Effects of response-produced stimuli upon conditional discrimination performance

In zero-delay matching procedures the performance of three groups of pigeons was examined when exteroceptive stimuli, response-produced stimuli associated with the completion of either of two fixed ratios, or a compound of exteroceptive and response-produced stimuli were available as samples. Exteroceptive samples were found to control a higher level of matching accuracy than response-produced samples, while compound samples controlled a higher level of accuracy than did exteroceptive samples alone. When all subjects were placed on a transfer procedure, during which the previously used red and green samples were replaced by horizontal and vertical lines, the availability of sample-specific fixed-ratios facilitated acquisition of the task.     

Effects of ratio reinforcement schedules on discrimination performance by Japanese monkeys

In Experiment 1, Japanese monkeys were trained on three conditional position-discrimination problems with colors as the conditional cues. Within each session, each problem was presented for two blocks of ten reinforcements; correct responses were reinforced under continuous-reinforcement, fixed-ratio 5, and variable-ratio 5 schedules, each assigned to one of the three problems. The assignment of schedules to problems was rotated a total of three times (15 sessions per assignment) after 30 sessions of acquisition training. Accuracy of discrimination increased to a moderate level with fewer trials under CRF than under ratio schedules. In contrast, the two ratio schedules, fixed and variable, were more effective in maintaining accurate discrimination than was CRF. With further training, as asymptotes were reached, accuracy was less affected by the schedule differences. These results demonstrated an interaction between the effects of reinforcement schedules and the level of acquisition. In Experiment 2, ratio sizes were gradually increased to 30. Discrimination accuracy was maintained until the ratio reached 20; ratio 30 strained the performance. Under FR conditions, accuracy increased as correct choice responses cumulated after reinforcement.     

Effects of a pre-aversive stimulus upon oddity performance in monkeys

Two monkeys (Macaca mulatta) were trained to perform an oddity discrimination using automatically projected patterned stimuli. After criteria for both response and discrimination stability were met, a tone followed by shock was superimposed upon the ongoing behavior. Each 60-sec tone was terminated with the onset of a 0.3-sec, 1 to 1.5-ma electric shock. During the tone, baseline responding was partially suppressed but discrimination performance was little altered from the pre-tone period. When shock was raised to 2 to 3 ma, responding was further suppressed, but discrimination performance was again essentially unaltered.     

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.     

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.