Sub-symbolic systems are those which use low-level representations such as the weights in a neural newtworks or the artificial insects in swarm computing. One could argue that there is still digital symbol manipulation when they execute, but not at a recognisable level. In contrast symbolic systems use symbols such as names, places, and concepts whch are manipulated by explicit rules.
Defined on page 2
Used on pages 2, 4, 8, 11, 28, 125, 126, 440, 515
Also known as sub-symbolic, sub-symbolic AI