For the philosopher, one introspects--and it works, sort of . . .
The scientist demands evidence: an independent/dependent variable, and a causal relationship, best expressed in a statistically significant differences.
There are two major ways--always relying on introspection to guide observation.
1. One way to study consciousness, is to carefully observe behavior. Best observable indicators are respiration, muscular body movements (controlled vs. reflexive), eye movements, head movements, in response to a stimulus.
2. Second way to study consciousness is to monitor neurological activities in the brain. This is devilishly difficult because the human skull attenuates neurological signals. Thus, one records only echoes of neural activities only vaguely connected to various parts of the brain.
This Method 2 study adds to the research design difficulty by using groups of patients who have been given psychedelic drugs (although only two of the three drugs administered were clearly psychedelic).
Finding different apparent locations of neural excitation in a correlational sort of way in comparison to sleep or a non drugged states tends to lead to a shrug: so what?
Does that really show heightened consciousness?
This is not very convincing.