Multiple information sources in interceptive timing

This study was designed to explore the limitations of tau (τ) as an explanatory construct for the timing of interceptive action. This was achieved by examining the effects of environmental structure and binocular vision on the timing of the grasp in a simple one-handed catch. In two experiments, subjects were required to catch luminous balls of different diameters (4, 6, 8 and 10 cm) in a completely darkened room. In the first experiment the influence of the presence vs. absence of an environmental background structure (both under monocular viewing) was tested, and in the second experiment the influence of monocular vs. binocular vision was examined. It was found that irrespective of the presence of environmental structure, an effect of ball size occurred in the monocular viewing conditions. That is, in monocular viewing conditions the grasp was initiated and completed earlier for the larger balls as compared to the smaller ones, while in the binocular viewing condition subjects behaved in accordance with a constant time to contact strategy: no effects of ball size were found. It is concluded that under binocular viewing a binocular information source is used, while in the monocular viewing condition a lower order information source like image size or image velocity is probably involved.     

The Development of a Clinical Rating Scale the McMaster Model of Family Functioning

This article describes the development and validation of the McMaster Clinical Rating Scale (MCRS). The MCRS is a 7-item scale designed to be completed by a trained rater after completion of an in-depth interview of the family. We present data from four new studies and review previously published articles concerning the reliability, validity, and clinical utility of the MCRS. Adequate interrater reliability and rater stability were obtained. The MCRS was found to correlate significantly with the self-report Family Assessment Device and to discriminate between families in different phases of a depressive disorder.     

ON ULTIMATE EPISTEMIC FOUNDATIONS1

This paper is a contribution to the debate on epistemic foundationalism. Section I expounds and criticises Hans Albert's critical rationalist antifoundationalism position. Section I1 discusses Karl-Otto Apel's ‘transcendental pragmatic’ argument for ultimate epistemic foundations. Section III suggests how the latter argument can be restated so as to avoid ambiguity and yield a plausible case for epistemic foundationalism.     

Racial categorization and preference among older children in The Netherlands

In this study the pervasiveness of racial categorization is investigated among children (10–12 years of age) in multi-racial schools. Subjects were asked to sort photographs of unknown contemporaries and to indicate preferences. Skin colour, sex and facial expression were used as three characteristics which varied systematically in the pictures. The results show, first, that children preferred to use different features simultaneously instead of a single feature only. Second, in a dichotomous classification task skin colour and sex were the most obvious visible features used for categorization. Gender was also used for explaining socially undesirable behaviour, and for indicating preferences. while race was not used in these tasks. In indicating preferences facial expression and not skin colour was used as a subordinate category. There were very few differences between ethnic Dutch, coloured and ethnic minority children in the use of skin colour or other features.     

Extraction of relief from visual motion

We quantified the ability of human subjects to discriminate the relative distance of two points from a slanted plane when viewing the projected velocities of this scene (orthographic projection). The relative distance from a plane (called relief) is a 3-D property that is invariant under linear (affine) transformations. As such, relief canin principle be extracted from the instantaneous projected velocity field; a metric representation, which requires the extraction of visual acceleration, is not required. The stimulus consisted of a slanted planeP (specified by three points) and two pointsQ ₁ andQ ₂ that are non-coplanar withP. This configuration of points oscillated rigidly around the vertical axis. We have measured thesystematic error andaccuracy with which human subjects estimate the relative distance of pointsQ ₁ andQ ₂ from planeP as a function of the slant of_P. The systematic error varies with slant: it is low for small slant values, reaches a maximum for medium slant values, and drops again for high slant values. The accuracy covaries with the systematic error and is thus high for small and large slant values and low for medium slant values. These results are successfully modeled by a simple relief-from-motion computation based on local estimates of projected velocities. The data are well predicted by assuming (1) a measurement error in velocity estimation that varies proportionally to velocity (Weber’s law) and (2) an eccentricity-dependent underestimation of velocity.     

The dynamics of Prägnanz

Summary There is quite wide-spread agreement about the relevance of pattern Pragnanz (Koffka, 1935) with respect to the human interpretation of visual patterns. There is less agreement about whether pattern Pragnanz is based solely on pattern information (static) or also on the history of the perceiver (dynamic). In Van Leeuwen and Van den Hof (1991), experimental data concerning serial patterns are presented within the framework of the dynamic-network approach initiated by Buffart (1986, 1987). These experimental data are claimed to give evidence against the static-coding approach initiated by Leeuwenberg (1969, 1971). In the present paper, however, I show first that Buffart's theoretical basis is incorrect, and that in fact Leeuwenberg's static-coding approach is the basis for the dynamic-network approach. Second, I show that those experimental data rather give evidence in favor of the static-coding approach, by using those same data for a test of the most recent static-coding model (Van der Helm & Leeuwenberg, 1991; Van der Helm, Van Lier, & Leeuwenberg, 1992). Finally, I propose a reconciliation between the two approaches, in the sense that the dynamic-network model could be shaped in such a way that it yields a simulation, and maybe even an enrichment, of the static-coding model.     

The Ethnic Hierarchy Among Majority and Minority Youth In The Netherlands

This study tests the hypothesis that ethnic groups have consensus about the relative position of ethnic out-groups in society. A survey among ethnic majority and minority youth in the city of Rotterdam indicated that: (a) each ethnic group preferred the in-group, (b) there was consensus on an ethnic hierarchy within ethnic groups, and (c) ethnic groups largely agreed on the ethnic rank order. Among the Dutch respondents, the ethnic hierarchy was found to be related to real cultural differences. The scheme of ethnic preferences corresponded inversely to the rank ordering of the ethnic groups in terms of collectivism. Among ethnic minority youth the rank ordering did not correspond to cultural differences but to existing socioeconomic status differences.