Second-Order Conditioning and Conditioned Inhibition in Different Moments of the Same Training: The Effect of A+ and AX− Trial Number

The feature negative discrimination (A+/AX−) can result in X gaining excitatory properties (second-order conditioning, SOC) or in X gaining inhibitory properties (conditioned inhibition, CI), a challenging finding for most current associative learning theories. Research on the variables that modulate which of these phenomena would occur is scarce but has clearly identified the trial number as an important variable. In the set of experiments presented here, the effect of trial number was assessed in a magazine training task with rats as a function of both the conditioning sessions and the number of A+ and AX− trials per session, holding constant the total number of trials per session. The results indicated that SOC is most likely to be found at the beginning of training when there are many A+ and few AX− trials, and CI (as assessed by a retardation test) is most likely to be found at the end of training when there are few A+ and many AX− trials. Both phenomena were also found at different moments of training when the number of A+ trials was equal to the number of AX− trials. These results cannot be predicted by acquisition-focused associative models but can be predicted by theories that distinguish between learning and performance.

Training protocol for touchscreen-based visual discrimination in mice

Automated touchscreen-based tasks are increasingly being used to explore a broad range of issues in learning and behavior in mice. Researchers usually report how they train mice before acquiring the target task concisely, and shaping protocols at this stage are typically flexible. In this report, we described a training protocol, developed in our laboratory, for mice acquiring a simultaneous discrimination performance using visual stimuli. C57BL/6N mice were first given magazine training. Nosepoke responses were then authoshaped and maintained on a continuous reinforcement schedule. Self-start response was then introduced in order to measure response time to complete each trial. The stimulus position was also varied across trials. We finally examined the contrast discrimination performance. Mice were tested with four different contrast ratios. Target stimuli were white and black targets and the brightness of distractors had values between targets and background. All mice successfully went through all training stages, confirming that this training protocol is promising for shaping appropriate discriminative behaviors in mice.

Dopamine and the elements of incentive learning

Dopamine and the elements of incentive learning explains how, in lever pressing for food tasks, incentive learning produces a gradient of attractiveness of environment stimuli: during magazine training, food activates dopaminergic neurons and the click and food cup become conditioned incentive stimuli, acquiring the ability to elicit approach and other responses; during lever-press training, the click activates dopaminergic neurons and the lever and lever-related stimuli become conditioned incentive stimuli. In conditioned place preference, amphetamine enhances dopaminergic neurotransmission and stimuli paired with amphetamine become conditioned incentive stimuli. In conditioned activity experiments, test-box stimuli paired with a dopamine-enhancer, e.g., cocaine, produce greater activity revealing incentive learning. In conditioned avoidance, the offset of an aversive warning stimulus putatively activates dopaminergic neurons leading safety-related stimuli to become conditioned incentive stimuli. If trained animals are treated with a dopamine receptor blocker, the initially intact ability of conditioned incentive stimuli to control responding declines over trials.

A Test of the Small-Trials Partial Reinforcement Extinction Effect in an Operant Conditioning Situation

Following familiarization and magazine training, three groups of rats received either: (1) four food pellets for each of four lever-presses, (2) food for only the first and third lever-presses, or (3) food for only the second and fourth lever-presses. Responding was then extinguished. There were no significant differences between the groups in number of lever presses during extinction or time to extinguish and no significant correlations between these two measures and the number of pellets received during magazine training or the elapsed time to emit the four lever-presses. These data contradict the small-trials partial reinforcement extinction effect commonly reported with the straight alley. However, these data are consistent with those recently reported by Nevin (1985) and with his concept of behavioral momentum, which may apply to the operant chamber but not to the runway.

An Examination of Autoshaped Keypecking in a Dark Chamber

Three experiments investigated critical variables influencing the development of autoshaping in a dark chamber. The context in which magazine-training occurred, length of intertrial interval, and CS intensity were the independent variables. Performance was best following magazine-training in the light; 60-sec. intertrial interval was better than 25; and little responding developed with a bright CS. These results are discussed with reference to the cue-localization hypothesis and a context-blocking effect.