The relative importance of responses to S+ and S- in simultaneous discrimination learning

Earlier research indicated that errors were more important in discrimination learning than correct responses (the Moss-Harlow effect). This conclusion was based on a variety of experimental designs each of which had basic methodological problems, usually involving novelty or order effects. A circular apparatus which allowed the simultaneous presentation of several different stimuli was used to study discrimination learning with S + and S - differentially weighted. It was found that variability in S - was more detrimental to discrimination learning than variability in S + although this finding depended on the presence of a constant stimulus. The results were interpreted as supporting the proposition that in discrimination learning rats learn more to avoid S- than to approach S+.     

Mediated generalization in discrimination learning by Rhesus monkeys

Monkeys received discrimination training in which the choice of either a simultaneous or a serial compound of two visual images was rewarded before we assessed the monkeys' conditioned preference for one of the images from the compound. This preference was reduced or blocked if the other image had been associated with reward rather than nonreward prior to compound training. By contrast, the preference was enhanced if the other image was associated with reward rather than nonreward after compound training. The magnitudes of the blocking and enhancement were unaffected by the temporal structure, simultaneous or serial, of the stimulus compound. These results are discussed in terms of the representation of stimulus compounds, the role of within-compound associations, and the similarities between serial and simultaneous visual compounds as processed by monkeys.     

Mediated generalization in discrimination learning by Rhesus monkeys

Monkeys received discrimination training in which the choice of either a simultaneous or a serial compound of two visual images was rewarded before we assessed the monkeys' conditioned preference for one of the images from the compound. This preference was reduced or blocked if the other image had been associated with reward rather than nonreward prior to compound training. By contrast, the preference was enhanced if the other image was associated with reward rather than nonreward after compound training. The magnitudes of the blocking and enhancement were unaffected by the temporal structure, simultaneous or serial, of the stimulus compound. These results are discussed in terms of the representation of stimulus compounds, the role of within-compound associations, and the similarities between serial and simultaneous visual compounds as processed by monkeys.     

Determinants of serial discrimination learning by squirrel monkeys

Squirrel monkeys were presented multiple serial discriminations 1, 2, 4, and 8 problems long. They were then presented problems designed to separate the effects of within-list associative interference from the effects of within-problem intertrial interval as list length was increased. The Ss committed consistently fewer errors after Trial 1 reward than after Trial 1 nonreward and showed strong stimulus perseveration. An increase in within-problem intertrial interval from 30 sec to 4 min had no effect whereas the associative interference resulting from increased problem length caused a small but significant performance decrement. Old and new problems had about equal effects on serial discrimination. The findings indicated that squirrel monkeys are relatively insensitive to within-problem associative interference.     

Cognitive discrimination in brain-damaged adults: color vs form preference

The relative preference of color, form, and other dimensions as the basis for discrimination between stimuli has been investigated in a variety of normal and language-impaired populations. In aphasic adults, previous studies have been contradictory, and no studies of non-aphasic, brain-damaged adults have been reported. In this study color vs form preference was examined in 20 left brain-damaged, aphasic adults, 20 right brain-damaged non-aphasic adults, and 20 control subjects. Significant differences were found among all groups, with preference of color over form greatest for left brain-damaged subjects, followed by right-damaged and control subjects.