How to Assess a Model's Testability and Identifiability

Formal definitions are given of the following intuitive concepts: (a) A model is quantitatively testable if its predictions are highly precise and narrow. (b) A model is identifiable if the values of its parameters can be ascertained from empirical observations. (c) A model is redundant if the values of some parameters can be deduced from others or if the values of some observables can be deduced from others. Various rules of thumb for nonredundant models are examined. The Counting Rule states that a model is quantitatively testable if and only if it has fewer parameters than observables. This rule can be safely applied only to identifiable models. If a model is unidentifiable, one must apply a generalization of the Counting Rule known as the Jacobian Rule. This rule states that a model is quantitatively testable if and only if the maximum rank (i.e., the number of linearly independent columns) of its Jacobian matrix (i.e., the matrix of partial derivatives of the function that maps parameter values to the predicted values of observables) is smaller than the number of observables. The Identifiability Rule states that a model is identifiable if and only if the maximum rank of its Jacobian matrix equals the number of parameters. The conclusions provided by these rules are only presumptive. To reach definitive conclusions, additional analyses must be performed. To illustrate the foregoing, the quantitative testability and identifiability of linear models and of discrete-state models are analyzed. Copyright 2000 Academic Press.     

The sounds of dominance.

A study was conducted to determine the effects of vocal cues on judgements of dominance in an interpersonal influence context. Physical measures of human vocal cues and participant ratings of dominance were obtained from videotapes of actors delivering short influence messages. After controlling for linguistic and visual content of messages, results indicated that mean amplitude and amplitude standard deviation were positively associated with dominance judgments, whereas speech rate was negatively associated with dominance judgments. An unexpected interaction revealed that mean fundamental frequency (F₀) was positively associated with dominance judgments for male speakers but not significantly associated with dominance judgments for female speakers. F₀ standard deviation was not significantly associated with dominance judgments. Results support the conclusion that dominance judgments are inferred from multiple sources of information and that some vocal markers of dominance are more influential than others.     

Detail-oriented cognitive style and social communicative deficits,within and beyond the autism spectrum: Independent traits that grow into developmental interdependence

At the heart of debates over underlying causes of autism is the “Kanner hypothesis” that autistic deficits in social reciprocity, and a cognitive/perceptual ‘style’ favouring detail-oriented cognition, co-vary in autistic individuals. A separate line of work indicates these two domains are normally distributed throughout the population, with autism representing an extremity. This realisation brings the Kanner debate into the realm of normative co-variation, providing more ways to test the hypothesis, and insights into typical development; for instance, in the context of normative functioning, the Kanner hypothesis implies social costs to spatial/numerical prowess. In light of this growing body of research, we review relevant factor analytic and correlational, behavioural studies. Findings are then synthesised into three themes: an alternative triad of primary autistic trait categories – Social Interaction Deficits, Cognitive Inflexibility, and Sensory Abnormalities – that more accurately reflects the factor structure of autistic traits; continuity between clinical and non-clinical autism-spectrum trait presentation; and indications that although social and non-social autistic traits may be initially independent, Kanner-like co-variance emerges behaviourally from dynamic trait interactions over the course of development. A dynamic developmental model subsuming these patterns is offered, and its advantages demonstrated in a novel account of ritualistic behaviours: as developmentally emergent, compensatory mechanisms for interactions between cognitive inflexibility and sensory abnormalities. We conclude with the broader imperative that behavioural scientists appealing for directly and exclusively genetic links may instead benefit from a developmental framing within their own discipline.     

Hypothalamo-Pituitary-Adrenocortical Regulation Following Lesions of the Central Nucleus of the Amygdala

Previous reports indicate that the central nucleus of the amygdala (CeA) stimulates adrenocorticotropin and corticosterone secretion, suggesting a role for this region in central hypothalamo-pituitary-adrenocortical (HPA) stress regulation. To evaluate this hypothesis, this study assessed the impact of CeA lesion on the response of hypophysiotrophic paraventricular nucleus (PVN) neurons to acute restraint and chronic unpredictable stress exposure. In contrast to previous reports, CeA lesions did not affect corticosterone or ACTH secretion induced by acute stress. Acute restraint increased PVN corticotropin releasing hormone (CRH) mRNA expression, increased the number of parvocellular PVN neurons expressing the co-secretagogue arginine vasopressin (AVP), and induced cFOS mRNA expression in the parvocellular PVN. However, there was no additional effect of CeA lesion on any measure of PVN activation. Chronic unpredictable stress exposure induced long-term activation of the HPA axis, noted by thymic involution, adrenal hypertrophy and increased PVN CRH mRNA expression. Stress-induced changes in thymus and adrenal weights were not affected by CeA lesion. Further, CeA lesion rats did not differ from controls in post-stress CRH mRNA expression. However, basal CRH mRNA expression was increased in the PVN of CeA rats, suggesting that the CeA plays a role in long-term inhibition of the PVN. The results of these studies are not consistent with the hypothesis that the CeA is necessary for stress-induced pituitary-adrenocortical activation. Rather, this region may play a stressor-specific modulatory role in regulation of HPA function.     

