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.     

Restoring the associability of a pre-exposed CS by a surprising event

Three experiments are reported which use rats and the conditioned suppression technique. The first two confirmed a previous finding that prior exposure to a stimulus predicting a weak shock retards further learning when this same stimulus is subsequently used to signal a stronger shock. They further showed that this loss of stimulus associability could be attenuated by inserting trials on which the stimulus was presented alone in the absence of shock before the phase of training with the stronger shock. Experiment III demonstrated that, for animals given prior exposure to two stimuli, the insertion of nonreinforced trials with one of the stimuli will restore the associability only of that stimulus. These results are taken to show that a surprising event (the omission of an expected shock) can restore the associability of a pre-exposed conditioned stimulus.     

Stimulus Salience and Negative Patterning

Rats in Experiment 1 received a negative patterning discrimination in which food was delivered after either of two auditory stimuli when they were presented individually, but not when they were presented in compound. The stimuli were of different intensity. The discrimination between the compound and the stimulus of lower intensity was acquired more readily than was the discrimination between the compound and the more intense stimulus. A similar pattern of results was found in the remaining two experiments, which also employed a negative patterning discrimination, but either with stimuli from different modalities (Experiment 2) or with pigeons rather than rats (Experiment 3). The results were predicted more readily by a configural than by an elemental theory of conditioning.     

Predictive accuracy and not reduction in uncertainty influences responding during serial autoshaping

Two experiments with pigeons employed a serial autoshaping design in which food was presented on every trial, and the initial element was of variable duration. When the first element was followed randomly by one stimulus of fixed short duration and another stimulus of fixed long duration, then it elicited a relatively high rate of responding. But when the second elements were of equal mean durations, whether fixed or variable, then responding during the first element was relatively slow. Two explanations for these findings were considered. One stipulates that the rate of responding during a stimulus is related to its predictive accuracy, the other stipulates that responding is influenced by the reduction in uncertainty that follows the offset of a stimulus. It is argued that the evidence favours the first of these alternatives.     

Partial Reinforcement in Appetitive Pavlovian Conditioning with Rats

Four experiments examined the effects of a partial reinforcement schedule on extinction using appetitive Pavlovian conditioning. Extinction was slower after partial than after continuous reinforcement when the schedules were administered to different groups (Experiment 1). The opposite result was found in Experiments 2 and 3 when both schedules were presented to the same group in the same context. When the schedules were presented to the same group in different contexts, then extinction was again slower after partial reinforcement (Experiment 3). Experiment 4 demonstrated that a change of context facilitates extinction to a greater extent after conditioning with a partial reinforcement schedule than with a continuous one. The results are explained by assuming that the nonreinforced trials of a partial reinforcement schedule create an internal state that serves as a contextual cue.     

Infants’ sense of approximate numerosity: Heritability and link to other concurrent traits

The ability to perceive approximate numerosity is present in many animal species, and emerges early in human infants. Later in life, it is moderately heritable and associated with mathematical abilities, but the etiology of the Approximate Number System (ANS) and its degree of independence from other cognitive abilities in infancy is unknown. Here, we assessed the phenotypic specificity as well as the influence of genetic and environmental factors on the ANS in a sample of 5-month-old twins (N = 514). We found a small-to-moderate but statistically significant effect of genetic factors on ANS acuity (heritability = 0.18, 95% CI: 0.02, 0.33), but only when differences in numerosity were relatively large (1:4 ratio). Non-verbal ability assessed with the Mullen Scales of Early Learning (MSEL) was found to be heritable (0.47; 95% CI: 0.34, 0.57) and the phenotypic association between ANS acuity and non-verbal ability performance was close to zero. Similarly, we found no association between ANS acuity and general attention during the task. An unexpected weak but statistically significant negative association between ANS acuity and scores on the receptive language scale of the MSEL was found. These results suggest that early ANS function may be largely independent from other aspects of non-verbal development. Further, variability in ANS in infancy seems to, to some extent, reflect genotypic differences in the population.

Highlights

• Assessing 514 infant twins with eye tracking, we found that infants' sense of approximate numerosity is heritable and not positively associated with concurrent attentional, cognitive or motor abilities.
• These results have implications for our understanding of development of mathematical ability and the link between cognitive abilities early in postnatal life.