Sz~mmary.-Two groups of squirrel monkeys, Saimiri sciureris, were trained in learning set (LS) ro determine the effect of making the stimulus objects' rightleft position assignments contingent upon Ss' responses. In the first group, objects were assigned according to a random sequence, but in the second group the position of objects was conticgent upon the nature of the preceding response. For this latter group, the right-left position assignments changed on each trial that followed a correct and reinforced trial; on all other trials the assignments remained unchanged. In subsequert test problems in which position assignments for both groups were on a random basis, the group that had its initial training in the response-contingent LS condition was significantly superior ( F = 16.7, 9 < .01).Results were interpreted in accord with the logic that the response-contingent method served to efficiently suppress the differential cue error factor.In discrimination learning set (LS) experimencs, the right-lefc position assignments for stimulus objects typically follow some predetermined sequence unrelated to Ss' responses. The purpose of che present experiment was co study the effects of making such assignmencs systematically contingent upon S's response on the preceding trial, excludicg, of course, Trial 1.According to Harlow ( 1959), LS is acquired through the ordered suppression of certain inappropriate reaction tendencies or error factors (EFs), identified as stirn~~lus perseveration, differential cue, response shift, and position preference. Differential cue error, of particular relevance to the present srudy, refers co the concurrent, hence ambiguous, reinforcement of boch the position and stimulus chosen on any given trial (Spence, 1936). Braun, Patton, and Barnes ( 1952), Davis, McDowell, andThorson ( 1953), andHarlow ( 1950) have shown that EF is a function of the number of trials preceding the differential cue trial ( D C T ) , the first trial on which che stimuli change their positions. Ostensibly, then, assigning objecc positions in such a way as to minimize the number of s~~ccessive trials on which ambiguous reinforcement occurs should lead to a faster rate of error suppression and, consequently, to Inore rapid LS formation.T h e following experiment was conducted to test this hypothesis. T w o groups of Ss were compare;. One group received conventional training in which the objeccs' right-left positioning followed a random sequence. The second group received response-contingent training defined as the systematic variation of object position from crial to trial in a manner contingent upon the response made by S
The study explored the effect of introducing novel cues on a learned color discrimination. 6 squirrel monkeys were initially trained to discriminate between plaques covered with green and brown construction paper. In a series of transfer tests, these color cues were then presented in 6 different patterns and varied in 4 sizes. The results indicate that some patterns will produce more disruption than others. Furthermore, reducing the size of the cues may also lead to a decrement in performance level. The outcome corresponds well with those of studies which show that contextual variables influence the acquisition of discriminative responses.
The effect of the presence or absence of the Plexiglas shell portion of the bins used to encase learning set (LS) problem objects, as in the apparatus used by Rumbaugh and Rice (1962), was assessed with 2 groups of 5 squirrel monkeys in the learning of a single discrimination problem, 6-trial/problem LS training, and the learning of 10 LS problems to a criterion. It was determined that quite apart from the fact that the transparent shell prevents direct hand contact with the stimulus objects, the bins appear to have characteristics that render squirrel monkeys nearly learning-setless in a 6-trial LS training situation.
Extended criterional learning-set (LS) training prior to test on a series of 6-tr/LS problems provided a significant, but transitory, advantage for Ss trained in a situation where problem objects were encased in Plexiglas bins. Criterional training appeared to compensate, at least partially, for those characteristics of this method of problem presentation which render squirrel monkey Ss learning-setless when given just 6-tr/LS training (Rumbaugh, Ternes, & Abordo, 1965). Rumbaugh, Ternes, and Abordo ( 1965 ) have reported that, when squirrel monkeys were trained in a 6-tr/problem learning set (LS; Harlow, 1949) situation where problem objects were presented to Ss either on Plexiglas bases or in Plexiglas bins, secured to the stimulus tray by sets of tracks, Ss remained learningsetless even after 500 problems. The purpose of the present study was to compare performance of the Plexiglas-bin-training group of that study with that of another group given extensive criterional LS training, prior to encounter of a set of 200 6-tr/problems, and to determine whether by so doing this kind of training might effectively offset those conditions which had deterred the formation of LS in the former group. To the degree that criterional training might, for example, compensate for the relatively low-level learning ability of the squirrel monkey (Rumbaugh & McQueeney, 1963) and/or reduce the difficulty of the learning task (Stevens, 1964) the development of LS should be facilitated.Ss were four experimentally naive, male squirrel monkeys whose characteristics, maintenance conditions, and adaptation procedures in every way paralleled those of Ss in the Rumbaugh, Ternes, and Abordo study; the test apparatus and stimulus tray used for their training was that used in their Plexiglas-bin-training condition.Ss first learned to criterion the square vs circle problem at rates which proved very equivalent to those of Ss in the Plexiglas-bin group, the t test for mean scores of the two groups falling far short of significance ( t = .09, df = 7, p > .05 ) . Ss then commenced criterional-LS training consisting of 1800 trials (equivalent in trial count to 300 6-tr/LS problems) in which each of a series of object-quality discrimination problems was learned to the intraproblem criterion of 20 responses correct wichin a span of 25 trials. They then received the set -----
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