Variation within categories

Two aspects of variation within categories, relating to different models of categorization, were investigated — frequency of dimensional values and typicality differences within values. The influence of range of typicality experienced during learning and of informational value of feedback was also studied. Finally, differential forgetting of values was examined.In the experiment subjects learned to categorize faces, and then performed a classification test task and pairwise comparisons of faces. A variety of dependent variables was employed, including the galvanic skin response (GSR).Typicality and frequency of values appeared to influence categorization performance independent of each other. It was concluded that both prototype distance models and frequency models explain different aspects of variation within the same categories, and that models of classification should account for frequency of values in contrasting categories. Results showed furthermore (1) the influence of typicality range on the extension of a category; (2) no influence of specific feedback regarding representativeness of a face; (3) less decay with more important values; and (4) a positive relationship between uncertainty reduction and GSR.     

Adolescents' communication styles and learning about birth control

Adolescents have different communication styles for acquiring information about birth control from a mass medium--interactant or noninteractant, depending on whether they involve communication with others in the process of media use. Three interactant styles are identified: a home-oriented style, where communication is primarily with immediate members and friends; a peer-oriented style, where communication is primarily with own-age peers and personal friends; and multi-source user, where communication is with more than one cluster of sources and the majority of one's communication is not with any particular source. The noninteractant style identified is a media-oriented style, where the adolescent relies exclusively on the mass media for information acquisition without communicating with anyone about the content or process of learning. Data suggest that the interactant style, especially for the multi-source user, is most beneficial for new learning. Gender and the presence of siblings at home are important moderators of the relationship between communication styles and knowledge of birth control. For example, females with a media-oriented style know more about birth control than females with a home-oriented style. Implications of the findings for the delivery of birth control information to adolescents are discussed.     

The pupillary response as an indicator of arousal and cognition

Psychological research on the pupillary response since 1960 has focused on an arousal interpretation and a cognitive interpretation. Experiment 1 was an attempt to manipulate some arousal factors while controlling the cognitive demands of the task. Pupil size was cinematographically recorded while subjects who had different degrees of reported fear of snakes listened to passages describing imagined interactions with a snake in different proximities. There was also a set of control passages that made no mention of snakes but were otherwise semantically and syntactically identical to the aversive passages. The pupillary response showed no influence of the arousal manipulations, but rating and behavioral data indicated that the arousal variables had been effective. The cognitive demands of the task were clearly indicated by the pupillary response. In Experiment 2 two types of tasks were used: one that employed both arousal (incentive) and cognitive factors and another that had an arousal manipulation (threat of shock) but no explicit cognitive demands. The pupil response was recorded as well as heart rate, skin conductance, and EMG. The pupillary response showed an effect of the arousal manipulations only when cognitive demands were minimal. The results of both experiments are consistent with the view that cognitive demands take priority over arousal factors in affecting the pupillary response. Heart rate did show arousal effects that were not preempted by cognitive demands.     

AIDS Knowledge,Attitudes, Beliefs,and Practices (KABP) in Two Caribbean Countries: A Comparative Analysis1

The present paper presents the results of AIDS Knowledge, Attitudes, Beliefs, and Practices (KABP) surveys conducted in two Caribbean countries: St. Vincent and St. Lucia. Despite religious, socioeconomic, and literacy differences between the two countries, their citizens are remarkably similar with respect to AIDS knowledge, attitudes, beliefs, and practices. The major differences between the two countries concern the perception of AIDS risk and the relative position of AIDS as a serious problem facing the country. These differences, however, appear unrelated to AIDS knowledge, sexual practices, or the likelihood of engaging in AIDS-protective behaviors. These findings question the role of perceived risk of AIDS as a determinant of AIDS-protective behaviors, and, more important, they question the utility of increasing perceived risk as a strategy in AIDS prevention programs.     

A latent class approach to fitting the weighted Euclidean model,clascal

A weighted Euclidean distance model for analyzing three-way proximity data is proposed that incorporates a latent class approach. In this latent class weighted Euclidean model, the contribution to the distance function between two stimuli is per dimension weighted identically by all subjects in the same latent class. This model removes the rotational invariance of the classical multidimensional scaling model retaining psychologically meaningful dimensions, and drastically reduces the number of parameters in the traditional INDSCAL model. The probability density function for the data of a subject is posited to be a finite mixture of spherical multivariate normal densities. The maximum likelihood function is optimized by means of an EM algorithm; a modified Fisher scoring method is used to update the parameters in the M-step. A model selection strategy is proposed and illustrated on both real and artificial data.The second author is supported as Bevoegdverklaard Navorser of the Belgian Nationaal Fonds voor Wetenschappelijk Onderzoek.     

Numerical support,information processing and attitude change

In two experiments we studied the prediction that majority support induces stronger convergent processing than minority support for a persuasive message, the more so when recipients are explicitly forced to pay attention to the source's point of view; this in turn affects the amount of attitude change on related issues. Convergent processing is the systematic elaboration on the sources position, but with a stronger focus on verification and justification rather than falsification. In Experiment 1 it was found that numerical support is related to information processing as predicted: The greater the support, the more convergent the processing. Experiment 2 replicated this result, and furthermore confirmed our expectations regarding attitude change: The more convergent processing occurs, the less subjects change their attitude on related issues.     

A thurstonian pairwise choice model with univariate and multivariate spline transformations

A probabilistic choice model is developed for paired comparisons data about psychophysical stimuli. The model is based on Thurstone's Law of Comparative Judgment Case V and assumes that each stimulus is measured on a small number of physical variables. The utility of a stimulus is related to its values on the physical variables either by means of an additive univariate spline model or by means of multivariate spline model. In the additive univariate spline model, a separate univariate spline transformation is estimated for each physical dimension and the utility of a stimulus is assumed to be an additive combination of these transformed values. In the multivariate spline model, the utility of a stimulus is assumed to be a general multivariate spline function in the physical variables. The use of B splines for estimating the transformation functions is discussed and it is shown how B splines can be generalized to the multivariate case by using as basis functions tensor products of the univariate basis functions. A maximum likelihood estimation procedure for the Thurstone Case V model with spline transformation is described and applied for illustrative purposes to various artificial and real data sets. Finally, the model is extended using a latent class approach to the case where there are unreplicated paired comparisons data from a relatively large number of subjects drawn from a heterogeneous population. An EM algorithm for estimating the parameters in this extended model is outlined and illustrated on some real data.The first author is supported as Bevoegdverklaard Navorser of the Belgian Nationaal Fonds voor Wetenschappelijk Onderzoek. The authors are indebted to Ulf Böckenholt and Yoshio Takane for useful comments on an earlier draft of this paper.     

A latent class unfolding model for analyzing single stimulus preference ratings

A multidimensional unfolding model is developed that assumes that the subjects can be clustered into a small number of homogeneous groups or classes. The subjects that belong to the same group are represented by a single ideal point. Since it is not known in advance to which group of class a subject belongs, a mixture distribution model is formulated that can be considered as a latent class model for continuous single stimulus preference ratings. A GEM algorithm is described for estimating the parameters in the model. The M-step of the algorithm is based on a majorization procedure for updating the estimates of the spatial model parameters. A strategy for selecting the appropriate number of classes and the appropriate number of dimensions is proposed and fully illustrated on some artificial data. The latent class unfolding model is applied to political science data concerning party preferences from members of the Dutch Parliament. Finally, some possible extensions of the model are discussed.The first author is supported as Bevoegdverklaard Navorser of the Belgian Nationaal Fonds voor Wetenschappelijk Onderzoek. Part of this paper was presented at the Distancia meeting held in Rennes, France, June 1992.