Production of narrative discourse in aphasia

The study described the abilities of a group of 15 moderately impaired aphasics and 15 normals to produce narrative discourse. The experimental tasks included telling stories, summarizing stories, and giving morals to stories. The data were analyzed in terms of sentential grammar, discourse grammar, and subjective ratings of content and clarity of language. The results showed that aphasics produced well-structured discourse. The language of the aphasics' discourse was reduced in both complexity and amount, as compared to that produced by normals. The reduction of language reflected selective reduction of hierarchically organized information. The findings of the study confirm the results of previous research on mildly impaired aphasics, which also showed preservation of discourse structure with selective reduction of information.     

The effect of reinforcement differences on choice and response distribution during stimulus compounding

In Experiments I and II, rats were trained to respond on one lever during light and another during tone. The absence of tone and light controlled response cessation. In the multiple schedule of Experiment I, all reinforcements were received for responding in tone or light; in the chain schedule of Experiment II, all reinforcements were received in no tone + no light for not responding. Experiment I subjects, for which tone and light were associated with response and reinforcement increase, responded significantly more to tone-plus-light than to tone or light alone (additive summation). Experiment II subjects, for which tone and light were associated with response increase and reinforcement decrease, responded comparably to tone, light, and tone + light. Thus, additive summation was observed when stimulus-response and stimulus-reinforcer associations in tone and light were both positive, but not when they were conflicting. All subjects in both experiments responded predominantly on the light-correlated lever during tone + light, even when light intensity was reduced in testing. Furthermore, when a light was presented to a subject engaged in tone-associated responding, all subjects immediately switched the locus of responding to the light-correlated lever. No change in locus occurred when a tone was presented to a subject engaged in light-associated responding, irrespective of the stimulus-reinforcer association conditioned to tone. The light-lever preference in tone + light indicates that the heightened responding observed in Experiment I was not the summation of tone-associated behavior with light-associated behavior. Rather, it appears to be the result of a facilitation of one operant (light-associated responding) by the reinforcement-associated cue for the other.     

The negative reinforcing functions of nonconformity

Employing the general approach which Neal Miller called “extension of liberalized S-R theory,” two experiments (N = 108) found that Ss would learn an instrumental response, the reinforcement for which was the opportunity to escape from a situation in which they were a nonconformist. When the nonconformity situations were presented on an intermittent basis, speed of the response was found to be a function of the percentage of nonconformity trials (p <.001). When the opportunity to escape was delayed (0, 1.5, or 3 sec), response acquisition was found to be an inverse function of the length of the delay (p <.001). The results of both experiments correspond to data collected in instrumental escape conditioning experiments on delay of reinforcement and intermittent shock using similar procedures.     

Summation of conditioned suppression

Four rats were trained to suppress responses in the presence of two separately presented stimuli that signalled shock in a conditioned-suppression paradigm. The two stimuli that signalled shock were then presented simultaneously to evaluate the effect of stimulus compounding on conditioned suppression. Two rats were tested by presenting the compound conditioned stimulus while conditioned suppression was being maintained to the individual conditioned stimuli. The other two rats were tested by giving them random presentations of the compound conditioned stimulus and the single conditioned stimuli during extinction of conditioned suppression. All four rats showed greater suppression to the compound stimulus than to either stimulus presented alone.     

A computer analysis of serial interactions in spaced responding

Serial dependencies in interresponse times were studied by means of a digital computer. In monkeys exposed to a DRL 20-sec schedule of reinforcement, serial interactions appeared at all stages of training. Early in training the serial effects consisted of trains of relatively long interresponse times interspersed among trains of relatively short ones. Later on, the serial effects appeared to be characterized by a tendency to drift up and down in long wavelength periods around the minimum interval required for reinforcement. After training to a point at which most interresponse times produced reinforcement, serial effects of a still more subtle nature appeared. These effects were made apparent by autocorrelation and power spectrum methods and consisted of both long-term and extremely short-term fluctuations in interresponse times.     

Characteristics of aversive thresholds measured by a titration schedule

Three variables were studied for their single and joint effects on aversive thresholds obtained by a titration schedule with electric shock as the aversive stimulus. One variable was the interval between the periodic increments in shock amplitude. Another was the size of this increment. The third was the size of the decrement produced when the subject responded. Both monkeys and humans tolerated more shock at the shorter increment-to-increment intervals than at the longer ones, confirming rat data previously obtained. Reducing the decremental step size also led to an increase in the amount of shock tolerated by monkeys. In addition, simply reducing both incremental and decremental step size without changing the interval between increments led monkeys to tolerate more shock. The attempt to explain these data was based on the changes that such manipulations might produce in the amount of avoidance behavior elicited.