Persuasion and the structure of affect.

Participants viewed eight PSAs, providing data on their cognitive and emotional responses to each, as well as judgments of the perceived effectiveness of the messages. They also responded to Carver and White's (1994) BIS/BAS scales designed to measure individual differences in the behavioral inhibition and behavioral activation systems. Consistent with dual‐systems theories of affect, the BIS scales predicted arousal of negative emotions, while BAS was associated with the elicitation of positive emotions. However, when predicting perceived message effectiveness, the positive affects showed variation in the sign and magnitude of the coefficients, as did the negative affects. This latter finding supports a discrete‐emotions perspective. Knowledge that the two affect structures are appropriate to different conceptual domains (i.e., elicitation vs. effect) should enable researchers to formulate more precise questions regarding the role of affect in persuasion.     

Effects of spatial separation between stimuli in whole report from brief visual displays

Direct measurements of the effects of spatial separation between stimuli in whole report from brief visual displays are reported. The stimuli were presented on the periphery of an imaginary circle centered on fixation. In Experiment 1, each display showed two capital letters (letter height approximately equal 1.3 degrees, width approximately equal 0.9 degree, eccentricity approximately equal 5.5 degrees). The proportion of correctly reported letters was a strictly increasing, decelerating function of the spatial separation between the letters for center-to-center separations ranging from less than 2 degrees to more than 10 degrees of visual angle. Experiment 2 yielded similar results with triples of letters. Experiment 3 showed that accuracy increased with spatial separation for report of two short words, and Experiment 4 showed the same result for words presented upside down. The results are explained by a model of lateral masking (crowding) based on competitive interactions within receptive fields of cortical neurons.     

A structured pictorial questionnaire to assess DSM-III-R-based diagnoses in children (6–11 years): Development,validity, and reliability

This paper presents a structured pictorial instrument, the Dominic questionnaire, to assess mental disorders in 6- to 11-year-old children. Ninety-nine drawings represent situations corresponding to DSM-III-R based ADHD, CD, ODD, MDD, SAD, OAD, and SPh. However, cognitive limitation of 6- to 11-year-old children do not allow for time-related measurement. The instrument takes 15–20 min to administer. Reliability and validity of the Dominic questionnaire were studied in Parent DISC-2 positive and negative outpatient and general population samples and against clinical judgement. The pictorial approach provides acceptable test-retest reliability and the instrument makes standardized assessment possible for children as young as 6 years of age.This investigation was supported by the National Health Research and Development Program (Ottawa) grant #6605-2780-42. The authors wish to thank L. Houde and S. Lepine for their collaboration and J. J. Breton, P. Cohen, K. Minde, K. Munir, and D. Shaffer for their suggestions and editorial comments.     

Correlates of Depressive Disorders in the Quebec General Population 6 to 14 Years of Age

There are relatively few community-based epidemiological studies in which correlates of depressive disorders were identified through multivariate analyses in children and adolescents aged 6--14 years. Moreover, several family characteristics (e.g., parent-child relationship) have never been explored in this regard. The purpose of this study was twofold. Using data from the Quebec Child Mental Health Survey, it sought: (1) to identify psychosocial correlates associated with depressive disorder in two age-groups (6--11 and 12-14 years) according to informant (child/adolescent, parent); and (2) to interpret the relative importance of correlates by ranking variables according to strength and consistency of association across age-groups. Logistic regression models show correlates to be inconsistent across informants. The ranking of correlates indicates a major contribution of only-child status/ordinal position, parent's major depressive disorder, stressful family events, and parent-child relationship, thereby supporting the hypothesis of the relevance of family context in the development of depression.     

Not Only Whites: Racial Priming Effect for Black Faces in Black People

Black people are widely negatively stereotyped. The presence of unconscious stereotypes can be effectively assessed with the administration of “racial priming tasks.” An ethnically diverse group was subjected to a priming paradigm to test whether racial cues could bias the identification of target objects. Participants were asked to categorize objects (either as dangerous or nondangerous) after the presentation of Black/White faces as primes. Results show that both Black and White participants were faster in categorizing dangerous objects when primed with Black faces compared to the control condition (i.e., scrambled faces). One possible explanation for this effect is that Black faces are generally associated with a feeling of danger, which ultimately leads to faster responses.