Halliday & Matthiessen (1999: 588-9):
The scientific model is metaphorical; and it stands as a metaphor for the congruent folk model. As [Figure 14-9] makes explicit, there is a considerable loss of ideational information as one moves from the congruent mode to the metaphorical mode: grammatically, a clause complex is compressed into a clause, and the clauses that are combined in the clause complex are compressed into nominal groups. As a result, the subtle distinction between the cognitive projection of ideas (sb believing that....) and the perceptive sensing of acts (sb seeing sth happen) is lost, and participants can be left implicit. …
The possibility of leaving participants implicit means in practice that Sensers are effaced in the scientific model and, as a result, the consciousness we experience in the living of life is also construed out of the picture, being replaced with unconscious processes not accessible to our experience.