Biomedical subjects

F K Chua

Publications and source records attributed to F K Chua.

5 recordsLinked to original sources

PubMed2001

Nature of codes extracted during the attentional blink.

This set of 6 experiments used a 2-target rapid serial visual presentation paradigm to address 2 main questions: (a) What is the nature of the code retrieved from nontarget (i.e., unselected) items? and (b) How do the processing demands of the target affect the nature of the codes extracted from its proximate distractors? There were 3 main results: First, unless a nontarget receives attentional processing, its codes remain dormant. The type of activated codes depends on the perceptual load imposed by the other items that also underwent processing. Second, the item trailing the target invariably gets processed, but those farther downstream are excluded. If target selection is exacting, the codes of the item leading the target may also be enhanced. Third, the magnitude of the attentional blink increases with target selection difficulty; it is, however, unaffected by the perceptual load imposed by the target.

Attention↗

PubMed1994

Hyper-stimulation of monoclonal antibody production by high osmolarity stress in eRDF medium.

An earlier study (Chua et al., 1994) showed that hybridoma 2HG11 cultivated in a basal medium called eRDF, which is enriched in amino acids, enabled higher immunoglobulin (Ig) production with and without serum, when compared to two other traditional media RPMI and DMEM/F12. A further enhancement of Ig productivity was achieved when the osmolarity of the culture medium was increased from 300 mOsm to 350 mOsm (Oh et al., 1993). To determine whether the eRDF media was indeed better, three other cell lines, two IgG producers (TB/C3 and I13/17) and an IgM producer (B10), were tested. The results showed that maximum viable cell densities in eRDF medium were up to 3-times higher than in RPMI and maximum Ig titres were 2-8-times higher than in DMEM/F12 and RPMI. The three cell lines were similarly subjected to osmotic increases from 300 mOsm to 350 and 400 mOsm by addition of NaCl. There was an increase in Ig titres of between 30% to 100% compared to the control medium, although cell growth was reduced. Thus, hyper-stimulation by osmolarity stress was found to be generally effective in eliciting higher Ig production; the extent of enhancement being more pronounced for certain cell lines. Other osmolytes such as sucrose and KCl demonstrated similar effects of increasing Ig productivity. Study on the mechanism of action of osmotic stress on hybridoma 2HG11 revealed that hyper-stimulation of Ig productivity was fundamentally related to a greater availability of amino acids to cells as the cells actively accumulated more salt and amino acids to compensate for the higher medium osmolarity. Uptake of the amino acid analogues 14C-aminoisobutyric acid and 3H-methylaminoisobutyric acid into cells increased to 2.34 x 10(3) cpm per cell per min and 6.35 x 10(3) cpm per cell per min, respectively, under osmotic stress. This corresponds to an 85% increase in uptake via the Na(+)-dependent symport and a 50% increase in uptake via the Na(+)-independent and Na(+)-dependent symports. In the 350 mOsm medium, hybridomas also demonstrated an increase in metabolic activities of 5-10% compared to the control. This, together with the reduced specific growth rate in cells under osmotic stress, suggests that more energy was channelled into the biosynthetic pathway of Ig production.

Amino Acids↗

PubMed1991

A human colon cancer cell line established from collagen matrix cultures transplanted into nude mice.

A new human colon cancer cell line (020588) has been derived by means of a combined in vitro matrix-in vivo xenograft technique. The tumour cell line is carcino-embryonic antigen positive, displays a marker chromosome and proliferates in chemically-defined serum-free culture medium. The chemosensitivity pattern for the tumour cell line was similar to that observed for the parent tumour cells. The novel method used to establish this continuous human tumour cell line may have several advantages over standard techniques.

Animals↗

PubMed1990

The role of colon fibroblasts in malignant large bowel obstruction--an experimental in vitro model.

The mechanism of bowel obstruction in colorectal cancer is likely to involve interactions between tumour cells, host fibroblasts and the extracellular matrix. The role of fibroblast-mediated matrix reorganisation in malignant structures of the large bowel was examined in an in vitro collagen matrix model in which tumour cells and fibroblasts were cultured under serum-free conditions. Colon cancer cells secreted a factor(s) which enhanced the ability of colon fibroblasts to contrast a collagen matrix without an associated mitogenic response by the fibroblasts. Within uncontracted collagen gels marked elongation of fibroblast cell processes was observed in the presence of the tumour-derived factor(s). We propose that matrix reorganisation by host fibroblasts in the wall of the human colon is responsible, at least in part, for malignant large bowel obstruction.

Cell Communication↗

PubMed1990

The processing of spatial frequency and orientation information.

Three identification experiments were completed to disambiguate the associations between spatial frequency and orientation information at the sensory, decisional, and response levels. The stimuli were gratings generated by crossing four levels each of spatial frequency and orientation. In Experiment 1, the subjects made a single identification response to the stimuli. In Experiment 2, two identification responses were made, one for the spatial frequency component and the other for the orientation component. In Experiment 3, the subjects identified either the spatial frequency or the orientation component in any block of trials. The data were confusion matrices, and an information-transmission approach was used to investigate the interactions in the system. The results show that although there were sensory associations, there were no interactions at the decisional level. Performance parity was found: there was no significant difference between the single- and double-judgment paradigms in terms of information transmitted. Overall, the results suggest that although spatial frequency and orientation information is coded jointly at the sensory level, subsequent processing is independent, with each dimension drawing upon different attentional resources.

Adult↗