1 Psychology Department, King Alfred’s College, Winchester

2 Neurocognitive Development Unit, Institute of Child Health, London

In this paper we introduce two dimensions over which current and recent theories of consciousness vary. These dimensions are (1) vehicle versus process theories, and (2) non-specialized versus specialized theories. Vehicle theories of consciousness propose that consciousness arises from some inherent property of mental representations of neural systems, irrespective of the computations they perform. Process theories propose that consciousness arises as a result of a particular form of computation. Non-specialized theories view consciousness as potentially arising from any part of the mind/brain with the appropriate property or performing the appropriate computations. Specialised theories view consciousness as arising from dedicated machinery. We review and situate nine theories of consciousness in the 2x2 matrix generated by the two dimensions. We then examine some difficulties with the precise characterizations of these dimensions. With regard to the vehicle/process dimension, we conclude that this dimension is best thought of as a continuum, in which the position is marked by the relative emphasis on computation versus implementation. Vehicle theories are those that place greater emphasis on implementation. With regard to the specialised/non-specialised dimension, we conclude that this dimension is a dynamic one, such that transitions may be possible over an evolutionary or developmental time scale, whereby initially non-specialised components may become conscious. We conclude that current advances in our understanding have been driven forward by an emphasis on computation; but that we are no closer to understanding why phenomenal experience should arise from certain computational events.