Excitatory and inhibitory learning with absent stimuli.

Three experiments showed that 2 associatively activated stimulus representations may engage in excitatory or inhibitory learning, depending on their temporal relationship. Experiment 1a suggested that simultaneously activated stimulus representations show evidence of inhibitory learning in an acquisition test. Experiment 1b showed similar evidence of inhibition in a summation test. Experiment 2 found that activation of 2 stimulus representations in a serial compound resulted in excitatory learning between the antecedent and the subsequent (forward) and inhibitory learning between the subsequent and the antecedent (backward). The results show the dynamic influence of temporal contiguity on mediated learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Simultaneous backward conditioned inhibition and mediated conditioning.

Demonstrations of retrospective revaluation suggest that remembered stimuli undergo a reduction in association with the unconditioned stimulus (US) present during learning. Conversely, demonstrations of mediated conditioning in flavor-conditioning experiments with rats suggest that remembered stimuli undergo an increase in association with the US present during learning. In a food allergy prediction task with 23 undergraduates, we demonstrated simultaneous backward conditioned inhibition and mediated conditioning effects. These results are compatible with the hypothesis that the direction of change (decrease or increase) in associative strength depends on whether the remembered stimulus was of a different category (conditioned stimulus/antecedent) or the same category (US/outcome) as the presented US. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Backward associations.

A review of the literature on backward associations in paired associate (PA) learning is presented, with an initial section being devoted to definitional and measurement problems. Similar to forward PA learning, backward learning was conceptualized as involving 2 processes: (1) stimulus learning and (2) backward associative learning. A review of the variables involved in backward learning and a discussion of the evidence for and against the Asch-Ebenholtz principle of associative symmetry follow. Finally, the role of backward associations in different verbal-learning situations is discussed with particular reference to transfer, retroactive and proactive inhibition, mediation, S-R similarity, and prefamiliarization. (2 p. ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perceptual Learning Enhances Retrospective Revaluation of Conditioned Flavor Preferences in Rats.

Forward and backward blocking of taste preference learning was compared in rats. In the forward condition, thirsty rats were exposed to a flavor (A) in sucrose solution (+) or in water (-), after which they were exposed to A in compound with another flavor (B) in sucrose solution (i.e., AB+). In the backward condition, these phases were reversed. Consumption of B alone was assessed when rats were food deprived. In the forward condition, rats given A+ consumed less B than rats given A-, providing evidence of forward blocking, whereas in the backward condition, rats given A+ drank more of B than those given A-. Subsequent experiments found that alternating but not blocked preexposure to A and B, when given prior to training, produced blocking of B whether A+ was given before or after AB+, suggesting that prior failures to observe backward blocking reflect failures of discrimination. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Timed excitatory conditioning under zero and negative contingencies.

Rats (rattus norvegicus) anticipated the arrival of a food pellet unconditioned stimulus (US) even when the conditioned stimulus (CS) signaled no overall change or a substantial decrease in the overall rate of US occurrence. Pellet USs were scheduled probabilistically in the intertrial interval at either an equivalent rate (Experiment 1) or a four times higher rate (Experiments 2 and 3) than in the CS, which included one fixed-time target US. Conditioning has been said to involve learning "whether" (contingency) the CS signals a change in the US, and if so, "when" (contiguity) the US is scheduled to arrive. Our results suggest that "when" trumps "whether," challenging the received view that a positive CS-US contingency is necessary for successful conditioning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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

Three experiments with rats investigated how the associative strengths of the representations that underlie conditional learning change when they are conditioned in compound. The results of each experiment suggest that the representation whose associative strength is most discrepant from the asymptote supported by the outcome of the trial undergoes the greatest change in associative strength. These results parallel those from simple Pavlovian conditioning (e.g., R. A. Rescorla, 2000). are inconsistent with unique-cue and configural accounts of conditional learning, and support a connectionist analysis of learning in which a "winner-takes-all" rule applies to the hidden units that can be activated and acquire associative strength at a given point in time. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Additional exposures reverse the latent inhibitory effects of recent and remote exposures.

We studied the learning produced by simple exposures to a stimulus. Exposures depressed orienting and subsequent conditioned freezing in rats. A remotely preexposed conditioned stimulus (CS) conditioned better and overshadowed a novel CS more than a recently preexposed CS. Additional preexposures reversed these effects: a remotely preexposed CS elicited more orienting, conditioned worse and overshadowed less than a recently preexposed CS. Exposure to a compound composed of a novel CS and a remotely preexposed CS resulted in the novel CS subsequently conditioning better than a novel CS exposed in compound with a recently preexposed CS. The results were interpreted to mean that stimulus-alone exposures produce a loss in associability which recovers across time, that this restoration deepens the loss in associability, and that this deepening is regulated by a common error term. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The rat prelimbic cortex mediates inhibitory response control but not the consolidation of instrumental learning.

