Constrained classification: The use of a priori information in cluster analysis

In many classification problems, one often possesses external and/or internal information concerning the objects or units to be analyzed which makes it appropriate to impose constraints on the set of allowable classifications and their characteristics. CONCLUS, or CONstrained CLUStering, is a new methodology devised to perform constrained classification in either an overlapping or nonoverlapping (hierarchical or nonhierarchial) manner. This paper initially reviews the related classification literature. A discussion of the use of constraints in clustering problems is then presented. The CONCLUS model and algorithm are described in detail, as well as their flexibility for use in various applications. Monte Carlo results are presented for two synthetic data sets with appropriate discussion of the resulting implications. An illustration of CONCLUS is presented with respect to a sales territory design problem where the objects classified are various Forbes-500 companies. Finally, the discussion section highlights the main contribution of the paper and offers some areas for future research.We wish to thank C. Mallows and J. D. Carroll for some helpful technical discussion and L. Clark and D. Art for their valuable computer assistance. We also wish to thank H. Pollak, R. Gnanadesikan, and J. Kettenring for their thorough reviews of a previous draft of this paper. Finally, we acknowledge helpful comments of the editor and two anonymous reviewers.     

An Observational Study on How Situational Factors Influence Media Multitasking With TV: The Role of Genres,Dayparts, and Social Viewing

This study responds to the need for research on individuals' media multitasking behavior using observational data. Media multitasking can have a profound impact on media processing and effects. However, we have little knowledge on when people are likely to engage in media multitasking and, consequently, when these effects are likely to occur. This study examines how three important situational factors—television genres, dayparts, and social viewing—influence the amount of media multitasking. Granular observational data obtained by directly monitoring and recording media consumption behaviors of a large panel at 10-second intervals are used for the analysis. The study reveals that media multitasking with television is most prevalent when people watch sports or engage in channel surfing and less prevalent with commercials, news, and entertainment. Furthermore, the extent of media multitasking is greater in the morning and afternoon than in the evening, and also greater when individuals watch television alone than in the presence of others. Daypart differences are larger for genres associated with incidental viewing (commercials and channel surfing) than for genres associated with intentional viewing (news, entertainment, and sports). Sports is the only genre that is associated with higher amounts of media multitasking when watching television with others.     

Human and machine perception of biological motion

More than 30 years ago, Johansson was the first to show that humans are capable of recovering information about the identity and activity of animate creatures rapidly and reliably from very sparse visual inputs – the phenomenon of biological motion. He filmed human actors in a dark setting with just a few strategic points on the body marked by lights – so-called moving light displays (MLDs). Subjects viewing the MLDs reported a vivid impression of moving human forms, and were even able to tell the activity in which the perceived humans were engaged. Subsequently, the phenomenon has been widely studied and many attempts have been made to model and to understand it. Typical questions that arise are: How precisely is the sparse low-level information integrated over space and time to produce the global percept, and how important is world knowledge (e.g., about animal form, locomotion, gravity, etc.)? In an attempt to answer such questions, we have implemented a machine-perception model of biological motion. If the computational model can replicate human data then it might offer clues as to how humans achieve the task. In particular, if it can do so with no or minimal world knowledge then this knowledge cannot be essential to the perception of biological motion. To provide human data for training and against which to assess the model, an extensive psychophysical experiment was undertaken in which 93 subjects were shown 12 categories of MLDs (e.g., normal, walking backwards, inverted, random dots, etc.) and were asked to indicate the presence or absence of natural human motion. Machine perception models were then trained on normal sequences as positive data and random sequences as negative data. Two models were used: a k-nearest neighbour (k-NN) classifier as an exemplar of ‘lazy’ learning and a back-propagation neural network as an exemplar of ‘eager’ learning. We find that the k-NN classifier is better able to model the human data but it still fails to represent aspects of knowledge about body shape (especially how relative joint positions change under rotation) that appear to be important to human judgements.     

Movement abnormalities predict conversion to Axis I psychosis among prodromal adolescents

Evidence suggests that movement abnormalities are a precursor of psychosis. The link between movement abnormalities and psychotic disorders is presumed to reflect common neural mechanisms that influence both motor functions and vulnerability to psychosis. The authors coded movement abnormalities from videotapes of 40 adolescents at risk for psychosis (designated prodromal on the Structured Interview for Prodromal Symptoms; T. J. Miller et al., 2002). Following initial assessment, participants were evaluated for diagnostic status at 4 times annually. Ten participants converted to an Axis I psychosis (e.g., schizophrenia) over the 4-year period. Comparisons of converted and nonconverted participants at baseline indicated that the groups did not differ on demographic characteristics or levels of prodromal symptomatology, but those who converted exhibited significantly more movement abnormalities. Movement abnormalities and prodromal symptoms were strongly associated and logistic regression analyses indicated that abnormalities in the face and upper body regions were most predictive of conversion. Findings suggest that individuals with elevated movement abnormalities may represent a subgroup of prodromal adolescents who are at the highest risk for conversion. The implications for neural mechanisms and for identifying candidates for preventive intervention are discussed.     

