Associative Change in the Representations Acquired During Conditional Discriminations: Further Analysis of the Nature of Conditional Learning

Perceptual learning with tactile stimuli in rodents: Shaping the somatosensory system

The animal kingdom contains species with a wide variety of sensory systems that have been selected to function in different environmental niches, but that are also subject to modification by experience during an organism’s lifetime. The modification of such systems by experience is often called perceptual learning. In rodents, the classic example of perceptual learning is the observation that simple preexposure to two visual stimuli facilitates a subsequent (reinforced) discrimination between them. However, until recently very little behavioral research had investigated perceptual learning with tactile stimuli in rodents, in marked contrast to the wealth of information about plasticity in the rodent somatosensory system. Here we present a selective review of behavioral analyses of perceptual learning with tactile stimuli, alongside evidence concerning the potential bases of such effects within the somatosensory system.

An associative analysis of object memory

Different aspects of recognition memory in rodents are commonly assessed using variants of the spontaneous object recognition procedure in which animals explore objects that differ in terms of their novelty, recency, or where they have previously been presented. The present article describes three standard variants of this procedure, and outlines a theory of associative learning, SOP which can offer an explanation of performance on all three types of task. The implications of this for theoretical interpretations of recognition memory and the procedures used to explore it are discussed.

Differential outcome effects in pavlovian biconditional and ambiguous occasion setting tasks

Three experiments with rats explored the differential outcome effect (DOE) using a pavlovian magazine approach conditioning preparation. Experiment 1 compared groups trained on a biconditional discrimination (AX+, AY-, BX-, BY+) with differential or nondifferential outcomes, and Experiment 2 examined this using an ambiguous occasion setting task (e.g., AX+, X-, Y+, AY-). In both experiments, subjects trained with differential outcomes learned the tasks better than subjects trained with nondifferential outcomes. Furthermore, subjects given differential outcome training learned the positive occasion setting component of the ambiguous task more efficiently than the negative occasion setting component, although both were enhanced by differential outcome training. Experiment 3 demonstrated that the ambiguous occasion setting task was reversed more readily when the target-outcome relations (as opposed to the modulator-outcome relations) were maintained during the reversal phase. These data suggest that an acquired distinctiveness effect may be responsible for the DOE in pavlovian learning.

Transfer of configural learning between the components of a preexposed stimulus compound: implications for elemental and configural models of learning

In 2 experiments, rats received preexposure to 2 compound contexts: AB and CD for the congruent group and AC and BD for the incongruent group. Subsequently, all rats received a configural discrimination in which separate placement in contexts A or B indicated that presentations of stimulus X would be followed by food and presentations of Y would not, and separate placement in contexts C and D indicated that Y would be followed by food and X would not. In both experiments, rats in the congruent group acquired the conditional discrimination more rapidly than those in the incongruent group. These results are inconsistent with conventional associative accounts of either stimulus preexposure effects or configural learning and instead provide support for a connectionist account.

Associative change in connectionist networks: an addendum

The results of a recent study have provided direct support for the suggestion that conditional learning in rats is best characterized by a 3-layer connectionist network (M. J. Allman, J. Ward-Robinson, & R. C. Honey, 2004). In the 2 experiments reported here, rats were used to investigate the nature of the changes that occur when a stimulus compound is presented, whose components activate hidden units associated with food and no food, and either food or no food is presented. The results of both experiments, while controlling for the possible contribution of associations between these hidden units (within-layer links), provide evidence that the distribution of associative change between units in the hidden layer that are activated by the stimulus compound and those in the output layer (between-layer links) are unequal. They also indicate that associative change is more marked on trials on which no food was presented than on trials on which food was presented.

Excitotoxic Lesions of the Entorhinal Cortex Leave Gustatory Within-Event Learning Intact

The ability of rats with ibotenate lesions of the entorhinal cortex to form memories for events was assessed by using a gustatory within-event learning procedure. Rats first received exposure to 2 events, AX and BY, each composed of a pair of flavors. Following this exposure period, Flavor X alone was paired with the delivery of lithium chloride. Lesioned and control rats showed a greater aversion to A than to B and to AX than to BX. These results challenge theories that suppose that the entorhinal cortex plays a general role in forming representations of patterns of stimulation.