A jackknife test of homogeneity of variance with paired replicates data

A nonparametric test of dispersion with paired replicates data is described which involves jackknifing logarithmic transformations of the ratio of variance estimates for the pre- and post-treatment populations. Results from a Monte Carlo simulation show that the test performs well underH _o and has good power properties. Examples are given of applying the procedure on psychiatric data.A referee called our attention to valuable references which related to our work, and he suggested the inclusion of competing jackknife procedures into our studies.     

Case specificity of the stimulus probability effect

Four memory scanning experiments investigated the effect of the probability of occurrence of one case of a letter (e.g., “A”) on response time to the other case of that same letter (“a”). There was no effect: Responses to one case of a letter did not depend on the probability of occurrence of the other case of the letter. This finding indicates that facilitation of visual encoding by high probability of occurrence is not caused by increased activation at the level of the name code. Previous results rule out the possibility that facilitation occurs at the level of feature detectors responding to the individual visual features of the high-probability stimuli, and these results were replicated in the present experiments. It appears that facilitation is caused by activation along specific routes by which visual features activate letter names. This conclusion has implications for the locus of effect of stimulus probability in models of letter coding     

Somatic and autonomic indexes of recovery from electroconvulsive shock-induced amnesia in rats

Autonomic response indexes of experimental amnesia have recently been found to have higher electroconvulsive shock (ECS) intensity thresholds and steeper retrograde gradients than have traditional somatic indexes. The present studies examined the hypothesis that recovery from somatically indexed experimental amnesia depends upon the existence of autonomically available residual memory. In a between-subjects design, a 200-mA ECS was used to produce amnesia for a tone-footshock pairing as indicated by lick suppression, defection, and bradycardia. The next day, these amnesic animals received a reminder footshock outside of the training apparatus, which was found to restore memory on a test trial 24 hr later. The behavior of control groups indicated that this reminder effect was due to the restoration of specific memory rather than systemic consequences of treatment. With a within-subjects design, a second experiment obtained a reminder effect in animals individually shown to be "fully" amnesic by all three response indexes monitored. A third experiment varied the intensity of the reminder footshock and revealed that the different memory indexes examined do not have reminder-footshock thresholds inversely related to their initial resistance to amnesia. The results support a retrieval-failure view of experimental amnesia and suggest that the same fundamental physiological processes underlie both autonomically indexed memory and somatically indexed memory.     

Matching as a multivariate power law: Frequency of behavior versus frequency and magnitude of reinforcement

Two groups of food-deprived rats responded for access to liquid reinforcers on a wide range of concurrent variable-interval schedules. During the first part of the experiment, one group chose between two different sucrose solutions; for a second group, the choice involved a sucrose solution and a solution of condensed milk. In the latter part of the experiment, the two groups chose between identical sucrose solutions. A variety of multivariate equations were applied to data obtained from both conditions. The best-fitting equation proved to be a multivariate power function, which is an extension of Herrnstein's basic matching law.     

Adaptation effect in nonfluent speech behavior of controlled stutterers and nonstutterers

The adaptation effect in stuttering behavior has received considerable attention. Adaptation effect is defined as the reduction in the frequency of nonfluencies in the speech of subjects during successive readings of the same passage. The objective of this investigation was to assess the adaptation effect of nonfluent speech behavior of controlled stutterers and nonstutterers. The subjects included 35 controlled stutterers and 35 nonstutterers matched for factors of sex, grade level, and age. Results suggest a significant mean difference between the number of nonfluencies between trials of controlled stutterers with evidence of adaptation in the speech of nonstutterers. Nonstutterers demonstrate significant mean differences in nonfluencies among replicated testing occasions. Findings of this investigation suggest that both controlled stutterers and nonstutterers demonstrate similar adaptation regarding their nonfluent speech behavior. Issues and import for future research are offered.     

Isolating visual units in the perception of words and nonwords

In three experiments, reaction times for same-different judgments were obtained for pairs of words, pronounceable nonwords (pseudowords), and unpronounceable nonwords. The stimulus strings were printed either in a single letter case or in one of several mixtures of upper- and lowercase letters. In Experiment 1, the stimuli were common one- and two-syllable words; in Experiment 2, the stimuli included both words and pseudowords; and in Experiment 3, words, pseudowords, and nonwords were used. The functional visual units for each string type were inferred from the effects that the number and placement of letter case transitions had onsame reaction time judgments. The evidence indicated a preference to encode strings in terms of multiletter perceptual units if they are present in the string. The data .also suggested that whole words can be used as functional visual units, although the extent of their use depends on contextual parameters such as knowledge that a word will be presented.     

Prevention education and substance abuse treatment

Relapse prevention is influenced by a number of variables including stress and negative mood states, motivation and commitment to abstinence, social support, physiological factors, withdrawal symptoms, and a repertoire of cognitive and behavioral strategies utilized in responding to the relapse process. Diverse theoretical approaches have emphasized conditioning models as well as information processing, cognitive and affective components of treatment, cognitive and behavioral coping responses, and a variety of other procedures. Outcome studies related to treatment have failed to consistently support the effectiveness of several of these components. To overcomes this, the authors advocate a single subject design in the study of these approaches. This article emphasizes the role of relapse prevention, and training and education in facilitating long-term abstinence, particularly with those intervention methods that are based on social learning theory and cognitive-behavioral models.     

EFFICACY AND MAINTENANCE OF AN EDUCATION PROGRAM FOR A CONSUMER COOPERATIVE

We examined the effects of contingency management on participation in and maintenance of an education program by new members of a student housing cooperative. With credit and fine contingencies in place, the percentage of participants completing study guides was five times higher than without the contingencies. Members continued to implement the program for 9 years without researcher involvement.