A parallel algorithm for real-time computation of optical flow

The precise management of two-dimensional field of velocities from time-varying two-dimensional images is impossible in general. It is, however, possible to compute suitable 'optical flows' that are qualitatively similar to the velocity field in most cases. We describe a simple, parallel algorithm that computes an optical flow from sequences of real images, which is consistent with human psychophysics and suggests plausible physiological models. In particular, our algorithm runs on a Connection Machine supercomputer in close-to-real time. It shows several of the same 'illusions' that are perceived by humans. A natural physiological implementation of the model is consistent with data from cortical areas V1 and MT.     

The extracellular matrix during heart development

The embryonic extracellular matrix, which is comprised of glycosaminoglycans, glycoproteins, collagens, and proteoglycans, is believed to play multiple roles during heart morphogenesis. Some of these ECM components appear throughout development, however, certain molecules exhibit an interesting transient spatial and temporal distribution. Due to significant new data that have been gathered predominantly in the past 10 years, a comprehensive review of the literature is needed. The intent of this review is to highlight work that addresses mechanisms by which extracellular matrix influences vertebrate heart development.     

Timing of the steps in transformation of C3H 10T 1/2 cells by X-irradiation

Transformation of cells in culture by chemical carcinogens or X rays seems to require at least two steps. The initial step is a frequent event; for example, after transient exposure to either methylcholanthrene or X rays, almost every cell of established lines of mouse embryo fibroblasts proved capable of yielding transformed, tumorigenic descendants. Although results were interpreted as indicating that 100% of the progeny of methylcholanthrene-treated cells were potentially transformed, later experiments showed that only a very small minority of the progeny of cells initiated by X rays or methylcholanthrene actually produced transformed colonies. We thus concluded that there must be a second step in transformation that is a very rare event. We assumed that this event occurred after the cultures became confluent, a time when transformed cells have a selective growth advantage. Since then, however, others have shown that transformation can occur soon after initiation and that clones of transformed cells may already be present by the time initiated cultures become confluent. It has been hypothesized that the second step behaves like a spontaneous mutation in having a constant but small probability of occurring each time an initiated cell divides. We show here that the clone size distribution of transformed cells in growing cultures initiated by X rays is, indeed, exactly what would be expected on that hypothesis.