Comparing Latent Structures of the Grade of Membership,Rasch, and Latent Class Models

This paper focuses on model interpretation issues and employs a geometric approach to compare the potential value of using the Grade of Membership (GoM) model in representing population heterogeneity. We consider population heterogeneity manifolds generated by letting subject specific parameters vary over their natural range, while keeping other population parameters fixed, in the marginal space (based on marginal probabilities) and in the full parameter space (based on cell probabilities). The case of a 2 × 2 contingency table is discussed in detail, and a generalization to 2^J tables with J ≥ 3 is sketched. Our approach highlights the main distinction between the GoM model and the probabilistic mixture of classes by demonstrating geometrically the difference between the concepts of partial and probabilistic memberships. By using the geometric approach we show that, in special cases, the GoM model can be thought of as being similar to an item response theory (IRT) model in representing population heterogeneity. Finally, we show that the GoM item parameters can provide quantities analogous to more general logistic IRT item parameters. As a latent structure model, the GoM model might be considered a useful alternative for a data analysis when both classes of extreme responses, and additional heterogeneity that cannot be captured by those latent classes, are expected in the population. This work was supported by Award #1R03 AG18986-01 from the National Institute on Aging and NIH grant #1R01 CA94212-01. The presentation of the ideas in this paper owes much to discussions with Stephen Fienberg and Brian Junker, Carnegie Mellon University. The author thanks Jim Ramsay and two anonymous reviewers for their valuable comments on earlier drafts of this paper.     

Stimulus-dominance effects and lateral asymmetries for language in normal subjects and in patients with a single functional hemisphere

The assessment of language laterality by the dichotic fused-words test may be impaired by interference effects revealed by the dominant report of one member of the stimuli-pair. Stimulus-dominance and ear asymmetry were evaluated in normal population (48 subjects of both sex and handedness) and in 2 patients with a single functional hemisphere. Results show that in normals the number of stimulus-dominated responses is five times higher than in patients, and is negatively correlated to the index of laterality. It is suggested that dichotic stimuli may interfere one with another during the subcortical acoustic processing and at cortical level, when competing for verbal output. Subcortical interference accounts for stimulus-dominance in the single-hemisphere patients. In normal subjects, the dichotic discrimination is disturbed mainly during the hemispheric cross-talk needed for the oral-verbal processing of dichotic inputs. The frequency of 'interhemispheric' interference, as well as the extents of ear asymmetry, may both depend on differences in the processing stage of the competing inputs, and then they may be influenced by differential verbal skills of LH and RH. Very unequal levels of verbal analysis of the dichotic stimuli may hinder reciprocal interference during the hemispheric cross-talk thus yielding large ear asymmetries associated to small dominance effects.     

Processing of temporal information: Evidence from eye movements

In two experiments, we recorded eye movements to study how readers monitor temporal order information contained in narrative texts. Participants read short texts containing critical temporal information in the sixth sentence, which could be either consistent or inconsistent with temporal order information given in the second sentence. In Experiment 1, inconsistent sentences yielded more regressions to the second sentence and longer refixations of it. In Experiment 2, this pattern of eye movements was shown only by readers who noticed the inconsistency and were able to report it. Theoretical and methodological implications of the results for research on text comprehension are discussed.     

Visual but not spatial working memory deficit in children with spina bifida

Twenty children with spina bifida and twenty controls were assessed on a battery of visuospatial working memory tests. Children with spina bifida performed as well as the control group in the visuospatial test and in the forward and backward versions of the Corsi test, but were impaired in the 'House Visual Span.' This test, designed in our lab, provides specific information regarding visual ability to discriminate between pictorial targets and lures, and requires specific visual processing of stimuli. These results are discussed in terms of working memory models and are viewed as supporting the distinction between the visual and spatial components of working memory.     

Timed picture naming in seven languages

Timed picture naming was compared in seven languages that vary along dimensions known to affect lexical access. Analyses over items focused on factors that determine cross-language universals and cross-language disparities. With regard to universals, number of alternative names had large effects on reaction time within and across languages after target-name agreement was controlled, suggesting inhibitory effects from lexical competitors. For all the languages, word frequency and goodness of depiction had large effects, but objective picture complexity did not. Effects of word structure variables (length, syllable structure, compounding, and initial frication) varied markedly over languages. Strong cross-language correlations were found in naming latencies, frequency, and length. Other-language frequency effects were observed (e.g., Chinese frequencies predicting Spanish reaction times) even after within-language effects were controlled (e.g., Spanish frequencies predicting Spanish reaction times). These surprising cross-language correlations challenge widely held assumptions about the lexical locus of length and frequency effects, suggesting instead that they may (at least in part) reflect familiarity and accessibility at a conceptual level that is shared over languages.     

