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.     

Identifying emergent leaders in psychotherapy groups

This paper is the second in the series on group development and emergent leadership. It describes the design of a sociometric instrument which will be used for the identification of the four emerging leaders from the perspective of the group participants themselves. These four leaders, Task, Emotional, Scapegoat and Defiant, perform ongoing maintenance functions in the group and take up the critical function of spokesmen in the group's dialectical processing of phase-specific, group level issues. The goal here is to design an instrument which would allow both clinician and researcher to identify these critical persons early in a group's life.Ariadne P. Back is in private practice in Chicago, Illinois.     

Engaging families in therapy: A pilot study

Engagement is reviewed as a central component of marriage and family therapy and presented as a viable means of assessing the nature and outcome of therapy. A tentative model containing six differentiated engagement categories is described and documented with clinical data and case examples. Conclusions drawn indicate engagement has merit as a construct for evaluating marriage and family therapy and as a means of generating process hypotheses in research. Recommendations to validate, refine and revise the model are posited and further research relative to engagement is advocated.James P. Trotzer, Ph.D. is Professor of Counselor Education at the University of Visconsin-River Falls, River Falls, Wisconsin 54022, marriage and family therapist in private practice     

Relationships between judgements of the complexity,pleasingness and interestingness of music

Forty unfamiliar, one-minute samples of modern jazz were rated by 132 undergraduates for judged complexity, pleasingness and interestingness, in a between-subjects design. Pleasingness and interestingness were positively correlated and both were decreasing linear functions of complexity, although the correlation between interestingness and complexity was low and only marginally significant. It appears that pleasingness acts as a suppressor on the interestingness/complexity correlation: with pleasingness partialled out the correlation was positive and highly significant. Partialling had only small effects on the other correlations. Results suggest that techniques used previously to study non-musical stimuli may also be applicable to music.     

Response competition effects insame-different judgments

An account ofsame-different discriminations that is based upon a continuous-flow model of visual information processing (C. W. Eriksen & Schultz, 1979) and response competition and inhibition between the responses by which the subject signifies his judgment is presented. We show that a response signifyingsame will on the average be executed faster due to less priming or incipient activation of the competing response,different. In the experiment, the subjects matched letters on the basis of physical identity. The degree of priming ofdifferent responses on same trials and ofsame responses ondifferent trials was manipulated by an extraneous noise letter placed in the display. Latency for judgments onsame trials increased as the feature overlap of noise and target letters decreased. Latencies were shorter ondifferent trials when the noise letter was dissimilar to either target letter than when the noise letter was the same as one of the targets. These results were consistent with the response-competition interpretation.     

Visual comparison processes: Identity and similarity decisions

In the first experiment, in which two successively presented free-form visual patterns varied in their similarity to each other, subjects had to decide, in one condition, if the patterns were “identical” and in two other conditions if the patterns were “similar.” Qualitative individual differences in the effect of similarity on the time required to make a decision were found in the “identity” condition, and these differences interacted with the “similarity” conditions. The individual differences and the experimental effects are interpreted in terms of a two-process model of the visual comparison process—a holistic matching process that is sometimes accompanied by an analytic difference detection process. In the second experiment, the same subjects repeatedly categorized subsets of the free-form visual patterns on the basis of similarity. There appeared to be no individual differences in the subjects’ perceptions of similarity, but subjects’ perceptions did differ from the assumptions made by the experimenters when they established the response criteria for the first experiment.     

Stimulus intensity effects on auditory and visual reaction processes.

Literature on the effect of stimulus intensity on reaction processes was reviewed. It was shown that there is no agreement as to whether intensity effects are limited to encoding or whether they are extended to later processing stages. The situation can be characterized as an asymmetry between modalities: vision is consistent with the first alternative and audition with the second.Chronometric analysis was used to bear on the question. It was shown that the effects of visual intensity and foreperiod (FP) are additive in a simple RT situation both for constant and mixed blocks FP. Auditory intensity and FP interact in both simple and two-choice situations. In a control experiment visual intensity and S-R compatibility were found to be additive. The asymmetry was accounted for by auditory alerting, previously discussed by several authors.The framework of stimulus intensity research utilizing RT measures was briefly evaluated.