The potential role of the prelimbic cortex of the rat in the acquisition of instrumental responding is currently uncertain. In addition, modeling the acquisition of Pavlovian and spatial conditioning tasks has suggested that the process of acquisition can, for certain forms of learning, be step like and consequently misrepresented in averaged group curves. Here, the authors report an experiment investigating the potential involvement of the prelimbic cortex in instrumental acquisition, in which the authors used the control data to model individual acquisition curves mathematically. The authors show that instrumental acquisition under fixed interval schedules was a gradual process extending over 4 instrumental sessions that is well represented in averaged group curves. Postsession infusion of a protein synthesis inhibitor into the prelimbic cortex did not affect any measure of acquisition, showing that during acquisition the prelimbic cortex does not mediate postsession consolidation of instrumental learning. However, inactivation of the prelimbic cortex increased responding, suggesting that the prelimbic cortex mediates a form of inhibitory response control. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Associative activation of stimulus representations restores lost salience: Implications for perceptual learning.

In 3 experiments, rats received preexposure to presentations of a compound flavor BX. The effective salience of B was then tested by assessing its ability to interfere with the aversion controlled by another flavor or the tendency to drink a saline solution after the induction of a salt need. It was found that the effective salience of B was maintained when during preexposure, presentations of BX alternated with presentations of X alone. This was true both when BX was presented as a simultaneous compound (Experiment 1) and as a serial compound (X→B; Experiments 2 and 3); salience was not maintained when the serial compound took the form B→X (Experiments 2 and 3a). It was argued that the salience of B declines during preexposure but is restored when presentations of X are able to activate the representation of B by way of the associative X-B link. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dissociations between expectancy and performance in simple and two-choice reaction-time tasks: A test of associative and nonassociative explanations.

Perruchet, Cleeremans, and Destrebecqz (2006) reported a striking dissociation between trends in the conscious expectancy of an event and the speed of a response that is cued by that event. They argued that this indicates the operation of independent processes in human associative learning. However, there remains a strong possibility that this dissociation is not a consequence of associative learning and is instead caused by changes in vigilance or sensitivity based on the recency of events on previous trials. Three experiments tested this possibility with versions of a cued reaction time task in which trends in performance could not be explained by these nonassociative factors. Experiment 1 introduced a dual-response version of the task, in which response-related vigilance should be held relatively constant, and Experiments 2 and 3 used a differential conditioning procedure to separate the influence of recent response cue presentation from the recent associative history of the trial events. In all experiments, similar trends in reaction time were evident, suggesting a genuine influence of associative learning on response performance. Experiment 3 demonstrated that the associative contribution to these trends was not caused by commensurate changes in expectancy of the response cue. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Simultaneous activation of the representations of absent cues results in the formation of an excitatory association between them.

It is a common assumption of associative theories of learning that no change in the strength of an associative connection between 2 cues is possible in the absence of those cues. However, recently suggested modifications to associative theory (A. Dickinson & J., Burke 1996) have questioned this assumption by arguing that if the representations of 2 cues are simultaneously retrieved from memory, an association will be formed between them even though the cues themselves are not present. A flavor preference procedure was used to find evidence for such associations. In 3 experiments a novel excitatory connection was formed between the representations of peppermint and sucrose in their absence. This suggests that the assumption that cues cannot undergo a change of associative strength in their absence should be abandoned. The tension between the current results and accounts of mediated conditioning is discussed, and some suggestions regarding the difference between the 2 procedures are proposed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Neurotrophins induce formation of functional excitatory and inhibitory synapses between cultured hippocampal neurons

Cell cultures were used to analyze the role of brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3) in the development of synaptic transmission. Neurons obtained from embryonic day 18 (E18) rat hippocampus and cultured for 2 weeks exhibited extensive spontaneous synaptic activity. By comparison, neurons obtained from E16 hippocampus expressed very low levels of spontaneous or evoked synaptic activity. Neurotrophin treatment produced a sevenfold increase in the number of functional synaptic connections in the E16 cultures. BDNF induced formation of both excitatory and inhibitory synapses, whereas NT-3 induced formation of only excitatory synapses. These effects were independent of serum or the age of the glia bed used for the culture. They were not accompanied by significant changes in synaptic-vesicle-associated proteins or glutamate receptors. Treatment of the cultures with the neurotrophins for 3 d was sufficient to establish the maximal level of functional synapses. During this period, neurotrophins did not affect the viability or the morphology of the excitatory neurons, although they did produce an increase in the number and length of dendrites of the GABAergic neurons. Remarkably, only BDNF caused an increase in the number of axonal branches and in the total length of the axons of the GABAergic neurons. These results support a unique and differential role for neurotrophins in the formation of excitatory and inhibitory synapses in the developing hippocampus.     

A direct laboratory comparison of Pavlovian conditioning and traditional associative learning.

24 adult human Ss were presented with a learning task which combined salivary conditioning with traditional associative learning: paired-associate learning of a 50 word Russian-English vocabulary and serial motor learning of a sequence of 100 adjacent bolts. Conditioning proceeded best when Ss did not know they were being conditioned, while associative learning was reasonably effective when Ss knew what they were associating. The view is expressed that the present data support strongly the hypothesis that Pavlov's laws of conditioning are primarily laws of unconscious biological learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

An investigation of several methods of teaching contour interpretation.

