Biomedical subjects

Rick Mehta

Publications and source records attributed to Rick Mehta.

4 recordsLinked to original sources

PubMed2005

Resistance to interference in complex negative patterning.

Resistance to interference was examined in rats that received a complex negative patterning discrimination in which XA and XB were followed by food reinforcement and XAB was not Retention of the discrimination was evident after separate reinforcement of both A and B (Experiment 3), but not after reinforcement of either AB (Experiments 1 and 3) or XAB (Experiments 2 and 3). These data suggest that complex negative patterning discriminations are acquired configurally and that the relative similarity of the original discrimination and subsequent interference trials dictates the final degree of retention observed.

Animals↗

PubMed2004

Conditions favoring superconditioning of irrelevant conditioned stimuli.

Three appetitive conditioning experiments with rats found partial learning of complex XA+, XB+, XAB- (+ stands for reinforced; - stands for unreinforced) negative patterning discriminations with intermixed A+ and B+ trials (Experiment 1). AB+ trials (Experiment 2), and A+, B+, and AB+ trials (Experiment 3). In all experiments, differential responding emerged more slowly during the learning of the negative patterning discriminations than during learning of the XA+, XB+, XC- control discriminations. Additionally, the negative patterning groups responded more to X than to a separately reinforced Y on unreinforced test trials: thus, X derived superexcitatory properties. This pattern was reversed in the control groups. Results are consistent with theories that allow for different activation patterns when elements are combined.

Animals↗

PubMed2003

Learned irrelevance and retrospective correlation learning.

In 1973 Mackintosh reported an interference effect that he called learned irrelevance in which exposure to uncorrelated (CS/US) presentation of the unconditional stimulus (US) and the conditioned stimulus (CS) interfered with future Pavlovian conditioning. It has been argued that there is no specific interference effect in learned irrelevance; rather the interference is the sum of independent CS and US exposure effects (CS + US). We review previous research on this question and report two new experiments. We conclude that learned irrelevance is a consequence of a contingency learning and a specific learned irrelevance mechanism. Moreover even the independent exposure controls, used in previous experiments to support the CS and US exposure account, provide support for the correlation learning process.

Animals↗

PubMed2002

Acquisition of superexcitatory properties by an irrelevant background stimulus.

Six appetitive conditioning experiments with rats demonstrated that an irrelevant X accompanying a negative patterning discrimination (XA+, XB+, XAB-) acquires extraordinarily high levels of conditioned excitation. Responding to X was similar to that evoked by 2 excitors in combination (Experiment 1) and was greater than responding to a separately reinforced Y (Experiments 2-5). Superexcitatory properties were not acquired by X in the nonpatterning discriminations of Experiments 2-4. Experiment 5 found that A and B, if anything, were weakly excitatory. Making them more strongly excitatory after conditioning did not interfere with retention of the original discrimination (Experiment 6). Results support a counterintuitive prediction of associative theories that, under carefully arranged conditions, irrelevant stimuli may acquire superexcitatory properties.

Animals↗