Blocking of incidental information in young children

Methods of increasing learning efficiency through a blocking technique were examined in young children. An experimental group of children was trained on an initial task with one relevant dimension, followed by redundancy training in which an incidental dimension also became relevant. A control group given only redundancy training was compared to this group to test how much the experimental subjects blocked or screened out the incidental dimension. In order to increase blocking, three methods were used: a preset transfer problem, an overtraining on the initial task, and a delay following training. The most important finding was increased blocking through the Preset Condition. Overtraining and Delay Conditions had no effect. In addition, more slow learners on the initial task learned about the incidental dimension than fast or intermediate learners. Also, fewer subjects given form on the initial task learned about the incidental dimension than those given color. The Combined Blocking, Delay, and Overtraining group showed partial blocking, while the Preset group demonstrated complete blocking. No developmental differences occurred. The results were interpreted using a modification of Trabasso and Bower's attention model (Attention in learning: Theory and research. New York: Wiley, 1968).     

Anorexia and conditioned taste aversions in the rat

The present study examined whether or not certain anorexic agents produced flavor aversions. Rats showed comparable anorexia when injected with lithium chloride, ammonium sulfate, arginine·HCl, and d-glucose. Only lithium chloride produced a flavor aversion to either a novel liquid or food. Only arginine was found to interfere with the formation or recall of an association. The effects of the other chemicals were discussed in terms of the relationship between anorexia and induced sickness.     

Fixed-interval punishment of running in hamsters

Four hamsters received brief electric shocks contingent upon running in a wheel. The fixed interval between shocks was varied systematically from 0 to 60 sec. Time spent running was directly related to the length of the fixed interval, while running speed remained roughly constant. Running depended on the fixed interval between shocks in the same way as bar-pressing maintained by food reinforcement, despite the fact that running was not established with nor maintained by explicit reinforcement.     

Startbox-goalbox confinement durations as determinants of self-punitive behavior

Two levels of confinement duration (5 or 60 sec) in either startbox or goalbox were factorially combined with presence or absence of shock during extinction of a runway escape response in a self-punitive paradigm under a spaced-trials procedure. All groups were equated for amount and temporal spacing of handling before and after each trial. Shocked rats were more resistant to extinction than nonshocked rats only when startbox confinement was short. When startbox confinement was long, shock facilitated extinction. Long goalbox confinement enhanced running speed for shocked rats, but only in the presence of shock. It was suggested that duration of startbox confinement affects strength of conditioned fear, with long confinement leading to its extinction.     

Short-term retention of response outcome as a determinant of serial reversal learning

The correlation between short-term retention of the outcome of the preceding response and overall learning proficiency was investigated for serial reversal learning. Pigeons were trained to asymptote on a serial reversal problem and then were presented a percentage reinforcement schedule where only some correct trials were rewarded. Nonrewarded correct trials were treated exactly as incorrect trials. The difference in error probability following the two types of correct trials was then used as a measure of short-term retention. When intertrial intervals (ITI) were short (6 sec), substantial differences occurred. When the ITI's were increased, the difference in accuracy declined regularly to no difference at an ITI of 60 sec. This demonstration of a short-term retention gradient, coupled with the finding that overall reversal learning was much better with the shorter ITI's, suggests that a primary mechanism of improvement in serial reversal learning is the acquisition of a conditional discrimination based on the outcome of the preceding response.     

Effects of postresponse visual stimuli on visual discrimination learning in the rhesus monkey

To learn more about the mechanism (or mechanisms) involved with postresponse stimulus processing during discrimination learning, a series of studies was conducted with monkeys to determine why the combined relevant and irrelevant stimuli impair learning more than irrelevant stimuli appearing alone. It was found that: (a) the greater size and complexity of the combination of stimuli were not responsible for the greater deficit, while the presence of the relevant stimuli (S^D and S^Δ) within the stimulus combination apparently was; (b) the more similar the postresponse irrelevant stimuli were to the relevant stimuli the greater the deficit that resulted; and (c) monkeys that had earlier learned to discriminate the relevant and irrelevant features of a combination showed no learning impairment when this same stimulus combination was later presented after the response during a new learning problem. These results were interpreted as evidence that: (1) processes associated with learning a discrimination problem do not end with the execution of a choice response; (2) postresponse stimuli produce greater impairment in discrimination learning when they are distorted versions of the relevant stimuli; and (3) the impairment resulting from postresponse irrelevant stimuli occurs primarily when this misinformation is processed and misperceived as being relevant to learning the discrimination problem.     

Configural conditioning in the CER: Loss of element strength after repeated reinforced compound CS trials

Different groups of rats received different numbers of compound CS (light/noise) conditioning trials in the CER procedure. The amount of suppression evident to the single elements of the compound decreased as a function of the number of previous compound trials. This loss of CR strength was interpreted as a configuring effect. Further experimental comparisons indicated that the configuring effect could not be readily explained in terms of a generalization decrement or a stimulus novelty hypothesis.     

Positive contrast following gradual and abrupt increases in reward magnitude using delay of reinforcement

In Experiment 1, rats were given a 1-pellet reward for 48 preshift trials. During a subsequent 20-trial postshift phase, one group was shifted to a 12-pellet reward on Trial 1, a second was shifted on Trial 11, and a third was given 1 more pellet each trial and then 12 pellets for the last 10 trials. The speeds of all three groups increased to a level above that of a control group given a 12-pellet food reward throughout training (positive contrast). In experiment 2, rats were shifted from 1 to 12 pellets either gradually or abruptly following either abbreviated training (9 trials) or extended training (20 trials). One group of control subjects received 12 pellets throughout training. The results revealed a positive contrast effect for gradually shifted subjects following extended training but not following abbreviated training. The abrupt shift procedure produced positive contrast following abbreviated training but only a marginal effect following extended training. These results indicate that, contingent upon the amount of preshift training, either gradual or abrupt reward increases may produce positive contrast.