Fast regression estimates of missing data

A recent comparison of methods for estimating missing data concluded that when there is sufficient redundancy to justify using a more elaborate method than the mean of each variable, the principal components and regression methods are equally good and superior to the other methods investigated. Principal components was preferred because of its tremendous computational savings over the regression method. This note proposes an alternate implementation of the regression method which should be slightly faster than the principal components method.     

The effect of rearing environments on the contrafreeloading phenomenon in rats

Eight naive rats were reared in enriched or impoverished environments for 39 days after weaning and then lived in operant chambers, in which they could obtain food pellets freely or by lever pressing, for 25 or 30 days. The animals raised in an impoverished environment acquired the bar-press response quickly when placed in the operant chambers and maintained a preference for obtaining food via bar pressing. Animals raised in an enriched environment did not learn to lever press, as demonstrated by low levels of responding and the lack of bar pressing when free food was subsequently removed. It was concluded that restricting animals' postweaning environments facilitated learning in a choice situation, probably because of increased activity levels. The results are interpreted in relation to previous studies on rearing environments and on contrafreeloading.     

Producing a change from competition to sharing: effects of large and adjusting response requirements

Pairs of high-school students matched-to-sample for money. On each trial, the first pair member to complete a fixed ratio of knob-pulling responses could work the matching problem on that trial. Competition occurred when both pair members responded for the problem. Sharing occurred when only one pair member responded on each trial, and the subjects alternated trials. Hence, sharing requires less responding and still allows a moderate number of reinforcers for each subject. Recent research has shown that increasing the response requirement to the point that it may have aversive properties will produce a change from competition to sharing. A related variable is an adjusting schedule that adjusts the subjects' response requirements so that their abilities to take reinforcers are equal. In this way, subjects might learn that competition requires more responding but produces no more reinforcers. However, recent research also suggests that competition decreases over sessions without experimental manipulations. Because of this possibility of a time-related variable, ratio size and an adjusting schedule were studied in a group design. Competition did decrease for all groups over sessions, but the large-ratio groups switched from competition to sharing sooner than the low-ratio groups. The adjusting schedule had a similar but smaller effect.     

Multiple encoding of word attributes in memory

Two experiments employing the release from PI method were conducted to determine whether degree of release could be predicted by the amount of denotative attribute overlap between the control and experimental groups. This theory was very appropriate for predicting the results of the first experiment, but was less successful in the second unless a connotative attribute is also introduced. It is suggested that this class of attribute should be included in semantic memory conceptualization.     

Memory and frequency estimation processes in a decision task

Two experiments examined the role of information storage and frequency estimation processes in a simple decision task. On each trial from one to five simultaneous sequences of information were presented, and subjects were required to monitor and respond to each sequence. In one study independent groups of subjects gave decisions, recognition responses. or frequency judgments. In a second study recall responses were obtained from subjects as part of the decision and frequency judgment tasks. Changes in performance as the number of simultaneous sequences increased suggested an independence of decisions from memory for specific information. Performance on the decision and frequency judgment tasks exceeded at times that which was possible on the basis of specific information available. Other data suggested that subjects in the frequency estimation tasks maintained an accurate frequency count when possible, but in the decision task kept little more than a record of their currently favored hypothesis. When direct counting was prevented in the second experiment. performance in the two tasks was not significantly different, suggesting that the two processes are very similar under such conditions.     

Manipulation of response-contingent unconditioned-stimulus intensity in human eyelid conditioning: A two-phase model analysis

Four groups of human subjects were given 360 classical eyeblink conditioning trials. All groups received the same UCS (unconditioned stimulus) intensity on[Formula: see text] (nonconditioned response) trials but differed in the intensity presented on CR trials. Response probability increased as a positive function of UCS intensity on CR trials. Phase 1 of the two-phase model was longer when no UCS was presented on CR trials, but did not differ in duration among the remaining three groups. Most subjects could be described with a single operator in Phase 2, the operator limit increasing as a positive function of CR-contingent UCS intensity. For subjects requiring different operator limits on CR and[Formula: see text] trials, the latter was lower with high CR-trial intensities but higher with low CR-trialintensities. The results were interpreted to be more consistent with drive theory than with "law-of-effect" or two-factor theories.     

Capacity limitations in human information processing

The nature of processing demands during a letter-match task was investigated in an extension of the Posner and Boies (1971) paradigm. In Experiment I, a visual probe was employed in addition to an auditory probe in two different experimental conditions. The shape of the auditory probe reaction time (RT) function was similar to that found by Posner and Boies. However, in contrast to their findings, RT was greatly increased shortly after presentation of the first letter for the visual probe function. It was concluded that perceptual as well as postperceptual limitations on processing capacity exist. A second experiment provided further support for this hypothesis.     

Physical distance and attraction: An intensification effect

This study was designed to test the effects of both interaction distance and the quality of the interaction upon attraction. It was found that close interaction distances amplified the quality of the interaction so that for a positive interaction there was more liking for a close rather than a far partner, while for a negative interaction a close partner was liked less. The implications of this finding for research concerning crowding is discussed, as are possible explanatory mechanisms.