Halliday & Matthiessen (1999: 595-6):
Since figures of sensing are reified as participants, they can themselves be construed in participant rôles. Here another feature of the folk model is taken over: its spatial metaphor is retained and further elaborated. Thus the mind is construed as a space where the metaphorical participants of sensing are involved in processes of doing-&-happening and of being-&-having: thoughts, concepts, memories, images are stored located, retrieved, activated and so on.