A model of perceptual classification in children and adults

The developmental trend from overall-similarity to dimensional-identity classifications is explained by a quantitative model. I begin with the assumption that objects are represented in terms of constituent dimensions and that the representation of objects changes little with development. Given this assumption, the model has three major parts. First, the similarity between objects is a function of the combination of the constituent dimensional differences. I propose developmental change in the likelihood that dimensions are differentially weighted in the calculation of similarity. Second, the perceived similarities between objects are valued for the purpose of constructing classifications. I propose that similarities are valued more dichotomously with age, such that identity becomes increasingly special. Third, the valued similarities are used to choose the best classification of those possible. The model provides good qualitative fits to the extant data. Three experiments examining classifications in 2- to 8-year-olds and in adults support specific new claims of the model. The data and the model provide new insights about development, classification, and similarity.     

Why the Principle of the Identity of Indiscernibles is not contingently true either

Faced with strong arguments to the effect that Leibniz'sPrinciple of the Identity of Indiscernibles (PII) is not a necessary truth, many supporters of the Principle have staged a strategic retreat to the claim that it is contingently true in this, the actual, world. The purpose of this paper is to examine the status of the various forms of PII in both classical and quantum physics, and it is concluded that this latter view is at best doubtful, at worst, simply wrong.I would like to thank Michael Redhead and an anonymous referee for several useful suggestions and criticisms relating to the earlier version of this paper. I must also acknowledge the support given by the Centre of Logic, Epistemology and History of Science of the University of Campinas and the Brazilian National Council for Scientific and Technological Development in the later stages of the preparation of this work.     

A neuroscience model of stuttering

Using motor control systems analysis and a reductionist approach, we provide a unified model of stuttering. This model views stuttering as a momentary instability in a complex multiloop control system. The model predicts the temporal conditions under which this instability will occur. Furthermore, these temporal conditions account for the efficacy of fluency-evoking maneuvers, therapy, and the variability of speech output in stutterers.     

Behavioral correlates of developmental expressive language disorder

The association of behavior problems with preschool language disorders has been documented extensively. However, researchers have typically failed to differentiate subgroups of language-impaired children, to use observational data in documenting the behavior disorders, or to study children at the youngest ages. Using a multimodal assessment, this study examined parent-child interaction and behavior problems in a clearly defined subgroup of language-impaired children, those with developmental expressive language disorder (ELD). These children exhibit a delay in expressive language compared with receptive language and nonverbal cognitive skills. Subjects were identified and studied at the youngest age at which the disorder can be assessed. A group of ELD children, averaging 27 months of age, was contrasted with a group of normally developing children, matched for age, sex, and receptive language ability. Groups were compared on observed parent-child interactions as well as maternal responses on the Parenting Stress Index, the Eyberg Child Behavior Inventory, and a behavior-related structured interview. ELD children, when compared with normally developing children, exhibited higher levels of negative behavior and were perceived as different by their parents.Portions of these data were presented at the biennial meeting of the Society for Research in Child Development, Baltimore, April 1987, and at the annual meeting of the Society for Pediatrie Research, Anaheim, California, April 1987. This work has been supported by NIMH grant no. 1 R03 MH41603 to author Fischel, and by NICHD grant no. 1 ROI HD19245 to authors Whitehurst and Fischel. It has also been supported by grants of equipment from Commodore Business Machines, Inc., Koala Corporation, and NEC Telephones. We thank the Department of Pediatrics at the Nassau County Medical Center for the use of their facilities.     

Ratings of kinetic depth in multidot displays

Subjects saw kinetic depth displays whose shape (sphere or cylinder) was defined by luminous dots distributed randomly on the surface or in the volume of the object. Subjects rated perceived 3-D depth, rigidity, and coherence. Despite individual differences, all 3 ratings increased with the number of dots. Dots in the volume yielded ratings equal to or greater than surface dots. Each rating varied with 3 of 4 factors (shape, distribution, numerosity, and perspective), but the ratings either between trials or between conditions were often uncorrelated. Object shape affected rigidity but not depth ratings. Veridically perceived polar displays had slightly lower rigidity but higher depth ratings than parallel projection displays. (Reversed polar displays were always grossly nonrigid.) The interaction of ratings and stimulus parameters requires theories and experiments in which different KDE ratings are not treated interchangeably.     

Right hemisphere contribution to lexical access in an aphasic with deep dyslexia

Three hemifield tachistoscopic studies of a right-handed patient with acquired Broca's aphasia and deep dyslexia, but with intact visual fields, are presented to support the hypothesis of right hemisphere (RH) participation in deep dyslexic reading. A systematic comparison of this deep dyslexic with the disconnected RHs of two patients with complete cerebral commissurotomy disclosed a similar, but not identical, pattern of abilities. The results demonstrate partial reliance on the RH for accessing the meaning of single words, but not for phonological encoding in this patient.     

Written spelling agraphia

When a disorder of single word writing is seen in conjunction with preserved oral spelling and intact written grapheme formation ("written spelling agraphia"), the deficit may be presumed to lie somewhere between letter choice and written motor output. Two potential deficits are considered: (1) visual letter codes are not activated properly and (2) the information contained within properly activated visual letter codes fails to reach intact graphic motor patterns. Two patients with written spelling agraphia were each given a series of tests aimed at distinguishing between the two possibilities. Results suggest that the written spelling agraphia seen in these two patients arises from different underlying deficits. The results are discussed in terms of the patients' CT scan lesion sites, which were markedly different.     

Memory for internally generated words in Alzheimer-type dementia: breakdown in encoding and semantic memory

The "generation effect" is a phenomenon in which words that are generated by the subject are remembered better than words which are read. The present experiments examined this effect in patients with mild-to-moderate dementia of the Alzheimer type (DAT), healthy elderly adults, and young adults under a variety of different encoding and retrieval conditions. Experiment 1 employed an intentional learning task with multiple study/test trials using the same list of words. While both the young and elderly adults exhibited higher recall for internally generated words than read words, the DAT patients failed to demonstrate the effect even after repeated exposures to the same stimulus list. Experiment 2 replicated this same pattern of results using an incidental learning paradigm with both recall and recognition tests. Various explanations as to why the DAT patients failed to show the generation effect were discussed with particular emphasis placed on the role of semantic memory and encoding failure.     

Psychic phenomena following near-death experiences: An Australian study

This study examines the incidence of reports of psychic phenomena and associated beliefs both before and after the near-death experience (NDE). The near-death experiencers interviewed reported no more psychic phenomena before the NDE than the general population. There was a statistically significant increase following the NDE in the incidence of 14 of 15 items examined.     

On the development of procedural knowledge

Amnesic patients demonstrate by their performance on a serial reaction time task that they learned a repeating spatial sequence despite their lack of awareness of the repetition (Nissen & Bullemer, 1987). In the experiments reported here, we investigated this form of procedural learning in normal subjects. A subgroup of subjects showed substantial procedural learning of the sequence in the absence of explicit declarative knowledge of it. Their ability to generate the sequence was effectively at chance and showed no savings in learning. Additional amounts of training increased both procedural and declarative knowledge of the sequence. Development of knowledge in one system seems not to depend on knowledge in the other. Procedural learning in this situation is neither solely perceptual nor solely motor. The learning shows minimal transfer to a situation employing the same motor sequence.