Automatic spatial coding of perceived gaze direction is revealed by the Simon effect

In a typical Simon task, the (irrelevant) spatial position of the stimulus interferes with the processing of the salient characteristic (e.g., color). We used the Simon effect to investigate the automatic processing of gaze cues. We show that a simple drawing of schematic eyes automatically generates a spatially defined code of gaze direction. Although completely irrelevant to the task, direction of gaze influenced reaction times in a spatially selective two-choice discrimination based on eye color. Moreover, in one experiment employing an orthogonal manipulation of stimulus position and gaze direction, we found that coding of gaze direction is independent of stimulus spatial coding. Our finding of a “gazedirection Simon effect” is congruent with the hypothesis that gaze direction is coded by a specialized mechanism.     

The SNARC effect: an instance of the Simon effect?

Our aim was to investigate the relations between the Spatial-Numerical Association of Response Codes (SNARC) effect and the Simon effect. In Experiment 1 participants were required to make a parity judgment to numbers from 1 to 9 (without 5), by pressing a left or a right key. The numbers were presented to either the left or right side of fixation. Results showed the Simon effect (left-side stimuli were responded to faster with the left hand than with the right hand whereas right-side stimuli were responded to faster with the right hand), and the SNARC effect (smaller numbers were responded to faster with the left hand than with the right hand, whereas larger numbers were responded to faster with the right hand). No interaction was found between the Simon and SNARC effects, suggesting that they combine additively. In Experiment 2 the temporal distance between formation of the task-relevant non-spatial stimulus code and the task-irrelevant stimulus spatial code was increased. As in Experiment 1, results showed the presence of the Simon and SNARC effects but no interaction between them. Moreover, we found a regular Simon effect for faster RTs, and a reversed Simon effect for longer RTs. In contrast, the SNARC effect did not vary as a function of RT. Taken together, the results of the two experiments show that the SNARC effect does not simply constitute a variant of the Simon effect. This is considered to be evidence that number representation and space representation rest on different neural (likely parietal) circuits.     

What compound nouns mean to preschool children

Compound nouns have multiple meanings in English. The purpose of this study was to explore when children know that compound nouns refer to two objects, one ideally interacting with the other (e.g., "fish shoes" are shoes with fish on them, not next to them). Thirty-five English-speaking three- and four-year-old children participated in this study. They were given both a production and comprehension task with novel compound nouns. The results showed that the three-year-olds and the four-year-olds were equally likely to produce compounds to name two interacting objects. However, the three-year-olds were less likely than the four-year-olds to understand that a compound referred necessarily to two objects. These results demonstrate that children's knowledge of the meaning of compound nouns is still developing in the preschool years. Three possible interpretations of the mismatch in comprehension and production are discussed: (1). there are modality differences in processing by children, (2). the meaning tapped by production and comprehension is not identical, and (3). the tasks differed in complexity.     

CONSERVATION IN COMMUNITY SCHOOL CHILDREN FROM THE MILNE BAY AND MOROBE PROVINCES OF PAPUA NEW GUINEA

Three hundred and forty primary level boys and girls from the Milne Bay and Morobe Provinces of Papua New Guinea were tested for conservation of number, length, quantity, and area. Relationships observed between schooling, age, sex and conservation confirmed previous conclusions from work in Papua New Guinea about the importance of the first two of these variables for conservation. Comparisons between different language-culture groups suggested that explanations of any lag in achieving conservation in Papua New Guinean children must give attention to specific characteristics of children's environments since groups which were significantly superior performers on some tasks were significantly inferior on others.     

Temperament and behaviour problems in children: A multilevel analysis of cross-cultural differences

Early temperament attributes have been linked to emerging behaviour problems and significant long-term consequences; however, these relations are rarely examined cross-culturally. The present study addresses this gap, employing multilevel modelling to explain within- and between-culture variances with respect to temperament predicting a spectrum of behaviour problems across 14 nations from the Joint Effort Toddler Temperament Consortium (JETTC). A total of 865 children between 17 and 40 months, with approximately equal age distribution across this developmental period and about equivalent representation of genders, were recruited from 14 nations. Greater negative emotionality was associated with more internalizing problems, whereas higher surgency and effortful control predicted fewer internalizing difficulties. Controlling for age and gender, temperament explained significant within- and between-culture variances in internalizing and externalizing problems (at the broad-band and fine-grained levels), as well as sleep problems. For internalizing difficulties, temperament accounted for more between-culture variance. In contrast, for externalizing difficulties, temperament accounted more for how individuals within the same culture differed from their same-culture counterparts. The within-culture findings suggest universal patterns of temperament-problem relations, informing cultural adaptation of interventions; between-culture findings enhance understanding of the implications of the cultural niche for normative behaviour and adjustment.