NX is the Network Architectural Specification Language used for defining network structure and connectivity in NEXUS. Creating an NX file consists of defining a set of parameters which (1) describe the functional properties and spatial layout of networks of cells (or units) and (2) specify the spatial and weighting properties of the cells’ connection fields. The limited syntax of the NX language makes it easy to learn-creating new architectures requires no more than editing an existing NX file and changing the relevant parameters. A particularly attractive feature of NEXUS is that it consists of an easy-to-use interactive graphics display for testing and simulating models constructed with NX. The following section will describe the menu functions available in NEXUS.