"Two companies of 162 Ss each were trained by the use of various combinations of concrete or abstract representations of terrain (a terrain board, two-dimensional slides and three-dimensional slides of the terrain), and concrete or abstract symbols (contour lines on two-dimensional or three-dimensional maps). Learning resulting from these methods was compared to the Standard Army method, and a No-Training (control) condition… the training method involving representation of terrain by two-dimensional slides, and presenting the symbols on a three-dimensional map, generally led to highest proficiency." (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Olfactory-Mediated Fear Conditioning in Mice: Simultaneous Measurements of Fear-Potentiated Startle and Freezing.

This study demonstrates that mice display olfactory-cued fear as measured with both freezing and fear-potentiated startle. Following a preconditioning test to measure any unconditioned responses to odor, mice received 5 pairings of a 10-s odor with a 0.25-s, 0.4-mA footshock. The next day, startle and freezing were measured in the presence and absence of the odor. Both fear measures increased after training with amyl acetate (Experiment 1) and acetophenone (Experiment 2). The enhancement of startle did not occur when the same number of odors and shocks were presented in an unpaired fashion (Experiment 3). Furthermore, mice were able to discriminate between an odor paired with shock and a nonreinforced odor (Experiment 4). (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effects of concomitant colored and uncolored pictorial representations on the learning of stimulus words.

To study the effect of varying degrees of compounding signs of objects denoted by the words, twenty-five stimulus words were presented under three learning conditions: (a) Words alone, (b) words with their uncolored pictures, (c) words with their colored pictures. It was concluded that support was given the hypothesis that "with the number of presentations… held constant, the number of… words recalled by Ss should vary positively within limits with the number of simultaneously presented additional signs." (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A note on the use of the terms conditioning and reinforcement.

The "… term conditioning was originally used… to denote the behavioral fact that a stimulus inadequate for some response could become adequate by virtue of being combined one or more times with a stimulus adequate for the response… . The situation at present is as follows. Conditioning is being used as an all-covering account of both Pavlovian and Skinnerian learning which by all tokens are quite distinct—and even divergent—from each other methodologically, operationally, behaviorally, and functionally. And reinforcement, in its turn, wields four different meanings." The author claims that "… not only is such a mixing of terms in itself unjustified but in twenty years has hardly caught on beyond the reign of its immediate proponents." (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sequential and simultaneous feature positive discriminations: Occasion setting and configural learning in human Pavlovian conditioning.

Using a conditioned suppression preparation, the authors investigated sequential (X→A+/A–) versus simultaneous (XA+/A–) feature positive (FP) discrimination learning in humans. The sequential discrimination was expected to be resolved by means of a Feature X Modulated Target A–US association and the simultaneous discrimination by a feature X–US association. After sequential FP training, extinction of Feature X did not affect discriminative X→A/A responding (Experiment 1), and X transferred its modulatory ability only to new targets, B, that had also been modulated (Experiment 2). This suggests that the sequential FP discrimination indeed resulted in occasion setting. Unlike expected, Feature X Extinction did not affect discriminative XA/A responding after simultaneous FP training (Experiment 3), while at the same time Feature X did show the predicted nonselective transfer to new targets, B (Experiment 4). J. M. Pearce's (1987) configural learning theory can account for most but not all findings of Experiments 3 and 4. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perceiving imitatible stimuli: Consequences of isomorphism between input and output.

For more than a century, psychologists have been intrigued by the idea that mental representations of perceived human actions are closely connected with mental representations, of performing those same actions. In this article, connections between input and output representations are considered in terms of the potential for imitation. A broad range of evidence suggests that, for imitatible stimuli, input and output representations are isomorphic to one another, allowing mutual influence between perception and motoric planning that is rapid, effortless, and possibly obligatory. Thus, the cognitive consequences of imitability may underlie such diverse phenomena as phoneme perception; imitation in neonates; echoic memory; stimulus–response compatibility; conduction aphasia; maintenance rehearsal; and a variety of developmental and social activities such as language acquisition, social learning, empathy, and monitoring one's own behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Conditioning with masked stimuli affects the timecourse of skin conductance responses.

In Pavlovian fear conditioning, an aversive unconditional stimulus (UCS) is repeatedly paired with a neutral conditional stimulus (CS). As a consequence, the subject begins to show conditional responses (CRs) to the CS that indicate expectation and fear. There are currently two general models competing to explain the role of subjective awareness in fear conditioning. Proponents of the single-process model assert that a single propositional learning process mediates CR expression and UCS expectancy. Proponents of a dual-process model assert that these behavioral responses are expressions of two independent learning processes. We used backward masking to block perception of our visual CSs and measured the effect of this training on subsequent unmasked performance. In two separate experiments we show a dissociation between CR expression and UCS expectancy following differential delay conditioning with masked CSs. In Experiment I, we show that masked training facilitates CR expression when the same CSs are presented during a subsequent unmasked reacquisition task. In Experiment II we show that masked training retards learning when the CS+ is presented as part of a compound CS during a subsequent unmasked blocking task. Our results suggest that multiple memory systems operate in a parallel, independent manner to encode emotional memories. (PsycINFO Database Record (c) 2010 APA, all rights reserved)