Matthias Michel is among the sharpest critics of the methods of consciousness science. His forthcoming paper, "Consciousness Doesn’t Do That", convincingly challenges background assumptions behind recent efforts to discover the causes, correlates, and prevalence of consciousness. It should be required reading for anyone tempted to argue, for example, that trace conditioning correlates with consciousness in humans and thus that nonhuman animals capable of trace conditioning must also be conscious.
But Michel does make one claim that bugs me, and that claim is central to the article. And Hakwan Lau – another otherwise terrific methodologist – makes a similar claim in his 2022 book In Consciousness We Trust, and again the claim is central to the argument of that book. So today I’m going to poke at that claim, and maybe it will burst like a sour blueberry.
The claim: Signal strength (performance capacity, in Lau’s version) is a confound in consciousness research.
As Michel uses the phrase, "signal strength" is how discriminable a perceptible feature is to a subject. A sudden, loud blast of noise has high signal strength. It’s very easy to notice. A faint wavy pattern in a gray field, presented for a tenth of second, has low signal strength. It is easy to miss. Importantly, signal strength is not the same as (objective, externally measurable) stimulus intensity, but reflects how well the perceiver responds to the signal.
Signal strength clearly correlates with consciousness. You’re much more likely to be conscious of stimuli that you find easy to discriminate than stimuli that you find difficult to discriminate. The loud blare is consciously experienced. The faint wavy pattern might or might not be. A stimulus with effectively zero signal strength – say, a gray dot flashed for a millionth of a second and immediately masked – will normally not be experienced at all.