The interaction between discriminative stimuli and outcomes during instrumental learning

Rats were trained on a biconditional discrimination in which the delivery of a food pellet stimulus signalled that pressing on one of two levers would be reinforced, whereas the delivery of a sucrose solution stimulus signalled that the reward was contingent on pressing the other lever. The outcome was the same food type as the discriminative stimulus in the congruent group but the other food type in the incongruent group. Both responses were rewarded with the same outcome in the same group. All the three groups learned the discrimination at statistically indistinguishable rates. Prefeeding one of the outcomes selectively reduced the associated response thereby demonstrating that responding was mediated by a representation of the outcome. Moreover, the outcome of one trial controlled responding on the next trial in accord with the stimulus function of the food type. These results are discussed in relation to the associative structures mediating the discriminative control of instrumental performance.     

The role of the instrumental contingency in the motivational control of performance

In four experiments we investigated an irrelevant incentive effect based upon a transition from hunger to thirst. Hungry rats were trained to lever press either for sucrose solution or for food pellets before performance was tested in extinction while they were thirsty. Reinforcer-specific motivational control was found in the first experiment in that the animals pressed the lever more on tests following training with the sucrose solution rather than with food pellets. Moreover, this effect was seen only when testing was conducted following water, but not following food deprivation. The outcome of the remaining experiments suggests that this motivational control is not mediated by the instrumental contingency between lever pressing and the sucrose reinforcer during training. In these studies lever pressing and chain pulling were reinforced concurrently, one with sucrose and the other with food pellets, in order to equate the noninstrumental functions of the incentives. Following this training, lever pressing in extinction under thirst was unaffected by the type of incentive used as its reinforcer during training.     

Perceived Group Identity Alters Task-Unrelated Thought and Attentional Divergence During Conversations

Task-unrelated thought (TUT) occurs frequently in our daily lives and across a range of tasks, but we know little about how this phenomenon arises during and influences the way we communicate. Conversations also provide a novel opportunity to assess the alignment (or divergence) in TUT during dyadic interactions. We conducted a study to determine: (a) the frequency of TUT during conversation as well as how partners align/diverge in their rates of TUT, (b) the subjective and behavioral correlates of TUT and TUT divergence during conversation, and (c) if perceived social group identity impacts TUT and TUT divergence during conversation. We used a minimal groups induction procedure to assign participants (N = 126) to either an ingroup, outgroup, or control condition. We then asked them to converse with one another via a computer-mediated text chat application for 10 min while self-reporting TUTs. On average, participants reported TUT about once every 2 min; however, this rate was lower for participants in the ingroup condition, compared to the control condition. Conversational pairs in the ingroup condition were also aligned more in their rates of TUT compared to the outgroup condition. Finally, we discuss subjective and behavioral correlates of TUT and TUT divergence in conversations, such as valence, turn-taking ratios, and topic shifts.     

The effect of the instrumental training contingency on susceptibility to reinforcer devaluation

Two experiments investigated performance of instrumental lever pressing by rats following post-conditioning devaluation of the sucrose reinforcer produced by establishing an aversion to it. In Experiment I rats responded less in an extinction test after being averted from the sucrose following training on a ratio schedule, but not following an equivalent amount of training on an interval schedule. This was true even though the devalued sucrose would not act as an effective reinforcer on either the ratio or interval schedule. Experiment II provided a further investigation of the insensitivity of interval responding to reinforcer devaluation by comparing test performance under simple extinction with responding when the devalued reinforcer was presented on either a response-contingent or non-contingent schedule during the test. Once again simple extinction performance was unaffected by prior reinforcer devaluation. Furthermore, neither non-contingent nor contingent presentations of the devalued reinforcer significantly depressed responding below the level seen in the extinction condition. Ratio, but not interval performance appears to be controlled by knowledge about the instrumental contingency that encodes specific properties of the training reinforcer.     

Irrelevant incentive learning during training on ratio and interval schedules

Two experiments investigated the effect of a motivationally-induced change in the value of the training reinforcer on instrumental performance. Initially, thirsty rats were trained to lever press for either a sodium or a potassium solution. Responding in an extinction test was then measured following the induction of sodium appetite. In Experiment I sodium-trained rats responded faster in a test given one day following the end of instrumental training. Furthermore, the relative size of this irrelevant incentive effect did not depend upon whether a ratio or interval schedule was employed during training. Delaying the test for eight days following the end of training abolished the difference between the test performance of sodium- and potassium-trained animals. Experiment II provided a further study of the effect of the training schedule when the introduction of the sodium reinforcer was delayed until responding was well established. Again the relative size of the difference between the performance of sodium- and potassium-trained animals was comparable following training on ratio and interval schedules. The insensitivity of this irrelevant incentive effect to the training contingency is in marked contrast to previous failures to detect an effect of reinforcer revaluation brought about by aversion conditioning following training on an interval schedule (Dickinson, Nicholas and Adams, 1983).     

Loss of associability by a conditioned inhibitor

In each of three experiments two groups of rats received inhibitory conditioning to one stimulus. Prior to a test phase of excitatory conditioning to this stimulus, one group was repeatedly exposed to the inhibitory stimulus by itself while the other group received no such exposure. Excitatory conditioning occurred most slowly in the group which received the exposure training. The first experiment indicated that this difference was not due to the exposure treatment enhancing the inhibitory properties of the stimulus. The results of Experiment III confirmed this conclusion and also indicated that the differences between the two groups during testing were due to differences in the associability of the inhibitory stimulus.