If
you drag and drop rendering nodes on top of each other, Maya automatically
connects them in a default way. The default depends on the type
of node. For example:
Middle-mouse
button drag a 2D or 3D texture swatch over a material to automatically
connect the texture’s output color to the material’s output color.
Middle-mouse
button drag a Bump2d General utility node
over a material node to automatically connect the bump map to the
material’s Bump Mapping attribute.