The interaction between stimulus and reinforcer control on remembering.

In a symbolic matching-to-sample task, 6 pigeons obtained food by pecking a red side key when the brighter of two white lights had been presented on the center key and by pecking a green side key when the dimmer of two white lights had been presented on the center key. Across Part 1 and Parts 6 to 10, the delay between sample-stimulus presentation and the availability of the choice keys was varied between 0 s and 25 s. Across Parts 1 to 5, the delay between the emission of a correct choice and the delivery of a reinforcer was varied between 0 s and 30 s. Although increasing both types of delay decreased stimulus discriminability, lengthening the stimulus-choice delay produced a greater decrement in choice accuracy than did lengthening the choice-reinforcer delay. Additionally, the relative reinforcer rate for correct choice was varied across both types of delay. The sensitivity of behavior to the distribution of reinforcers decreased as discriminability decreased under both procedures. These data are consistent with the view, based on the generalized matching law, that sample stimuli and reinforcers interact in their control over remembering.     

Stimulus discriminability in free-operant and discrete-trial detection procedures.

Six pigeons were trained to discriminate different light intensities in four experimental procedures. Experiment 1 compared stimulus discriminability in a yes-no signal-detection task with discriminability measures obtained from two free-operant procedures. Discriminability estimates were significantly lower in the detection procedure. Experiment 2 showed this lowered discriminability to be a function of the delay between stimulus presentation and the availability of the choice-response keys in the standard detection task. In addition, reinforcement sensitivity was lowest when correct choice responses were intermittently, rather than continuously, reinforced.     

Semantic processing and organization in free recall

It was hypothesized that both semantic processing and organizational activity are necessary for optimal free recall performance. In a series of three experiments, subjects were presented with a list of randomly selected nouns and were asked to make up a meaningful sentence for each noun. The subjects also rated the difficulty of using each noun. The subjects were instructed to try to remember words that were labeled "remember" words. For words that were labeled "story" words, the subjects were instructed only to make each sentence, using the word, part of an ongoing story which each subject was to make up. A test of retention for all presented words, using retention intervals of both 1 min and 24 h, showed that the story words were always recalled better than were the remember words. However, the amount of sequential organization was the same for both the story and the remember words. Recognition performance was found to be the same for both types of words. In addition, the story words were rated as being more difficult than the remember words. It was concluded that extensive semantic processing without organization is not sufficient for optimal recall.     

Periodicity pitch perception and its upper frequency limit in cats

We have established a procedure for behavioral assessment of periodicity pitch perception in the cat. This procedure requires the training of cats to make a differential response to two different pure tones, and then testing for the transfer of learning when complex stimuli known to produce periodicity pitch sensations in humans are substituted for the pure tones. Complex stimuli consisted of three to five harmonically related frequencies of the same amplitude and phase. Eight cats were the subjects of these experiments. Two of them were controls. It is demonstrated here that cats do perceive periodicity pitch. We also used this procedure to measure the upper frequency limit of periodicity pitch perception for two cats. The frequencies tested were 100, 200, 300, 400, 600, 800, 900, and 1,200 Hz. The data indicate that the upper frequency limit of periodicity pitch perception in the cat is on the order of 600 to 800 Hz. There is a trend of decreasing prominence of the perception of periodicity pitch as the component frequencies are increased. These results are parallel to the human psychophysical data.