Time, trials, and extinction.

Four experiments investigated the effect of number of trials and total duration of nonreinforced exposure to the conditioned stimulus (CS) on extinction of Pavlovian conditioning. Rats were first trained in a magazine approach paradigm with multiple CSs, each paired with the unconditioned stimulus (US) on a variable CS-US interval. During subsequent extinction, CSs would differ in the number and length of their extinction trials but would be matched for the total duration of exposure (e.g., 1 CS would have 20 trials per session with a mean length of 5 s; another CS would have 5 trials per session with a mean length of 20 s). In each case, extinction proceeded more quickly for the CS given more trials per session. Indeed, there was no difference in rate of extinction between CSs that were matched on number of trials but differed on the duration of each trial, indicating that duration of exposure has no effect on extinction. We discuss the implications of these findings for trial-based and time-based theories of conditioning. (PsycINFO Database Record

Asymmetry between excitatory and inhibitory learning.

Five experiments investigated how learning about the added feature in a feature-positive discrimination or feature-negative discrimination is related to the change in reinforcement rate that the feature signals. Rats were trained in a magazine-approach paradigm with 2 concurrent discriminations between A versus AX and B versus BY. In 2 experiments (1 and 3), X and Y signaled an increase of 0.3 in the probability of reinforcement, from 0.1 to 0.4 (A vs. AX), or from 0.6 to 0.9 (B vs. BY). After extended training, each session included probe test trials in which X and Y were presented alone (Experiment 1) or in compound with another excitatory conditional stimulus (CS), C (Experiment 3). There was no difference in response rate between the 2 types of test trial (X vs. Y; XC vs. YC), consistent with the fact that X and Y signaled the same absolute change in reinforcement. In Experiments 2 and 4, X and Y signaled a decrease of 0.3 in the probability of reinforcement, from 0.4 to 0.1 (A vs. AX) or from 0.9 to 0.6 (B vs. BY). Test trials in which X or Y was presented with C showed that X had greater inhibitory strength than Y, consistent with the fact that X signaled a larger relative change in reinforcement. This was confirmed in Experiment 5, in which X and Y had the same inhibitory strength on test after training in which they signaled the same relative change in reinforcement but different absolute changes (0.3 to 0.1 for A vs. AX; 0.9 to 0.3 for B vs. BY). The results show that excitatory conditioning is linearly related to the increase in reinforcement rate, whereas inhibitory learning is not linearly related to the decrease in reinforcement rate. Implications of this for theories of associative learning are discussed. (PsycINFO Database Record

Does the Theory of Planned Behaviour Explain Condom Use Behaviour Among Men Who have Sex with Men? A Meta-analytic Review of the Literature.

The aim of this meta-analysis was to explore whether the constructs in the theory of planned behaviour (TPB; i.e., attitude, subjective norm, perceived behavioural control, intention) explain condom use behaviour among men who have sex with men (MSM). Electronic databases were searched for studies that measured TPB variables and MSM condom use. Correlations were meta-analysed using a random effects model and path analyses. Moderation analyses were conducted for the time frame of the behavioural measure used (retrospective versus prospective). Attitude, subjective norm and perceived behavioural control accounted for 24.0 % of the variance in condom use intention and were all significant correlates. Intention and PBC accounted for 12.4 % of the variance in condom use behaviour. However, after taking intention into account, PBC was no longer significantly associated with condom use. The strength of construct relationships did not differ between retrospective and prospective behavioural assessments. The medium to large effect sizes of the relationships between the constructs in the TPB, which are consistent with previous meta-analyses with different behaviours or target groups, suggest that the TPB is also a useful model for explaining condom use behaviour among MSM. However, the research in this area is rather small, and greater clarity over moderating factors can only be achieved when the literature expands.

Conditioned inhibition and reinforcement rate.

