We present the rst randomized O(logn) time and O(m + n) work EREW PRAM algorithm for nding a spanning forest of an undirected graph G = (V; E) with n vertices and m edges. Our algorithm is optimal with respect to time, work and space. As a consequence we get optimal randomized EREW PRAM algorithms for other basic connectivity problems such as nding a bipartite partition, nding bridges and bicon...

Earlier models for the self-organization of orientation preference and orientation selectivity maps are explicitly designed to reproduce the functional structures observed in cortical tissue. They mostly use formal though biologically motivated implementations and artifical assumptions to achieve this result. In particular, orientation selective cells are usually encoded by doubling the orienta...

In the primary visual cortex of monkey and cat, ocular dominance and orientation are represented continuously and simultaneously, so that most neighboring neurons respond optimally to visual stimulation of the same eye and orientation. Maps of stimulus orientation are punctuated by singularities referred to as "pinwheel centers," around which all orientations are represented. Given that the ori...

In macaque primary visual cortex (V1), neuronal responses to stimuli inside the receptive field (RF) are modulated by stimuli in the RF surround. This modulation is orientation specific. Previous studies suggested that, for some cells, this specificity may not be fixed but changes with the stimulus orientation presented to the RF. We demonstrate, in recording studies, that this tuning behavior ...

One major role of primary visual cortex (V1) in vision is the encoding of the orientation of lines and contours. The role of the local recurrent network in these computations is, however, still a matter of debate. To address this issue, we analyze intracellular recording data of cat V1, which combine measuring the tuning of a range of neuronal properties with a precise localization of the recor...

We explored the time course of surround suppression and found clear evidence for two distinct mechanisms: one strong, transient, and largely monocular, the other weaker, sustained, and binocular. We measured detection thresholds for a Gabor target at 8 deg eccentricity surrounded by a large annulus of matching spatial frequency and orientation. At short stimulus durations surround suppression w...

INTRODUCTION : Magnetic susceptibility difference between brain gray and white matter results in strong phase contrast between these two types of tissues at high magnetic field strength (1, 2). Here, we report, for the first time, a surprising observation of tissue-level magnetic susceptibility anisotropy in the central nervous system (CNS) using a mouse model. Specifically, we propose a method...

To investigate site fidelity and homing behavior in juvenile loggerheads (Caretta caretta, L.), a markrecapture study spanning four years (1998–2001) was conducted in Core Sound, N.C., USA. Each year of the study, approximately half of the turtles captured were tagged and released near the capture sites (n=207), while the remaining turtles were displaced 15–20 km and released (n=198). Loggerhea...

All triangulations of euclidean oriented matroids are of the same PLhomeomorphism type by a result of Anderson. That means all triangulations of euclidean acyclic oriented matroids are PL-homeomorphic to PL-balls and that all triangulations of totally cyclic oriented matroids are PL-homeomorphic to PLspheres. For non-euclidean oriented matroids this question is wide open. One key point in the p...