Tools and tests for measuring the presence and type of consciousness are becoming available, but there is no established theoretical approach for what these tools are measuring. This paper looks at various categories of tests for measuring the presence and type of consciousness and suggests ways in which different theories of consciousness may be empirically distinguished. We label the various testable correlates of consciousness as the "measurable correlates of consciousness" (MCC). There are three sub-categories of MCC: 1) Neural correlates of consciousness (NCC); 2) Behavioral correlates of consciousness (BCC); 3) Creative correlates of consciousness (CCC). We also look specifically at ways in which the General Resonance Theory of consciousness may be tested and compared to other theories like the Integrated Information Theory of consciousness and Global Workspace Theory. We suggest additional simplified approaches under the hypothesis that electrical and magnetic fields are the seat of consciousness. Last, we reflect on how broader philosophical views about the nature of consciousness, such as materialism and panpsychism, may also become scientifically tractable.
  1. Introduction
How can we know if any person, animal or any thing is actually conscious and not just simulating various aspects of consciousness? The nature of consciousness makes it by necessity a wholly private affair (Libet 2005; Koch 2019). The only consciousness I can know with certainty is my own. Everything else is inference.
How do we create a reliable “consciousness-ometer” (what I’ll call a psychometer in the rest of this paper)? This inquiry has been relegated to philosophical musings until the last few years, but we are at a juncture where tools for measuring consciousness are starting to mature. This paper looks at the various kinds of tools and tests available, how they can be used to test for the presence and type of consciousness, and makes some suggestions for how a reliable psychometer could be created and refined over time.
Theories of consciousness are abundant, but often untested or even untestable (Michel et al. 2019). A major coordinated testing program has yet to be conducted, but the Templeton World Charity Foundation embarked in 2019 [Fn 1] on a multi-year effort to examine a number of the more prominent theories of consciousness in a series of one-on-one adversarial experimental tests, with the express intent of distinguishing the various theories. The first head-to-head contest will feature Global Neuronal Workspace theory (Dehaene 2014) and the Integrated Information Theory of consciousness (Oizumi, et al. 2013).
Footnote 1.  Limited details are available at Templeton’s website here: https://www.templetonworldcharity.org/arc. Additional details on the program and approach are available here: https://www.quantamagazine.org/neuroscience-readies-for-a-showdown-over-consciousness-ideas-20190306/. Additional details were released at an October 2019 announcement: https://sci-hub.tw/https://science.sciencemag.org/content/366/6463/293.full.
In thinking about ways to test theories of consciousness, it is important to keep in mind at all times that we can’t know if any person, any animal, or anything else at all is actually conscious, rather than a sophisticated simulation of consciousness. We can and frequently do in practice, nevertheless, make reasonable inferences about the presence of other consciousnesses. Libet 2005 agrees: “[S]ubjective experience cannot be directly measured by external objective devices or by external observations. Conscious subjective experience is accessible only to the individual having the experience.”
Attempts to assess the presence or nature of consciousness in any particular circumstance, and related attempts to assess different theories of consciousness and their predictions, will face the problem of reasonable inference (abduction) because of this fundamental limitation on our individual and collective knowledge. But this problem is surmounted frequently in practice in that we, each of us, reasonably infer that other people are conscious, based on their behavior and appearance. The same holds true for pets and many other animals. Testing for the presence of consciousness throughout the physical world relies on making similar reasonable inferences.
Koch 2019 (p. 155) makes a similar argument: “Because you are so similar to me, I abduce that you too have subjective, phenomenal states. The same logic applies to other people. Apart from the occasional solitary solipsist this is uncontroversial.” Koch proceeds through the course of his book to offer various ways that scientists may, now and in the future, test for the presence and character of consciousness in humans, animals and even non-biological entities – all based on abduction (reasonable inference).
We propose in the present paper a general quantification framework that rests on various “measurable correlates of consciousness” (MCC). This rubric includes the “neural correlates of consciousness” and the related but broader notion of “behavioral correlates of consciousness.” It also includes a newly-coined “creative correlates of consciousness” (CCC) category that is explained below. MCC refers to any means identified for measuring aspects of consciousness.
This paper identifies various ways in which MCC can be identified and tested. We also suggest ways for testing and contrasting specific theories of consciousness, including the General Resonance Theory (GRT) of consciousness that has been developed by Hunt and Schooler over the last decade. We also argue that the various metaphysical positions with respect to the nature of consciousness may, contrary to widespread opinion on this subject, be tested.
These questions are more than philosophical. With the coming age of intelligent digital assistants, self-driving cars, and other robots serving us and increasingly running our lives, does it matter if these AIs are actually conscious or just simulating consciousness?
More relevant for today’s needs, how can we know that coma victims, or patients in vegetative or minimally conscious states, are conscious or not? Or if they are likely to recover? How can a family know whether to take a patient off life support or not, if they don’t know with any certainty what kind of consciousness is or is not present, or is likely to re-enter over time?
  1. The Measurable Correlates of Consciousness
There is a small but growing field looking at how to assess the presence and even quantity of consciousness in various entities. I’ve divided possible tests into three broad categories that comprise collectively what I call the “measurable correlates of consciousness” (MCC) (Fig. 1). The MCC represent all possible scientific measures for inferring the presence of consciousness. They are “correlates” because we can’t know with certainty, as discussed above, whether consciousness is actually present. We can only infer, based on our measurements and best judgments. But they, nevertheless, “measurable,” and this term is meant to capture both of these key features.