A further study of partial reinforcement in the turtle

Two matched groups of mature painted turtles, Chrysemys picta picta, were trained in a simple runway, one with partial and the other with consistent reinforcement, following which both groups were extinguished. The partially reinforced animals ran more slowly in acquisition, but showed somewhat greater resistance to extinction. The results are compared with those obtained in analogous experiments with other animals.     

Observing responses in rats: Support for the secondary reinforcement hypothesis

Rats' lever presses on a retractable lever earned brief presentations of discriminative stimuli signalling periods in which responding on an alternative lever was either non-reinforced (extinction) or reinforced on a random ratio schedule. The predictions of two theoretical accounts of this behaviour were tested by studying the effects of omitting either the stimulus signalling the reinforced or that signalling the non-reinforced schedule component. Under these conditions rats' behaviour is determined by the conditioned, affective properties of the stimuli rather than by their purely informational properties.     

A further study of stimulus generalization following three-stimulus discrimination training

A group of pigeons was trained in a Skinner box to peck for VI reinforcement when the key was illuminated by a monochromatic light of 540 or 580 mμ but were non-reinforced for responding to 560 mμ. Two control groups, differing in amount of training, received only the two positive stimuli. At the completion of training all Ss received generalization tests under extinction. Both control groups produced bi-modal generalization gradients with the peaks of responding at the S+ values. The post-discrimination gradient revealed peaks displaced from the S+ values in the direction away from the S−, low responding and increased steepness in the region of S− and a general elevation of the gradient.     

Conditioned reinforcement and discrimination performance

Pigeons were trained in a three-key chamber to peck one side key in the presence of a vertical line on the center key and to peck the other side key in the presence of a horizontal line. Correct choice responses were reinforced with food according to fixed- and variable-ratio, fixed-interval, and differential-reinforcement-of-long-latency schedules of reinforcement. For each schedule, the birds performed under each of two conditions: (1) each correct choice response produced a brief presentation of stimuli intermittently paired with food, then the next trial; (2) each correct choice response produced an intertrial interval only. For all schedules except one long latency schedule, response rates were higher under the condition of brief stimulus presentation than under the comparable control condition. Presentation of brief magazine stimuli increased choice accuracy. The amount of change in accuracy was correlated with the rate of food presentation. Performance under the schedules with highest food reinforcement rates showed no enhancement; performance under the schedules with the lowest reinforcement rates showed the greatest enhancement.     

Hostility in fantasy: A further test of the hypoglycemia-aggression hypothesis

In a recent investigation carried out among the Qolla Indians of Peru, Bolton (1973a) tested the hypothesis that hypoglycemia tends to produce high levels of individual aggressiveness. Glycemic condition was determined by the readings on a 4-hour glucose tolerance test performed on a sample of 54 adult males. Key informants then ranked these subjects on overt aggressiveness. A correlational analysis of the data supported the hypothesis that moderately hypoglycemic subjects would be more aggressive than the normoglycemic subjects. The present paper responds to questions raised about this study and describes the results of an additional test of the hypoglycemia-aggression hypothesis. The dependent variable in this follow-up study is fantasy aggression. Aggression scores were derived from Sentence Completion Test protocols for the same sample of subjects used in the first study. The results indicate a significant correlation between glycemic condition and aggression scores (Biserial, 0.57), thus providing further confirmation of the hypoglycemia-aggression hypothesis.     

A further experiment on the discrimination of open and closed shapes by rats

In a previous experiment on the visual discrimination of open and closed shapes by rats (Sutherland, Carr, and Mackintosh, 1962) it was found that (1) at the beginning of training the animals exhibited a strong preference for the more open shape; (2) shapes differing in their horizontal projections only were more discriminable than shapes differing in their vertical projections only. The present experiment is a replication of the earlier one using different shapes and different apparatus. The first result was fully confirmed and some confirmation was obtained for the second, although late in training the differences between groups trained with shapes differing on opposite projections were not statistically significant.