Alternating exposure to two compound flavors creates inhibitory associations between their unique features

Rats were exposed to two compound solutions, saline-lemon and sucrose-lemon. In Group ALT, trials with one solution alternated with trials with the other. Group BLK received all trials with one solution before any trials with the other. Previous retardation tests had implied that only alternating exposure would establish sucrose as an inhibitor of saline. To provide a complementary summation test for this inhibition, in Experiment 1, all the animals received pairings of peppermint and saline and were tested for consumption of peppermint-sucrose under sodium depletion. Consumption was increased by sodium depletion only in Group BLK. In Experiment 2, a retardation test was used to show that presentation of saline-lemon before sucrose-lemon on each exposure day would establish sucrose as an inhibitor of saline. Neither exposure to sucrose-lemon before saline-lemon nor alternating exposure to sucrose and saline alone had the same effect. These results provide support for an associative theory of perceptual learning that suggests that exposure to complex stimuli aids later discrimination partially as a result of establishing inhibitory associations between their unique elements.     

Cognitive Bias Modification: The Critical Role of Active Training in Modifying Emotional Responses

Training participants to select threat or nonthreat interpretations of emotionally ambiguous stimuli or passively exposing them to valenced scenarios can modify later interpretation of ambiguity. However, only when encouraged to actively select meanings do congruent changes in emotional response occur during training itself (Mathews & Mackintosh, 2000). The present study assessed the more critical question of whether active training is also necessary for modifying subsequent emotional responses to images of new ambiguous scenarios presented after training. As predicted, active training did lead participants to rate their images of emotionally ambiguous scenarios as being more unpleasant after training as compared to a matched passive condition. This finding supports the view that active generation of meaning during interpretive training is critical for the modification of later emotional responses.     

Categorization by People and Pigeons: The Twenty-second Bartlett Memorial Lecture

In one set of experiments, the experience of categorizing sets of variable exemplars of two categories enhanced subjects' ability to discriminate between two new instances of one of these categories. In a second set, subjects that had categorized two sets of exemplars responded more accurately to the hitherto unseen prototype than to a new exemplar close to the category boundary; but in some cases they responded even more accurately to a new exemplar, even further from the category boundary, than to the prototype. In both sets of experiments, people and pigeons behaved in similar ways. The implication is that at least in some situations human behaviour is controlled by a relatively simple set of associative processes, whose operations have been elucidated by conditioning experiments in animals.     

A re-examination of one-trial blocking in conditioned suppression

Three experiments on the conditioned suppression of licking in rats examined the amount of conditioning produced by a single conditioning trial to a clicker-light compound and the effect of prior conditioning to the light on the level of conditioning to the clicker. In Experiment I, prior conditioning to the light, far from blocking conditioning to the clicker, actually enhanced it, whether the clicker was presented in a simultaneous compound with the light or in a serial compound preceding the light. Experiment II, however, showed that this potentiation effect could be abolished if a trace interval was inserted between the clicker and light in the serial compound arrangement. Moreover, Experiment III demonstrated a significant blocking effect when a trace interval separated the clicker and light on the single compound trial. These results establish that one-trial blocking of conditioned suppression is possible, and suggest that in some earlier studies blocking may have been masked by higher-order conditioning to the target stimulus.     

Don't look now: Attentional avoidance of emotionally valenced cues

It is often assumed that emotional stimuli receive high priority for processing, and that the distinction between positive and negative valence is fundamental. However, studies of attention to symbolic stimuli, such as words of different valence, have proved inconclusive. In four experiments, control over the emotional attributes of previously neutral line sketches was achieved by associating them with valenced captions. When these newly valenced sketches were paired with neutral stimuli in an attentional search task, they elicited equivalent attentional avoidance. In contrast, in a final experiment, strongly valenced colour pictures captured attention. We suggest that a mechanism acting to limit unnecessary interruptions of ongoing behaviour can inhibit processing of relatively mild emotional stimuli.     

Learned Irrelevance Is Not the Sum of Exposure to CS and US

In three experiments hungry rats received appetitive conditioning trials with a light that signalled the delivery of sucrose solution. In Experiment 1, prior exposure to uncorrelated presentations of the conditioned stimulus (CS) and unconditioned stimulus (US) retarded conditioning significantly more than did prior exposure to the CS alone. In Experiments 2 and 3, groups exposed to uncorrelated presentations of the CS and US within the same session conditioned significantly more slowly than groups given separate sessions of exposure to the CS followed by sessions of exposure to the US (or vice versa). Some part of the learned irrelevance effect depends on exposure to a zero correlation between the CS and US, perhaps because this promotes learning that the CS predicts no change in the probability of the US.     

Comparison and Contrast as a Mechanism of Perceptual Learning?

In a series of flavour aversion experiments, rats received different schedules of pre-exposure to two compound flavours (AX and BX). Discrimination between them was assessed by establishing an aversion to AX and measuring generalization of this aversion to BX. Experiment 1 demonstrated that alternating pre-exposure to AX and BX resulted in less generalization than did blocked exposure, where animals received all exposure to AX before exposure to BX (or vice versa). This difference was not accompanied by any difference in the strength of the aversion conditioned to the common X element. Varying the interval between exposure to AX and BX in the alternating condition from a minute or two to several hours had no effect on generalization. However, Experiments 2 and 3 showed that when the interval between exposure to AX and that to BX was reduced to zero sec, the alternating schedule increased generalization between AX and BX. In this case, the increase in generalization was accompanied by an increase in the strength of the aversion conditioned to X.     

Inhibitory conditioning resulting from a reduction in the magnitude of reinforcement

Five experiments, all employing conditioned suppression in rats, studied inhibitory conditioning to a stimulus signalling a reduction in shock intensity. Experimental subjects were conditioned to a tone signalling a 1·0 mA shock and to a tone-light compound signalling a 0·4 mA shock. On a summation test in which it alleviated the suppression maintained by a third stimulus also associated with the 1·0 mA shock, the light was established as a conditioned inhibitor. Retardation tests gave ambiguous results: the light was relatively slow to condition when paired, either alone or in conjunction with another stimulus, with the 0·4 mA shock, but the difference from a novel stimulus control group was not significant. Two final experiments found no evidence at all of inhibition on a summation test in which the light was presented in conjunction with a stimulus that had itself been associated with the 0·4 mA shock. The results of these experiments have implications for the question of what animals learn during the course of inhibitory conditioning.