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N J Mackintosh

Publications and source records attributed to N J Mackintosh.

11 recordsLinked to original sources
PubMed1992

Cognitive and educational attainment in different ethnic groups.

The educational attainment of over 2000 children aged 7-15 years from six different ethnic groups was assessed. Children of Pakistani and of Bangladeshi origin tended to obtain the lowest mean scores on all tests, often well below those of West Indian children, who tended to perform as well as Indian children and often no worse than the indigenous majority. There were few signs of any reliable trends over age. Differences were more pronounced on tests of reading and vocabulary than on tests of mathematics but, on tests of non-verbal reasoning, most ethnic minorities also obtained low scores. Many of these differences were associated with differences in social and family circumstances.

Adolescent↗
PubMed1992

Role of context in perceptual learning in maze discriminations.

Three experiments with rats in a maze examined the effects of pre-exposure to the relevant discriminative stimuli (rubber- and sandpaper-covered maze arms) or the extra-maze context (the maze was surrounded either by black curtains or by variety of extra-maze landmarks) on the learning of a discrimination between rubber and sandpaper arms. In Experiment 1, pre-exposure to the extra-maze context facilitated subsequent discrimination learning. Experiments 2 and 3 showed that pre-exposure to rubber and sandpaper arms facilitated subsequent discrimination learning only when these cues were presented in the same context during pre-exposure and discriminative training. Taken together, the results are consistent with the hypothesis that a major cause of perceptual learning is the latent inhibition of stimuli or features common to the two discriminative stimuli, and that such latent inhibition may be disrupted by a radical change of context.

Animals↗
PubMed1992

Reciprocal overshadowing between intra-maze and extra-maze cues.

In three experiments, rats learned a maze discrimination where the location of food was defined either by reference to extra-maze cues alone, or by both extra- and intra-maze cues. Experiment 1 confirmed earlier results in showing that the presence of intra-maze cues failed to overshadow learning about extra-maze cues, in spite of the former's apparently greater salience. Experiment 2, however, suggested that this result was an artefactual consequence of differences between groups in the proportion of reinforced and unreinforced trials during the course of discriminative training. In Experiment 3, the discrimination was taught by a series of reinforced and unreinforced placement trials, and a significant overshadowing effect was observed. Intra-maze and extra-maze cues seem to compete for association with reinforcement in exactly the same way as any other cues.

Animals↗
PubMed1991

Perceptual learning in maze discriminations.

In Experiment 1, rats were trained on a discrimination between rubber- and sandpaper-covered arms of a maze after one group had been pre-exposed to these intra-maze cues. Pre-exposure facilitated subsequent discrimination learning, unless the discrimination was made easier by adding further discriminative stimuli, when it now significantly retarded learning. In Experiment 2, rats were trained on an extra-maze spatial discrimination, again after one group, but not another, had been pre-exposed to the extra-maze landmarks. Here too, pre-exposure facilitated subsequent discrimination learning, unless the discrimination was made substantially easier by arranging that the two arms between which rats had to choose were always separated by 135 degrees. The results of both experiments can be explained by supposing that perceptual learning depends on the presence of features common to S+ and S-.

Animals↗
PubMed1991

Perceptual learning in flavour aversion conditioning.

In each of four experiments, rats drank a solution of saline or of lemon and saline shortly before receiving an injection of lithium chloride, and the generalization of the resulting aversion to sucrose or to lemon and sucrose was measured. There was little generalization from saline alone to sucrose alone, and prior exposure to the two solutions had no effect on their discriminability. An aversion conditioned to lemon-saline, however, did generalize to lemon-sucrose, and the extent of this generalization was substantially reduced by prior exposure to the two compound solutions. This perceptual learning effect was partly, but not entirely, attributable to the latent inhibition of the common element, lemon, produced by exposure to the two compounds: animals pre-exposed to lemon alone discriminated between lemon-saline and lemon-sucrose better than animals pre-exposed to saline and sucrose alone; but exposure to the three elements in isolation was not as effective as exposure to the two compound solutions in enhancing their discriminability. The final experiment established that one critical feature of compound pre-exposure is that it involves experience of saline and sucrose in the presence of the same common element. According to an associative theory of perceptual learning, this would result in the establishment of inhibitory associations between saline and sucrose, thus reducing generalization between the two compound solutions.

Animals↗
PubMed1990

A change of context can enhance performance of an aversive but not of an appetitive conditioned response.

In four experiments rats received pairings of one auditory CS and mild shock in one context and of a second auditory CS and shock in a second context. When tested with one of these CSs in the context in which it had never been experienced, they consistently showed enhanced levels of suppression. In one of these experiments, suppression was measured over 15-sec intervals throughout a 90-sec long CS. A change of context resulted in an increased level of suppression at all points throughout the CS, a finding which does not encourage the belief that it was due to an increase in unconditioned suppression at the onset of the CS. Another experiment provided equally little support for an alternative account in terms of increased arousal. The results therefore suggest that a change of context can increase the level of conditioned suppression elicited by a CS paired with mild shock. Two final experiments employing the same CSs and contexts, however, found no evidence that a change of context had any effect at all on the performance of an appetitively conditioned response.

Animals↗
PubMed1975

Blocking of conditioned suppression: role of the first compound trial.

Four experiments, all employing the conditioned suppression of licking in thirsty rats, examined the extent to which reinforcement of one component, A, of a compound conditioned stimulus, AB, would "block" conditioning to the other element, B, on the first compound trial. Suppression to B was unaffected by prior reinforcement of A; that is, no evidence of blocking was obtained. If additional reinforced trials were given to the AB compound, further conditioning to B was blocked by prior reinforcement of A. Thus blocking appeared to take at least one trial to develop. These results suggest that blocking is not due to any competition between stimuli for association with reinforcement, but is a consequence of the animals' ignoring the added element once they have learned that it is redundant.

Acoustic Stimulation↗