Rick Mehta

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Photodynamic Therapy (PDT), with topically applied 5-aminolaevulinic acid as the photosensitiser, is an effective treatment for various malignant and pre-malignant skin conditions. Several studies have shown the importance of fluence rate as well as fluence in the efficacy of PDT. We propose a measure of PDT efficacy, Photodynamic Damage Dose (PDD), which(More)
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(More)
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(More)
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(More)
In two experiments, participants acquired one of two target configural discriminations (a biconditional or negative patterning discrimination) in a predictive learning task. In Experiment 1, participants were pretrained with either a configural or an elemental discrimination; in Experiment 2, they were pretrained with a configural discrimination, an(More)
The Downs bipolar coagulator is a precision microsurgical instrument for use in cataract surgery and other ophthalmic operations. Its chief advantages are robustness, ease of sterilization, mechanical reliability, and small size. The coagulation is delivered by a fine pair of forceps (designed for ophthalmic use). Precision can be achieved together with the(More)
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(More)
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