Halliday & Matthiessen (1999: 551):
Behavioural processes such as listen, watch share some features with material processes ('present-in-present' as unmarked tense; no projection), other features with mental processes (the Medium/Behaver is a conscious being). They lie on the borderline between 'doing' and 'sensing’ (so can be re-iterated as do in some contexts but not in all).