Inhibitory grids and the assignment problem.

A family of symmetric neural networks that solve a simple version of the assignment problem (AP) is analyzed. The authors analyze the suboptimal performance of these networks and compare the results to optimal answers obtained by linear programming techniques. They then use the interactive activation model to define the network dynamics-a model that is closely related to the Hopfield-Tank model. A systematic analysis of hypercube corner stability and eigenspaces of the connection strength matrix leads to network parameters that give feasible solutions 100% of the time and to a projection algorithm that significantly improves performance. Two formulations of the problem are discussed: (i) nearest corner: encode the assignment numbers as initial activations, and (ii) lowest energy corner: encode the assignment numbers as external inputs.

Correcting two-dimensional kinematic errors for chick embryonic movements in ovo.

In motor behavior studies of chick embryos in ovo, kinematic recording is limited to a single camera system and produces kinematic data that are distorted if out-of-plane movements are not considered. CONVERT is a rule based algorithm designed to calculate 3D limb movements given 2D kinematic data. CONVERT's calculations are based on a stationary reference point, limited translation of the chick embryo's trunk point, a multi-linked model of the body, and approximate limb segment lengths. Simulations indicate CONVERT calculates joint movements from 2D data with a maximum error of 6 degrees compared to a maximum error of 79 degrees if out-of-plane considerations are ignored. The approach used to correct two-dimensional kinematic measurement errors can be readily applied to other experimental conditions that restrict video recording to single camera systems.

Kinematic analysis of wing and leg movements for type I motility in E9 chick embryos.

Based on studies using direct observation methods, type I motility, the first motility pattern to emerge in chick embryos, is characterized as random, uncoordinated movement. Yet, electromyographic (EMG) studies indicate that leg muscles are recruited in orderly patterns of alternating flexor and extensor activity during type I motility. It has been suggested that this apparent paradox may be attributable to perturbations arising during movement in ovo under buoyant conditions. It is also possible that direct observation methods are insufficient to detect the extent of coordination between body parts during type I motility. To address the apparent discrepancy between random features reported in observational studies and reliable features reported in EMG studies, embryos were video recorded continuously for 60 min at embryonic day 9 and criteria were established to obtain homogeneous samples of motility for kinematic analysis of synchronous wing and leg movements. Limited to a single camera attached to a stereomicroscope, methods were developed to correct for out-of-plane movements of the ipsilateral wing and leg. Also, amniotic fluid was extracted from the egg in some recordings to test the possibility that movement under buoyant conditions may mask coordinated movement. Extended sequences of activity were digitized and analyzed. Results indicated that within a limb (wing or leg), direction and timing of excursions at adjacent joints co-varied and limb excursions were characterized by reliable patterns of alternating flexion and extension consistent with EMG studies.(ABSTRACT TRUNCATED AT 250 WORDS)