We investigated conditioned inhibition in a magazine approach paradigm. Rats were trained on a feature negative discrimination between an auditory conditioned stimulus (CS) reinforced at one rate versus a compound of that CS and a visual stimulus (L) reinforced at a lower rate. This training established L as a conditioned inhibitor. We then tested the inhibitory strength of L by presenting it in compound with other auditory CSs. L reduced responding when tested with a CS that had been reinforced at a high rate, but had less or even no inhibitory effect when tested with a CS that had been reinforced at a low rate. The inhibitory strength of L was greater if it signaled a decrease in reinforcement from an already low rate than if it signaled an equivalent decrease in reinforcement from a high rate. We conclude that the strength of inhibition is not a linear function of the change in reinforcement that it signals. We discuss the implications of this finding for models of learning (e.g., Rescorla & Wagner, 1972) that identify inhibition with a difference (subtraction) rule.

Magazine approach during a signal for food depends on Pavlovian, not instrumental, conditioning.

In the conditioned magazine approach paradigm, rats are exposed to a contingent relationship between a conditioned stimulus (CS) and the delivery of food (the unconditioned stimulus, US). As the rats learn the CS-US association, they make frequent anticipatory head entries into the food magazine (the conditioned response, CR) during the CS. Conventionally, this is considered to be a Pavlovian paradigm because food is contingent on the CS and not on the performance of CRs during the CS. However, because magazine entries during the CS are reliably followed by food, the increase in frequency of those responses may involve adventitious ("superstitious") instrumental conditioning. The existing evidence, from experiments using an omission schedule to eliminate the possibility of instrumental conditioning (B. J. Farwell & J. J. Ayres, 1979, Stimulus-reinforcer and response-reinforcer relations in the control of conditioned appetitive headpoking (goal tracking) in rats. Learning and Motivation, 10, 295-312; P. C. Holland, 1979, Differential effects of omission contingencies on various components of Pavlovian appetitive conditioned responding in rats. Journal of Experimental Psychology: Animal Behavior Processes, 5, 178-193), is ambiguous: rats acquire magazine CRs despite the omission schedule, demonstrating that the response does not depend on instrumental conditioning, but the response rate is greatly depressed compared with that of rats trained on a yoked schedule, consistent with a contribution from instrumental conditioning under normal (nonomission) schedules. Here we describe experiments in which rats were trained on feature-positive or feature-negative type discriminations between trials that were reinforced on an omission schedule versus trials reinforced on a yoked schedule. The experiments show that the difference in responding between omission and yoked schedules is due to suppression of responding under the omission schedule rather than an elevation of responding under the yoked schedule. We conclude that magazine responses during the CS are largely or entirely Pavlovian CRs.

The content of compound conditioning.

In three experiments using Pavlovian conditioning of magazine approach, rats were trained with a compound stimulus, AB, and were concurrently trained with stimulus B on its own. The reinforcement rate of B, rB, was either 1/2, 2/3, or 2/5 of rAB. After extended training, the conditioning strength of A was assessed using probe trials in which A was presented alone. Responding during A was compared with that during AB, B, and a third stimulus, C, for which rC = rAB - rB. In each experiment, the rats' response rate during A was almost identical to that during C (and during B, when rB = 1/2rAB). This suggests that, during AB conditioning, the rats had learned about rA as being equal to [rAB - rB], and implies that the content of their learning was a linear function of r. The findings provide strong support for rate-based models of conditioning (e.g., Gallistel & Gibbon, 2000). They are also consistent with the associative account of learning defined in the Rescorla and Wagner (1972) model, but only if the learning rate during reinforcement equals that during nonreinforcement.

Summation of reinforcement rates when conditioned stimuli are presented in compound.

Three experiments used delay conditioning of magazine approach in rats to examine the summation of responding when two conditioned stimuli (CSs) are presented together as a compound. The duration of each CS varied randomly from trial-to-trial around a mean that differed between the CSs. This meant that the rats' response rate to each CS was systematically related to the reinforcement rate of that CS, but remained steady as time elapsed during the CS (Harris & Carpenter, 2011; Harris, Gharaei, & Pincham, 2011). When the rats were presented with a compound of two CSs that had been conditioned separately, they responded more during the compound than during either of the CSs individually. More significantly, however, in all three experiments, the rats responded to the compound at the same rate as they responded to a third CS that had been reinforced at a rate equal to the sum of the reinforcement rates of the two CSs in compound. We discuss the implications of this finding for associative models (e.g., Rescorla & Wagner, 1972) and rate-based models (Gallistel & Gibbon, 2000) of conditioning.