Biomedical subjects

Klaus G Melchers

Publications and source records attributed to Klaus G Melchers.

4 recordsLinked to original sources

PubMed2006

The comparator theory fails to account for the selective role of within-compound associations in cue-selection effects.

In a human causal learning experiment, we investigated cue selection effects to test the comparator theory (Denniston, Savastano, & Miller, 2001; Miller & Matzel, 1988). The theory predicts that the occurrence of cue selection is independent of whether the relevant learning trials are presented in a standard forward manner or in a backward manner and that within-compound associations are of equal importance in both cases. We found that the strength of the cue-selection effect was positively correlated with knowledge of within-compound associations in the backward condition but not in the forward condition. Furthermore, cue-selection effects were less pronounced in the former than in the latter condition. These results are at variance with the comparator hypothesis but are in agreement with a modified associative theory and with the suggestion that retrospective revaluation might be due to rehearsal processes.

Adult↗

PubMed2006

Extinction of conditioned inhibition through nonreinforced presentation of the inhibitor.

In previous studies that have tried to extinguish conditioned inhibition through nonreinforced presentations of the inhibitor, researchers have repeatedly failed to find evidence for such extinction. The present study revealed that extinction can be achieved through nonreinforcement of the inhibitor, depending on properties of the reinforcer. In a human causal learning experiment, we found complete extinction in a scenario in which the reinforcer could take on negative values. Thereby, this scenario reflected the assumed symmetrical continuum on which associative strength can vary, according to the Rescorla-Wagner theory of associative learning. In contrast to this, the inhibitory cue retained its inhibitory potential in another condition, in which the scenario did not allow negative values of the reinforcer.

Attention↗

PubMed2005

The experimental task influences cue competition in human causal learning.

Participants were shown A+ and C- trials followed by AB+ and CD+ trials. These trials were embedded in a causal learning task in which participants had to learn either the relationship between different foods and allergic reactions or the relationship between different stocks and an increase in the stock market index. The authors orthogonally varied the manner in which the different cues were presented to participants during training. Cue competition was related to the causal learning scenario but not to the manner in which the different cues were presented. These results question claims of a human bias toward configural processing that were based on difficulties in finding cue competition in some previous causal learning experiments.

Adult↗

PubMed2004

Within-compound associations in retrospective revaluation and in direct learning: a challenge for comparator theory.

In three human causal learning experiments we investigated the role of within-compound associations in learning about absent cues versus learning about present cues. Different theoretical approaches agree that within-compound associations are essential for learning about absent cues-that is, for retrospective revaluation. They differ, however, with regard to the role of within-compound associations for learning about present cues-that is, for direct learning. A memory test was used to assess within-compound associations. Experiment 1 used a blocking/release from overshadowing design, Experiment 2 used a conditioned inhibition design, and Experiment 3 used a higher-order cue selection design. In all experiments, first-order retrospective revaluation was significantly correlated with within-compound associations, but no significant correlations were found for the direct learning conditions. In addition to this, second-order retrospective revaluation in Experiment 3 was positively correlated to joint knowledge of first-order and second-order within-compound associations. Furthermore, cue selection effects were stronger for direct learning conditions than for retrospective learning conditions. These results are at variance with the comparator hypothesis but are in agreement with a modified associative theory and with the suggestion that retrospective revaluation might be due to rehearsal processes.

Adolescent↗