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Two experiments were conducted with the goal of exploring the effect of experiencing associative interference upon concurrent learning about conditioned stimuli and contexts in rats' appetitive conditioning. During the first training phase, two groups of rats received a conditioned stimulus (CS1) followed by food, whereas another conditioned stimulus (CS2) was presented alone. During a second training phase, discrimination was reversed in group R, while it remained the same in group D. A new conditioned stimulus (CS3) was concurrently trained followed by food during this second Phase (Experiment 1). Reversal discrimination did not facilitate concurrent conditioning of the new stimulus, but there was a trend towards facilitation of contextual conditioning, measured by magazine entries in the absence of stimuli, that was confirmed in Experiment 2. These results suggest that the interference treatment may facilitate context conditioning under circumstances and with boundaries that are yet to be established.Associations among different stimuli are not always stable in nature. The environment changes, and what it was certain at a given point may not *

Lymphoid cell maintenance, at early stages of differentiation, was significantly promoted by BM-MSC in normal and leukaemic cells. Co-cultures also modulated the expression of antigens associated with the B-ALL asynchronous phenotype as CD10 co-expressed with CD19 and CD20. To our knowledge, this is the first time that CD10, CD19 and CD20 leukaemic antigens have been reported as being regulated by BM-MSC.

Previous work showed that prior experience with discriminations requiring configural solutions (e.g. biconditional discrimination) confers an advantage for the learning of new configural discriminations (e.g. negative patterning) in comparison to prior experience with elemental discriminations. This effect is well established but its mechanism is not well understood. In the studies described below we assessed whether the saliences of configural and element cues were affected by prior training. We observed positive transfer to a new configural discrimination after configural pre-training but we were unable to find evidence for changes in cue salience using a signal-detection task. Our results confirm previous work by demonstrating experience dependent flexibility in cue processing but they also suggest that this flexibility occurs at a point in the stimulus processing pipeline later than 1-2s after the presentation of stimulus inputs. Successful learning implies acquisition of specific responses to specific stimulus situations but may also involve acquisition of general strategies which can be deployed in new tasks. For example, better discrimination performance after an intra-dimensional, rather than after an extra-dimensional shift condition (e.g. Roberts, Robbins, & Everitt, 1988) suggests that something is learned about the stimulus dimensions and this generalises between tasks. Intra-dimensional shift superiority could involve enhanced attention to the relevant dimension, ignoring the irrelevant dimension, or a combination of both. In a similar vein Alvarado and Rudy (1992) found evidence for changes in configural information processing with transverse patterning problems in rats. In transverse patterning a set of simple simultaneous discriminations is learned.For example, whenever cues A and B are presented reinforcement is obtained for selection of A (A+/B-trials). Whenever cues B and C are presented reinforcement is contingent on selection of B (B+/C-trials). Finally, whenever cues C and A are presented, reinforcement is given for selection of C (C+/A-trials). Although these discriminations are individually simple, successful performance in transverse patterning cannot be explained by simple elemental models of associative learning such as the Rescorla-Wagner Model (RWM, Rescorla & Wagner, 1972). In such models the associative strengths of stimuli A, B, and C would be the same due to the fact that they each occur on reinforced and non-reinforced trials equally often. In contrast, to explain performance in transverse patterning, it seems necessary for subjects to process the stimulus configurations (e.g. Pearce, 1987Pearce, , 1994Rescorla, 1973;) that are present on each trial in order to select the appropriate response.However, Alvarado and Rudy's contribution was not the demonstration that rats could solve transverse patterning problems per se. It was the demonstration that components of transverse patterning problems could be solved more readily after 'configural' than after 'elemental' pre-trai...

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