Contention scheduling and the control of routine activities

The control of routine action is a complex process subject both to minor lapses in normals and to more severe breakdown following certain forms of neurological damage. A number of recent empirical studies (e.g. Humphreys & Ford, 1998; Schwartz rt al., 1991, 1995, 1998) have examined the details of breakdown in certain classes of patient, and attempted to relate the findings to existing psychological theory. This paper complements those studies by presenting a computational model of the selection of routine actions based on competitive activation within a hierarchically organised network of action schemas (cf. Norman & Shallice, 1980, 1986). Simulations are reported which demonstrate that the model is capable of organised sequential action selection in a complex naturalistic domain. It is further demonstrated that, after lesioning, the model exhibits behaviour qualitatively equivalent to that observed by Schwartz et at., in their action disorganisation syndrome patients.