The Tricky Business of Measuring Consciousness

Jason Pontin for Wired:

In a groundbreaking study, 102 healthy subjects and 48 responsive but brain-injured patients were “zapped and zipped” when conscious and unconscious, creating a value called a “perturbational complexity index” (PCI). Remarkably, across all 150 subjects, when the PCI value was above a certain value (0.31, is it happens) the person was conscious; if below, she or he was always unconscious.

Massimini’s test is important because it is the first real proof of integrated information theory (IIT), a theory of consciousness invented by neuroscientist and psychiatrist Giulio Tononi at the University of Wisconsin.

IIT doesn’t try to answer the hard problem. Instead, it does something more subtle: It posits that consciousness is a feature of the universe, like gravity, and then tries to solve the pretty hard problem of determining which systems are conscious with a mathematical measurement of consciousness represented by the Greek letter phi (Φ).