Book reviews

Form and Validity in Indian Logic. Vijay Bharadwaja, 1990. Simla, Indian Institute of Advanced Study. 127 pp.

The Word and The World: India's Contribution to the Study of Language. Bimal Krishna Matilal, 1990 Delhi, Oxford University Press ix+189pp., Rs175.00

The Basic Ways of Knowing. Govardhan P. Bhatt, 1989 Delhi, Banarasidas xxviix+435 pp.

The Quest for Man. J. Van Nispen & D. Tiemersma (Eds), 1991 Assen/Maastricht, Van Gorcum ix+203 pp., Dfl39.50

Muslim‐Christian Encounters: Perceptions and Misperceptions. William Montgomery Watt, 1991 London, Routledge 164 pp.

Socrates in Mediaeval Arabic Literature. Islamic Philosophy, Theology and Science, Texts and Studies Vol. X. Ilai Alon, 1991. Leiden: E. J. Brill/Jerusalem, The Magnes Press. pp. 198, US$50

Tsung‐mi and the Sinification of Buddhism. Peter N. Gregory, 1991 Princeton, Princeton University Press 368 pp., US$49.50

Modern Civilization: A Crisis of Fragmentation. S. C. Malik, 1989. New Delhi, Abhinav Publications. 182 pp., Rs 150.00

Nature in Asian Traditions of Thought: Essays in Environmental Philosophy. J. Baird Callicott & Roger T. Ames (Eds), 1989 Albany, NY, State University of New York Press 335+xxi pp., US$16.95     

The Contribution of Neuroimaging to the Study of Language and Aphasia

New structural and functional imaging methods continue to be developed at a rapid pace. In the last 25 years, advanced imaging techniques have provided insights into how language is represented and processed in the brain and how it can be disrupted by damage to, or dysfunction of, various parts of the brain. Imaging studies have also yielded new information regarding how individuals recover language after stroke. We briefly review the strengths and weaknesses of the various radiological methods currently used to study language and aphasia.     

Bee-eaters (<Emphasis Type="Italic">Merops orientalis</Emphasis>) respond to what a predator can see

Two sets of experiments are reported that show that the small green bee-eater (Merops orientalis, a small tropical bird) can appreciate what a predator can or cannot see. Bee-eaters avoid entering the nest in the presence of a potential nest predator. In the first set of experiments bee-eaters entered the nest more frequently when the predator was unable to see the nest from its position, as compared to an approximately equidistant position from which the nest could be seen. In the second set of experiments bee-eaters entered the nest more frequently when the predator was looking away from the nest. The angle of gaze from the nest was associated significantly positively with the probability of entering the nest whereas the angle from the bird was not. Birds showed considerable flexibility as well as individual variation in the possible methods of judging the predator's position and direction of gaze. Electronic Publication     

Effect of couple stress at the interfaces of a nano-hole on the anti-plane electro-mechanical behavior

In piezoelectric nanocomposites, surface/interface plays an important role in determining the size-dependent behavior of media. Within the framework of couple stress, the effect of surface/interface around a nano-hole on the anti-plane electro-mechanical behavior is examined. By introducing a surface/interface model, the stress and electric displacement effects on the size-dependent behavior are both considered. The governing equations in piezoelectric materials are decoupled into the classical ones. The displacement and electric potential are expressed by Bessel functions. By satisfying the boundary conditions around the hole with the interface/surface effect, the expanded coefficients are obtained. Through analysis, it is shown that the mechanical and electrical fields drastically depend on the relative size of the hole with respect to the characteristic length of the material. The effects of couple stresses on the stress and electric field are also addressed. Comparison with the existing results is also given.     

Identification of a new tetragonal phase in the Nb-Ti-Al system

During the course of investigation of the phase equilibria in the Nb-Ti-Al system, a new phase, designated theta, was observed in three Nb-Ti-40at.%Al alloys following ageing at low temperatures (less than 1000 C). Using X-ray diffraction and transmission electron microscopy techniques, this phase was determined to have a bct structure, with lattice parameters a₀ = 5.106 A and c₀ = 28.168A, a space group of I 4₁/amd (number 141) and composition near 45at.%Nb25at.%Ti-30at.%Al. An orientation relationship between the new tetragonal phase and the gamma-TiAl phase of [101]_gamma//[120]_theta and (111)_gamma//(001)_theta was observed within the microstructure.