Indexador

Resumo não informado pela fonte indexada.

A tone ending with unavoidable electrical shock was periodically presented to pigeons while they pecked a key for food. A second group of birds was exposed to these tone‐shock contingencies and also to a second tone which never ended with shock. The gradient of stimulus generalization following training to a single stimulus was symmetrical, whereas the gradient following discrimination training was asymmetrical, but there was no evidence of peak shift. During testing, suppression to all tones gradually extinguished and in both groups the slope of the gradient increased markedly. A second experiment with the discrimination birds revealed that free shock caused a recovery of the gradient, but the asymmetry persisted.

The introduction of a warning signal preceding shocks greatly increased the effectiveness of avoidance responding. Periods of “warm‐up” at the beginning of the session were eliminated, and the number of shocks received by the subjects was greatly reduced. With response‐shock interval constant, response rate increased as the interval between the response and the onset of the warning signal was shortened. The response tended to occur shortly after the onset of the warning signal regardless of the duration of these “safe” periods. A greatly elevated response rate was maintained even when the duration of the safe period was reduced to 0.3 sec. Thus, the pre‐shock signal obtained nearly exclusive control of the responding and overrode the usual “temporal discrimination” of the response‐shock interval.

Four pigeons were trained with VI reinforcement to peck a key which was briefly illuminated by a flickering light. Generalization gradients were then obtained with nine different rates of flicker, four faster than S+ and four slower. Two birds were then trained to discriminate between S+ and the fastest stimulus (S—). These birds were then trained to discriminate between S+ and the two fastest stimuli, alternated as S—'s. This procedure was continued, adding one new S— at a time, until all four stimuli faster than S+ were S—'s. The remaining two birds were trained on this latter discrimination without intervening training. In a final stage, using the first two birds, the slowest stimulus was added as a fifth S—. Generalization gradients in extinction were obtained from each bird after each stage of training. As more stimuli from one end of the continuum served as S—'s, responding increased in the presence of stimuli from the other end of the continuum, and the gradient tended to become flattened at this end.

Generalization gradients along a line‐tilt continuum were obtained from groups of pigeons that had been trained to peck a key on different schedules of reinforcement. In Exp. I, gradients following training on a differential‐reinforcement‐of‐low‐rate (DRL) schedule proved to be much flatter than gradients following the usual 1‐min variable interval (VI) training. In Exp. II, the value of the VI schedule itself was parametrically studied; Ss trained on long VI schedules (e.g., 4‐min) produced much flatter gradients than Ss trained on short VI schedules (30‐sec; 1‐min). The results were interpreted mainly in terms of the relative control exerted by internal, proprioceptive cues on the different reinforcement schedules. Several implications of the results for other problems in the field of stimulus generalization are discussed.

Three pigeons were trained to respond to seven spectral stimulus values ranging from 490 to 610 mμ and displayed in random order on a response key. After response rates had equalized to these values, a brief electric shock was administered when the subject (S) responded to the central value (550 mμ) while positive reinforcement for all values was maintained. Initially, there was broad generalization of the resulting depression in response rate, but the gradients grew steeper in the course of testing. When punishment was discontinued, the rates to all values recovered, and equal responding to all stimuli was reattained by two of the Ss. Stimulus control over the effects of punishment was clearly demonstrated in the form of a generalization gradient; this probably resulted from the combined effects of generalization of the depression associated with punishment and discrimination between the punished value and neutral stimuli.

Resumo não informado pela fonte indexada.

Resumo não informado pela fonte indexada.

Resumo não informado pela fonte indexada.

Resumo não informado pela fonte indexada.