabbit reticulocyte cell-free protein synthesising system, of HeLa cell cytoplasmic RNA shows that the prominent 72,000-74,000 Mr heat shock protein band comprises seven polypeptide species (namely alpha d beta gamma delta epsilon zeta) and these polypeptides are directly encoded by both polyadenylated and nonpolyadenylated mRNA.

Animals↗
PubMed1978

An assessment of laparotomy in the management of patients with Hodgkin's disease.

Planned laparotomy and splenectomy has been a safe investigation for sixty patients with clinical Stage I, II or III Hodgkin's disease. Twenty-four of the 60 patients (40%) changed stage and 18 patients had their treatment altered as a consequence of the procedure. Forty-three per cent of patients without a palpably enlarged spleen had unsuspected disease when the organ was examined pathologically, although a false positive spleen was uncommon. Eight of 55 patients (14.5%) had intra-abdominal disease which was not detected by lymphangiography. Intra-abdominal disease occurred with all histological sub-types and was found in two patients who had clinical Stage I disease and lymphocyte predominance in their node histology. Sarcoid-like granulomata were found in ten patients, seven in the spleen, one in the liver and spleen, one in the skin and one in the original node biopsy. In the majority of patients, granulomata were associated with nodular sclerosing or mixed cellular histology. In all ten patients the Hodgkin's disease was suppressed by appropriate chemotherapy and disease has not recurred. No patient has shown any clinical evidence of sarcoidosis and the Kveim test done in three patients was negative. Our experience encourages us to recommend staging laparotomy for all adult patients with Hodgkin's disease which does not show obvious generalized spread beyond lymph nodes.

Adolescent↗
PubMed1976

Serum ferritin concentration in untreated Hodgkin's disease.

Serum ferritin has been estimated in 125 untreated patients with Hodgkin's disease. Increasing concentrations are found at each advancing stage of the disease and high concentrations are found in patients with systemic symptoms. In all cases this is associated with a low serum Fe concentration and reduced transferrin saturation. There is no relationship between serum ferritin concentration and histological type of disease. The findings are compatible with a non-specific response of the reticuloendothelial system to malignancy, producing a secondary disorder of Fe metabolism.

Ferritins↗