Search PubMed⌕ Search

Biomedical subjects

L G Allan

Publications and source records attributed to L G Allan.

At least 19 recordsLinked to original sources
PubMed2001

Temporal bisection with trial referents.

In temporal bisection, the subject is required to compare the similarity of a probe duration with two referent durations. Two bisection experiments with human subjects are reported in which performance under three referent conditions was compared. In two of the conditions, no-referent and fixed-referent, the referent pair was constant throughout the session and was varied between sessions. In the no-referent condition, samples of the referents were presented at the beginning of a block of trials, but not on the probe trials. In contrast, in the fixed-referent condition, the referent pair was presented on each probe trial. In the third referent condition, roving-referent, the referent pair was also presented on each probe trial, but the values of the pair varied during a session rather than between sessions. The pseudologistic Model (PLM; Killeen, Fetterman, & Bizo, 1997) provided an excellent account of the data from all referent conditions and indicated that (1) the scalar variability was located in the perception of the probe and was independent of the structure of the bisection task, (2) the role of the referents was to set the criterion, (3) the probe was compared with the criterion rather than with the referents, and (4) the comparison of the probe with the criterion occurred even when trial referents were available.

Adult↗
PubMed1998

Learning and homeostasis: drug addiction and the McCollough effect.

The contribution of conditioned responses (CRs) to homeostasis may be seen by examining seemingly disparate phenomena of color vision (aftereffects and chromatic adaptation) and drug addiction (withdrawal symptoms and tolerance). Color aftereffects may be elicited by nonchromatic stimuli previously paired with color (the McCollough effect, [ME]). Similarly, pharmacological aftereffects may be elicited by nonpharmacological stimuli previously paired with a drug (withdrawal symptoms). The authors summarize evidence indicating that both the ME and withdrawal symptoms are CRs. The chromatic CR is expressed as chromatic adaptation in the presence of color, and the ME in the absence of color. The pharmacological CR is expressed as pharmacological adaptation (tolerance) in the presence of the drug, and withdrawal symptoms in the absence of the drug. Both drug withdrawal symptoms and the ME are manifestations of the contribution of conditioning to normal homeostatic regulation. The authors discuss the implications of this conclusion for understanding regulatory processes and the evolution of behavioral mechanisms.

Color Perception↗
PubMed1998

Effect of remifentanil on the auditory evoked response and haemodynamic changes after intubation and surgical incision.

We have observed the effect of intubation and incision, as measured by the auditory evoked response (AER) and haemodynamic variables, in 12 patients undergoing hernia repair or varicose vein surgery who received remifentanil as part of either an inhaled anaesthetic technique using isoflurane or as part of a total i.v. technique using propofol. Anaesthesia was induced with remifentanil 1 microgram kg-1 and propofol, neuromuscular block was achieved with atracurium 0.6 mg kg-1 before intubation, and anaesthesia was maintained with a continuous infusion of remifentanil in combination with either a continuous infusion of propofol or inhaled isoflurane. The AER and haemodynamic variables were measured before and after intubation and incision. The effects of intubation and incision on the AER and haemodynamic variables were not significantly different between the remifentanil-propofol and remifentanil-isoflurane groups. However, the study had a low power for this comparison. When the data for the two anaesthetic combinations were pooled, the only significant effects were increases in diastolic arterial pressure and heart rate immediately after intubation; these were not seen 5 min after intubation. There were no cardiovascular responses to incision. There were no significant changes in the AER after intubation or incision.

Analgesics, Opioid↗
PubMed1997

Contingent color aftereffects: reassessing old conclusions.

Although there is considerable evidence supporting an associative interpretation of contingent color aftereffects, there are data that appear inconsistent with this interpretation. New findings from seven experiments are presented indicating that, contrary to earlier claims, contingent color aftereffects are observed after induction with (1) single orthogonal black bars on colored backgrounds, (2) geometric forms, and (3) two orthogonal grids of the same color. The results of these experiments are relevant to an associative interpretation of contingent color aftereffects, as well as to assessing alternative interpretations of the phenomenon.

Adult↗
PubMed1997

Isoluminance and contingent color aftereffects.

In the typical induction of the orientation-contingent color aftereffect (CCAE), the stimuli are composed of elements that differ in both color and luminance. Three experiments are reported that show that chromatic contrast between stimulus elements is insufficient for the induction of the orientation-CCAE and that luminance contrast is necessary. These experiments expand on previous research concerned with the role of luminance contrast in the induction of orientation-CCAEs by eliminating alternative explanations.

Adult↗
PubMed1995

An associative interpretation of the indirect McCollough effect.

Following an induction procedure in which a coloured grid is alternated with a square of a complementary colour, subjects report colour after-effects on both the grid orientation present during induction and the orthogonal non-induced grid orientation. The after-effect reported on the induced grid orientation is called the McCollough effect (ME). The after-effect reported on the non-induced grid orientation is called the indirect ME. There is evidence that the ME represents an instance of Pavlovian conditioning. The present results support a conditioning interpretation of the indirect ME and are inconsistent with interpretations of the indirect ME that attribute the phenomenon to special orthogonal coding mechanisms within the visual system.

Adult↗
PubMed1994

Scanning and form-contingent color aftereffects.

G. K. Humphrey, A. M. Herbert, L. A. Symons, and S. Kara (1994) and J. Broerse and P. Grimbeek (1994) suggested that the form-contingent color aftereffect reported by S. Siegel, L. G. Allan, and T. Eissenberg (1992) would not be obtained if Ss were instructed to scan the induction and assessment forms. The authors present data from Ss who were instructed to scan the forms. These scanning Ss displayed aftereffects that were no different from those described earlier by Siegel et al. Scanning Ss do display spatiotopic contingent color aftereffects.

Color Perception↗
PubMed1994

A new temporal illusion or the TOE once again?

Recently, Nakajima, ten Hoopen, and van der Wilk (1991) and Nakajima, ten Hoopen, Hilkhuysen, and Sasaki (1992) described what they believed to be a new illusion of auditory time perception. They reported that the perceived duration of a temporal interval was influenced by an immediately preceding or succeeding temporal interval. The influence of a neighboring temporal interval on perceived duration is not a new illusion, however, but is another demonstration of the time-order error.

Acoustic Stimulation↗
PubMed1993

Human contingency judgments: rule based or associative?

The study of the mechanism that detects the contingency between events, in both humans and nonhuman animals, is a matter of considerable research activity. Two broad categories of explanations of the acquisition of contingency information have received extensive evaluation: rule-based models and associative models. This article assess the two categories of models for human contingency judgments. The data reveal systematic departures in contingency judgments from the predictions of rule-based models. Recent studies indicate that a contiguity model of Pavlovian conditioning is a useful heuristic for conceptualizing human contingency judgments.

Conditioning, Classical↗
PubMed1993

McCollough effects as conditioned responses: reply to Dodwell and Humphrey.

P. C. Dodwell and G. K. Humphrey (1990) criticized the Pavlovian conditioning analysis of the McCollough effect, claiming that it was conceptually flawed and that it did not assign the McCollough effect any useful function. In this article, it is suggested that the error-correction interpretation that Dodwell and Humphrey proposed as an ostensible alternative to the conditioning interpretation can be subsumed by the conditioning interpretation. Furthermore, the conditioning interpretation does ascribe a useful function to the McCollough effect.

Attention↗
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↗