An elemental model of retrospective revaluation without within-compound associations

Associative structure of conditioned inhibition produced by inhibitory perceptual learning treatment

Exposure to a set of complex stimuli yields an enhanced ability to discriminate between these stimuli. In previous experimental studies, two distinguishable stimuli, X and A, were each repeatedly paired with a common Stimulus B to create compound Stimuli XB and AB. Prior evidence suggests that unique Features X and A form mutually inhibitory associations. This was evidenced by pairing Feature A with a biologically relevant stimulus (i.e., an unconditioned stimulus [US]) and observing that Stimulus X alone later serves to inhibit anticipatory behaviors for that US. These observations may reflect the mutually inhibitory nature of the two Features X and A. However, by assessing the influence of X on behavior that anticipates the US rather than Feature A, these experiments tested inhibition only indirectly. In the present experiments, a more direct measure of inhibition is proposed and tested with rats. We found evidence of retardation and negative summation of associations between unique Features X and A in their capacity to serve as competing cues during overshadowing treatments. Stimulus X was less susceptible to overshadowing by A (which is indicative of retardation of the establishment of an X-A within-compound association) and was able to suppress overshadowing by A of another stimulus (Y) when X was presented with Y at test (which is indicative of negative summation of the representation of A by X). Thus, XB/AB trials were seen to establish an inhibitory relationship between X and A.

ecco: An error correcting comparator theory

Building on the work of Ralph Miller and coworkers (Miller and Matzel, 1988; Denniston et al., 2001; Stout and Miller, 2007), I propose a new formalization of the comparator hypothesis that seeks to overcome some shortcomings of existing formalizations. The new model, dubbed ecco for "Error-Correcting COmparisons," retains the comparator process and the learning of CS-CS associations based on contingency. ecco assumes, however, that learning of CS-US associations is driven by total error correction, as first introduced by Rescorla and Wagner (1972). I explore ecco's behavior in acquisition, compound conditioning, blocking, backward blocking, and unovershadowing. In these paradigms, ecco appears capable of avoiding the problems of current comparator models, such as the inability to solve some discriminations and some paradoxical effects of stimulus salience. At the same time, ecco exhibits the retrospective revaluation phenomena that are characteristic of comparator theory.

The sometimes competing retrieval and Van Hamme & Wasserman models predict the selective role of within-compound associations in retrospective revaluation

The correlation between blocking and within-compound memory is stronger when compound training occurs before elemental training (i.e., backward blocking) than when the phases are reversed (i.e., forward blocking; Melchers et al., 2004, 2006). This trial order effect is often interpreted as problematic for performance-focused models that assume a critical role for within-compound associations in both retrospective revaluation and traditional cue competition. The present manuscript revisits this issue using a computational modeling approach. The fit of sometimes competing retrieval (SOCR; Stout & Miller, 2007) was compared to the fit of an acquisition-focused model of retrospective revaluation and cue competition. These simulations reveal that SOCR explains this trial order effect in some situations based on its use of local error reduction.

Retrospective revaluation: The phenomenon and its theoretical implications

Retrospective revaluation refers to an increase (or decrease) in responding to conditioned stimulus (CS X) as a result of decreasing (or increasing) the associative strength of another CS (A) with respect to the unconditioned stimulus (i.e., A-US) that was previously trained in compound with the target CS (e.g., AX-US or just AX). We discuss the conditions under which retrospective revaluation phenomena are most apt to be observed and their implications for various models of learning that are able to account for retrospective revaluation (e.g., Dickinson and Burke, 1996; Miller and Matzel, 1988; Van Hamme and Wasserman, 1994). Although retroactive revaluation is relatively parameter specific, it is seen to be a reliable phenomenon observed across many tasks and species. As it is not anticipated by many conventional models of learning (e.g., Rescorla and Wagner, 1972), it serves as a critical benchmark for evaluating traditional and newer models.

Internally generated sequences in learning and executing goal-directed behavior

A network of brain structures including hippocampus (HC), prefrontal cortex, and striatum controls goal-directed behavior and decision making. However, the neural mechanisms underlying these functions are unknown. Here, we review the role of 'internally generated sequences': structured, multi-neuron firing patterns in the network that are not confined to signaling the current state or location of an agent, but are generated on the basis of internal brain dynamics. Neurophysiological studies suggest that such sequences fulfill functions in memory consolidation, augmentation of representations, internal simulation, and recombination of acquired information. Using computational modeling, we propose that internally generated sequences may be productively considered a component of goal-directed decision systems, implementing a sampling-based inference engine that optimizes goal acquisition at multiple timescales of on-line choice, action control, and learning.