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Biomedical subjects

L G Allan

Publications and source records attributed to L G Allan.

10 recordsLinked to original sources
PubMed1992

The associative basis of contingent color aftereffects.

According to a conditioning analysis of the orientation-contingent color aftereffect (McCollough effect, ME), orientation stimulus (grids) become associated with color. Contrary to this interpretation are reports that simple forms cannot be used to elicit illusory color and that the ME is not degraded by decreasing the grid-color correlation. The present results indicate: (a) Form stimuli can contingently elicit color aftereffects; (b) even a non-patterned stimulus--the lightness of a frame surrounding a colored area--can contingently elicit color aftereffects; (c) this frame lightness-contingent aftereffect, like the ME, persists for at least 24 hr; and (d) the frame lightness-contingent aftereffect can be used to demonstrate that correlational manipulations affect the ME, as they affect other types of conditional responses.

Adult↗
PubMed1991

Characteristics of the indirect McCollough effect.

Induction of contingent color aftereffects with a single chromatic grid sometimes results in an illusory color on a grid different from the one presented during induction. Such illusory color, contingently elicited by a noninduced grid, has been termed the indirect McCollough effect (indirect ME). We show that the indirect ME occurs only when the color complementary to the grid color is present during induction (either physically present or as a color afterimage), and that the indirect ME is seen only on gratings that are orthogonal to the induction orientation. These findings are in accord with the account of the indirect ME proposed by Humphrey, Dodwell, and Emerson (1989). We also show that characteristics of the indirect ME (seen following one-grid induction), both on induced and orthogonal orientations, are similar to those observed with the direct ME (seen following the usual two-grid induction procedure). Both procedures result in contingent aftereffects that display substantial retention and that do not display interocular transfer.

Adult↗
PubMed1990

Spatial contingency and the McCollough effect.

On the basis of a conditioning analysis of the orientation-contingent color aftereffect (McCollough effect, ME), orientation stimuli become associated with simultaneously presented chromatic stimuli. This account suggests that decreasing the contingency between the grid orientation and color should decrease the strength of the aftereffect. Results of previous research indicate that decreasing the temporal contingency (by presenting homogeneous chromatic stimuli between presentations of chromatic grids) does not decrease the ME. However, it has been suggested that the appropriate contingency-degradation procedure would involve decreasing spatial (rather than temporal) contingency. That is, the illusion should be attenuated by extending the color beyond the confines of the grid. Contrary to this hypothesis, the results of the present experiments provide no evidence that decreasing the spatial contingency between grid and color decreases the ME; rather, the aftereffect is increased by such a manipulation.

Adult↗
PubMed1989

The Cyclops 33 radiation thermometer. An appraisal for use in anaesthesia.

The Cyclops 33 is a portable infrared radiation thermometer. It has many potential advantages over existing thermometers in anaesthetic practice. The technical details are described and the benefits over other instruments discussed. This apparatus offers considerable scope for advance in the field of thermometry in anaesthesia.

Anesthesiology↗
PubMed1989

Color aftereffect contingent on text.

During adaptation, two different letter strings (each five or six letters) were presented to subjects alternately, one in green and the other in magenta. The extent to which these letter strings subsequently elicited a color aftereffect was assessed. In different experiments, the chromatic letter strings consisted of words and nonwords. The results indicated that letter strings that form English words can contingently elicit a color aftereffect. This was the case even when the words were anagrams. There was no evidence that nonword letter strings could contingently elicit such an aftereffect, even when the nonwords conformed to English orthography. The results are relevant to understanding other contingent color aftereffects (McCollough effects), illusory color noted by computer operators who work at monochrome (green or amber) displays, and the processing of text.

Adult↗
PubMed1988

Plasma glutathione S-transferase concentration as a measure of hepatocellular integrity following a single general anaesthetic with halothane, enflurane or isoflurane.

The plasma concentration of hepatic glutathione S-transferase (GST) was measured in matched groups of patients who received halothane, enflurane or isoflurane anaesthesia for elective minor surgery. The GST concentrations increased significantly at 3 h after anaesthesia in patients who received halothane or enflurane, but not in patients who were given isoflurane. A secondary increase in GST concentration, at 24 h, was seen in a small number of individuals who received halothane or enflurane. Abnormal GST concentrations were found in 50% of patients following halothane anaesthesia, 20% following enflurane and 11% after isoflurane. The small but significant increases in GST concentrations in patients receiving halothane or enflurane suggests an impairment of hepatocellular integrity following the administration of these anaesthetics. In contrast, isoflurane anaesthesia did not appear to be associated with this effect.

Adult↗
PubMed1987

Hepatic glutathione S-transferase release after halothane anaesthesia: open randomised comparison with isoflurane.

Plasma concentrations of hepatic glutathione S-transferase (GST) are a more sensitive measure of acute hepatic damage than aminotransferase activity. Plasma GST concentrations have been measured by radioimmunoassay in an open randomised study after halothane or isoflurane anaesthesia. The concentration of GST was significantly increased after anaesthesia in patients who received halothane in 30% oxygen/70% nitrous oxide (n = 37) and in patients who received halothane in 100% oxygen (n = 17). The frequency of abnormal GST concentrations, defined as 4 micrograms/l or more, was 35% and 24%, respectively. GST concentrations usually reached a peak 3-6 h after the end of anaesthesia. In 17 patients who received isoflurane in 30% oxygen/70% nitrous oxide, there was no significant rise in GST concentration and no patient had a concentration above 4 micrograms/l. No patient in any of the groups had a significant increase in alanine aminotransferase. In clinically identical situations, anaesthesia with halothane but not isoflurane leads to demonstrable impairment of hepatocellular integrity.

Adult↗