Effects of list length and first-trial reward upon concurrent discrimination performance

Rhesus monkeys were given 2304 two-trial object discrimination problems that were presented as members of lists consisting of two, four, or eight problems. The problems within each list were presented concurrently, Trial 1 for all problems in the list being presented before initiation of Trial 2 for any problem. Each problem involved exposure of a single object on Trial 1, which was either rewarded or not rewarded, followed by presentation of the Trial 1 object along with a second object on Trial 2. Performance varied inversely with list length, and this effect became more prominent as a function of training. Performance after Trial 1 nonreward was substantially better than that after Trial 1 reward, and this effect became enhanced both with continued training and with increased list length. The findings were discussed in terms of Bessemer's short-term memory analysis of learning set.     

Differential aversive learning enhances orientation discrimination

A number of recent studies have documented rapid changes in behavioural sensory acuity induced by aversive learning in the olfactory and auditory modalities. The effect of aversive learning on the discrimination of low-level features in the visual system of humans remains unclear. Here, we used a psychophysical staircase procedure to estimate discrimination thresholds for oriented grating stimuli, before and after differential aversive learning. We discovered that when a target grating orientation was conditioned with an aversive loud noise, it subsequently led to an improvement of discrimination acuity in nearly all subjects. However, no such change was observed in a control group conditioned to an orientation shifted by ±90° from the target. Our findings cannot be explained by contextual learning or sensitisation factors. The results converge with those reported in the olfactory modality and provide further evidence that early sensory systems can be rapidly modified by recently experienced reinforcement histories.     

Differential effects of instructions and consequences on human conditional discrimination performance

Two studies evaluated the differential behavioral effects of instructions and feedback in matching-to-sample procedures. In Experiment 1, 20 college students received true or false instructions and trial-by-trial or delayed feedback in three phases. In a fourth, final phase the instructions remained the same, but feedback changed from trial-by-trial to delayed, or from delayed to trial-by-trial. In Experiment 2, half of another 20 participants received true instructions during three phases, followed by false instruction in a fourth phase; the other half of the participants received false instructions during three phases, followed by true instructions in the fourth phase. Feedback sequences were as in Experiment 1. The results of both experiments revealed historical effects of instructions and feedback. Most participants demonstrated strong instructional control, overriding the control by contingencies. These results suggest that the present procedure offers optimal possibilities to make the differential effects of instructions and feedback on human behavior clearly identifiable when conditional discrimination tasks are used.     

Memory retrieval and discrimination learning

A better reinforcement schedule may be associated with one exteroceptive stimulus (S+) than with another exteroceptive stimulus (S−). While all theories agree that performance in such discrimination tasks is affected by the reinforcement schedules associated with the exteroceptive S+ and S− cues, some theories suggest that performance is also affected by the reinforcement schedule associated with interoceptive reward produced cues. The two experiments reported here were concerned with identifying the conditions under which the interoceptive cues produced by nonreward come to affect performance. According to one hypothesis, such cues will acquire control over approach responding if animals make an approach response in their presence, but not otherwise. According to the memory hypothesis, the memory of nonreinforcement will become a signal for reinforcement, thus invigorating performance, if it is retrieved on a rewarded trial. In two experiments, two groups made strong approach responses to the nonreinforced cues on S− trials, but the memory of nonreward was better retrieved on a subsequent rewarded trial in one group than in the other. Subsequently, both groups were extinguished. The extinction findings support the memory view.     

Observing responses and discrimination learning

An operant response in the pigeon, whose performance results in exposure to the discriminative stimuli, is described and suggested as an experimental analogue for “observing.” Such an operant response is then used to explore the relationship between observing responses and discrimination learning in a variety of discrimination situations, of progressively increasing complexity. In general, the results support the contention that the development and maintainence of observing responses is closely related to the degree of differential behaviour manifested toward the discriminative stimuli. Certain modifications are suggested in the theoretical formulation underlying the concept of “observing responses.”     

Fading procedures and conditional discrimination in children

A discrimination reversal task followed by a conditional discrimination problem was administered to children (age range 36 to 107 months). A fading procedure was used during the discrimination reversal training of some subjects and other subjects were trained by a traditional procedure. More subjects trained by the fading procedure performed without errors during training and more subjects in the traditional group solved the conditional discrimination problem.     

Association learning and visual discrimination

The effect of learned stimulus associations on visual discrimination was measured in four experiments. The stimuli were visual shapes which had been scaled for similarity. Two shapes were selected as discriminanda, and each S was pretested and posttested for discrimination of these briefly presented simultaneous pairs of “same” and “different” shapes. During the training, each discriminandum was paired with another simultaneously presented associated shape on a paired-associate response-learning task. The two associated shapes were very similar, intermediate in similarity, or very dissimilar. There was more improvement in posttest discrimination following training with dissimilar associates. We conclude that learned stimulus associations affect visual discrimination.     

Differential effects of stress-inducing instructions on anxiety, learning and performance

Marton, F. I., Fransson, A., Jonsson, B., Klenell, A.-Ch. & Roos, B. Differential effects of stress-inducing instructions on anxiety, learning and performance. Scand. J. Psychol., 1973, 14, 213–219.-In an attempt to investigate the effects of induced stress on anxiety, learning and performance, the separate effects on the learning and performance phases were obtained by varying the timing of the introduction and the removal of stressinducing instructions. Stess-inducing instructions had a positive effect on learning but were not significantly related to the level of anxiety in the learning phase. In the performance phase the results were reversed, i.e. the stress-inducing instructions had a significantly positive effect on the level of anxiety but none on performance. The apparent paradox stemming from the significant negative relationship between anxiety and achievement within conditions could be resolved by considering the common confusion concerning statistical vs. causal relationship.