Biomedical subjects

P Dibbets

Publications and source records attributed to P Dibbets.

5 recordsLinked to original sources

PubMed2002

Serial and simultaneous feature positive discriminations in a human Skinner box.

In the present experiment participants were presented either a serial (F-->T+/T-) or a simultaneous (FT+/T-) feature positive discrimination using a Skinner box for humans. After the participants mastered the discrimination, the associative properties of F were examined using a transfer test and a counterconditioning manipulation. F affected responding to a transfer target less in the Serial than in the Simultaneous condition. However, counterconditioning of F did not affect initial discrimination performance in either condition. These results were discussed in the framework of occasion setting, elemental learning, configural learning, and a neural network model.

Journal Article↗

PubMed2002

Contextual dependencies in a stimulus equivalence paradigm.

Two experiments with human subjects assessed contextual dependencies in a stimulus equivalence paradigm. Subjects learned to form two sets of stimuli in a matching-to-sample training procedure. Each set was presented against one of two different background colours, the contextual cues. At test, the influence of a context change-that is, presenting each set against the other context-was measured on baseline, symmetry, and equivalence trials. These three trial types reflect a difference in task complexity. It was predicted that the magnitude of context-dependent effects would be a positive function of task complexity. In Experiment 1, the context change was realized by switching the stimulus set at test while keeping the background colour constant. In Experiment 2, the stimulus set remained constant, and the background colour was switched. In both experiments, a change in context only resulted in an increase in response latency on equivalence trials; no effect was seen on symmetry and baseline trials. Results were discussed in the framework of switch costs, habituation to contextual stimuli, and a model based on Shea and Wright (1995) that explains the differential influence of a context switch on easy versus difficult tasks.

Adult↗

PubMed2001

Contextual dependencies in predictive learning.

Two experiments assessed contextual dependencies in a predictive-learning task. Subjects learned to associate each of four pictorial stimuli with the occurrence or non-occurrence of a specific outcome. Each of these stimuli, the intentional stimuli, was presented against one of two different visual (Experiment 1) or auditory (Experiment 2) context stimuli. These context stimuli were incidental: subjects were not explicitly instructed to pay any attention to them and each of them in isolation was not predictive of the outcome. During acquisition and testing, subjects expressed the expected relationship between intentional stimulus and outcome by an appropriate key press. At test, intentional stimuli were presented either with the same contextual stimulus as also present during acquisition (same trials), or with the other one (switched trials). The response latency was slower on switched trials than on same trials in each experiment, a result extending previous findings on the effect of environmental contextual stimuli on task performance. Results are discussed in the framework of contextual occasion setting and habituation to contextual stimuli.

Adolescent↗

PubMed2000

Comparison of gated single-photon emission computed tomography with magnetic resonance imaging for evaluation of left ventricular function in ischemic cardiomyopathy.

To perform a head-to-head comparison between magnetic resonance imaging (MRI) and gated single-photon emission computed tomography (SPECT) for the evaluation of left ventricular (LV) function (LV ejection fraction [LVEF], LV volumes, and regional wall motion) in patients with ischemic cardiomyopathy, we studied 22 patients with chronic coronary artery disease and LV dysfunction. Multislice, multiphase echoplanar MRI was performed with Philips Gyroscan ACS-NT15. Image analysis was performed using the MASS software package to determine LV end-systolic volume, LV end-diastolic volume, and LVEF. The same parameters were calculated using quantitative gated SPECT software (QGS, Cedars-Sinai Medical Center). The different parameters were compared using linear regression, and correlation coefficients were calculated. Regional wall motion was also determined from both techniques, according to a 13-segment model and a 3-point scoring system (from 1 = normokinesia to 3 = akinesia or dyskinesia). A summed wall motion score was also calculated for MRI and gated SPECT. Good correlations were found between MRI and gated SPECT for all parameters: (1) summed wall motion scoreMRI versus summed wall motion scoreSPECT: y = 0.74x + 8.0, r = 0.88, p <0.01; (2) LV end-systolic volumeMRI versus LV end-systolic volumeSPECT: y = 0.94x - 12.3, r = 0.87, p <0.01; (3) LV end-diastolic volumeMRI versus LV end-diastolic volumeSPECT: y = 0.93x - 18.4, r = 0.84, p <0.01; and (4) LVEFMRI versus LVEFSPECT: y = 0.97x + 0.68, r = 0.90, p <0.01. For regional wall motion, an exact agreement of 83% was found, with a kappa statistic of 0.77 (95% confidence intervals 0.71 to 0.83, SE 0.03), indicating essentially excellent agreement. Thus, close and significant correlations were observed for assessment of LVEF, LV volumes, and regional wall motion by MRI and gated SPECT in patients with ischemic cardiomyopathy.

Aged↗

PubMed2000

Interaction between positional but not between non-positional cues in human predictive learning.

Four experiments with human subjects examined the cue-interaction effects using a computer-controlled predictive learning task. In Phase 1, subjects learned that cue P was consistently associated with the occurrence of an outcome (P+), whereas cue N was never followed by the outcome (N-). In Phase 2, two neutral cues, R and I, were compounded with P and N, respectively. Each compound was followed by the outcome (PR+ and NI+). Thus, cue R was compounded with the already predictive cue P, whereas cue I was compounded with the non-predictive cue N. In each phase, subjects rated the contingency between the different cues and the outcome. In experiments 1 and 2, the spatial position of the cues was fixed, whereas it was variable in experiments 3, 4a and 4b. Verbal cues were used in experiments 1-3, whereas the cues consisted of geometrical figures in experiments 4a and 4b. Evidence for cue interaction, as indicated by giving cue I a higher contingency rating than cue R after or during Phase 2, was only found under the conditions of experiments 1 and 2. The results indicate that the use of positional cues facilitates the occurrence of cue-interaction effects. Possible reasons for this finding are discussed.

Journal Article↗