Indexador

Resumo não informado pela fonte indexada.

Four male, 12‐week‐old Sprague‐Dawley rats were used to determine the threshold for behavioral response to X‐irradiation using the conditioned suppression technique. They were maintained at 80 per cent body weight and initially trained to stable performance on a VI 1 min schedule with 16 per cent sucrose solution as reinforcement. After a stable baseline was obtained, animals were placed in the instrumental conditioning box beneath the X‐ray machine for a half‐hour session each day. While subjects were actively pressing the lever for reinforcement, 15‐sec X‐ray exposures of 0.5 R/sec were administered, followed immediately by electric shock. After all animals had exhibited conditioned suppression, the dose‐rate was decreased in subsequent sessions in an effort to establish threshold. The results indicate that X‐rays at a dose‐rate as low as 0.004 R/sec can be an effective pre‐aversive stimulus for the rat.

Nine cats, each with two hypothalamic electrodes in sites which when stimulated produced either quiet attack or attack accompanied by certain forms of vocalization, were trained to escape from tail shock by jumping onto a stool. They were then tested for transfer of the escape response to brain stimulation. Stimulation of the seven sites that yielded quiet biting attack did not elicit the learned response of jumping onto the stool. Stimulation of eight of the 11 sites that yielded attack accompanied by vocalization did elicit the learned response. It was concluded that attack behavior elicited by brain stimulation should not be considered a special case of the response to aversive stimulation, but that attack and response to aversive stimulation involve independent but overlapping systems.

Two groups of pigeons received daily discrimination training at two values on a line‐tilt continuum. S+ (VI 1) and S– (EXT) intervals alternated, and a 30‐sec criterion of no responding to S– was required before S+ returned. Rates of responding to S+ showed two separate contrast effects: at an intermediate stage of training a high peak rate appeared which declined, later in training, to a stable level still in excess of the VI baseline rate. The peak rate was correlated with the total number of responses to S–, while the final rate was not; suggesting that the peak rate and final rate may not be functions of the same variable. These results were compared with performance on a red‐green discrimination where the two stages were not so clear. A line‐tilt discrimination was repeated with fixed length S– intervals terminated by TO, and showed the same contrast magnitude in the final rate without any peak. The peak rate was interpreted as an effect of the ‘punishment’ contingency where responding to S– prolongs S– for 30 sec, while the final rate was taken to be analogous to previous demonstrations of contrast.

Resumo não informado pela fonte indexada.

Resumo não informado pela fonte indexada.

Resumo não informado pela fonte indexada.

Resumo não informado pela fonte indexada.

Resumo não informado pela fonte indexada.

Resumo não informado pela fonte indexada.