Effects of preexposure on stimulus discrimination: an investigation of the mechanisms responsible for human perceptual learning

The effect of preexposure on human perceptual learning was investigated in four experiments. In Experiments 1a and 1b, participants were preexposed to one pair of visual stimuli on an intermixed schedule (AX/BX) and one on a blocked schedule (CX_DX). The ability to discriminate between AX and BX and between CX and DX was then assessed by examining the extent to which key presses assigned to each member of a stimulus pair generalized to the other member (Experiment 1a) and by looking at the accuracy of same-different responses (Experiment 1b). Stimuli were more easily discriminated following intermixed than following blocked preexposure on both the generalization and same-different tasks. This suggests that two stimuli are more perceptually distinct after intermixed preexposure. Experiments 2a and 2b investigated the mechanisms responsible for perceptual learning using same-different tasks. The results support the suggestion that the enhanced discrimination observed after intermixed preexposure is due to increases in the salience of the unique elements.     

Roles of instruments in psychological research

What roles have instruments played in psychology and related disciplines? How have instruments affected the dynamics of psychological research, with what possibilities and limits? What is the psychological instrument? This article provides a conceptual foundation for specific case studies concerning such questions. The discussion begins by challenging widely accepted assumptions about the subject and analyzing the general relations between scientific experimentation and the uses of instruments in psychology. Building on this analysis, a deliberately inclusive definition of what constitutes a psychological instrument is proposed. The discussion then takes up the relation between instrumentation and theories and differentiates in greater detail the roles instruments have had over the course of psychology's history. Finally, the authors offer an approach to evaluating the possibilities and limitations of instruments in psychology.     

Memory and suggestibility in maltreated children: age,stress arousal,dissociation, and psychopathology

The present study was designed to assess children's memory and suggestibility in the context of ongoing child maltreatment investigations. One hundred eighty-nine 3-17-year-olds involved in evaluations of alleged maltreatment were interviewed with specific and misleading questions about an anogenital examination and clinical assessment. For the anogenital examination, children's stress arousal was indexed both behaviorally and physiologically. For all children, individual-difference data were gathered on intellectual and short-term memory abilities, general psychopathology, and dissociative tendencies. Interviewers' ratings were available for a subset of children concerning the amount of detail provided in abuse disclosures. Results indicated that general psychopathology, short-term memory, and intellectual ability predicted facets of children's memory performance. Older compared to younger children evinced fewer memory errors and greater suggestibility resistance. Age was also significantly related to the amount of detail in children's abuse disclosures. Neither dissociation nor stress arousal significantly predicted children's memory. Implications for understanding maltreated children's eyewitness memory are discussed.     

Contextual overlap and eyewitness suggestibility

Studies of eyewitness suggestibility have traditionally used a paradigm that maximizes the extent to which the postevent interview overlaps with the witnessed event in terms of narrative content, narrative structure, and environmental context. The present study explored whether these dimensions of overlap contribute to people's tendency to confuse suggested details for those they have actually witnessed. We systematically manipulated the extent to which the postevent questionnaire overlapped with the witnessed event. Across two experiments, overlap in narrative content, narrative structure, or environmental context was not found to increase suggestibility effects, even though the manipulation did have other memory effects (e.g., it improved cued recall of the actual source of the suggestions, Experiment 2). These findings suggest that understanding the interaction between the structure and content of the objective context in which misinformation is encountered and various remembering contexts (e.g., recognition vs. recall) is important for advancing our understanding of source confusion in an eyewitness situation.     

Prospects for prenatal gene therapy in disorders causing mental retardation

Advances in understanding the genetics and pathogenesis of disease and in prenatal diagnosis have lead to an exploration of ways to intervene earlier and earlier in the disease process. The possibility of prenatal gene therapy for severe genetic and developmental disorders has sparked new research and debate as to its feasibility, reliability, and ethics as a therapeutic option. Recent animal studies have demonstrated the feasibility of introducing a vector into the developing fetus. The optimal timing and best mode of delivery, however, have yet to be defined. Whether or not this research should be pursued also has been the subject of recent bioethical debates. There is additional concern with the possibility of in utero gene transfer inducing mutagenesis and subsequent tumor formation. This review will provide a summary of the current state of knowledge in the field of prenatal gene therapy and possible directions for the future research.     

The Latent Structure of Substance Use Among American Indian Adolescents: An Example Using Categorical Variables

Researchers frequently have only categorical data to analyze and cannot, for theoretical or methodological reasons, assume that the observed variables are discrete representations of an underlying continuous variable. We present latent class analysis as an alternative method of measuring latent variables in these circumstances. Latent class analysis does not require the assumptions of factor analyses about the nature of manifest and latent variables, but does allow the use of more precise model selection than techniques such as cluster analysis. We modeled the lifetime substance use of American Indian youth. The latent class model of American Indian teenagers' substance use had four classes: Abstaining, Predominantly Alcohol, Predominantly Alcohol and Marijuana, and Plural Substance. We then demonstrated the usefulness of this latent variable by using it to differentiate levels of several variables in a manner consistent with Social Cognitive Theory.